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Executive Summary
Most people who use the Internet rely on the Domain Name System (DNS) and navigation aids and services to find the resources they seek or to attract users to the resources they provide. Yet, although they perform well, both the DNS and Internet navigation services face challenges arising from technological change and from institutions with a wide variety of commercial, cultural, social, and political agendas. Individually, or together, those pressures could force operational changes that would significantly reduce access to Internet-linked resources by segments of the user community, reducing the Internet’s value as a global resource.
This document reports the conclusions of an assessment of the current state and the future prospects of the DNS and its interactions with Internet navigation, including its uses as a means of navigation itself and as an infrastructure for navigation by other means. The assessment is the result of the deliberations of a committee that encompasses a wide range of disciplines, experience, and viewpoints. The report is addressed to the technologists, policy makers, and others whose decisions will affect the future of the DNS and Internet navigation aids and services. The specific conclusions and recommendations of the Committee on Internet Navigation and the Domain Name System appear throughout this summary in boldface type.
DOMAIN NAME SYSTEM
Domain names are commonly used to designate services and devices on the Internet, as a more memorable and more permanent alternative tothe numerical addresses employed by its routing computers. They are the valued, often valuable, and often user-friendly names on the signposts that designate many things connected to the Internet. Consequently, which names are available, who controls their allocation, what is charged for their use, how their uses are managed, and the answers to many related questions are important to virtually everyone who uses the Internet, whether as information seeker or provider.
Overall, the DNS’s technical system and institutional framework have performed reliably and effectively during the two decades of the DNS’s existence. The DNS has coped with the extremely rapid expansion of Internet usage driven by the wide deployment of the World Wide Web in the 1990s and the widespread adoption of e-mail. The hierarchical, distributed structure of the DNS technical system, operated collaboratively by a group of mostly autonomous organizations, has proven to be scalable, reliable, secure, and efficient.
The DNS technical system can continue to meet the needs of an expanding Internet. Early in the committee’s assessment it became apparent that it would not be fruitful to consider alternate naming systems. As noted, the DNS operates quite well for its intended purpose and has demonstrated its ability to scale with the growth of the Internet and to operate robustly in an open environment. Moreover, significantly increased functionality can be achieved though applications—such as navigation systems—built on the DNS, or offered independently, rather than through changing the DNS directly. Hence, the need did not seem to be to replace the DNS, but rather to maintain and incrementally improve it. Furthermore, given the rapidly increasing installed base and the corresponding heavy investments in the technical system and the institutional framework, the financial cost and operational disruption of replacing the DNS would be extremely high, if even possible at all.
However, the continued successful operation of the DNS is not assured; many forces, driven by a variety of factors, are challenging the DNS’s future. Required and desirable technologies to increase security and enable the use of non-Roman scripts for domain names are not being incorporated into the technical system as quickly as many would like. There are persistent and substantial controversies concerning the structure and policies of the DNS’s institutional framework. Moreover, there have been many efforts to use the DNS, because it exists and is so widely deployed, for many purposes for which it may not be appropriate. In addition, national legislation and court decisions are addressing Internet and domain name issues with potentially conflicting consequences for the operation of the DNS. Security Challenges
Like all public networked systems, the system of public domain name servers is threatened by a variety of purposeful attacks, both malicious and mischievous, by individuals or groups that aim to disable or divert their operations. The operators of the DNS are responding to these threats, but not all the desirable steps to ensure security have yet been implemented.
Denial-of-Service Attacks
Denial-of-service attacks attempt to overwhelm key name servers and their links to the Internet with so much traffic that they are incapable of responding to legitimate queries. The root name servers have the capacity and capability to respond to many times the normal number of queries they receive, and have alternate connections to the network if some are blocked. Their ability to respond to attacks has been improved by some operators’ recent addition of multiple distributed copies (called “anycast” servers) of the base name servers, increasing both capacity and connectivity. In anticipation of future denial-of-service attacks and normal growth in demand, and to improve service globally, anycast server deployment should be expanded.
Physical Vulnerability
Notwithstanding the deployment of anycast servers and installation of backup servers at remote locations, the concentration of root name server facilities and personnel in the Washington, D.C., area and, to a lesser extent, in the Los Angeles area is a potential vulnerability. The need for further diversification of the location of root name servers and personnel should be carefully analyzed in the light of possible dangers, both natural and human in origin.
Message Alteration
In response to the threat of alteration of messages being transmitted among name servers, the technical community has developed DNS Security Extensions (DNSSEC), which uses digital signatures to verify that the content of a message to or from a name server arrives unaltered and that its origin is as stated. DNSSEC only gives assurance that what was sent was not changed during transmission; it cannot and is not intended to assert that the message is factually correct. For example, DNSSEC has nocapability to guarantee that it is communicating the correct address for a given domain name. The security of the DNS would be significantly improved if DNSSEC were widely deployed among name servers for the root zone and top-level domains in particular, and throughout the DNS in general.
Performance Monitoring
Although some steps have been taken, more could be done to continuously monitor the performance and traffic flows of the DNS so as to enable rapid detection of and response to attacks or outages.
Governance Challenges
The DNS works through the voluntary cooperation of its autonomous component entities. That cooperation, in turn, depends on their tacit agreement on two principles that together enable the Internet and the DNS to evolve and remain effective:
Universal open standards. The first principle is that the protocols and standards defining operation of the Internet and the DNS will be open and established by the Internet Engineering Task Force (IETF), an international voluntary organization of technical specialists. This technical framework enables every device on the Internet to connect to and communicate with every other, and it has been critical to the success of the Internet and the DNS. Because changes in Internet and DNS protocols, standards, and practices are matters of consequence beyond specific Internet services, alterations to the functions of or modifications to established standards and practices have traditionally been vetted by the IETF before being implemented.
Innovation at the edges. The second principle is that applications should be offered by devices on the edges of the Internet, rather than at the Internet’s internal nodes or on its links. In general, applications located at the edges have little effect on the stability of the Internet, so there is no need to regulate them. The DNS is not, strictly speaking, internal to the Internet (the translation service is performed by computers at the edges), but functions as though it were. It can thus be thought of as a core service, which although not absolutely necessary, is extremely useful in giving a relatively user-friendly face to Internet resources, and for enabling access to those resources even when their Internet addresses change. Moreover, it is a deeply embedded and ubiquitous service that enables other services and functions, including most aids to Internet navigation. This tacit agreement governs the basic behavior of the many autonomous operators of the DNS, but there is also a need for an authority to make decisions about the allocation of limited resources central to DNS operations. The most critical of these decisions are the determination of which top-level domains (TLDs) shall appear in the root zone file of the DNS, which organizations shall be designated as responsible for their operation, and the terms under which those organizations shall operate.
The principal organizations that constitute this authority are, currently, the U.S. Department of Commerce (DOC) and the Internet Corporation for Assigned Names and Numbers (ICANN), although national bodies have considerable influence over the operations of the associated country-code top-level domains (ccTLDs). Both the DOC and ICANN face significant challenges to their authority and legitimacy in management of the DNS.
Stewardship of the DNS
As the Internet has become an increasingly important component of the international infrastructure, there has been growing pressure to introduce some form of international political control over the DNS. This pressure comes both from existing international organizations seeking authority over the Internet or the DNS, and from individual countries that would like to end the stewardship role of the United States.
Governance of the DNS is part, but not all, of governing the Internet. Efforts to leverage it to influence broader Internet policy are, therefore, likely to be ineffective and could also be detrimental to the DNS. Many of the governance issues that concern governments—control of spam and uses of the Internet for illegal purposes; resolving the disparities between developed and developing countries in Internet usage; protection of privacy, freedom of expression, and intellectual property other than domain names; and the facilitation and regulation of e-commerce—have little or nothing to do with the DNS per se. The DNS would not be an effective vehicle for addressing such issues. Attempts to change the DNS or extend its management and administrative processes to do so could interfere with reaching agreements on the already contentious issues concerning the DNS itself.
Governance of the DNS is not an appropriate venue for the playing out of national political interests. One valued and essential quality of the DNS institutional framework has been its relative freedom from direct pressures arising from conflicts among competing national interests and policy agendas (apart from sovereignty-associated issues such as ccTLD delegations and redelegations).
International disputes arising in other contexts have largely been kept away from the DNS—as they should be.
For that reason: The committee does not support efforts to put the
DNS directly under the control of governments or intergovernmental agencies. In practical terms, the U.S. government, which must agree, has not supported turning DNS stewardship over to other governments or an international organization, although that could change. Although the 2005 U.N.-sponsored World Summit on the Information Society (WSIS) may produce proposals for a non-governmental agent—an internationally negotiated convention or multi-stakeholder organization—with oversight or other influence over the DNS, no proposal that can be evaluated for either practicality or feasibility has yet (in June 2005) been made.
One way to respond to concerns about the U.S. government’s role as steward of the DNS is for it to transfer its stewardship role to a non-governmental body—specifically, ICANN. In the September 2003 revision of its agreement with ICANN, the DOC stated its intent to transfer its stewardship to ICANN if within 3 years ICANN is able to fulfill a mutually agreed set of tasks.
If ICANN does not fulfill the agreed tasks, and a proposal for creation of a non-governmental organization having Internet governance responsibilities results from the WSIS process before the transfer date, the DOC could consider transferring the stewardship role to the proposed organization. That would entail comparing a not-yet-existing organization to one with 8 years of experience and evolution.
Life without the stewardship of the U.S. government will open ICANN to political and commercial pressures. A free-standing ICANN would lack the oversight and, importantly, the protection provided by the U.S. government’s stewardship. If ICANN becomes steward of the DNS, legitimacy based on the “consent of the governed” would be the principal basis for its continued authority and its ability to resist inappropriate pressure from governments and other powerful interests. Final responsibility for satisfying the needs of its constituencies in an equitable, open, and efficient manner would lie with its board.
Before completing the transfer of its stewardship to ICANN (or any other organization), the Department of Commerce should seek ways to protect that organization from undue commercial or governmental pressures and to provide some form of oversight of performance.
Legitimacy of ICANN
ICANN is a work in progress; its long-term success is not assured. After a troubled start, it has introduced several innovations to the institutional framework of the DNS, including competition among registrars and an arbitral process for resolving disputes over domain names, the Uniform Domain Name Dispute Resolution Policy. In 2003 it had to undertake a major reform of its own organization, stimulated by dissatisfaction with its operation under its initial structure. It is working on the revision of key decision
processes in response to complaints about their lack of transparency and fairness. Furthermore, ICANN has been unable to conclude formal agreements with many of the organizations critical to its responsibilities, notably the root name server operators and the vast majority of the ccTLD registries. Nevertheless, through its responsibility for recommending changes in the root zone file, which defines which TLDs are in the DNS and where their operators are located on the Internet, ICANN has been able to exercise authority over the coherence and stability of the DNS.
Since its beginning, ICANN has been the subject of controversy and contention flowing from the many diverse constituencies that have been attracted to it and their correspondingly diverse views. The critics’ concerns have been with ICANN’s scope, its organizational structure, and its management processes. The concern about scope has been principally the extent to which ICANN has exceeded its technical-administrative responsibilities, for example, to regulate TLD registry operations; but others have been disappointed by its unwillingness to take on broader issues. The structural concerns have included perceptions of imbalance in the
historical composition of ICANN’s board, of failings in the board selection processes, and of inadequate representation of certain constituency groups. The process concerns have been the perceived lack of transparency, effectiveness, accountability, and recourse in ICANN’s electoral and decision processes.
ICANN is more likely to achieve perceived legitimacy by narrowing its scope and by improving its processes rather than by seeking an ideally representative composition of its board. No composition of its board is likely by itself to confer the perception of legitimacy on ICANN among all its possible constituency groups. A narrowing of scope and improvement of processes are elements of the path that ICANN claims to be following in carrying out its 2003 reform. However successful its reform, ICANN faces the challenge of reaching an effective modus operandi with three critical sets of participants in the DNS’s institutional framework: the root name server operators, the generic TLD registries, and the ccTLD registries.
Root Name Server Operators
No greater oversight of the root name server operators will be necessary so long as they continue to operate effectively and reliably and to improve the DNS’s security, stability, and capability. The effective daily operation of the root, and therefore the DNS, lies in the hands of the operators of the 13 critical root name servers. They have provided reliable and efficient service as the Internet has undergone rapid growth in the numbers of its users and providers. Although the DOC has assigned ICANN responsibility for the stability and security of the root name server system, ICANN’s authority has not been sufficient for it to manage or regulate the root name
server operators directly, nor is it clear that doing so is desirable or necessary. The real challenge to ICANN is to identify how it can best ensure the stability and security of the root name server system, given the long-standing autonomy of the operators and the effectiveness of their operations.
More formal coordination of the root name server operators is desirable in the longer term. ICANN is currently the most appropriate organization to assume the coordination role. Although direct management or oversight may be neither necessary nor feasible, with continued growth in the Internet and demands on the DNS, a more formal process of coordination of the root name server operators with ICANN’s facilitation will become desirable so as to ensure rapid response to persistent security needs and to other challenges.
The present independent funding arrangements for the root name servers are advantageous and should continue, because the multiplicity of sources contributes to the resilience, autonomy, and diversity of the root name server system. The root name server operators do not receive direct compensation for the services they perform. While running a root server may only add an incremental cost in the range of tens of thousands of dollars for an organization already operating a secure Internet site, fully loaded costs have been estimated at up to $1 million or more depending on numerous factors including the number of locations, bandwidth requirements, and staffing levels. The costs are covered by each organization as part of other operations. Although a central source of funds to compensate all the root name server operators for their services might appear desirable, it is likely to be accompanied by an unacceptable regulatory or control role for the funding organization and would reduce the robustness of the current arrangement.
ICANN should work with the root name server operators to establish a formal process for replacing operators that directly engages the remaining root name server operators. Under the process, ICANN would be responsible for the final decision on the basis of recommendations from the root name server operators. One or more of the current root name server operators may withdraw for organizational or performance reasons, and it would be reasonable to have in place an agreed process to deal with such eventualities.
Generic Top-Level Domain Registries
A major challenge to ICANN since its founding has been deciding whether, when, and how to add generic top-level domains (gTLDs) and, if any are added, how many. It has faced strong
pressures both to add gTLDs and to stop, or at least moderate, the pace of such additions. The committee addressed the issue of gTLD addition broadly in terms of both
effects and constituencies affected, but for simplicity the multidimensional arguments for and against new gTLDs were clustered into two groups: technical and operational performance, and user needs and economic benefits.
Considering technical and operational performance alone, the addition of tens of gTLDs per year for several years poses minimal risk to the stability of the root. However, an abrupt increase (significantly beyond this rate) in the number of gTLDs could have technical, operational, economic, and service consequences that could affect domain name registrants, registries, registrars, and Internet users.
From the standpoint of user needs and economic benefits, neither the arguments in favor of nor those against additional gTLDs are conclusive. Thus, the decision to add gTLDs is one requiring judgment and cannot be determined by formal analysis alone.
If new gTLDs are added, they should be added on a regular schedule that establishes the maximum number of gTLDs (on the order of tens per year) that could be added each time and the interval between additions. Addition of gTLDs should be carried out cautiously and predictably, so that on the one hand, the stability and reliability of the system can be protected, and on the other hand, those considering acquiring a gTLD can do so with a realistic view of future prospects.
A mechanism to suspend the addition of gTLDs in the event that severe technical or operational problems arise should accompany a schedule of additions. It should explicitly specify who has the authority to suspend additions and under what conditions.
A neutral, disinterested party should conduct an evaluation of new gTLDs approximately 1 or 2 years after each set of new gTLDs is operational to make recommendations for improving the process for selecting and adding gTLDs.
If new gTLDs are to be created, the currently employed comparative hearing or expert evaluation processes should not be assumed to be the only processes for selecting their operators. In its addition of gTLDs in 2000, ICANN used a comparative hearing process to select 7 from the 44 applicants. In its 2004 addition of sponsored gTLDs, ICANN used a non-competitive process that replaces subjective judgments by its staff and board with judgments by expert groups that are insulated from lobbying, but whose decision-making processes are not transparent. By doing so, it has reduced a few of the potential sources of dissatisfaction with the resultant selections compared with the process used in 2000. However, the question remains as to whether it is necessary for ICANN to qualify new gTLDs, as this process does, on such matters as sponsorship by a community, business and financial plans, and addition of new value to the name space.
In organic chemistry, aliphatic compounds ( /ˌælɨˈfætɨk/; G. aleiphar, fat, oil) are acyclic or cyclic, non-aromatic carbon compounds.[1] Thus, aliphatic compounds are opposite to aromatic compounds.
Contents
[hide]
1 Structure 2 Properties 3 Examples for aliphatic compounds 4 Aliphatic acids 5 See also 6 References
[edit] Structure
In aliphatic compounds, carbon atoms can be joined together in straight chains, branched chains, or non-aromatic rings (in which case they are called alicyclic). Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (alkenes) or triple bonds (alkynes). Besides hydrogen, other elements can be bound to the carbon chain, the most common being oxygen, nitrogen, sulphur, and chlorine.
The simplest aliphatic compound is methane (C H 4). Aliphatics include alkanes (e.g. paraffin hydrocarbons), alkenes (e.g. ethylene) and alkynes (e.g. acetylene). Fatty acids consist of an unbranched aliphatic tail attached to a carboxyl group.
[edit] Properties
Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in Bunsen burners and as Liquified Natural Gas (LNG), and acetylene in welding.
[edit] Examples for aliphatic compounds
The most important group of aliphatic compounds are:
n-, Iso- and Cyclo-Alkanes (Saturated Hydrocarbons) n-, Iso- and Cyclo-Alkenes and -Alkynes (Unsaturated Hydrocarbons).
Important examples of low-molecular aliphatic compounds can be found in the list below (sorted by the number of carbon-atoms):
Formula Name CAS-Number Structural Formula Chemical Classification
CH4 Methane 74-82-8 Alkane
C2H2 Ethyne 74-86-2 Alkyne
C2H4 Ethene 74-85-1 Alkene
C2H6 Ethane 74-84-0 Alkane
C3H4 Propyne 74-99-7 Alkyne
C3H6 Propene - Alkene
C3H8 Propane - Alkane
C4H6 1,2-Butadiene 590-19-2 Diene
C4H6 1-Butyne - Alkyne
C4H8 Butene -e.g.
Alkene
C4H10 Butane - Alkane
C6H10 Cyclohexene 110-83-8 Cycloalkene
C5H12 n -pentane 109-66-0 Alkane
C7H14 Cycloheptane 291-64-5 Cycloalkane
C7H14 Methylcyclohexane 108-87-2 Cyclohexane
C8H8 Cubane 277-10-1 Cyclobutane
C9H20 Nonane 111-84-2 Alkane
C10H12 Dicyclopentadiene 77-73-6 Diene, Cycloalkene
C10H16 Phellandrene 99-83-2 Terpene, Diene Cycloalkene
C10H16 α-Terpinene 99-86-5 Terpene, Cycloalkene, Diene
C10H16 Limonene 5989-27-5 Terpene, Diene, Cycloalkene
C11H24 Undecane 1120-21-4 Alkane
C30H50 Squalene 111-02-4 Terpene, Polyene
C2nH4n Polyethylene 9002-88-4 Alkane
[edit] Aliphatic acids
Aliphatic acids are the acids of nonaromatic hydrocarbons, such as acetic, propionic, and butyric acids.
From Wikipedia, the free encyclopedia
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"Arene" redirects here. For other uses, see Arene (disambiguation).
An aromatic hydrocarbon or arene[1] (or sometimes aryl hydrocarbon)[2] is a hydrocarbon with alternating double and single bonds between carbon atoms. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH).
Some non-benzene-based compounds called heteroarenes, which follow Hückel's rule, are also aromatic compounds. In these compounds, at least one carbon atom is replaced by one of the heteroatoms oxygen, nitrogen, or sulfur. Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes an oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one nitrogen atom.[3]
Contents
[hide]
1 Benzene ring model 2 Arene synthesis 3 Arene reactions
o 3.1 Aromatic substitution o 3.2 Coupling reactions o 3.3 Hydrogenation o 3.4 Cycloadditions
4 Benzene and derivatives of benzene 5 Polyaromatic hydrocarbons
o 5.1 Occurrence and pollution o 5.2 List of PAHs o 5.3 Human health o 5.4 Chemistry o 5.5 PAH compounds o 5.6 Aromaticity o 5.7 Origins of life o 5.8 Detection
6 Tables 7 See also
8 References 9 External links
[edit] Benzene ring model
Benzene
Main article: aromaticity
Benzene, C6H6, is the simplest aromatic hydrocarbon and was recognized as the first aromatic hydrocarbon, with the nature of its bonding first being recognized by Friedrich August Kekulé von Stradonitz in the 19th century. Each carbon atom in the hexagonal cycle has four electrons to share. One goes to the hydrogen atom, and one each to the two neighboring carbons. This leaves one to share with one of its two neighboring carbon atoms, which is why the benzene molecule is drawn with alternating single and double bonds around the hexagon.
The structure is also illustrated as a circle around the inside of the ring to show six electrons floating around in delocalized molecular orbitals the size of the ring itself. This also represents the equivalent nature of the six carbon-carbon bonds all of bond order ~1.5. This equivalency is well explained by resonance forms. The electrons are visualized as floating above and below the ring with the electromagnetic fields they generate acting to keep the ring flat.
General properties:
1. Display aromaticity.2. The carbon-hydrogen ratio is high.3. They burn with a sooty yellow flame because of the high carbon-hydrogen ratio.4. They undergo electrophilic substitution reactions and nucleophilic aromatic substitutions.
The circle symbol for aromaticity was introduced by Sir Robert Robinson in 1925 and popularized starting in 1959 by the Morrison & Boyd textbook on organic chemistry. The proper use of the symbol is debated, it is used to describe any cyclic pi system in some publications, or only those pi systems that obey Hückel's rule on others. Jensen [4] argues that in line with Robinson's original proposal, the use of the circle symbol should be limited to monocyclic 6 pi-electron systems. In this way the circle symbol for a 6c–6e bond can be compared to the Y symbol for a 3c–2e bond.
[edit] Arene synthesis
A reaction that forms an arene compound from an unsaturated or partially unsaturated cyclic precursor is simply called an aromatization. Many laboratory methods exist for the organic synthesis of arenes from non-arene precursors. Many methods rely on cycloaddition reactions. Alkyne trimerization describes the [2+2+2] cyclization of three alkynes, in the Dötz reaction an alkyne, carbon monoxide and a chromium carbene complex are the reactants.Diels-Alder reactions of alkynes with pyrone or cyclopentadienone with expulsion of carbon dioxide or carbon monoxide also form arene compounds. In Bergman cyclization the reactants are an enyne plus a hydrogen donor.
Another set of methods is the aromatization of cyclohexanes and other aliphatic rings: reagents are catalysts used in hydrogenation such as platinum, palladium and nickel (reverse hydrogenation), quinones and the elements sulfur and selenium.[5]
[edit] Arene reactions
Arenes are reactants in many organic reactions.
[edit] Aromatic substitution
In aromatic substitution one substituent on the arene ring, usually hydrogen, is replaced by another substituent. The two main types are electrophilic aromatic substitution when the active reagent is an electrophile and nucleophilic aromatic substitution when the reagent is a nucleophile. In radical-nucleophilic aromatic substitution the active reagent is a radical. An example is the nitration of salicylic acid [6]:
[edit] Coupling reactions
In coupling reactions a metal catalyses a coupling between two formal radical fragments. Common coupling reactions with arenes result in the formation of new carbon-carbon bonds e.g., alkylarenes, vinyl arenes, biraryls, new carbon-nitrogen bonds (anilines) or new carbon-oxygen bonds (aryloxy compounds). An example is the direct arylation of perfluorobenzenes [7]
[edit] Hydrogenation
Hydrogenation of arenes create saturated rings. The compound 1-naphthol is completely reduced to a mixture of decalin-ol isomers.[8]
The compound resorcinol, hydrogenated with Raney nickel in presence of aqueous sodium hydroxide forms an enolate which is alkylated with methyl iodide to 2-methyl-1,3-cyclohexandione:[9]
[edit] Cycloadditions
Cycloaddition reaction are not common. Unusual thermal Diels-Alder reactivity of arenes can be found in the Wagner-Jauregg reaction. Other photochemical cycloaddition reactions with alkenes occur through excimers.
[edit] Benzene and derivatives of benzene
Benzene derivatives have from one to six substituents attached to the central benzene core. Examples of benzene compounds with just one substituent are phenol, which carries a hydroxyl group and toluene with a methyl group. When there is more than one substituent present on the ring, their spatial relationship becomes important for which the arene substitution patterns ortho, meta, and para are devised. For example, three isomers exist for cresol because the methyl group and the hydroxyl group can be placed next to each other (ortho), one position removed from each other (meta), or two positions removed from each other (para). Xylenol has two methyl groups in addition to the hydroxyl group, and, for this structure, 6 isomers exist.
Representative arene compounds
Toluene
Ethylbenzene
p-Xylene
m-Xylene
Mesitylene
Durene
2-Phenylhexane
Biphenyl
Phenol
Aniline
Nitrobenzene
Benzoic acid
Aspirin
Paracetamol
Picric acid
The arene ring has an ability to stabilize charges. This is seen in, for example, phenol (C6H5-OH), which is acidic at the hydroxyl (OH), since a charge on this oxygen (alkoxide -O–) is partially delocalized into the benzene ring.
[edit] Polyaromatic hydrocarbons
An illustration of typical polycyclic aromatic hydrocarbons. Clockwise from top left: benz(e)acephenanthrylene, pyrene and dibenz(ah)anthracene.
Crystal structure of a hexa-tert-butyl derivatized hexa-peri-hexabenzo(bc,ef,hi,kl,no,qr)coronene, reported by Klaus Müllen and co-workers.[10] The tert-butyl groups make this compound soluble in common solvents such as hexane, in which the unsubstituted PAH is insoluble.
Poly-aromatic hydrocarbons (PAHs), also known as polycyclic aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents.[11] Naphthalene is the simplest example of a PAH. PAHs occur in oil, coal, and tar deposits, and are produced as byproducts of fuel burning (whether fossil fuel or biomass). As a pollutant, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in cooked foods. Studies have shown that high
levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish.[12][13][14]
They are also found in the interstellar medium, in comets, and in meteorites and are a candidate molecule to act as a basis for the earliest forms of life. In graphene the PAH motif is extended to large 2D sheets.
[edit] Occurrence and pollution
Polycyclic aromatic hydrocarbons are lipophilic, meaning they mix more easily with oil than water. The larger compounds are less water-soluble and less volatile (i.e., less prone to evaporate). Because of these properties, PAHs in the environment are found primarily in soil, sediment and oily substances, as opposed to in water or air. However, they are also a component of concern in particulate matter suspended in air.
Natural crude oil and coal deposits contain significant amounts of PAHs, arising from chemical conversion of natural product molecules, such as steroids, to aromatic hydrocarbons. They are also found in processed fossil fuels, tar and various edible oils.[15]
PAHs are one of the most widespread organic pollutants. In addition to their presence in fossil fuels they are also formed by incomplete combustion of carbon-containing fuels such as wood, coal, diesel, fat, tobacco, and incense.[16] Different types of combustion yield different distributions of PAHs in both relative amounts of individual PAHs and in which isomers are produced. Thus, coal burning produces a different mixture than motor-fuel combustion or a forest fire, making the compounds potentially useful as indicators of the burning history. Hydrocarbon emissions from fossil fuel-burning engines are regulated in developed countries.[17]
[edit] List of PAHs
Although the health effects of individual PAHs are not exactly alike, the following 17 PAHs are considered as a group in this profile issued by the Agency for Toxic Substances and Disease Registry (ATSDR):[18]
acenaphthene acenaphthylene anthracene benz[ a ]anthracene benzo[ a ]pyrene benzo[ e ]pyrene benzo[ b ]fluoranthene benzo[ ghi ]perylene benzo[ j ]fluoranthene
benzo[ k ]fluoranthene chrysene dibenz(a,h)anthracene fluoranthene fluorene indeno(1,2,3-cd)pyrene phenanthrene pyrene
[edit] Human health
PAHs toxicity is very structurally dependent, with isomers (PAHs with the same formula and number of rings) varying from being nontoxic to being extremely toxic. Thus, highly carcinogenic PAHs may be small or large. One PAH compound, benzo[ a ]pyrene , is notable for being the first chemical carcinogen to be discovered (and is one of many carcinogens found in cigarette smoke). The EPA has classified seven PAH compounds as probable human carcinogens: benz[ a ]anthracene , benzo[ a ]pyrene , benzo[ b ]fluoranthene , benzo[ k ]fluoranthene , chrysene, dibenz(a,h)anthracene, and indeno(1,2,3-cd)pyrene.
PAHs known for their carcinogenic, mutagenic and teratogenic properties are benz[ a ]anthracene and chrysene, benzo[ b ]fluoranthene , benzo[ j ]fluoranthene , benzo[ k ]fluoranthene , benzo[ a ]pyrene , benzo[ ghi ]perylene , coronene, dibenz(a,h)anthracene (C20H14), indeno(1,2,3-cd)pyrene (C22H12) and ovalene.[19]
High prenatal exposure to PAH is associated with lower IQ and childhood asthma.[20] The Center for Children's Environmental Health reports studies that demonstrate that exposure to PAH pollution during pregnancy is related to adverse birth outcomes including low birth weight, premature delivery, and heart malformations. Cord blood of exposed babies shows DNA damage that has been linked to cancer. Follow-up studies show a higher level of developmental delays at age three, lower scores on IQ tests and increased behaviorial problems at ages six and eight.[21]
[edit] Chemistry
The simplest PAHs, as defined by the International Union of Pure and Applied Chemistry (IUPAC) (G.P Moss, IUPAC nomenclature for fused-ring systems), are phenanthrene and anthracene, which both contain three fused aromatic rings. Smaller molecules, such as benzene, are not PAHs.
PAHs may contain four-, five-, six- or seven-member rings, but those with five or six are most common. PAHs composed only of six-membered rings are called alternant PAHs. Certain alternant PAHs are called benzenoid PAHs. The name comes from benzene, an aromatic hydrocarbon with a single, six-membered ring. These can be benzene rings interconnected with each other by single carbon-
carbon bonds and with no rings remaining that do not contain a complete benzene ring.
The set of alternant PAHs is closely related to a set of mathematical entities called polyhexes, which are planar figures composed by conjoining regular hexagons of identical size.
PAHs containing up to six fused aromatic rings are often known as "small" PAHs, and those containing more than six aromatic rings are called "large" PAHs. Due to the availability of samples of the various small PAHs, the bulk of research on PAHs has been of those of up to six rings. The biological activity and occurrence of the large PAHs does appear to be a continuation of the small PAHs. They are found as combustion products, but at lower levels than the small PAHs due to the kinetic limitation of their production through addition of successive rings. In addition, with many more isomers possible for larger PAHs, the occurrence of specific structures is much smaller.
PAHs possess very characteristic UV absorbance spectra. These often possess many absorbance bands and are unique for each ring structure. Thus, for a set of isomers, each isomer has a different UV absorbance spectrum than the others. This is particularly useful in the identification of PAHs. Most PAHs are also fluorescent, emitting characteristic wavelengths of light when they are excited (when the molecules absorb light). The extended pi-electron electronic structures of PAHs lead to these spectra, as well as to certain large PAHs also exhibiting semi-conducting and other behaviors.
Naphthalene (C10H8 constituent of mothballs), consisting of two coplanar six-membered rings sharing an edge, is another aromatic hydrocarbon. By formal convention, it is not a true PAH, though is referred to as a bicyclic aromatic hydrocarbon.
Aqueous solubility decreases approximately one order of magnitude for each additional ring.
[edit] PAH compounds
Chemical compound Chemical compound
Anthracene Benzo[ a ]pyrene
Chrysene Coronene
Corannulene Tetracene
Naphthalene Pentacene
Phenanthrene Pyrene
Triphenylene Ovalene
The United States Environmental Protection Agency (EPA) has designated 32 PAH compounds as priority pollutants. The original 16 are listed. They are naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[ a ]anthracene , chrysene, benzo[ b ]fluoranthene , benzo[ k ]flouranthene , benzo[ a ]pyrene , dibenz(ah)anthracene, benzo[ ghi ]perylene , and indeno(1,2,3-cd)pyrene. This list of the 16 EPA priority PAHs is often targeted for measurement in environmental samples.
[edit] Aromaticity
Although PAHs clearly are aromatic compounds, the degree of aromaticity can be different for each ring segment. According to Clar's rule (formulated by Erich Clar in 1964)[22] for PAHs the resonance structure with the most disjoint aromatic п-sextets—i.e., benzene-like moieties—is the most important for the characterization of the properties.[23]
Phenanthrene (1) Anthracene (2) Chrysene (3) Clar rule
For example, in phenanthrene (1) one Clar structure has two sextets at the extremities, while the other resonance structure has just one central sextet. Therefore in this molecule the outer rings are firmly aromatic while its central ring is less aromatic and therefore more reactive. In contrast, in anthracene (2) the number of sextets is just one and aromaticity spreads out. This difference in number of sextets is reflected in the UV absorbance spectra of these two isomers. Phenanthrene has a highest wavelength absorbance around 290 nm, while anthracene has highest wavelength bands around 380 nm. Three Clar structures with two sextets are present in chrysene (3) and by superposition the aromaticity in the outer ring is larger than in the inner rings. Another relevant Clar hydrocarbon is zethrene.
Two extremely bright stars illuminate a mist of PAHs in this Spitzer image.
[edit] Origins of life
Main article: PAH world hypothesis
In January 2004 (at the 203rd Meeting of the American Astronomical Society), it was reported[24] that a team led by A. Witt of the University of Toledo, Ohio studied ultraviolet light emitted by the Red Rectangle nebula and found the
spectral signatures of anthracene and pyrene (no other such complex molecules had ever before been found in space). This discovery was considered as a controversial[25] confirmation of a hypothesis that as nebulae of the same type as the Red Rectangle approach the ends of their lives, convection currents cause carbon and hydrogen in the nebulae's core to get caught in stellar winds, and radiate outward. As they cool, the atoms supposedly bond to each other in various ways and eventually form particles of a million or more atoms. Witt and his team inferred[24] that since they discovered PAHs—which may have been vital in the formation of early life on Earth—in a nebula, by necessity they must originate in nebulae.[25] More recently, fullerenes (or "buckyballs"), have been detected in other nebulae.[26] Fullerenes are also implicated in the origin of life; according to astronomer Letizia Stanghellini, "It’s possible that buckyballs from outer space provided seeds for life on Earth.”[27]
[edit] Detection
Detection of PAHs in materials is often done using gas chromatography-mass spectrometry or liquid chromatography with ultraviolet-visible or fluorescence spectroscopic methods or by using rapid test PAH indicator strips.
[edit] Tables
[show]v · d · e Polycyclic aromatic hydrocarbons
[show]v · d · eConsumer food safety
[show]v · d · e Hydrocarbons
[edit] See also
Asphaltene Hydrodealkylation Simple aromatic rings Aromatic substituents: Aryl, Aryloxy and Arenediyl
[edit] References
1. ̂ Definition IUPAC Gold Book Link2. ̂ Mechanisms of Activation of the Aryl Hydrocarbon Receptor by Maria Backlund,
Institute of Environmental Medicine, Karolinska Institutet
3. ̂ HighBeam Encyclopedia: aromatic compound4. ̂ The Origin of the Circle Symbol for Aromaticity by William B. Jensen 424 Journal of
Chemical Education Vol. 86 No. 4 April 20095. ̂ Jerry March Advanced Organic Chemistry 3Ed., ISBN 0-471-85472-76. ̂ Webb, K. (1995). "A mild oxidation of aromatic amines". Tetrahedron Letters 36 (14):
2377–2378. doi:10.1016/0040-4039(95)00281-G. edit7. ̂ Lafrance, M.; Rowley, C.; Woo, T.; Fagnou, K. (2006). "Catalytic intermolecular direct
arylation of perfluorobenzenes.". Journal of the American Chemical Society 128 (27): 8754–8756. doi:10.1021/ja062509l. PMID 16819868. edit
8. ̂ Organic Syntheses, Coll. Vol. 6, p.371 (1988); Vol. 51, p.103 (1971). http://orgsynth.org/orgsyn/pdfs/CV6P0371.pdf
9. ̂ Organic Syntheses, Coll. Vol. 5, p.743 (1973); Vol. 41, p.56 (1961). http://orgsynth.org/orgsyn/pdfs/CV5P0567.pdf
10. ̂ Herwig, Peter T.; Enkelmann, Volker; Schmelz, Oliver; Müllen, Klaus (2000). "Synthesis and Structural Characterization of Hexa-tert-butyl- hexa-peri-hexabenzocoronene, Its Radical Cation Salt and Its Tricarbonylchromium Complex". Chemistry: A European Journal (Chem.-Euro.J.) 18 (10): 1834–1839. doi:10.1002/(SICI)1521-3765(20000515)6:10<1834::AID-CHEM1834>3.0.CO;2-L.
11. ̂ Fetzer, J. C. (2000). "The Chemistry and Analysis of the Large Polycyclic Aromatic Hydrocarbons". Polycyclic Aromatic Compounds (New York: Wiley) 27 (2): 143. doi:10.1080/10406630701268255. ISBN 0471363545.
12. ̂ "Polycyclic Aromatic Hydrocarbons – Occurrence in foods, dietary exposure and health effects". European Commission, Scientific Committee on Food. December 4, 2002. http://ec.europa.eu/food/fs/sc/scf/out154_en.pdf.
13. ̂ Larsson, B. K.; Sahlberg, GP; Eriksson, AT; Busk, LA (1983). "Polycyclic aromatic hydrocarbons in grilled food". J Agric Food Chem. 31 (4): 867–873. doi:10.1021/jf00118a049. PMID 6352775.
14. ̂ "Polycyclic Aromatic Hydrocarbons (PAHs)". Agency for Toxic Substances and Disease Registry. 1996. http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=121&tid=25.
15. ̂ Glenn Michael Roy (1995). Activated carbon applications in the food and pharmaceutical industries. CRC Press. p. 125. ISBN 1566761980. http://books.google.com/?id=nmmpK0oDE20C&pg=PA125.
16. ̂ "Incense link to cancer". BBC News. 2001-08-02. http://news.bbc.co.uk/2/hi/health/1467409.stm.
17. ̂ For example, EPA regulations for small engines are at 40 CFR §90.103; see emission standard for more information.
18. ̂ ATSDR19. ̂ Luch, A. (2005). The Carcinogenic Effects of Polycyclic Aromatic Hydrocarbons.
London: Imperial College Press. ISBN 1-86094-417-5.20. ̂ Exposure to Common Pollutant in Womb Might Lower IQ21. ̂ http://www.ccceh.org/pdf-press/Time10-4-10.pdf22. ̂ Clar, E. (Erich) (1964). Polycyclic Hydrocarbons. New York: Academic Press. LCCN
63012392.23. ̂ Portella, Guillem; Poater, Jordi; Solà, Miquel (2005). "Assessment of Clar's aromatic
π-sextet rule by means of PDI, NICS and HOMA indicators of local aromaticity". Journal of Physical Organic Chemistry 18 (8): 785. doi:10.1002/poc.938.
24. ^ a b Battersby, S. (2004). "Space molecules point to organic origins". New Scientist. http://www.newscientist.com/article/dn4552-space-molecules-point-to-organic-origins.html. Retrieved 2009-12-11.
25. ^ a b Mulas, G.; Malloci, G.; Joblin, C.; Toublanc, D. (2006). "Estimated IR and phosphorescence emission fluxes for specific polycyclic aromatic hydrocarbons in the Red Rectangle". Astronomy and Astrophysics 446 (2): 537. arXiv:astro-ph/0509586. Bibcode 2006A&A...446..537M. doi:10.1051/0004-6361:20053738.
26. ̂ García-Hernández, D. A.; Manchado, A.; García-Lario, P.; Stanghellini, L.; Villaver, E.; Shaw, R. A.; Szczerba, R.; Perea-Calderón, J. V. (2010-10-28). "Formation Of Fullerenes In H-Containing Planatary Nebulae". The Astrophysical Journal Letters 724 (1): L39–L43. Bibcode 2010ApJ...724L..39G. doi:10.1088/2041-8205/724/1/L39.
27. ̂ Atkinson, Nancy (2010-10-27). "Buckyballs Could Be Plentiful in the Universe". Universe Today. http://www.universetoday.com/76732/buckyballs-could-be-plentiful-in-the-universe. Retrieved 2010-10-28.
[edit] External links
Wikimedia Commons has media related to: Polycyclic aromatic hydrocarbons
ATSDR - Toxicity of Polycyclic Aromatic Hydrocarbons (PAHs) U.S. Department of Health and Human Services
Fused Ring and Bridged Fused Ring Nomenclature Database of PAH structures National Pollutant Inventory: Polycyclic Aromatic Hydrocarbon Fact Sheet Understanding Polycyclic Aromatic Hydrocarbons NASA Spitzer Space Telescope Astrobiology magazine Aromatic World An interview with Professor Pascale
Ehrenfreund on PAH origin of life. Accessed June 2006 Oregon State University Superfund Research Center focused on new technologies
and emerging health risks of Polycyclic Aromatic Hydrocarbons (PAHs) Carcinogenic FAC list in Portable Document Format. Toxicological profiles of PAH . LIST of PAH . Abiogenic Gas Debate 11:2002 (EXPLORER)
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IUPAC nomenclature of organic chemistryFrom Wikipedia, the free encyclopedia
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The IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended[1] by the International Union of Pure and Applied Chemistry (IUPAC). Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be drawn. There is also an IUPAC nomenclature of inorganic chemistry. See also phanes nomenclature of highly complex cyclic molecules.
For ordinary communication, to spare a tedious description, the official IUPAC naming recommendations are not always followed in practice except when it is necessary to give a concise definition to a compound, or when the IUPAC name is simpler (e.g. ethanol against ethyl alcohol). Otherwise the common or trivial name may be used, often derived from the source of the compound (See Sec 6. below)
Contents
[hide]
1 Basic principles 2 Alkanes 3 Alkenes and Alkynes 4 Functional groups
o 4.1 Alcohols o 4.2 Halogens (Alkyl Halides) o 4.3 Ketones o 4.4 Aldehydes o 4.5 Carboxylic acids o 4.6 Ethers o 4.7 Esters o 4.8 Amines and Amides o 4.9 Cyclic compounds
5 Order of precedence of groups 6 Common nomenclature - trivial names
o 6.1 Ketones o 6.2 Aldehydes
7 Ions o 7.1 Hydron o 7.2 Parent hydride cations o 7.3 Cations and substitution
8 See also 9 External links 10 References
[edit] Basic principles
In chemistry, a number of prefixes, suffixes and infixes are used to describe the type and position of functional groups in the compound.
The steps to naming an organic compound are:
1. Identify the parent hydrocarbon chain. This chain must follow the following rules, in order of precedence:
1. It should have maximum substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, use the one with highest precedence as shown here.
2. It should have maximum number of multiple bonds.3. It should have maximum number of carbons (Side chains included).4. It should have the maximum length.5. It should have maximum number of double bonds.
2. Identify the parent functional group, if any, with the highest order of precedence.3. Identify the side-chains. Side chains are the carbon chains that are not in the parent chain, but
are branched off from it.4. Identify the remaining functional groups, if any, and name them by the name of their ions (such
as hydroxy for -OH, oxy for =O , oxyalkane for O-R, etc.).Different side-chains and functional groups will be grouped together in alphabetical order. (The prefixes di-, tri-, etc. are not taken into consideration for grouping alphabetically. For example, ethyl comes before dihydroxy or dimethyl, as the "e" in "ethyl" precedes the "h" in "dihydroxy" and the "m" in "dimethyl" alphabetically. The "di" is not considered in either case). In the case of there being both side chains and secondary functional groups, they should be written mixed together in one group rather than in two separate groups.
5. Identify double/triple bonds.6. Number the chain. To number the chain, first number in both directions (left to right and right to
left), and then choose the numbering which follows these rules, in order of precedence: 1. Has the lowest locant (or locants) for the suffix functional group. Locants are the
numbers on the carbons to which the substituent is directly attached.2. Has the lowest locants for multiple bonds (The locant of a multiple bond is the number
of the adjacent carbon with a lower number).3. Has the lowest locants for double bonds4. Has the lowest locants for prefixes.
7. Number the various substituents and bonds with their locants. If there is more than one of the same type of substituent/double bond, add the prefix (di-, tri-, etc.) before it. The numbers for that type of side chain will be grouped in ascending order and written before the name of the side-chain. If there are two side-chains with the same alpha carbon, the number will be written twice. Example: 2,2,3-trimethyl- . If there are both double bonds and triple bonds, write the "ene" before the "yne". In case the main functional group is a terminal functional group (A group which can only exist at the end of a chain, like formyl and carboxyl groups), there is no need to number it.
8. Arrange everything like this: Group of side chains and secondary functional groups with numbers made in step 3 + prefix of parent hydrocarbon chain (eth, meth) + double/triple bonds with numbers (or "ane") + primary functional group suffix with numbers.Wherever it says "with numbers", it is understood that between the word and the numbers, you use the prefix(di-, tri-)
9. Add punctuation: 1. Put commas between numbers (2 5 5 becomes 2,5,5)2. Put a hyphen between a number and a letter (2 5 5 trimethylheptane becomes 2,5,5-
trimethylheptane)3. Successive words are merged into one word (trimethyl heptane becomes
trimethylheptane)Note: IUPAC uses one-word names throughout. This is why all parts are connected.
The finalized name should look like this: #,#-di<side chain>-#-<secondary functional group>-#-<side chain>-#,#,#-tri<secondary functional group><parent chain suffix><If all bonds are single bonds, use "ane">-#,#-di<double bonds>-#-<triple bonds>-#-<primary functional group>Note: # is used for a number. The group secondary functional groups and side chains may not look the same as shown here, as the side chains and secondary functional groups are arranged alphabetically. The di- and tri- have been used just to show their usage. (di- after #,#, tri- after #,#,# , etc.)
Example:Here is a sample molecule with the parent carbons numbered:
For simplicity, here is an image of the same molecule, where the hydrogens in the parent chain are removed and the carbons are shown by their numbers:
Now, we go by the steps:
1. The parent hydrocarbon chain has 23 carbons. It is called tricos-.2. The functional groups with the highest precedence are the two ketone groups.
1. The groups are on carbon atoms 3 & 9. As there are two, we write 3,9-dione.2. The numbering of the molecule is based on the ketone groups. When numbering from
left to right, the ketone groups get numbered 3 and 9. When numbering from right to left, the ketone groups get numbered 15 and 21. 3 is less than 15, therefore, the numbering is done left to right, and the ketones are numbered 3 & 9. The lesser number is always used, not the sum of the constituents numbers.
3. The side chains are: an ethyl- at carbon 4, an ethyl- at carbon 8, and a butyl- at carbon 12.Note:The -O-CH3 at carbon atom 15 is not a side chain, but it is a methoxy functional group
o There are two ethyl- groups, so they are combined to create, 4,8-diethyl.o The side chains shall be grouped like this: 12-butyl-4,8-diethyl. (But this is not the final
grouping, as functional groups may be added in between.)4. The secondary functional groups are: a hydroxy- at carbon 5, a chloro- at carbon 11, a methoxy-
at carbon 15, and a bromo- at carbon 18. Grouped with the side chains, we get 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxy
5. There are two double bonds: one between carbons 6 & 7, and one between carbons 13 & 14. They will be called 6,13-diene. There is one triple bond between carbon atoms 19 & 20. It will be called 19-yne
6. The arrangement (with punctuation) is: 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-diene-19-yne-3,9-dione
The final name is 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-diene-19-yne-3,9-dione.
[edit] Alkanes
Main article: Alkane
Straight-chain alkanes take the suffix "-ane" and are prefixed depending on the number of carbon atoms in the chain, following standard rules. The first few are:
Number of carbo
ns
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 20 30 40 50
PrefixMeth
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
Undec
Dodec
Tridec
Tetradec
Pentadec
Eicos
Triacont
Tetracont
Pentacont
For example, the simplest alkane is CH4 methane, and the nine-carbon alkane CH3(CH2)7CH3 is named nonane. The names of the first four alkanes were derived from methanol, ether, propionic acid and butyric acid, respectively. The rest are named with a Greek numeric prefix, with the
exceptions of nonane which has a Latin prefix, and undecane and tridecane which have mixed-language prefixes.
Cyclic alkanes are simply prefixed with "cyclo-", for example C4H8 is cyclobutane and C6H12 is cyclohexane.
Branched alkanes are named as a straight-chain alkane with attached alkyl groups. They are prefixed with a number indicating the carbon the group is attached to, counting from the end of the alkane chain. For example, (CH3)2CHCH3, commonly known as isobutane, is treated as a propane chain with a methyl group bonded to the middle (2) carbon, and given the systematic name 2-methylpropane. However, although the name 2-methylpropane COULD be used, it is easier and more logical to call it simply methylpropane - the methyl group could not possibly occur on any of the other carbon atoms (that would lengthen the chain and result in butane, not propane) and therefore the use of the number "2" is not necessary.
If there is ambiguity in the position of the substituent, depending on which end of the alkane chain is counted as "1", then numbering is chosen so that the smallest number is used. For example, (CH3)2CHCH2CH3 (isopentane) is named 2-methylbutane, not 3-methylbutane.
If there are multiple side-branches of the same size alkyl group, their positions are separated by commas and the group prefixed with di-, tri-, tetra-, etc., depending on the number of branches (e.g. C(CH3)4 2,2-dimethylpropane). If there are different groups, they are added in alphabetical order, separated by commas or hyphens: 3-ethyl-4-methylhexane. The longest possible main alkane chain is used; therefore 3-ethyl-4-methylhexane instead of 2,3-diethylpentane, even though these describe equivalent structures. The di-, tri- etc. prefixes are ignored for the purpose of alphabetical ordering of side chains (e.g. 3-ethyl-2,4-dimethylpentane, not 2,4-dimethyl-3-ethylpentane).
[edit] Alkenes and Alkynes
Main articles: Alkenes and Alkynes
Alkenes are named for their parent alkane chain with the suffix "-ene" and an infixed number indicating the position of the double-bonded carbon in the chain: CH2=CHCH2CH3 is but-1-ene. Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a": CH2=CHCH=CH2 is buta-1,3-diene. Simple cis and trans isomers are indicated with a prefixed cis- or trans-: cis-but-2-ene, trans-but-2-ene. More complex geometric isomerisations are described using the Cahn Ingold Prelog priority rules.
Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond: ethyne (acetylene), propyne (methylacetylene).
[edit] Functional groups
Family StructureIUPAC
nomenclature
IUPAC nomenclature for cyclic parent chains
(if different from straight chains)
Common nomenclature
Alkyl groups R— Alkyl - Alkyl
HalogensR—X
(halogen)Haloalkane - Alkyl halide
Alcohols R—OH Alkanol - Alkyl alcohol
Amines R—NH2 Alkamine - Alkyl amine
Carboxylic acids
(Alk + 1)anoic acid
Cycloalkanecarboxylic acid -
Aldehydes Alkanal Cycloalkanecarbaldehyde -
Ketones Alkanone -Alk(1)yl Alk(2)yl
ketone
Thiols R—SH Alkanethiol - -
Amides (Alk + 1)anamide Cycloalkanecarboxamide -
Ethers R1—O—R2 alkoxyalkane - Alk(1)yl Alk(2)yl ether
EstersAlk(1)yl
Alk(2)anoateAlk(1)yl Cycloalk(2)anecarboxylate
Alk(1)yl (Alk + 1)(2)anoate
[edit] Alcohols
Main article: Alcohols
Alcohols (R-OH) take the suffix "-ol" with an infix numerical bonding position: CH3CH2CH2OH is propan-1-ol. The suffixes -diol, -triol, -tetraol, etc., are used for multiple -OH groups: Ethylene glycol CH2OHCH2OH is ethane-1,2-diol.
If higher precedence functional groups are present (see order of precedence, below), the prefix "hydroxy" is used with the bonding position: CH3CHOHCOOH is 2-hydroxypropanoic acid.
[edit] Halogens (Alkyl Halides)
Main article: Halogens
Halogen functional groups are prefixed with the bonding position and take the form fluoro-, chloro-, bromo-, iodo-, etc., depending on the halogen. Multiple groups are dichloro-, trichloro-, etc., and dissimilar groups are ordered alphabetically as before. For example, CHCl3 (chloroform) is trichloromethane. The anesthetic Halothane (CF3CHBrCl) is 2-bromo-2-chloro-1,1,1-trifluoroethane.
[edit] Ketones
Main article: Ketones
In general ketones (R-CO-R) take the suffix "-one" (pronounced own, not won) with an infix position number: CH3CH2CH2COCH3 is pentan-2-one. If a higher precedence suffix is in use, the prefix "oxo-" is used: CH3CH2CH2COCH2CHO is 3-oxohexanal.
[edit] Aldehydes
Main article: Aldehydes
Aldehydes (R-CHO) take the suffix "-al". If other functional groups are present, the chain is numbered such that the aldehyde carbon is in the "1" position, unless functional groups of higher precedence are present.
If a prefix form is required, "oxo-" is used (as for ketones), with the position number indicating the end of a chain: CHOCH2COOH is 3-oxopropanoic acid. If the carbon in the carbonyl group cannot be included in the attached chain (for instance in the case of cyclic aldehydes), the prefix "formyl-" or the suffix "-carbaldehyde" is used: C6H11CHO is cyclohexanecarbaldehyde. If an aldehyde is attached to a benzene and is the main functional group, the suffix becomes benzaldehyde.
[edit] Carboxylic acids
Main article: Carboxylic acids
In general carboxylic acids are named with the suffix -oic acid (etymologically a back-formation from benzoic acid). As for aldehydes, they take the "1" position on the parent chain, but do not have their position number indicated. For example, CH3CH2CH2CH2COOH (valeric acid) is
named pentanoic acid. For common carboxylic acids some traditional names such as acetic acid are in such widespread use they are considered retained IUPAC names, although "systematic" names such as ethanoic acid are also acceptable. For carboxylic acids attached to a benzene ring such as Ph-COOH, these are named as benzoic acid or its derivatives.
If there are multiple carboxyl groups on the same parent chain, the suffix "-carboxylic acid" can be used (as -dicarboxylic acid, -tricarboxylic acid, etc.). In these cases, the carbon in the carboxyl group does not count as being part of the main alkane chain. The same is true for the prefix form, "carboxyl-". Citric acid is one example; it is named 2-hydroxypropane- 1,2,3-tricarboxylic acid, rather than 3-carboxy, 3-hydroxypentanedioic acid.
[edit] Ethers
Main article: Ethers
Ethers (R-O-R) consist of an oxygen atom between the two attached carbon chains. The shorter of the two chains becomes the first part of the name with the -ane suffix changed to -oxy, and the longer alkane chain become the suffix of the name of the ether. Thus CH3OCH3 is methoxymethane, and CH3OCH2CH3 is methoxyethane (not ethoxymethane). If the oxygen is not attached to the end of the main alkane chain, then the whole shorter alkyl-plus-ether group is treated as a side-chain and prefixed with its bonding position on the main chain. Thus CH3OCH(CH3)2 is 2-methoxypropane.
[edit] Esters
Main article: Esters
Esters (R-CO-O-R') are named as alkyl derivatives of carboxylic acids. The alkyl (R') group is named first. The R-CO-O part is then named as a separate word based on the carboxylic acid name, with the ending changed from -oic acid to -oate. For example, CH3CH2CH2CH2COOCH3 is methyl pentanoate, and (CH3)2CHCH2CH2COOCH2CH3 is ethyl 4-methylpentanoate. For
esters such as ethyl acetate (CH3COOCH2CH3), ethyl formate (HCOOCH2CH3) or dimethyl phthalate that are based on common acids, IUPAC recommends use of these established names, called retained names. The -oate changes to -ate. Some simple examples, named both ways, are shown in the figure above.
If the alkyl group is not attached at the end of the chain, the bond position to the ester group is infixed before "-yl": CH3CH2CH(CH3)OOCCH2CH3 may be called but-2-yl propanoate or but-2-yl propionate.
[edit] Amines and Amides
Main articles: Amine and Amide
Amines (R-NH2) are named for the attached alkane chain with the suffix "-amine" (e.g. CH3NH2 Methyl Amine). If necessary, the bonding position is infixed: CH3CH2CH2NH2 propan-1-amine, CH3CHNH2CH3 propan-2-amine. The prefix form is "amino-".
For secondary amines (of the form R-NH-R), the longest carbon chain attached to the nitrogen atom becomes the primary name of the amine; the other chain is prefixed as an alkyl group with location prefix given as an italic N: CH3NHCH2CH3 is N-methylethanamine. Tertiary amines (R-NR-R) are treated similarly: CH3CH2N(CH3)CH2CH2CH3 is N-ethyl-N-methylpropanamine. Again, the substituent groups are ordered alphabetically.
Amides (R-CO-NH2) take the suffix "-amide", or "-carboxamide" if the carbon in the amide group cannot be included in the main chain . The prefix form is both "carbamoyl-" and "amido-".
Secondary and tertiary amides are treated similarly to the case of amines: alkane chains bonded to the nitrogen atom are treated as substituents with the location prefix N: HCON(CH3)2 is N,N-dimethylmethanamide.
[edit] Cyclic compounds
Cycloalkanes and aromatic compounds can be treated as the main parent chain of the compound, in which case the position of substituents are numbered around the ring structure. For example, the three isomers of xylene CH3C6H4CH3, commonly the ortho-, meta-, and para- forms, are 1,2-dimethylbenzene, 1,3-dimethylbenzene, and 1,4-dimethylbenzene. The cyclic structures can also be treated as functional groups themselves, in which case they take the prefix "cycloalkyl-" (e.g. "cyclohexyl-") or for benzene, "phenyl-".
The IUPAC nomenclature scheme becomes rapidly more elaborate for more complex cyclic structures, with notation for compounds containing conjoined rings, and many common names such as phenol, furan, indole, etc. being accepted as base names for compounds derived from them.
[edit] Order of precedence of groups
When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The highest precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds only take suffix form (-en and -yn) and are used with other suffixes.
Prefixed substituents are ordered alphabetically (excluding any modifiers such as di-, tri-, etc.), e.g. chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either prefixed or suffixed, the position numbers are ordered numerically (thus ethane-1,2-diol, not ethane-2,1-diol.) The N position indicator for amines and amides comes before "1", e.g. CH3CH(CH3)CH2NH(CH3) is N,2-dimethylpropanamine.
Priority Functional group Formula Prefix Suffix
1Cations e.g. Ammonium
–NH3
+
-onio-ammonio-
-onium-ammonium
2
Carboxylic acids
Carbothioic S -acids
Carboselenoic Se -acids
Sulfonic acids
Sulfinic acids
–COOH–COSH–COSeH–SO3
H–SO2
H
carboxy-sulfanylcarbonyl-selanylcarbonyl-sulfo-sulfino-
-oic acid*-thioic S-acid*-selenoic Se-acid*-sulfonic acid-sulfinic acid
3 Carboxylic acid derivatives
–COOR–COX–CONH–CON=C<–C(=NH)NH
R-oxycarbonyl-halocarbonyl-carbamoyl--imido-amidino-
-R-oate-oyl halide*-amide*-imide*-amidine*
Esters
Acyl halides
Amides
Imides
Amidines
4Nitriles
–CN–NC
cyano-isocyano-
-nitrile*isocyanide
5Aldehydes
–CHO–CHS
formyl-thioformyl-
-al*-thial*
6
Ketones
Thiones
Selones
Tellones
=O=S=Se=Te
oxo-sulfanylidene-selanylidene-tellanylidene-
-one-thione-selone-tellone
7
Alcohols
Thiols
Selenols
Tellurols
–OH–SH–SeH–TeH
hydroxy-sulfanyl-selanyl-tellanyl-
-ol-thiol-selenol-tellurol
8
Hydroperoxides
Peroxols
Thioperoxols (Sulfenic acid)
Dithioperoxols
-OOH-SOH-SSH
hydroperoxy-hydroxysulfanyl-disulfanyl-
-peroxol--dithioperoxol
9Amines
–NH=NH–NHNH
amino-imino-hydrazino-
-amine-imine-hydrazine
10 Ethers –O– -oxy-
–S––Se–
-thio--seleno-
11Peroxides
–OO––SS–
-peroxy--disulfanyl-
*Note: These suffixes, in which the carbon atom is counted as part of the preceding chain, are the most commonly used. See individual functional group articles for more details.
[edit] Common nomenclature - trivial names
Common nomenclature is an older system of naming organic compounds. Instead of using the prefixes for the carbon skeleton above, another system is used. The pattern can be seen below.
[edit] Ketones
Common names for ketones can be derived by naming the two alkyl or aryl groups bonded to the carbonyl group as separate words followed by the word ketone.
Acetone Acetophenone Benzophenone Ethyl isopropyl ketone Diethyl ketone
The first three of the names shown above are still considered to be acceptable IUPAC names.
[edit] Aldehydes
The common name for an aldehyde is derived from the common name of the corresponding carboxylic acid by dropping the word acid and changing the suffix from -ic or -oic to -aldehyde.
Formaldehyde Acetaldehyde
[edit] Ions
The IUPAC nomenclature also provides rules for naming ions.
[edit] Hydron
Hydron is a generic term for hydrogen cation; protons, deuterons and tritons are all hydrons.
[edit] Parent hydride cations
(See also Onium compounds.)
Simple cations formed by adding a hydron to a hydride of a halogen, chalcogen or nitrogen-family element are named by adding the suffix "-onium" to the element's root: H4N+ is ammonium, H3O+ is oxonium, and H2F+ is fluoronium. Ammonium was adopted instead of nitronium, which commonly refers to NO2
+.
If the cationic center of the hydride is not a halogen, chalcogen or nitrogen-family element then the suffix "-ium" is added to the name of the neutral hydride after dropping any final 'e'. H5C+ is methanium, HO-(O+)-H2 is dioxidanium (HO-OH is dioxidane), and H2N-(N+)-H3 is diazanium (H2N-NH2 is diazane).
[edit] Cations and substitution
The above cations except for methanium are not, strictly speaking, organic, since they do not contain carbon. However, many organic cations are obtained by substituting another element or some functional group for a hydrogen.
The name of each substitution is prefixed to the hydride cation name. If many substitutions by the same functional group occur, then the number is indicated by prefixing with "di-", "tri-" as with halogenation. (CH3)3O+ is trimethyloxonium. CH3F3N+ is trifluoromethylammonium.
[edit] See also
Preferred IUPAC name IUPAC nomenclature of inorganic chemistry International Union of Biochemistry and Molecular Biology Cahn Ingold Prelog priority rules Organic nomenclature in Chinese Nucleic acid notation
[edit] External links
IUPAC Nomenclature of Organic Chemistry (online version of the "Blue Book") IUPAC Recommendations on Organic & Biochemical Nomenclature, Symbols, Terminology, etc.
(includes IUBMB Recommendations for biochemistry) Bibliography of IUPAC Recommendations on Organic Nomenclature (last updated 11 April 2003) ACD/Name Software for generating systematic nomenclature ChemAxon Name <> Structure - ChemAxon IUPAC (& traditional) name to structure and structure to
IUPAC name software. As used at chemicalize.org chemicalize.org A free web site/service that extracts IUPAC names from web pages and annotates a
'chemicalized' version with structure images. Structures from annotated pages can also be searched.
G. A. Eller, Improving the Quality of Published Chemical Names with Nomenclature Software. Molecules 2006, 9, 915-928 (online article)
American Chemical Society, Committee on Nomenclature, Terminology & Symbols
[edit] References
1. ̂ Nomenclature of Organic Chemistry (3 ed.). London: Butterworths. 1971 (3rd edition combined) [1958 (A: Hydrocarbons, and B: Fundamental Heterocyclic Systems), 1965 (C: Characteristic Groups)]. ISBN 0408701447.
1. ̂ Nomenclature of Organic Chemistry, Oxford: Pergamon Press, 1979; A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993, Oxford: Blackwell Scientific Publications, 1993.
Number ofcarbons
Prefix as in
new system
Common name
for alcohol
Common namefor aldehyde
Common name
for acid
1 Meth
Methyl alcohol(wood alcohol)
Formaldehyde Formic acid
2 EthEthyl alcohol(grain alcohol)
Acetaldehyde Acetic acid
3 PropPropyl alcohol
PropionaldehydePropionic acid
4 But Butyl alcohol Butyraldehyde Butyric acid
5 Pent Amyl alcohol Valeraldehyde Valeric acid
6 Hex - Caproaldehyde Caproic acid
7 HeptEnanthyl alcohol
EnanthaldehydeEnanthoic acid
8 OctCapryl alcohol
Caprylaldehyde Caprylic acid
9 Non - PelargonaldehydePelargonic acid
10 DecCapric alcohol
Capraldehyde Capric acid
11 Undec - - -
12 DodecLauryl alcohol
Lauraldehyde Lauric acid
14 Tetradec - Myristaldehyde Myristic acid
16 Hexadec Cetyl alcohol Palmitaldehyde Palmitic acid
17 Heptadec - -Margaric acid
18 OctadecStearyl alcohol
Stearaldehyde Stearic acid
20 EicosArachidyl alcohol
-Arachidic acid
22 DocosBehenyl alcohol
- Behenic acid
24 TetracosLignoceryl alcohol
-Lignoceric acid
26 HexacosCerotinyl alcohol
-Cerotinic acid
28 OctacosMountainyl alcohol
-Mountainic acid
30 TriacontMelissyl alcohol
- Melissic acid
40 Tetracont - - -
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