Organic Chemistry - School District 22 Vernon · UNIT X — ORGANIC CHEMISTRY 2 . B. Alkanes 1. A carbon atom can form bonds to four other atoms (carbon has a valence of four). A

Organic Chemistry

A. Introduction

1. Organic chemistry is defined as the chemistry of CARBON compounds. There are a huge number of organic compounds. This results from the fact that carbon forms chains involving several carbon atoms linked to each other in a straight-line fashion, in a “circular” pattern, or in a branched pattern. In addition, the carbon atoms may form single, double, or triple bonds to neighbouring atoms.

2. Organic compounds are found in petroleum, natural gas, and all

living things. The largest industry involving organic chemistry is the manufacture of petrochemicals. Petroleum is the starting material for a vast range of products. Petroleum is separated (“fractioned”) and refined for use in gasoline and oil, while other “fractions” of petroleum are chemically altered to serve as raw materials for a huge array of industrial processes such as the manufacture of plastics, solvents, pharmaceuticals, and personal care products.

UNIT X — ORGANIC CHEMISTRY 2

B. Alkanes

1. A carbon atom can form bonds to four other atoms (carbon has a valence of four).

A HYDROCARBON is a compound containing only hydrogen

and carbon.

There are many ways to represent a hydrocarbon formula, depending on how compact one wants to write the formula.

EXAMPLE X.1 REPRESENTING HYDROCARBONS

Problem: Write the structure of propane, C3H8 as full structure, condensed structure, molecular formula, and carbon skeleton.

Solution: Full Structure Condensed structure CH3—CH2—CH3 Molecular formula C3H8 Carbon skeleton C—C—C

H H H | | | H—C—C—C—H | | | H H H


2. ALKANES (A HOMOLOGOUS SERIES) methane = CH4

ethane = C2H6

propane = C3H8

butane = C4H10

Notice that each carbon forms four bonds. The number of H’s

attached is 4 minus the numbers of C’s attached.

methane 1 CH4

ethane 2 C2H6 CH3—CH3

propane 3 C3H8 CH3—CH2—CH3

butane 4 C4H10 CH3—CH2—CH2—CH3

pentane 5 C5H12 CH3—CH2—CH2—CH2—CH3

hexane 6 C6H14 CH3—CH2—CH2—CH2—CH2—CH3

heptane 7 C7H16 CH3—CH2—CH2—CH2—CH2—CH2—CH3

octane 8 C8H18 CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH3

nonane 9 C9H20

CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH3

decane 10 C10H22

CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH3

An ALKANE is a hydrocarbon in which all the carbon atoms are

connected by single bonds.

H | H—C—H | H

H H H | | | H—C—C—C—H | | | H H H

H H | | H—C—C—H | | H H

H H H H | | | | H—C—C—C—C—H | | | | H H H H


2. Each of the molecules differs by the number of carbon atoms linked to one another to form a “CARBON CHAIN”. A series of structures that differ from each other by one structural unit, in this case —CH2—, are called a HOMOLOGOUS SERIES.

Because the chain of carbon atoms extends in a straight-line they are called “STRAIGHT-CHAIN” or “UNBRANCHED” hydrocarbons.

The names of the all the above hydrocarbons end in “ANE” because they are “ALKANES”. Alkanes are said to be “SATURATED” hydrocarbons because each carbon atom is bonded to the maximum possible number of other atoms.

Each of the single bonds between carbon atoms is able to rotate

freely, leading to a highly flexible chain which can take many shapes.

The following molecules all represent heptane, C7H16

Assign #1 3. A hydrocarbon can also have “SIDE BRANCHES” which are

also hydrocarbon chains. The attached groups are called “ALKYL GROUPS”.

An ALKYL GROUP is an alkane, which has lost one hydrogen atom.

CH3—CH2 CH2—CH3 | | CH2—CH2—CH2

CH3—CH—CH2—CH2—CH2—CH3 | CH2—CH3

CH3—CH2—CH2—CH2—CH2—CH0—CH3

CH3—CH—CH3 | CH2—CH2—CH2—CH3


An alkyl group is named by changing the “ANE” ending of the

original hydrocarbon to “YL”.

ORIGINAL HYDROCARBON ALKYL GROUP

methane = CH4 methyl = CH3—

ethane = CH3—CH3 ethyl = CH3—CH2—

propane = CH3—CH2—CH3 propyl = CH3—CH2—CH2—

butane = CH3—CH2—CH2—CH3 butyl = CH3—CH2—CH2—CH2—

4. When an alkyl group is attached to another hydrocarbon, the

resulting molecule is called a SUBSTITUTED HYDROCARBON or a BRANCHED HYDROCARBON.

NAMING A SUBSTITUTED HYDROCARBON:

i) First find the longest continuous chain of carbon atoms. This longest chain is called the PARENT hydrocarbon. (Look at branch points.)

Assign 2bd ii) Write the CARBON NUMBER at which the alkyl group is

attached followed by a dash “—“. iii) Name the alkyl group.

C—C—C—C—C—C—C—C | C—C—C—C

9 Carbons

C—C—C—C C—C—C | | C—C—C—C—C—C—C | C—C

10 carbons


iv) Name the longest or parent hydrocarbon to which the alkyl group is attached. (The carbon atoms in the parent hydrocarbon are numbered consecutively from the end of the hydrocarbon which gives the lowest possible set of numbers (address) to the attached groups.

Assign 3-6ace v) If more than one different alkyl group is attached to the

hydrocarbon, then list the alkyl groups ALPHABETICALLY preceded by its number and a dash.

vi) If an alkyl group is repeated, list each carbon number where

the repeated group is attached, separated by commas and the prefix di, tri, tetra, etc. to show how many identical groups are attached.

EXAMPLE X.2 NAMING SUBSTITUTED HYDROCARBONS

Problem: Name the following substituted hydrocarbons.

Solution:

Assign 7-9 ace…

C—C—C—C—C—C—C—C | C—C

C | C—C—C—C—C—C—C—C—C | | | C—C C C

C—C—C—C—C—C—C | | C C—C

3–ethyloctane

3–ethyl–5–methylheptane

3–ethyl–4,4,6–trimethylnonane


C. Structural Isomers

1. It is possible for two or more molecules to have the same molecular formula (same number and types of atoms) but different arrangement of atoms (structure).

All of the following molecules have the molecular formula C5H12.

STRUCTURAL ISOMERS are compounds which have the same molecular formula but a different arrangement of atoms.

Assign 11-13 2. Hydrocarbons which connect in a head–to–tail “CIRCLE” are

called CYCLIC HYDROCARBONS or CYCLOALKANES. Assign 14

CH3—CH2—CH2—CH2—CH3

Pentane

CH3—CH—CH2—CH3 | CH3

2–methyl butane

CH3 | CH3—C—CH3 | CH3

dimethyl propane

H2C—CH2 \ / CH2 cyclopropane

H2C — CH2 | | H2C — CH2 cyclobutane cyclopentane cyclohexane


NAMING CYCLOALKANES:

i) follow the same rules as straight–chain alkanes, except that a single substituent does not use a number to indicate the position of attachment.

ii) If there is more than one substituent, the first substituent is

assumed to be at the “1” position and the remaining substituents are numbered either clockwise or anticlockwise to have the lowest set of overall values.

EXAMPLE X.3 NAMING CYCLOALKANES

Problem: Name the following cycloalkanes.

Solution: Ignore di, tri… when writing the order

Assign 15-16ace

—C

methyl cyclopentane —C

C—C /

C—

2–ethyl-1,4–dimethyl cyclohexane


D. Alkyl Halides

1. There are some organic compounds where the hydrogens are substituted by a halogen (–F, –Cl, —Br or —I). These compounds are called ALKYL HALIDES.

NAMING ALKYL HALIDES:

i) Attached F, Cl, Br and I atoms are called “fluoro”, “chloro”, “bromo” and “iodo” groups. Use numbers to indicate the position of attachment on the hydrocarbon chain.

ii) If more than one of the same kind of halogen is present, use

the prefixes di, tri, tetra, etc. iii) If a compound contains both alkyl and halo groups, list the

attached groups in alphabetical order. Start numbering from the end that gives the lowest set of numbers.

EXAMPLE X.4 NAMING ALKYL HALIDES

Problem: Name the following alkyl halides.

Solution:

CH3—CH—CH2—CH3 | F

2–fluoro butane

CH3—CH—CH2—CH—CH3 | | Cl Cl

CH2—CH3 | CH3—CH—C—CH2—CH3 | | Br F

2,4–dichloro pentane

2–bromo–3–ethyl–3–fluoro pentane


2. PROPERTIES OF ALKYL HALIDES • Alkyl halides tend to be insoluble in water. • Compounds with many fluorine atoms tend to be unreactive. • Chloro and bromo compounds are susceptible to chemical

attack, but require relatively drastic conditions. Iodo compounds are more reactive.

Assign 17-20ace


E. Multiple Bonds

1. Carbon atoms can form up to four bonds but it can form multiple bonds with other carbon atoms. When a carbon shares 4 electrons with a neighbouring carbon a DOUBLE BOND is formed and when is shares 6 electrons with a neighbouring carbon a TRIPLE BOND is formed.

An ALKENE is an organic compound containing a carbon–

carbon double bond. An ALKYNE is an organic compound containing a carbon–

carbon triple bond.

NAMING ALKENES AND ALKYNES: i) If a double bond is present, change the “ANE” ending of the

parent hydrocarbon to “ENE”. If a triple bond is present change the “ANE” ending of the

parent hydrocarbon to “YNE”. ii) Use a number to indicate the lower numbered carbon atom

involved in the bond. The number goes immediately in front of the name of the parent hydrocarbon, separated by a hyphen.

iii) Number the parent hydrocarbon to give the double/triple

bond the lowest possible number. If the number is the same starting from either end, start the numbering from the end closest to the 1st branch point (where a group is attached).


EXAMPLE X.5 NAMING ALKENES AND ALKYNES

Problem: Name the following alkenes and alkynes.

Solution:

2. REMEMBER:

single bonds double bonds triple bonds ANE ENE YNE

Assign 21-25ace Alkenes and alkynes are called UNSATURATED hydrocarbons

because they have less hydrogen atoms than equivalent alkanes. Alkanes are said to be saturated hydrocarbons because they contain the maximum number of hydrogens possible.

3. Whereas alkanes have flexible structures, alkenes have very rigid

structures. The double bonds “lock” the structure to prevent the attached atoms from “twisting” around the double bond. The triple bond in alkynes is also very rigid.

For an alkane, these two molecules are identical because the single bond is free to rotate.

H CH2—CH3 \ / C = C / \ H H

CH ≡ C—CH3 CH2 = CH—CH—CH3 | CH3

1–butene 3– methyl–1–butene propyne

H3C CH3 | | CH3—CH—CH—CH2—CH3

H3C | CH3—CH—CH—CH2—CH3 | CH3

2,3–dimethyl pentane 2,3–dimethyl pentane


Because the double bond in an alkene cannot rotate or twist, these two molecules are chemically different.

Notice that in the alkane both molecules have the same name

because they are the same molecule but in the alkene one is named “CIS” and the other “TRANS”.

4. CIS–TRANS isomerism is possible whenever a molecule has:

i) a double bond present, AND ii) groups (other than a hydrogen atom) attached to each of the

carbons involved in the double bond.

In a “CIS” isomer, the two groups are on the SAME SIDE of the double bond.

In a “TRANS” isomer, the two groups are “TRANSVERSE” to each other (that is, on opposite sides of the double bond).

Assign 26-28ace

H3C CH3 | | CH3—C = C—CH2—CH3

H3C | CH3—C = C—CH2—CH3 | CH3

2,3–dimethyl–trans–2–pentene 2,3–dimethyl–cis–2–pentene

H3C CH3 \ / C = C / \ H H

both CH3’s are on the same side

H3C H \ / C = C / \ H CH3

the CH3’s are on opposite sides


F. Aromatic Compounds

1. Benzene, C6H6, is an important molecule having the following structure.

The ring–like structure of benzene can be written in either of two

RESONANCE STRUCTURES, differing only in the placement of the double bonds. Each resonance structure consists of alternating single and double bonds. Benzene is frequently represented as follows.

2. The benzene ring, also known as an “AROMATIC RING”, is

present in a large number of molecules and many molecules contain two or more aromatic rings joined together.

An AROMATIC MOLECULE is a molecule containing one or

more benzene rings.

NAMING AROMATIC MOLECULES: i) The naming of simple aromatic compounds formed by

adding groups to a benzene ring is almost identical to the naming procedure used for cyclic hydrocarbons.

ii) When the benzene ring is attached to another hydrocarbon as

a substituent or group it is called a “PHENYL” group.

Benzene


EXAMPLE X.6 NAMING AROMATIC MOLECULES

Problem: Name the following aromatic molecules

Solution:

Assign 29-31ace

ethyl benzene

2–phenyl butane

4-ethyl-1,2-dimethylbenzene

CH2—CH3 |

CH2—CH3 |

\ CH3 |

H3C

CH3—CH—CH2—CH3 |


G. Functional Groups

1. On some organic molecules, one or more of the hydrogens may be substituted by an atom or a group of atoms. These substitutions are called FUNCTIONAL GROUPS.

A FUNCTIONAL GROUP is a specific group of atoms which

exists in a molecule and gives a molecule an ability to react in a specific manner or gives it special properties.

Hydrocarbons have a limited range of properties and uses.

Functional groups allow the addition of specific properties to a molecule. For example, by carefully choosing the functional group present in a molecule, a chemist can:

i) make a molecule act as a base, an acid, or both; ii) give the molecule a particular solubility; iii) give a molecule a pleasant or unpleasant smell; iv) make a molecule react with specific chemicals; v) make a molecule explosive.


O || —C—H

2. Different FUNCTIONAL GROUPS

a) ALCOHOL An ALCOHOL is an organic compound containing an –OH

group. NAMING AN ALCOHOL:

i) Number the hydrocarbon chain to give the LOWEST possible number to the –OH group.

ii) Place the number immediately before the name of the parent hydrocarbon separated by a dash.

iii) Indicate the presence of an –OH group by changing the “e” ending of the hydrocarbon chain to “ol”.

Assign 32-33ace b) ALDEHYDES An ALDEHYDE is an organic compound containing a

C=O group at the end of hydrocarbon chain. The aldehyde group actually looks like or simply —CHO.

CH3—OH CH3—CH2—OH

CH3—CH—CH2—CH3 | OH

CH3—CH—CH2—CH2—CH—CH2—CH3 | | CH3 OH

methanol ethanol

2–butanol 6–methyl–3–heptanol


NAMING ALDEHYDES: i) Change the “e” ending of the parent hydrocarbon to

“al”. ii) If there are substituents attached, they are numbered

starting from the —CHO group.

c) KETONES A KETONE is an organic compound containing a C=O

group at a position OTHER THAN AT THE END of a hydrocarbon chain.

The ketone group is represented by —CO—. NAMING KETONES: i) Number the hydrocarbon chain to give the LOWEST

possible number to the —CO— group. ii) Place the number immediately before the name of the

parent hydrocarbon separated by a dash.

O || H—C—H

CH3—CHO CH3—CH2—CH2—CH—CHO | CH3

CHO |

methanal (formaldehyde)

2–methyl pentanal ethanal

benzenal


iii) Change the “e” ending of the parent hydrocarbon to

“one”.

d) ETHERS An ETHER is an organic compound in which an oxygen

joins two hydrocarbon groups. The ether group is represented by —O—.

NAMING ETHERS: i) Name the shorter hydrocarbon chain. Replace the

“ane” with “oxy”. ii) Number the parent hydrocarbon so that the ether group

has the LOWEST possible number. iii) Use a number separated by a dash to indicate the

location of the ether group.

O || CH3—C—CH3 or CH3COCH3 CH3CH2COCH2CH2CH3

O ||

propanone (acetone)

cyclohexanone

3–hexanone

CH3CH2—O—CH2CH3

ethoxy ethane

CH3—O—CH2CH2CH3

1–methoxy propane

CH3 | CH3—C—CH2—CH2—O—CH3 | CH3

1–methoxy –3,3–dimethylbutane


e) AMINES An AMINE is an organic compound containing an —NH2

group.

NAMING AMINES: i) Number the parent hydrocarbon so that the amine has

the LOWEST possible number. ii) Name the —NH2 group “amino” and indicate the

location of the amine group by a number followed by a dash.

f) AMIDES An AMIDE is an organic compound containing a —CONH2

group.

CH3—CH—CH2—CH3 | NH2

CH3—CH2—NH2

amino ethane 2–amino butane

O || —C—NH2


NAMING AMIDES: i) Number the parent hydrocarbon from the —CONH2

group. ii) Remove the "e” ending and add “amide” to the end of

the name.

g) CARBOXYLLIC ACIDS A CARBOXYLLIC ACIDS is an organic compound

containing a —COOH group.

NAMING CARBOXYLLIC ACIDS: i) Number the parent hydrocarbon from the —COOH

group. ii) Remove the "e” ending and add “oic acid” to the end of

the name.

CH3 | CH3—C—CH2—CONH2 | CH3

CH3—CH2—CH2—CH2—CH2—CONH2 CH3—CONH2

ethanamide hexanamide

3,3–dimethylbutanamide

O || —C—OH

CH3COOH HCOOH CH3—CH2—CH2—COOH

ethanoic acid (acetic acid)

methanoic acid (formic acid)

butanoic acid (butyric acid)


h) ESTERS An ESTER is an organic compound containing a —COO—

group.

NAMING ESTERS: i) The hydrocarbon attached directly to the carbon side of

the —COO— group has its “e” changed to “oate”. ii) The hydrocarbon chain attached to the oxygen side of

the —COO— group is named as an alkyl group.

SUMMARY OF FUNCTIONAL GROUPS

NAME FUNCTIONAL GROUP

NAME FUNCTIONAL GROUP

alkene C = C ether —O—

alkyne C ≡ C amine —NH2

halide –F, –Cl, –Br, –I amide —CONH2

alcohol —OH carboxyllic acid —COOH

aldehyde —CHO ester —COO—

ketone —CO— aromatic ring

Assign 37 odd That’s all folks!

O || —C—O—

CH3—CH2—CH2—COO—CH3

methyl butanoate

HCOO—CH3—CH2—CH2—CH3

butyl methanoate

CH3—CH2—COO—CH2—CH3

ethyl propanoate

CH3—COO—CH2—CH2—CH3

propyl ethanoate

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Organic Chemistry - School District 22 Vernon · UNIT X — ORGANIC CHEMISTRY 2 . B. Alkanes 1. A carbon atom can form bonds to four other atoms (carbon has a valence of four). A