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Unit 6: Organic Chemistry
Cover introduction, alkanes, & cycloalkanes
There will be two quizzes
Standards Covered Today:
1. Describe the features of a homologous series.
2. State names and draw structural formulas for organic compounds using the IUPAC Naming System.
3. Draw structural formulas and state names of non-cyclic (straight chain) alkanes up to C10, including isomers.
4. Draw structural formulas and state names of cyclic structures up to C10
Introduction
In all organic compounds, all carbon atoms must make four bonds, all oxygen atoms must make two bonds, all nitrogen atoms must make three bonds, all hydrogen atoms must make one bond, and all halogens must make one bond.
Names of Structures
Lewis Structures Structural Formulas Condensed Formulas &
Structures Line Structures C6H14 or CH3(CH2)4CH3
Notes on Structures
Structural Formula: shows all bonds including hydrogen
Condensed Formula: These are generally written without lines indicating bonds, or showing lone pairs, and parentheses are used for identical groups.
Line Formula: Bonds are represented by lines, carbon atoms are assumed to be present at the start and finish of a line. Nitrogen, oxygen and halogens are labeled, but hydrogens
are only shown when bonded to a drawn atom. Each atom is assumed to have sufficient hydrogen atoms
around it to make it neutral.
Isomers
Draw a structural formula for C4H10
An isomer is a compound that has the same molecular formula as another.
Structural Isomers: these are isomers that differ in their bonding sequence. They have different bond connectivity.
CH3 CH2 CH2 CH3 CH3 CH
CH3
CH3
n-butane isobutane
Introduction to Nomenclature of Organic Molecules
Four Categories: Alkanes Alkenes Alkynes Cyclic Structures
Alkanes
Alkanes are the simplest organic molecules, they only contain C and hydrogen, and only contain single bonds. Considered to be hydrocarbons
Compounds that have the maximum number of bonded hydrogens, are said to be saturated. Therefore, alkanes are the most saturated
compounds General Formula: CnH2n + 2
Nomenclature for compounds The root name of the compound is based upon the
number of carbon atoms in the longest continuous chain.
Number of C atoms Root1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-
Any series that differs only by an increasing number of –CH2- groups is known as a homologous series. The individual members are said to be homologs of each other. The series must contain the same functional
group.
C C
H
C
H
HH
C
H
H
C
H
H
H
H
H
H C C
CH3
C
H
HH
C
H
H
H
H
H
H H3C C
CH3
CH3
CH3
pentaneC5H12
isopentaneC5H12
neopentaneC5H12
IUPAC Naming System: Alkanes
1) Find the longest continuous chain of carbon atoms. This is the base name of the compound.
2) Number the longest chain beginning with the end nearest a substituent.
3) Name the substituent groups attached to the longest chain as alkyl groups. Also state the location of each alkyl group according to its numbered carbon on the main chain.
4) When two or more substituents are present, list them in alphabetical order. If two or more of the same alkyl groups are present, use the prefixes di-, tri- etc. to avoid repetition.
Alkane Nomenclature Examples
1) CH2CH3
CH-CH2-CH2-CH3H3C
3-methylhexane
3-methyl hexane
• If there are two chains of equal length, choose the chain that has the highest number of substituents.
CH3
CH2HC
HC
H3C
HC
H3C HC
CH2CH3
CH3
CH3
CH3
CH2HC
HC
H3C
HC
H3C HC
CH2CH3
CH3
CH3
Numbering starts at the end nearest a substituent so that the alkyl substituents have as low numbers as possible.
CH3
CH2
HC
HC
H3C
HC
H3C HC
CH2CH3
CH3
CH3
CH3
CH2
HC
HC
H3C
HC
H3C HC
CH2CH3
CH3
CH3
Alkyl groups are named by replacing the –ane suffix of the alkane name with –yl.E.g. CH3CH3 Ethane CH3CH2- Ethyl group
CH3CH2CH3 PropaneCH3CH2CH2- Propyl group
Prefixes are used when there are more than one type of alkyl substituent. Di = 2 Tri = 3 Tetra = 4 Penta = 5
The prefixes do not count when alphabetizing.
CH3
CH2HC
HC
H3C
HC
H3C HC
CH2CH3
CH3
CH3
3-ethyl-2,4,5-trimethylheptane
Recognizing Types of Substitution
R C
H
H
R C
R
H
R C
R
R
Primary1o carbon
Secondary2o carbon
Tertiary3o carbon
Cycloalkanes
Cycloalkanes are simply alkanes that are cyclic. Just add cyclo-before their name. Notice the general formula for cycloalkanes is CnH2n
H2C CH2
H2C H2C
H2C CH2
CH2
H2C
cyclopropaneC3H6
cyclopentaneC5H10
Two simple rules of cycloalkanes
Rule A: Decide whether the cyclic or acyclic (non-cyclic) portion contains more carbons. This determines the base name. (Alkyl substituted cycloalkane or cycloalkane substituted alkane).
Rule B: Carbons are numbered to give the lowest numbers for substituted carbons.
CH3
CH
CH3
CHCH3
CH3
methylcyclopentane (1,2-dimethylpropyl)cyclohexane
Numbering starts at the most substituted carbon, and goes around in order to give the lowest numbers.
CH3
CH3
H
H3C
1,1,3-trimethylcyclopentane
1,1,3-trimethylcyclopentane
• When there are more acyclic than cyclic carbons, the cyclic part becomes a cycloalkyl substituent.
4-cyclopropyl-3-methyloctane
4-cyclopropyl-3-methyloctane
Complex Substituents
These are named as follows:
(a) The base alkyl group is numbered staring with the carbon bonded to the main chain.
(b)The substituents are listed with the appropriate numbers, and parentheses are used to separate the substituent name.
CH3
C-CH2
CH3
CH-CH3
CH3
a (1,1,3-trimethylbutyl) group
Examples
Draw structures for the following compounds:1.) 3-ethyl-3-methylpentane
2.) 3-methyl-5-propylnonane
3.) 2,2,4,4-tetramethylhexane
4.) pentylcyclohexane
5.) 2,3-dimethyl-4-propylnonane
Give the IUPAC names of the following alkanes:1.) (CH3)2CHCH2CH(C2H5)C(CH3)3
2.)
3.) (CH3CH2)3CH
4.) (CH3)2CH(CH2)3CH3
Physical Properties of Alkanes Nonpolar What type of intermolecular forces?
Since weak interactions….so low boiling point and melting point
As molecular weight increases, interactions increase
As interactions b/w molecules increase, so does the strength of the interactions….
So what conclusions can we make?
Dispersion Forces
The higher molecular weights…..
The more branches…
Leads to liquids, then solids
More compact structure, surface area decreases
Less contact between molecules, dispersion forces decrease, so lower boiling point
Try these: Arrange in increasing boiling point:
a. CH3CH2CH2CH3, CH3CH2CH2CH2CH2CH3, CH3(CH2)8CH3
b. CH3(CH2)6CH3, CH3C(CH3)2CH2CH(CH3)2,
CH3CHCH3(CH2)4CH3
c. 2-methyl butane, 2,2-dimethylpropane, pentane
Alkene and Alkyne Nomenclature Make sure you study the different functional
groups over the break (sheet of paper with table on it)
This will need to be memorized for the quiz and test.
Quiz when we get back!
Elements of Unsaturation
A saturated hydrocarbon: CnH2n+2
Each multiple bond (and each ring) decreases the number of H’s by two.
Each of these is an element of unsaturation. To calculate: find number of H’s if it were
saturated, subtract the actual number of H’s, then divide by 2.
Propose a Structure for C5H8
First calculate the number of elements of unsaturation.
Remember:A double bond is one element of
unsaturation.A ring is one element of unsaturation.A triple bond is two elements of
unsaturation.
Alkene Nomenclature
Parent is longest chain containing the double bond.
-ane changes to -ene. (or -diene, -triene) Number the chain so that the double bond
has the lowest possible number. In a ring, the double bond is assumed to be
between carbon 1 and carbon 2.
Try these:CH2 CH CH2 CH3
CH3 C
CH3
CH CH3
CH3
1-butene
2-methyl-2-butene
3-methylcyclopentene
CHCH2CH3H3C
2-(1-methyl propyl)-1,3-cyclohexadiene
3-propyl-1-heptene
Geometric Isomerism
Similar groups on same side of double bond, alkene is cis.
Similar groups on opposite sides of double bond, alkene is trans.
C CCH3
H
H
CH3CH2
C CBr
H
Br
H
trans-2-pentene cis-1,2-dibromoethene
Alkynes
Alkynes contain a triple bond. General formula is CnH2n-2
Two elements of unsaturation for each triple bond.
Alkyne Nomenclature
Find the longest chain containing the triple bond.
Change -ane ending to -yne. Number the chain, starting at the end closest
to the triple bond. Give branches or other substituents a
number to locate their position.
Try theseCH3 C CH
CH3 C C CH2 CH2 Br
CH3 CH
CH3
CH2 C C CH
CH3
CH3
propyne
5-bromo-2-pentyne
2,6-dimethyl-3-heptyne
CH2 CH CH2 CH
CH3
C CH 3-methyl-1-hexyn-5-ene
Practice Problems
Two worksheets
Agenda
Review of alkanes, alkenes, alkynes, & cyclic structures
Nomenclature of Functional Groups
Alcohols
Simple alcohols are named as derivatives of the parent alkane, using the suffix -ol, using the following simple rules:
Select the longest continuous carbon chain, containing the hydroxyl group, and derive the parent name by replacing the -e ending with -ol.
Number the carbon chain, beginning at the end nearest to the hydroxyl group.
Number the substituents and write the name, listing substituents alphabetically.
Alcohol Examples
Ether Nomenclature
Simple ethers are named either by identifying the two organic residues and adding the word ether .
CH3—O—CH3
Dimethyl ether
CH3CH2OCH2CH3
Diethyl ether
Aldehydes Nomenclature
Aldehydes are named by replacing the terminal -e of the parent alkane with the suffix -al
The parent chain selected must contain the carbonyl group.
Number the carbon chain, beginning at the end nearest to the carbonyl group.
Aldehyde Example
methanalbutanal
2-methyl butanal
Ketone Nomenclature
The suffix for ketones is -one. The parent chain selected must contain the
carbonyl group. Number the carbon chain, beginning at the
end nearest to the carbonyl group.
Ketone Examples
3-pentanone propanone
3-methyl-2-butanone
Carboxylic Acid Nomenclature
Simple carboxylic acids are named as derivatives of the parent alkane, using the suffix -oic acid
Select the longest continuous carbon chain, containing the carboxylic acid group, and derive the parent name by replacing the -e ending with -oic acid.
Number the carbon chain, beginning at the end nearest to the carboxylic acid group.
Number the substituents and write the name, listing substituents alphabetically.
Carboxylic acid substituents attached to rings are named using the suffix -carboxylic acid.
Carboxylic Acid Examples
Ester Nomenclature
Esters are named by replacing the terminal of end with the suffix -oate
The parent chain selected must contain the
Number the end of the carbon chain (after the
second O), and give it an –yl ending. Practice Problems
Amine Nomenclature
RNH2 , R2NH, R3N In amines, a nitrogen is bonded to one, two
or three carbon atoms. Practice Problems
Functional Groups as Isomers
Some functional groups can exist as isomers of each other.
Example: C4H8O2
Try the following: