Structure• Hydrocarbon: a compound composed only of carbon and
hydrogen
• Saturated hydrocarbon: a hydrocarbon containing only single bonds
• Alkane: a saturated hydrocarbon whose carbons are arranged in a chain
• Aliphatic hydrocarbon: another name for an alkane
Structure• Shape
– tetrahedral about carbon– all bond angles are approximately
109.5°
Nomenclature• Alkanes have the general formula CnH2n+2
Condensed Structural Formula
Molecular FormulaName
heptane
hexane
pentane
butane
propaneethanemethane CH4 CH4
C2H6 CH3CH3C3H8 CH3CH2CH3C4H10 CH3(CH2)2CH3C5H12 CH3(CH2)3CH3C6H14 CH3(CH2)4CH3C7H16 CH3(CH2)5CH3
Nomenclature• Alkanes (contd.)
tetradecane
hexadecane
octadecaneeicosane
decane
nonane
octane C8H18 CH3(CH2)6CH3C9H20 CH3(CH2)7CH3C10H22 CH3(CH2)8CH3
C14H30 CH3(CH2)12CH3C16H34 CH3(CH2)14CH3C18H38 CH3(CH2)16CH3C20H42 CH3(CH2)18CH3
dodecane C12H26 CH3(CH2)10CH3
Constitutional Isomerism• Compounds isomers: compounds with the
same molecular formula but a different connectivity (order of attachment of their atoms)– example: C4H10
CH3CH2CH2CH3 CH3CHCH3
CH3
Butane 2-Methylpropane
Constitutional Isomerism
4,111,846,763
4,347
75
3
1
Constitutional Isomers
Molecular Formula
CH4
C5H12
C10H22
C15H32
C30H62
World populationis about6,000,000,000
Nomenclature
• International Union of Pure and Applied Chemistry (IUPAC)
• Prefix tells the number of carbon atoms
• Suffix -ane specifies an alkane
Nomenclature• IUPAC system
undec-dodec-
tetradec-pentadec-hexadec-heptadec-
nonadec-eicos-
tridec-
11121314151617
octadec- 181920
Prefixmeth-eth-prop-but-pent-hex-
oct-non-dec-
1234567hept-89
10
Carbons
CarbonsPrefix
Nomenclature
• Parent name of the longest carbon chain is “alkane”
• Groups attached to the parent chain are called substituents
• Each substituent is given a name and a number– If substituent occurs more than once, di-, tri-, tetra-,
etc.
Nomenclature
• Number the chain to give the substituent encountered first the lowest number
• If there are different substituents, list them in alphabetical order. The following are not included in alphabetization.– di-, tri-, tetra-, etc.– hyphenated prefixes, such as sec- and tert-
Nomenclature
• Alkyl groups
isopropyl
propyl
ethyl
methyl
Condensed Structural Formula
Name
CH3
-CH2CH3
-CH3
-CH2CH2CH3
-CHCH3
Nomenclature• Alkyl groups
tert-butyl
sec-butyl
isobutyl
butyl
CH3
CH3CH3
CH3
-CH2CH2CH2CH3
-CH2CHCH3
-CHCH2CH3
-CCH3
Condensed Structural Formula
Name
Nomenclature
• Alkyl groups
neopentyl
isopentyl
pentyl
CH3
CH3
CH3
-CH2CH2CH2CH2CH3
-CH2CH2CHCH3
-CH2CCH3
Condensed Structural Formula
Name
Nomenclature1. The general name of an open-chain satuated
hydrocarbon is alkane
2. For branched-chain hydrocarbons, the alkane corresponding to the longest chain is taken as the parent chain and its name is the root name
3. Groups attached to the parent chain are called substituents. Each is given a name and a number
CH3CHCH3
CH3
2-Methylpropane
1 2 3
Nomenclature
4. If there is more than one substituent, number from the end of th chain that gives the substituent encountered first the lower number
2-Methylpentane
CH314 3 25
CH3CH2CH2CHCH3
Nomenclature5. If the same substituent occurs more than once, the
number of each carbon of the parent chain on which it occurs is given and the number of times it occurs is shown by di-, tri-, tetra-, etc.
6. If there are two identical substituents, number the chain to give the lower number to the substituent encountered first
CH3CHCH2CHCH3
CH3
2,4-Dimethylpentane
CH31 2 3 4 5
Nomenclature
7. If there are two or more different substituents, list them in alphabetical order, and number from the end of the chain that gives the substituent encountered first the lower number
CH3CH2CHCH2CHCH2CH3
3-Ethyl-5-methylheptane
CH3654321
CH2CH3
7
Nomenclature8. The prefixes di-, tri-, tetra- etc. are not included in
alphabetization
9. Neither are italicized prefixes such as sec- and tert-.
CH3CCH2CHCH2CH3
CH3
4-Ethyl-2,2-dimethylhexane
1 2CH2CH3
CH3
3 4 5 6
Classification of C & H• Primary (1°) C: a carbon bonded to one other carbon
– 1° H: a hydrogen bonded to a 1° carbon
• Secondary (2°): a carbon bonded to two other carbons– 2°H: a hydrogen bonded to a 2° carbon
• Tertiary (3°) C: a carbon bonded to three other carbons– 3° H: a hydrogen bonded to a 3° carbon
• Quaternary (4°) C: a carbon bonded to four other carbons
Cycloalkanes• General formula CnH2n
• Structure and nomenclature– to name, prefix the name of the corresponding open-
chain alkane with cyclo-, and name each substituent on the ring
– if only one substituent, no need to give it a number– if two or more substituents, number from the substituent
of lowest alphabetical order– where there is choice, number to give substituents the
lowest set of numbers
Cycloalkanes
• Line-angle drawings– each line represents a C-C bond– each angle represents a C
C
C CC
CCC
CH2C
H2C C
CH
C
CH
H2
H2 CH3
CH3
Cycloalkanes• Examples: name these cycloalkanes
a) b)
c) d)
