THEME 2: SATURATED HYDROCARBONS AND CONFORMATION
STRUCTURAL ISOMERISM IN ALKANES
‐ Alkanes are saturated hydrocarbons
o Straight chain or branched chain alkanes have formula CnH2n+2
o Cyclic alkanes have 2 H’s fewer than the max for each ring
‐ Conformers: molecules can fold into different 3-dimensional arrangements but
remain the same molecule
‐ Structural (constitutional) isomers: 2 different compounds with the same molecular
formula
‐ There are 5 structural isomers for C6H14
‐ The number of structural isomers increases with the size of the alkane
‐ Saturated C’s are classified as primary (1o), secondary (2o), tertiary (3o) or quaternary
(4o) according to the number of attached C groups → rather use names over symbols
IUPAC NAMING OF ORGANIC COMPOUNDS
‐ Names of straight chain alkanes indicate the carbon number and end in -ane
NUMBER OF CARBONS PARENT
1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-
‐ Branched chain alkanes must be named according to the longest chain (parent
chain), and the substituents
‐ A substituent is named according to the alkane it would have been
o Methyl (Me)
o Ethyl (Et)
o Propyl (Pr)
o Butyl (Bu)
‐ R- is used as the abbreviation to imply any random alkyl group (any hydrocarbon
group)
, NAMING BRANCHED ALKANES
1. Find the parent chain
o Choose the longest continuous carbon chain, with the most substituents
2. Number the atoms in the main chain
o Begin at the end, nearest to a branch
3. Name and number the substituents
o Group identical substituents and use the prefixes → di-, tri-, tetra- etc.
4. Write the complete name
o Arrange the substituents in alphabetical order
o Add the parent and functional group suffix (-ane)
‐ Separate numbers by commas and separate numbers from letters by hyphens →
take note there are no spaces in the name of an alkane
NAMES OF BRANCHED ALKYL GROUPS (NB!!)
‐ Sometimes the alkyl group is branched, there are 4 common branched alkyl groups
with their own names
‐ Every organic molecule must have its own IUPAC name even if the structural
drawings look different
CYCLOALKANES (CnH2n)
‐ A saturate hydrocarbon that contains C-atoms bonded to form a ring
‐ Five-membered (cyclopentane) and six-membered (cyclohexane) rings are abundant
in nature
IUPAC NAMES
‐ Named as a cycloalkane according to the C atoms in the ring, unless there is a longer
side chain, then it becomes a cycloalkyl substituent
o If only one substituent then no need to give it a number
o Number the C’s of the ring to ger the lowest possible set of numbers (i.e. if
you can number in multiple ways then use the smaller set)
STRUCTURAL ISOMERISM IN ALKANES
‐ Alkanes are saturated hydrocarbons
o Straight chain or branched chain alkanes have formula CnH2n+2
o Cyclic alkanes have 2 H’s fewer than the max for each ring
‐ Conformers: molecules can fold into different 3-dimensional arrangements but
remain the same molecule
‐ Structural (constitutional) isomers: 2 different compounds with the same molecular
formula
‐ There are 5 structural isomers for C6H14
‐ The number of structural isomers increases with the size of the alkane
‐ Saturated C’s are classified as primary (1o), secondary (2o), tertiary (3o) or quaternary
(4o) according to the number of attached C groups → rather use names over symbols
IUPAC NAMING OF ORGANIC COMPOUNDS
‐ Names of straight chain alkanes indicate the carbon number and end in -ane
NUMBER OF CARBONS PARENT
1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-
‐ Branched chain alkanes must be named according to the longest chain (parent
chain), and the substituents
‐ A substituent is named according to the alkane it would have been
o Methyl (Me)
o Ethyl (Et)
o Propyl (Pr)
o Butyl (Bu)
‐ R- is used as the abbreviation to imply any random alkyl group (any hydrocarbon
group)
, NAMING BRANCHED ALKANES
1. Find the parent chain
o Choose the longest continuous carbon chain, with the most substituents
2. Number the atoms in the main chain
o Begin at the end, nearest to a branch
3. Name and number the substituents
o Group identical substituents and use the prefixes → di-, tri-, tetra- etc.
4. Write the complete name
o Arrange the substituents in alphabetical order
o Add the parent and functional group suffix (-ane)
‐ Separate numbers by commas and separate numbers from letters by hyphens →
take note there are no spaces in the name of an alkane
NAMES OF BRANCHED ALKYL GROUPS (NB!!)
‐ Sometimes the alkyl group is branched, there are 4 common branched alkyl groups
with their own names
‐ Every organic molecule must have its own IUPAC name even if the structural
drawings look different
CYCLOALKANES (CnH2n)
‐ A saturate hydrocarbon that contains C-atoms bonded to form a ring
‐ Five-membered (cyclopentane) and six-membered (cyclohexane) rings are abundant
in nature
IUPAC NAMES
‐ Named as a cycloalkane according to the C atoms in the ring, unless there is a longer
side chain, then it becomes a cycloalkyl substituent
o If only one substituent then no need to give it a number
o Number the C’s of the ring to ger the lowest possible set of numbers (i.e. if
you can number in multiple ways then use the smaller set)
