Functional Groups
Naming ALKANES
There are some 15 important
Functional Groups
• (Hydrocarbons) = Alkanes, alkenes,
alkynes, and aromatics.
• (Single-bond Heteroatomic molecules) =
Alkyl halides, ethers, amines, and sulfides.
• (Simple carbonyls) = Ketone and Aldehyde
• (Carboxylic derivatives) = Carboxylic acid,
ester, amide, acid halide and nitriles.
Identifying Functional Groups
• When atoms are bonded together in specific arrangements, they
undergo specific chemical reactions.
• Such arrangements of atoms are called functional groups.
2-3
Summary of Important Families of
Organic Compounds
Ch. 2 - 4
Sulfides are missing – they are similar to alcohols since
sulphur is in the same group as oxygen in the periodic table.
sulfide/
thiol
It’s important to identify functional groups.
Firstly because the name is liked to the
functional group, and secondly because
the reactions and properties are typical of
the functional group.
Alkanes are the simplest organic
functional group.
They are also known as saturated
hydrocarbons
Saturated molecules only contain single bonds
Hydrocarbons only contain H and C
Nomenclature (IUPAC)


The International Union of Pure and
Applied Chemistry (IUPAC) is the
international body responsible for
setting up the system of “rules” for
naming chemicals.
Rule
1. Find the most important functional
group to take the suffix (ending).
In the IUPAC system the organic
compound’s name is divided into a
“prefix” a “parent” and a “suffix”
2
1
3
2-methylpropane
PREFIX – tells you what substituents
there are, how many and where they
are situated in the molecule.
PARENT – tells you how many carbons
there are in the longest continuous
carbon chain.
SUFFIX – tells you what family
(functional group) of organic compounds
the compound belongs to.
Most IMPORTANT functional group?



IUPAC is a committee that decides
regularly by consensus what functional
groups are important.
Mostly this is logical: More
heteroatoms are usually more reactive
and so are more multiple bonds.
So
Important confusing exception
• Alkenes (double bond) are more important
than alkynes (triple bond), but in naming
compounds that have BOTH an alkENE and
an alkYNE we use the term enyne. More
about this later.
Nomenclature of Alkanes

7
Rule
2. Use the longest continuous carbon
chain as parent name, numbering
the chain from one end to the other
6
5
4
3
CH3CH2CH2CH2CHCH3
2CH2
1 CH3
(3-Methylheptane)
6
5
4
3
2
1
CH3CH2CH2CH2CHCH3
NOT
CH2
CH3
(2-Ethylhexane)
Remember the IUPAC system is divided
into a “prefix” a “parent” and a “suffix”
2
1
3
2-methylpropane

The ending for all the names of alkanes
is –ane

The names of the longest chain stems
from Greek and Latin usually
one
two
three
four
five
meth-
eth-
prop-
but-
pent-
CH4
C 2H 6
C 3H 8
C4H10
C5H12
C6H14
methane
ethane
propane
butane
pentane
hexane
C7H16
C8H18
C9H20
heptane
octane
nonane
C10H22
decane
NOTE the –
ane at the
end of the
name infers
the family
of the
organic
compound
i.e. alkane

“Straight-chain” (unbranched) alkanes
Butane
Pentane
CH3CH2CH2CH3
CH3CH2CH2CH2CH3
These are the simplest structures that only have a
SUFFIX and a PARENT, which is enough
information to give EACH UNIQUE MOLECULE a
UNIQUE NAME.

The first 10 Unbranched or straight-chain
alkanes.
Name
Structure
Name
Structure
Methane CH4
Hexane
CH3(CH2)4CH3
Ethane
CH3CH3
Heptane CH3(CH2)5CH3
Propane
CH3CH2CH3
Octane
CH3(CH2)6CH3
Butane
CH3CH2CH2CH3
Nonane
CH3(CH2)7CH3
Pentane
CH3(CH2)3CH3
Decane
CH3(CH2)8CH3
These are sometimes also called “normal”
alkanes (n-alkanes are a common name)
If one hydrogen atom is removed from
an alkane an alkyl group remains e.g.
H
H C H
H
methane
H
H C
H
methyl group
Alkyl groups can be substituents in
branched alkanes.
A substituent is an atom or group of
atoms that replace (substitute) a
hydrogen atom in an organic molecule
e.g. the methyl group and the OH group
are BOTH substituents in the molecule
2- methylpropan-1-ol
methyl group
2 1
OH
alcohol
functional group
2-methylpropan-1-ol
Some common branched alkyl substituents
CH3CH
CH3
CH3CHCH2
CH3
Either 1-methylethylor isopropyl
Either 2-methylpropylor isobutyl
CH3CH2CH
CH3
CH3
Either 1-methyl-1-propylor sec-butyl
Either 1-methyl-2-propyl-
CH3C
or tert-butyl
CH3
Nomenclature of Unbranched
Alkyl substituents

Alkyl group
● Removal of one hydrogen atom from
an alkane

Alkyl group (Cont’d)
● For an unbranched alkane, the
hydrogen atom that is removed is a
terminal hydrogen atom
CH3 H
CH3CH2 H
CH3CH2CH2 H
Methane
Ethane
Propane
CH3
Methyl
(Me)
CH3CH2
Ethyl
(Et)
CH3CH2CH2
Propyl
(Pr)
Now we need more rules
This is not a simple straight
chain, n-alkane.
Some parts of the molecule
stick out from the chain and
are substituents.
The unsubstituted chain
might look like this
Can you spot the
difference?
If not, count the carbons.

Rule
3. Number the chain from the side that
gives the substituent the lowest number
4. Use the number obtained by Rule 3 to
designate the location of the substituent
along the chain.
7
6
5
4
3
CH3CH2CH2CH2CHCH3
2CH2
1 CH3
(3-Methylheptane)
1
2
3
4
5
CH3CH2CH2CH2CHCH3
NOT
6 CH2
7 CH3
(5-Methylheptane)

Rule (Cont’d)
5. When two substituents are present
on the same carbon, use that
number twice
1
2
3
4
5
6
7
8
(4-Ethyl-4-methyloctane)

Rule (Cont’d)
6. For two or more substituents, use
the lowest possible individual
numbers of the parent chain.
(NOTE NOT THE TOTAL NUMBER)
So 1,2,5-something is better than 2,6,7something.
Similarly, 2,7,8-trimethyldecane not
3,4,9-trimethyl… (DON’T ADD 3+4+9=16
and say its better than 2+7+8=17)

Rule (Cont’d)
6. Also, list all the substitutents
alphabetically. In deciding alphabetical
order, disregard multiplying prefix, such
as “di”, “tri” etc.
This sometimes gives a substituent
with a higher number written before one
with a lower number, but that’s OK.
See the example on the next slide.
Rule (Cont’d)

1
2
4
3
5
6
7
8
(6-Ethyl-2-methyloctane)
NOT
8
7
6
5
4
NOT
3
2
1
1
2
3
4
5
6
7
8
(3-Ethyl-7-methyloctane) (2-Methyl-6-ethyloctane)

Rule (Cont’d)
6. For identical substituents, use
prefixes di-, tri-, tetra- and so on
6
5
4
3
2
1
(2,4-Dimethylhexane)
NOT
1
7
6
5
4
3
2
1
(2,4,5-Trimethylheptane)
NOT
2
3
4
5
6
(3,5-Dimethylhexane)
1
2
3
4
5
6
7
(3,4,6-Trimethylheptane)
Rule (Cont’d)

7. When two chains of equal length
compete for selection as parent
chain, choose the chain with the
greater number of substituents
7
6
5
4
3
2
1
4
NOT
(2,3,5-Trimethyl4-propylheptane)
5
3
2
1
6
7
(only three substituents)

Rule (Cont’d)
8. When branching first occurs at an
equal distance from either end of
the longest chain, choose the name
that gives the lower number at the
first point of difference
6
5
4
3
2
1
(2,3,5-Trimethylhexane)
1
NOT
2
3
4
5
6
(2,4,5-Trimethylhexane)

Example 1
The most important functional group is alkane.
Next find the longest chain as parent
4
5
3
6
2
7
1
4
or
3
5
2
6
1
7

Example 1 (Cont’d)
●
Use the lowest numbering for
substituents
4
3
●
5
2
6
1
4
7
instead of
5
3
6
2
1
7
Substituents: two methyl groups
 dimethyl
4
3
5
2
6
1
7

Example 1 (Cont’d)
●
Complete name
4
3
5
2
6
7
1
(3,4-Dimethylheptane)
QUICK NOTE about dashes and commas. Use commas to separate
numbers like 2,3,3 or 1,4,8
Use dashes to separate a number from a letter 1,2-dimethyl or 3-bromo-2,3diene

Example 2

Example 2 (Cont’d)
●
Find the longest chain as parent
6-carbon chain
8-carbon chain
8-carbon chain

Example 2 (Cont’d)
●
Find the longest chain as parent
9-carbon chain
(correct!)
⇒ Nonane as parent
Example 2 (Cont’d)

●
Use the lowest numbering for
substituents
7
8
3
9
5
2
1
3
6
4
(3,4,7)
2
1
5
instead of
8
9
7
4
6
(3,6,7)

Example 2 (Cont’d)
●
Substituents
 3,7-dimethyl
 4-ethyl
7
8
9
5
2
1
3
4
6

Example 2 (Cont’d)
●
●
Substituents in alphabetical order
 Ethyl before dimethyl
(recall Rule 5 – disregard “di”)
Complete name
7
8
9
5
2
1
3
6
4
(4-Ethyl-3,7-dimethylnonane)
Nomenclature of Branched Alkyl
Substituents

For most alkane substituents more than
one alkyl group is possible

For example in three-carbon groups (C3)
Propyl
Isopropyl
(or 1-methylethyl)

Four-carbon groups
Butyl
sec-butyl
(1-methylpropyl)
Isobutyl
tert-butyl
(or 1,1-dimethylethyl)

Naming Practice Example 1

Clearly the ONLY Functional group is
Alkane.

Example 1 (Cont’d)
●
Find the longest chain as parent
(a)
6-carbon
chain
(b)
7-carbon
chain
(c)
8-carbon
chain
(d)
9-carbon
chain

Example 1 (Cont’d)
●
Find the longest chain as parent
(d)
⇒ Nonane as parent
1
2
3 4
5 6
7 8
9
or
9
8
7 6
5 4
3 2
1

Example 1 (Cont’d)
●
1
2
Use the lowest numbering for
substituents
3 4
5 6
7 8
9
or
9
5,6
8
7 6
5 4
3 2
1
4,5
(lower numbering)
⇒ Use 4,5

Example 1 (Cont’d)
●
Substituents
 Isopropyl (or 2-propyl)
 tert-butyl (or 2-methyl-2-propyl)
9
8
7 6
5 4
3 2
1
⇒ 4-isopropyl and 5-tert-butyl

Example 1 (Cont’d)
●
Alphabetical order of substituents
 tert-butyl before isopropyl
●
Complete name
9
8
7 6
5 4
3 2
1
5-tert-Butyl-4-isopropylnonane

Example 2
Again the most important functional group
is ALKANE, so ending is
……ANE

Example 2 (Cont’d)
●
Find the longest chain as parent
(a)
(b)
8-carbon
chain
(c)
9-carbon
chain
⇒ Octane as parent
10-carbon
chain

1
Example 2 (Cont’d)
2
3 4
5 6
7 8
9
10
or
10 9
8 7
6 5
4 3
2
1

Example 2 (Cont’d)
●
Use the lowest numbering for
substituents
5,6
1
2
3 4
5 6
7 8
9
10
or
⇒ Determined using
the next Rules
10 9
5,6
8 7
6 5
4 3
2
1

Example 2 (Cont’d)
●
Substituents
 sec-butyl
 Neopentyl
But is it
● 5-sec-butyl and 6-neopentyl or
● 5-neopentyl and 6-sec-butyl ?

Example 2 (Cont’d)
●
Since sec-butyl takes precedence
over neopentyl
 5-sec-butyl and 6-neopentyl
●
Complete name
10 9
8 7
6 5
4 3
2
1
5-sec-Butyl-6-neopentyldecane
The sec- and tert- are abbreviations of
the secondary and tertiary classification
of carbon atoms.
Primary C is bonded to ONE other C
Secondary C is bonded to TWO other C
Tertiary C is bonded to THREE other C
Quaternary C is bonded to FOUR other C
Naming compounds with other
functional groups is not much different….
Alcohols (R-OH) use the prefix “hydroxy”
OR the suffix “ol”
OH
4
1
2
3
2-hydroxy-3-methylbutane
OR
3-methylbutan-2-ol
Amines (R-NH2) use the prefix “amino”
OR the suffix “amine”
NH2
4
1
2
3
2-amino-3-methylbutane
OR
3-methylbutan-2-amine
Alkyl halides (R-X e.g. where X =
chlorine) use the prefix “chloro” OR the
suffix “-yl chloride”
Cl
4
1
2
3
2-chloro-3-methylbutane
OR
3-methyl-2-butyl chloride
A few more examples – do you agree with the numbers?
1
2
3
4
3
2
CH3
1
5
4 3
2
1
HOCH2CH2CH2Br
ClCH2CH2CHCH3
CH3CCH2CHCH3
3-bromo-1-propanol
OH
4-chloro-2-butanol
CH3 OH
4,4-dimethyl-2-pentanol
What about these examples?
CH3
CH3CHCHCH2CH3
Cl OH
2-chloro-3-pentanol
not
4-chloro-3-pentanol
CH3CH2CH2CHCH2CHCH3
OH
CH3
2-methyl-4-heptanol
not
6-methyl-4-heptanol
OH
3-methylcyclohexanol
not
5-methylcyclohexanol
A few more complex ones to show that the substituents are listed
in alphabetical order
CH2CH3
CH2CH3
CH3CHCH2CHCH2CHCH3
Br
H 3C
OH
6-bromo-4-ethyl-2-heptanol
OH
2-ethyl-5-methylcyclohexanol
HO
CH3
CH3
3,4-dimethylcyclopentanol
Nomenclature of Amines
1
4
3
2
1
2
3
4
5
3
6
CH3CH2CHCHCH2CH3
CH3CH2CH2CH2NH2
NHCH2CH3
1-butanamine
or
butan-1-amine
N-ethyl-3-hexamine
or
N-ethylhexan-3-amine
2
1
CH3CH2CH2NCH2CH3
CH3
N-ethyl-N-methyl-1-propanamine
or
N-ethyl-N-methylpropan-1-amine
• The substituents are listed in alphabetical order and a number or
an “N” is assigned to each one
4
3
2
1
1
2
3
CH3
4 5
Br
6
CH3CH2CHCHCHCH3
CH3CHCH2CH2NCH3
NHCH2CH3
Cl
3-chloro-N-methyl-1-butanamine
N-ethyl-5-methyl-3-hexanamine
CH2CH3
NHCH2CH2CH3
2-ethyl-N-propylcyclohexanamine
5
4
3
2
1
CH3CHCHCHCH3
N
H3C
CH3
4-bromo-N,N-dimethyl-2-pentanamine