This is the family of organic compounds with similar chemical properties in which each successive member differ by CH2 group or RMM of 14. Each member of the series is called a homologue e.g. alkanes, alkenes etc.
- Characteristics of homologous series
-All members obey a general molecular formula e.g. CnH2n+2 for alkanes
-There is a gradual change in physical properties in the same direction within the members of a series.
-They have a general method of preparation,
-All members have a similar chemical property which depend on their functional groups
-Successive members in series differ by a CH2 group
B. ALKYL GROUP (CnH2n+1)
They are derived from an alkane by the loose of a hydrogen atom. They are named after the parent al alkane by replacing the “ane” from the alkane with “yl”
- (Ethyl)
Functional groups
It is an atom or groups of atoms or a bond common to all the members of homologous series and which governs the principal chemical properties of the series.
The functional groups sometime in the name of a compound as a surface when it is the priority group and it is place after the stem when it is the substivent, it is place before the stem as a prefix. The table below shows the functional group of some homologous series.
Some homologous series and their functional groups
Functional group
|
Homologous series
|
Suffix
|
Prefix
|
example
|
-C=C-
|
Alkenes
|
-ene-
|
-
|
H2C=CH2 Ethene
|
-C = C-
|
Alkynes
|
-yne
|
-
|
H-C=C-H Ethyne
|
-X
(CL, F, Br, I)
|
Halo alkanes
|
-
|
Chloro, fluoro
|
CH=CL Chloromethane
|
-OH
|
Alcohols
|
-ol
|
Hydroxyl
|
CH3CH2OH Ethanol
|
-COOH
|
Carboxylic acid
|
-oic acid
|
Carboxy
|
CH3COOH Ethanoic acid
|
-CHO
|
Aldehydes
|
-al
|
Farmyl
|
CH3CHO Ethanol
|
C=O
|
Ketones
|
-one
|
Oxo
|
CH3COCH3 Propanone
|
-O-
|
Ether
|
Alkoxy ether
|
Alkoxy
|
CH3OCH3 Dimethyl ether
|
O
-C
CL
|
Acid chloride
|
Oyl chloride
|
-
|
CH3COCI Ethanol chloride
|
-C-OR
O
|
Esters
|
Oate
|
-
|
CH3COOC2H5 Ethyl ethanoate
|
-NH2
|
Amines
|
Amine
|
Amino
|
CH3CH2NH2 Ethyl amine
|
-C-NH2
O
|
Amides
|
Amide
|
Amido
|
CH3CONHE Ethanamide
|
-C=N
|
Nitrites
|
Nitrite
|
Cyano
|
CH3CN Ethanenitrite
|
-NO2
|
Nitro compounds
|
-
|
Nitro
|
C6H5NO2 Nitrobenzene
|
O
-C
O
-C
O
|
Acid anhydride
|
-
|
-oic anhydrid
|
O
CH3-C
O
CH3-C
O
|
Decreasing priority
|
-COOH carboxylic acid
-SO3H sulphoric acid
-COOR ester
-COCI acid chloride
-CONH2 amide
-CN nitrite
-CHO aldehyde
CO ketone
-OH alcohol
-NH2 amine
-O- ether
|