CHAINS, BRANCHES AND RINGS
The hydrocarbons may have branched, closed chains or ring or cyclic structures.
The alkanes containing three or less carbon atoms do not form branches.
Closed chains or cyclic hydrocarbon:
These hydrocarbons contain closed chain or rings of atoms in their molecules. These are of two types:
(A) Alicyclic hydrocarbon:
(B) Aromatic hydrocarbon:
Will you be my friend ? (functional group):
Properties of CH3-OH and CH3-CH2OH are similar and it is due to the presence of -OH (hydroxyl) group.
This group is known as alcoholic group.
Family of compounds having -OH group is called alcohols.
Some Functional Groups in Carbon compounds
"A series of organic compounds having similar structures similar chemical properties and same general formula in which the successive members differ in their molecular formula by -CH2 group".
The different members of the series are called homologous.
Characteristics of Homologous Series:
Table: Some members of alkane, alkene and alkyne homologous series
Q. What is a homologous series? Explain with an example.
(i) Yes, all these compounds are the members of a homologous series for alcohols.
(ii) CH3OH, C2H5OH, C3H7OH and C4H9OH -increasing carbon atoms. These four compounds form a homologous series.
Homologous series containing functional groups.
HCHO, CH3CHO, CH3CH2CHO, CH3CH2CH2CHO
Carboxylic acids: HCOOH, CH3COOH, CH3CH2COOH,CH3CH2CH2COOH
Amines: CH3NH2, CH3CH2NH2,CH3 CH2CH2NH2.
Ketones: CH3COCH3, CH3COCH2CH3, CH3COCH2CH2CH 3
Haloalkanes: CH3X, CH3CH2X, CH3CH2CH2X, CH3CH2CH2-CH2X
Q. How do physical properties change in a homologous series of hydrocarbons?
The physical properties of the various members of a homologous series change regularly with an increase in the molecular mass.
(i) Melting and boiling points : Melting point and boiling point of hydrocarbon in a homologous series increases with an increase in molecular mass.
(ii) Physical State:
Hydrocarbons containing lesser number of carbon atoms are gases.
Hydrocarbons containing large number of carbon atoms are solids.
Hydrocarbon containing intermediate number of carbon atoms are liquids.
Example: Hydrocarbon containing 1-4 carbon atoms are gases, these containing 5-16 carbon atoms are liquid and those containing more than 16 carbon atoms are solids.
Nomenclature of carbon compounds:
Carbon compounds can be called by their common names, but, then remembering millions of compounds by their individual names may be very difficult. Due to this reason, the International Union of Pure and Applied chemistry (IUPAC) has devised a very systematic method of naming these compounds.
Naming a carbon compound can be done by the following methods.
The number of carbon atoms in the molecule of a hydrocarbon is indicated by the following stems.
|No. of carbon atom||Stem|
Example: Saturated hydrocarbon.
Alkane → Meth + ane = Methane
Alkene → Eth + ene = Ethene
Alkyne → Eth + yne = Ethyne
"Functional group may be defined as an atom or a group of atoms which is responsible for most of the characteristic chemical properties of an organic compound".
The prefixes and suffixes of some substituents/functional group