NOMENCLATURE_TYPES OF ORGANIC COMPOUNDS

TYPESOF ORGANIC COMPOUNDS

            There are 6 million organic compounds. In dealing with such a large number of compounds some classification is essential. There are five main types of organic compounds.

(1)   Aliphatic Compounds.

            Compounds which consist of open-chain of carbon atoms are called aliphatic compounds. There is no limit to the number of atoms involved.

Examples:

Ethane (CH₃CH₃), Propane (CH₃CH₂CH₃), Ethyl alcohol (CH₃-CH₂-OH), Acetic acid (CH₃COOH), n-Butyl amine (CH₃CH₂CH₂CH₂NH₂)

(2)   Saturated and Unsaturated Compounds.

            Compounds which contain only carbon and hydrogen are called hydrocarbons. A hydrocarbon is said to be saturated if it contains only C—C single bonds. A hydrocarbon is said to be unsaturated if it contains C=C or C=C multiple bonds.

Examples:

Ethane(CH₃CH₃), Ethylene(CH₂= CH₂), Acetylene (HC==CH)

            The term unsaturation is also sometimes used to describe a compound containing multiple bonds between other pairs of atoms, e.g. C=O, C=N.

(3)   Aromatic Compounds.

            Benzene and all compounds that have structures and chemical Properties resembling benzene are called aromatic compounds.

 Examples: Benzene, Naphthalene, Toluene etc,

(4)   Alicyclic Compounds.

            Cyclic compounds which consist only of carbon atoms are called alicyclic or carbocyclic compounds. Examples are:

Cyclopropane, Cyclobutane, Cyclohexane etc.

(5)   Heterocyclic Compounds.

            Cyclic compounds in which the ring atoms are of carbon and some other element (For example, N, S or O) are called heterocyclic compounds.

Examples: Furan, Thiophene, Pyridine, Quinoline, Acridine etc.

FUNCTIONAL GROUPS

            A functional group is an atom or group of atoms in a molecule that gives the molecule its characteristic chemical properties. Double and triple bonds are functional groups. Other example includes -CI, -Br, -OR, -NH₂ –COOH, CHO groups etc. Remember that the functional group is the action group. The hydrocarbon portion remains inert.

            We often use the symbol R- to represent the hydrocarbon portion to which the functional group attached.

1. Functional groups serve as basis for nomenclature (naming) of organic compounds.

2. Functional groups serve to classify organic compounds into classes (families). All compounds with the same functional group belong to the same class.

3. A functional group is a site of chemical reactivity in a molecule. Compounds in the same class have similar chemical properties.

4. A molecule can contain more than one functional group.

 HOMOLOGOUS SERIES

            A homologous series is a series of compounds in which adjacent members differ by a CH₂ unit. The individual members are called Homologs.

 For example, the homologous series of alcohols are:

Methanol, ethanol, propanol, Butanol etc.

The general characteristics of a homologous series are:

1. All compounds in the series contain the same elements and the functional group.

2. All compounds in the series can be represented by a general formula.

3. The molecular formula of each homolog differs from one above it by a CH₂ unit.

4. All compounds in the series can be prepared by similar methods.

5. All compounds in the series have similar chemical properties.

6. There is a gradual variation in physical properties with increasing molecular weight.