Introduction
Organic compounds containing nitro (─NO2) group as the functional group are called nitro compounds.
General Formula
Structure of -NO2 functional group
Isomeric form of -NO2 functional group
Classification of nitro compounds
Nitro compounds are broadly classified into two types;
Examples with IUPAC Nomenclature
a)Aliphatic Nitro compounds
Isomerism in aliphatic nitro compounds
Isomers of C2H5NO2
Isomers of C2H5NO2
Isomer I &II compared with isomers III & IV are chain isomers of each other
General Method of preparation of aliphatic nitro compounds
a)From haloalkane
Note: When alcoholic solution of KNO2 or NaNO2 is used then alkyl nitrite is the major product because negatively charged oxygen atom acts as nucleophile whereas when alcoholic solution of AgNO2 is used then nitroalkane is the major product because N- atom with lone pair electron acts as nucleophile
b) From alkane
Note: Alkanes are difficult to nitrate and nitration results in the mixture of nitroalkanes because C-C bond of the alkane undergoes fission at high temperature.
Physical Properties of Nitroalkanes
i) State, Color and Odor: Nitroalkanes are colorless liquids with a pleasant odor.
ii) Solubility: Nitrobenzene are are slightly soluble in water while completely soluble in organic solvents.
iii) Boiling points: Nitroalkanes are polar in nature. Due to strong dipole-dipole interactions, these compounds show higher boiling points than the hydrocarbons of comparable molecular mass.
But lower boiling points than the alcohols and carboxylic acids of comparable
molecular mass due to absence of intermolecular H-bonding in nitroalkanes.
Chemical Properties of Nitroalkanes
Aromatic Nitro compounds
Nitrobenzene (Oil of mirbane)
Molecular formula: C6H5-
NO2 Structure:
Preparation of Nitrobenzene from Benzene
Nitrobenzene is prepared in laboratory by heating benzene with nitrating mixture (Conc.HNO3+ Conc. H2SO4) up to 60°C. This reaction is called nitration of benzene. It is an electrophilic substitution reaction. In This reaction nitronium ion (NO+2) acts as an electrophile produced from the reaction of nitrating mixture. Conc H2SO4 acts as acid and conc. HNO3 acts like base.
Physical properties of Nitrobenzene
i) Nitrobenzene is a pale-yellow oily liquid with bitter almond smell. It is also called “oil of Mirbane”
ii) It boils at 210°C.
iii) It is insoluble in water and soluble in organic solvents.
iv) It is a toxic compound since its vapors are absorbed through skin.
Chemical properties of Nitrobenzene
Electrophilic Substitution Reaction (ESR) in Nitrobenzene:
Nitrobenzene undergoes electrophilic substitution reaction at meta-position. This is because-NO2 group present in nitrobenzene is electron withdrawing and m-director in nature. Due to resonance in nitrobenzene, the electron density at ortho and para position decreases as compared to meta-position. Therefore, the incoming electrophile will prefer to attack meta-position in nitrobenzene
Some electrophilic substitution reactions of nitrobenzene are as follows
Uses of Nitro compounds
i) It is used for the preparation of dyes and explosives such as TNB (1,3,5-trinitrobenzene),
TNT (1,3,5-trinitrotoluene), etc.
ii) It is a precursor molecule in the manufacture of Aniline.
iii) It is used as solvent in making shoe polish.
iv) It is used as scenting material for making cheap soaps,
v) It is used to synthesize “artificial musk like odor” perfume also called toluene musk.
