1. Structure of Amines

Amines | Chemistry

Amines

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Unit 13

Amines

Objectives

After studying this Unit, you will be able to

• describe amines as derivatives of ammonia having a pyramidal structure;

• classify amines as primary, secondary and tertiary;

• name amines by common names and IUPAC system;

• describe some of the important methods of preparation of amines;

• explain the properties of amines;

• distinguish between primary, secondary and tertiary amines;

• describe the method of prepara-tion of diazonium salts and their importance in the synthesis of a series of aromatic compounds including azo dyes.

 

“The chief commercial use of amines is as intermediates in the synthesis of medicines and fibres” .

 NEETprep Audio Note: 

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  NEETprep Audio Note (English):  
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    Amines constitute an important class of organic compounds derived by replacing one or more hydrogen atoms of ammonia molecule by alkyl/aryl group(s). In nature, they occur among proteins, vitamins, alkaloids and hormones. Synthetic examples include polymers, dye stuffs and drugs. Two biologically active compounds, namely adrenaline and ephedrine, both containing secondary amino group, are used to increase blood pressure. Novocain, a synthetic amino compound, is used as an anaesthetic in dentistry. Benadryl, a well known antihistaminic drug also contains tertiary amino group. Quaternary ammonium salts are used as surfactants. Diazonium salts are intermediates in the preparation of a variety of aromatic compounds including dyes. In this Unit, you will learn about amines and diazonium salts.

I. Amines

 NEETprep Audio Note:  

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  NEETprep Audio Note (English):  
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   Amines can be considered as derivatives of ammonia, obtained by replacement of one, two or all the three hydrogen atoms by alkyl and/or aryl groups.

For example:


13.1 Structure of Amines

Like ammonia, nitrogen atom of amines is trivalent and carries an unshared pair of electrons. Nitrogen orbitals in amines are therefore, sp3 hybridised and the geometry of amines is pyramidal. Each of the three sp3 hybridised orbitals of nitrogen overlap with orbitals of hydrogen or carbon depending upon the composition of the amines. The fourth orbital of nitrogen in all amines contains an unshared pair of electrons. Due to the presence of unshared pair of electrons, the angle C–N–E, (where E is C or H) is less than 109.5°; for instance, it is 108o in case of trimethylamine as shown in Fig. 13.1.


Fig. 13.1 Pyramidal shape of trimethylamine