The properties of the simple amides are relevant to the chemistry of peptides and proteins, substances that are fundamental to all life as we know it. Indeed, the characteristics of peptides and proteins are primarily due to their polyamide structures. For this reason, it is important to know and understand the chemistry of simple amides.
- 24.1: Structural, Physical, and Spectral Characteristics of Amides
- An important feature of the amide group is that it is planar - the carbon, oxygen, nitrogen, and the first atom of each of the R groups on carbon and nitrogen lie in the same plane. This coplanarity is induces a large dipoles with simple amides have dipole moments in the range 3.7-3.8 debye. As a consequence of the polarity of the amide group, the lower-molecular-weight amides are relatively high-melting and water-soluble, as compared to esters, amines, alcohols, and the like.
- 24.2: Amides as Acids and Bases
- Amides with N−H bonds are weakly acidic. Nonetheless, amides clearly are far more acidic than ammonia, and this difference reflects a substantial degree of stabilization of the amide anion. However, amides still are very weak acids (about as weak as water) and, for practical purposes, are regarded as neutral compounds.
- 24.3: Synthesis of Amides
- Amides generally are formed from acid chlorides, acid azides, acid anhydrides, and esters. It is not practical to prepare them directly from an amine and a carboxylic acid without strong heating or unless the reaction is coupled to a second reaction that "activates" the acid. Notice that esters of phenols are more reactive toward amines than esters of alcohols because phenols are stronger acids than alcohols.
- 24.4: Hydrolysis of Amides
- Generally, amides can be hydrolyzed in either acidic or basic solution. The mechanisms are much like those of ester hydrolysis, but the reactions are very much slower, a property of great biological importance. Amide hydrolysis can be an important route to amines. Biological amide hydrolysis, as in the hydrolysis of peptides and proteins, is catalyzed by the proteolytic enzymes.
- 24.5: Nitriles
- The carbon-nitrogen triple bond differs considerably from the carbon-carbon triple bond by being stronger and much more polar. The degree of polarity of the carbon-nitrogen triple bond is indicate by the high dipole moment of the simple nitriles, which corresponds to about 70% of the dipole moment expected if one of the bonds of the triple bond were fully ionic. It is not surprising that liquid nitriles have high dielectric constants compared to most organic liquids and are soluble in water.
- 24.6: Nitro Compounds
- Nitro compounds are a very important class of nitrogen derivatives. The nitro group, −NO2, like the carboxylate anion, is a hybrid of two equivalent resonance structures with a hybrid structure that has a full positive charge on nitrogen and a half-negative charge on each oxygen. The polar character of the nitro group results in lower volatility of nitro compounds than ketones of about the same molecular weight.
- 24.7: Some Compounds with N-N Bonds
- Among the organic nitrogen compounds having nitrogen above the oxidation level of ammonia are a wide variety of substances with N−N bonds. We shall mention only a very few of the more important of these substances: hydrazines, azo and diazo compounds, and azides.
- 24.E: Organonitrogen Compounds II- Amides, Nitriles, and Nitro Compounds (Exercises)
- These are the homework exercises to accompany Chapter 24 of the Textmap for Basic Principles of Organic Chemistry (Roberts and Caserio).
Contributors and Attributions
John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."