Nonbasic nitrogen, stability

In contrast with amines, amides (RCONH ) are nonbasic. Amides don t undergo substantial protonation by aqueous acids, and they are poor nucleophiles. The main reason for this difference in basicity between amines and amides is that an amide is stabilized by delocalization of the nitrogen lone-pair electrons through orbital overlap with the carbonyl group. In resonance terms, amides are more stable and less reactive than amines because they are hybrids of two resonance forms. This amide resonance stabilization is lost when the nitrogen atom is protonated, so protonation is disfavored. Electrostatic potential maps show clearly the decreased electron density on the amide nitrogen. 

The polars describe mainly the resins, asphaltenes, and the poryphyrins, as well as the trace nitrogen found in bases, the nonbasic poryphyrins, the oxygen in the phenols, the napthenic acids and esters, and the sulfur in sulfide and disulfide bonds. The polars and the metalloporphyrins are indicated as emulsifier species involved in stabilizing the emulsions (24, 25). Resins, which will be discussed later with asphaltenes, contain O, N, and S in the form of car-bazoles, fluor-enones, fluorenols, carboxylic acids, and sulfoxides. These are attracted to water interfaces. 

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