Amides intermolecular forces

One example of a familiar amide is the pain-relieving drug sold as Tylenol (14) we shall see another important example when we consider the polymer known as nylon in Section 19.10. Many amides have N—H bonds that can rake part in hydrogen bonding, and so the intermolecular forces between their molecules are relatively strong. 

Lifson S, Hagler AT, Dauben P (1979) Consistent force field studies of intermolecular forces in hydrogen bonded crystals. I. Carboxylic acids, amides and the C-O—H hydrogen bonds. J Am Chem Soc 101 5111-5121... 

Successful partition chromatography requires a proper balance of intermolecular forces among the three participants in the separation process—the analyte, the mobile phase, and the stationary phase. These intermoleculai forces are described qualitatively in terms of the relative polarity possessed by each of the three components. In general, the polai ities of common organic functional groups in increasing order are aliphatic hydrocarbons < olefins < aromatic hydrocarbons < halides < sulfides < ethers < nitro compounds < esters = aldehydes = ketones < alcohols = amines < sulfones < sulfoxides < amides < carboxylic acids < water. 

S. Lifson, A. T. Hagler, and P. Dauber, /. Am. Chem. Soc., 101, 5111 (1979). Consistent Force Field Studies of Intermolecular Forces in Hydrogen-Bonded Crystals. 1. Carboxylic Acids, Amides, and the C = 0- H Hydrogen Bonds. 

Like the carboxylic acids, the primary and secondary amides have a hydrogen bonding contribution to their intermolecular forces. 

The degree to which a polymer can crystallise depends on the details of the chain. For example, the amide group is a polar unit and forms hydrogen bonds with the carboxyl oxygen in nylons (Scheme 6.13, p. 186). These intermolecular forces hold the... 

A consideration often overlooked in BAM studies is the possible influence of the compression rate on the domain structures. In the case of A-acylamino acid monolayers, the associations due to amide-amide hydrogen bonding are very strong and promote rapid domain growth and also make it unlikely that relaxation to an equilibrium domain shape can occur on any realistic experimental timeframe. Domain shape relaxation kinetics are noted to be dependent on the strength of intermolecular forces for example, dendritic condensed-phase domains formed in a phospholipid monolayer required 5 h to relax to equilibrium shapes and, for the phospholipid DMPE, compression rates as slow as 0.2 per molecule per minute were needed to observe equilibrium domain shapes. Examination of the variation of domain structure with time after then-formation or with compression rates are not commonly reported however, it is advisable to consider examining these variables when carrying out BAM experiments. 

Most simple covalent compounds whose intermolecular forces are London (dispersion) forces, for example iodine (Figure 4-92) and the halogenoalkanes, are poorly soluble in water, but are soluble in less polar or non-polar solvents. Simple covalent compounds whose intermolecular forces are hydrogen bonds are often soluble in water, for example amines, carboxylic acids, amides and sugars, provided they have relatively low molar mass or can form multiple hydrogen bonds. 

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