Hydrogen bonding esters

Hydrogen bonding Esters do not have an 0-H bond. Therefore, they cannot form hydrogen bonds with other ester molecules. 

Because of their inability to form hydrogen bonds, esters tend to be liquids with boiling points much lower than those of carboxyhc acids of similar molecular weights. 

No satisfactory method for calculating hydrogen bond interactions was available, so the early applications of this principle depended on the qualitative arrangement of solvents into three hydrogen-bonded classes alcohols, acids, and amines (strongly hydrogen bonded) esters, ketones, and ethers (moderately hydrogen bonded) and hydrocarbons (poorly... 

Esters can participate m hydrogen bonds with substances that contain hydroxyl groups (water alcohols carboxylic acids) This confers some measure of water solubil ity on low molecular weight esters methyl acetate for example dissolves m water to the extent of 33 g/100 mL Water solubility decreases as the carbon content of the ester increases Fats and oils the glycerol esters of long chain carboxylic acids are practically insoluble m water... 

Section 20 8 Esters are polar and have higher boiling points than alkanes of compa rable size and shape Esters don t form hydrogen bonds to other ester molecules so have lower boiling points than analogous alcohols They can form hydrogen bonds to water and so are comparable to alcohols m their solubility m water... 

Methyl salicylate is the methyl ester of o hydroxybenzoic acid Intramolecular (rather than mtermolecular) hydrogen bonding is responsible for its relatively low boiling point... 

Polyamides. The next two compounds are the amide counterparts of the esters listed under item (4). Although the values of AH j are less for the amides than for the esters, the values of T j, are considerably higher. This is a consequence of the very much lower values of AS j for the amides. These, in turn, are attributed to the low entropies of the amide in the liquid state owing to the effects of hydrogen bonding and chain stiffness arising from the contribution of the resonance form... 

Fig. 8. Rephcation. The amino adenosine X and the pentafluorophenyl ester Y form a hydrogen-bonded dimer XY, prior to reaction between the amine and the activated ester groups (shown in the circle). The reaction product is a <7 -amide conformer cis-Z that isomeri2es to the more stable trans- acnide Z. The rephcative process is cataly2ed by the reaction product Z (also referred to as the template). First, a termolecular complex XYZ is formed from X, Y, and Z.

The higher fatty acids undergo decarboxylation and other undesirable reactions when heated at their boiling points at atmospheric pressure. Hence they are distilled at reduced pressure (15,16). Methyl esters boil at lower temperatures than acids at the same pressure as the result of the absence of hydrogen bonding (17). A procedure for calculation of the vapor pressures of fatty acids at various temperatures has been described (18). 

Acetate fibers are dyed usually with disperse dyes specially synthesized for these fibers. They tend to have lower molecular size (low and medium energy dyes) and contain polar groups presumably to enhance the forces of attraction by hydrogen bonding with the numerous potential sites in the cellulose acetate polymer (see Fibers cellulose esters). Other dyes can be appHed to acetates such as acid dyes with selected solvents, and azoic or ingrain dyes can be apphed especially for black colorants. However thek use is very limited. 

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