oxygen atom can accept hydrogen bonds from water and the N–H hydrogen atoms can donate H-bonds. As a result of interactions such as these, the water solubility of amides is greater than that of corresponding hydrocarbons. These hydrogen bonds are also have an important role in the secondary structure of proteins. The solubilities of amides and esters are roughly comparable. Typically amides are less soluble than comparable amines and carboxylic acids since these compounds can both donate and accept hydrogen bonds. Tertiary amides, with the important exception of N,N-dimethylformamide, exhibit low solubility in water. Characterization The presence of the amide group is generally easily established, at least in small molecules. It can be distinguished from nitro and cyano groups in IR spectra. Amides exhibit a moderately intense νCO band near 1650 cm−1. By 1H NMR spectroscopy, CONHR signals occur at low fields. In X-ray crystallography, the center together with the three immediately adjacent atoms linked to C and N characteristically define a plane. Reactions Amides undergo many chemical reactions, although they are less reactive than esters. Amides hydrolyse in hot alkali as well as in strong acidic conditions. Acidic conditions yield the carboxylic acid and the ammonium ion while basic hydrolysis yield the carboxylate ion and ammonia. The protonation of the initially generated amine under acidic conditions and the deprotonation of the initially generated carboxylic acid under basic conditions render these processes non-catalytic and irreversible. Amides are also versatile precursors to many other functional groups. Electrophiles react with the carbonyl oxygen. This step often precedes hydrolysis, which is catalyzed by both Brønsted acids and Lewis acids. Enzymes, e.g. peptidases and artificial catalysts, are known to accelerate the hydrolysis reactions. Synthesis Many methods exist in amide synthesis. Amides can be prepared by coupling carboxylic acid with an amine. The direct reaction generally requires high temperatures to drive off the water: Many methods involve "activating" the carboxylic acid by converting it to a better electrophile; such as esters, acid chlorides (Schotten-Baumann reaction), or anhydrides (Lumière–Barbier method). Conventional methods in peptide synthesis use coupling agents such as HATU, HOBt, or PyBOP. A variety of reagents, e.g. tris(2,2,2-trifluoroethyl) borate have been developed for specialized applications. Other methods Dehydrogenative acylation of amines is catalyzed by organoruthenium compounds: The reaction proceed by one dehydrogenation of the alcohol to the aldehyde followed by formation of a hemiaminal, which undergoes a second dehydrogenation to the amide. Elimination of