GROUP FREQUENCIES amino acid hydrochlorides

Table 9.1. Important Group Frequencies, in cm of Amino Acids and Their Hydrochlorides (Rao, 1963)...

Two bands probably caused by NHJ deformations appear in all amino acids and their hydrochlorides in the regions 1660-1590 and 1550-1480 cm". These bands are known as the amino acid I and II bands, respectively, the latter usually being stronger than the former. Isovaline does not have the amino acid II band. Some amino acids display splitting of this band. In hydroxy acids the II band moves to higher frequencies as the OH and NHj groups are positioned nearer to each other. For example, the deformation motion at 1504 cm" in e-hydroxynorleucine shifts to 1522 cm" in (5-hydroxynorvaline, to 1538cm" in homoserine, and does not appear in serine, since it is obscured by the 1600 cm" carboxyl band. Amino acid salts do not have these bands. The NH 2 deformation of N-substituted amino acids lies near 1600 cm. ... 

Amino-acids can, of course, form basic and acidic salts, and the frequencies arising in hydrochlorides have already been discussed above. Salt formation through the carboxyl group removes the... 

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