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The amide is an important functional group present in a number of types of drugs molecules (local anesthetics, antiarrhythmics, etc) It is also the key linking moiety in proteins and peptide drug products: II Amide Solubility Amides contain carbonyl (C=O) and ether (N-C) dipoles arising from covalent bonding between
amide nitrogen of {3-lactams has substitution of two ester groups, the carbonyl band is shifted up to 1770 cm - 1 The {3-lactam carbonyl group in benzylpenicillin methyl ester (an example of a lactam ring fused to a second ring) has its C=O frequency at 1780 cm -1 (Thompson et at , 1949) This is much higher than the C=O frequency for
carbonyl stabilizes the charged resonance structure of the amide bond (Figure 1),17,18 which results in an increase in the C-N double bond character as the CdO bond order decreases; the C-N bond length decreases while the CdO bond lengthens 18 Thus, the AmII? band frequency would be expected to increase while the AmI band frequency decreases 19
The C=O stretching frequency aldehydes and ketones C=O aldehydes R(C=O)H 1740-1720 S(sh) 14 amide RCONR 2 1650-1620 S(sh) 23 anhydrides R(CO
Carbonyl - compounds For simple aldehydes and ketones, the stretching vibration of the carbonyl group has a strong infrared absorption between 1710 and 1740 cm-1 Alkyl substituents are Electron Donating Groups – inductive effect lower the bond strength of C=O ketone carbonyls have slightly lower stretching frequencies, 1715 ± 7 cm-1,
a10cm-1 shift for the amide I frequency for N-acetyl-alanine-methyl ester in vacuo, which appears inconsistent with the Figure 1 spectra of N-acetyl-alanine-methyl ester in water The shift in the amide I frequency presumably is related to the ? angular dependence of interactions between the methine hydrogen and the carbonyl
6 Carbonyl compounds 6 1 Aldehydes and ketones 6 2 Cyclic ketones 6 3 Carboxylic Acids 6 4 Esters 6 5 Cyclic esters 6 6 Amides 6 7 Cyclic amides
2 the carbonyl (C=O) absorption between 1690-1760cm-1; this strong band indicates either an aldehyde, ketone, carboxylic acid, ester, amide, anhydride rare cases where H-bonding is not present, the peak is sharp and at higher frequency