Amides Containing Specialised Structures

With cyclic systems such as succinimide and related compounds coplanarity is to be expected and now much greater separations are found. Succinimide shows bands at [ 157] 1781 and 1715 cm , and other compounds behave similarly [156, 157]. The frequency ranges are quite wide 1790—1735 and 1745—1680 cm . As with the anhydrides it is the antisymmetric mode which has the lower frequency and has the greater intensity in the infra-red. Sizeable frequency shifts in this band can occur if the nitrogen atom is also substituted [158]. It is at 1738 cm in phthalimide, at 1720 cm  

Trimeric isocyanates also contain the CO—N—CO system. AUcyl derivatives show their main band around 1700—1680 cm with a weaker shoulder at 1715—1710 cm . Aromatics have a higher frequency with the main band near 1715 cm and the weaker shoulder near 1780 cm This is parallel to the raised carbonyl frequencies of anilides as compared with alkyl amides. Isocyanate dimers are of some theoretical interest in that the carbonyl groups are in direct opposition so the symmetric mode is forbidden in the infra-red. Only a single carbonyl band is therefore seen, and this is near 1780 cm  

With cyclic compounds containing three carbonyl groups, those immediately adjacent to the NH group behave as above, whilst the third shows a normal CO absorption. The spectra of six trialkyl pyrolidine triones examined by Skinner and Perkins [32] show absorptions at 1786 cm , 1724 cm and 1667 cm . The absorption at 1724 cm is attributed to the CO group in the 3 position. 

Tertiary urethanes absorb close to 1685 cm in chloroform [159], rising to 1710 cm in carbon tetrachloride [148]. Urethane itself absorbs at 1618 cm , corresponding to the amide II absorption of an unsubstituted amide, whilst the iViV-di-substituted products show no band in this region. The simple A/ -mono-substituted urethanes [5] and carbamates show their NH stretching absorption for the solid products in the 3300—3250 cm region, which is normal for open-chain amides. 

This same residue occurs in cyclic systems, such as the oxazolones, which have been studied by Gompper and Herlinger [115] and compared with the corresponding thioketo compounds. The carbonyl frequency then falls near 1750 cm , and the amide III absorption is raised to 1380 cm . Cyclic urethanes have also been discussed by Hall and Zbinden [150]. 

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