Tuesday, 1 January 2013

Amide NMR

Butyramide

Chemical shifts

CO-N-H: 5.0 - 9.0 ppm. Varies and broadens like alcohols and amines. Resonance between the lone pair and carbonyl group restricts rotation around the N-C bond, so NH2 can become two peaks.


CH-CONH: 2.1 - 2.5 ppm. Like esters - slightly longer range than typical HC-C=O due to extra induction from the nitrogen.

CO-NH-CH: 2.2 - 2.9 ppm. Slightly deshielded by the nitrogen.

Coupling behavior

N-H: About 50 hz. Usually not seen, due to proton exchange or "quadrupolar interactions". I'm not sure how quadrupolar interactions work, but it is a property of nitrogen and results in the same thing as proton exchange - peak broadening and intensity reduction.

CH-N: About 0 hz. Usually not seen, same reasons as above.

CH-NH: About 0 hz. Usually not seen, same reasons as above.

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