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13 C NMR spectra of some amides and imides. Effect of inductive and mesomeric interactions, cyclization and hydrogen bonding on 13 C NMR chemical shifts
Author(s) -
Hasan Misbah Ul
Publication year - 1980
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270140605
Subject(s) - chemical shift , steric effects , chemistry , amide , electronic effect , ring (chemistry) , nmr spectra database , hydrogen bond , carbon 13 nmr , inductive effect , proton nmr , medicinal chemistry , stereochemistry , molecule , organic chemistry , spectral line , physics , astronomy
Carbon‐13 NMR chemical shifts in various amides and imides are examined. The compounds include mono‐ and diamides, acyclic imides and cyclic 5‐ and 6‐membered ring imides. The observed shifts can be satisfactorily rationalized on the basis of various electronic and steric factors which contribute to the chemical shifts in these systems. The 13 C shifts in amides and imides are further compared with the shifts in corresponding oxygen analogues, i.e. esters and anhydrides. The saturated and α, β‐unsaturated amide carbonyls absorb in the range of 173–178 ppm and 167–170 ppm, respectively. These shifts are downfield by 2–3 ppm in comparison with the corresponding esters. The carbonyl shifts in cyclic imides appear in the range 170–180 ppm. In comparison with the corresponding anhydrides and amides, these shifts are downfield by 5–7 ppm and 3–4 ppm, respectively. These differences are discussed in terms of electronic interactions and steric effects.