Torsional barriers in substituted NN-dimethylcarbamates. A probe for perturbational molecular orbital analyses of amide rotation

Nurit Kornberg, Daniel Kost

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Free energies of activation for torsion about the N-CO bond in four aryl NN-dimethylcarbamates, p-YC6H4X·CO· NMe2 (1)-(4), were measured using dynamic n.m.r. spectroscopy, and utilizing a lanthanide shift reagent to increase resolution between the diastereotopic N-methyl groups. Barriers were: (1; X = O, Y = H) 16.5 kcal/mol) (69.0 kJ/mol); (2; X = O, Y = NO2) 17.1 kcal/mol (71.5 kJ/mol); (3; X = S, Y = H) 14.9 kcal/mol; (62.3 kJ/mol) and (4; X = S, Y = NO2) 15.0 kcal/mol (62.8 kJ/mol). The results are discussed in terms of two recently proposed PMO analyses of amide rotation, one focusing on effects of the substituents at the torsional ground state and the other one on effects at the transition state. The higher barriers obtained for the para-nitro-substituted compounds relative to the unsubstituted ones is evidence for the dominance of ground-state effects in this system.

Original languageEnglish
Pages (from-to)1661-1664
Number of pages4
JournalJournal of the Chemical Society, Perkin Transactions 2
Issue number12
DOIs
StatePublished - 1 Jan 1979

ASJC Scopus subject areas

  • General Chemistry

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