TY - JOUR
T1 - Torsional barriers in substituted NN-dimethylcarbamates. A probe for perturbational molecular orbital analyses of amide rotation
AU - Kornberg, Nurit
AU - Kost, Daniel
PY - 1979/1/1
Y1 - 1979/1/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=33947258645&partnerID=8YFLogxK
U2 - 10.1039/P29790001661
DO - 10.1039/P29790001661
M3 - Article
AN - SCOPUS:33947258645
SN - 1472-779X
SP - 1661
EP - 1664
JO - Journal of the Chemical Society, Perkin Transactions 2
JF - Journal of the Chemical Society, Perkin Transactions 2
IS - 12
ER -