N-arylamides and N-arylcarbamates NCO internal rotation barrier study by molecular modeling

Amides and carbamates present an energetic barrier associated to NC(O) bond rotation, which determines two different equilibrium geometries. In this work, the conformational equilibrium of formanilide, acetanilide, methyl and t‐butyl phenylcarbamates, and their N‐methylderivatives was studied by AM...

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Bibliographic Details
Published in:International journal of quantum chemistry 2012-03, Vol.112 (6), p.1678-1687
Main Authors: Grasel, Fábio Dos Santos, De Oliveira, Tiago Charão, Fontoura, Luiz Antonio Mazzini, Da Cruz Rigotti, Italo José, Netz, Paulo Augusto
Format: Article
Language:English
Subjects:
amide
carbamate
rotational barrier
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Summary:Amides and carbamates present an energetic barrier associated to NC(O) bond rotation, which determines two different equilibrium geometries. In this work, the conformational equilibrium of formanilide, acetanilide, methyl and t‐butyl phenylcarbamates, and their N‐methylderivatives was studied by AM1 and B3LYP/6‐31G(d,p) calculations. The effect of aryl p‐substituents (MeO, Me, Cl, Br, CN, and NO2) was also studied. Amide barriers were found by DFT calculation between 12 and 21 kcal/mol. Carbamates, on the other hand, showed barriers between 11 and 15 kcal/mol. AM1 underestimates the energetic barriers and provides values around half those obtained by B3LYP/6‐31G(d,p) calculations. Electron withdrawing substituents on aryl group decrease the barrier. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
ISSN:0020-7608
1097-461X
DOI:10.1002/qua.23151