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A PM 3 study on intrinsic decarboxylation process of methyl–ethyl‐α–pyridylacetic acid
Author(s) -
Nakajima Yasushi,
Sakagishi Yoshikatsu,
Shiibashi Michio,
Suzuki Yuuji,
Kato Hitoshi
Publication year - 1995
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560540108
Subject(s) - dihedral angle , decarboxylation , chemistry , mndo , dissociation (chemistry) , enthalpy , crystallography , molecular geometry , transition state , pyridine , geometry , computational chemistry , thermodynamics , medicinal chemistry , molecule , organic chemistry , hydrogen bond , physics , mathematics , catalysis
To probe the decarboxylation process of methyl–ethyl–α pyridylacetic acid (MEPA), molecular orbital calculations on the optimized geometry, transition‐state geometry, and intrinsic reaction coordinate were performed by the MNDO – PM 3 method. The salient features of the optimized structure of MEPA are that the carboxyl anion is nearly on the plane of the pyridine ring (the dihedral angle of C8C7C2N1 is 14.7°) and that the interatomic distance … is used for a noncovalent bond, such as N + 1 … O −9 . of O − 9 … H1′ is 1.6 Å (exchange of electrons exists between their atoms). The transition‐state geometry of the decarboxylation process has the following features: (1) the activation enthalpy is 6.0 kcal/mol, (2) the dihedral angle of C8C7C2N1 is −50.2°, and (3) the interatomic distance of O − 9H1′ and C7C8 increase by 111 and 124%, respectively, as compared with the optimized geometry. From the extreme beginning of the intrinsic decarboxylation process, the exchange of electrons between O − 9 … H1′ begins to decrease. This decrease, which is considered to be induced by the rotation of C2C7, seems to initiate the dissociation of C7C8. © 1995 John Wiley & Sons, Inc.