ISSN:
0192-8651
Schlagwort(e):
Computational Chemistry and Molecular Modeling
;
Biochemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Informatik
Notizen:
The molecular geometries of three conformations of methyl propanoate (MEP) (C—C—C=O torsions of 0°, 120°, and 180°) and the potential-energy surfaces of MEP (C—C—C=O torsions) and of the methyl ester of glycine (MEG) (N—C—C=O torsions) have been determined by ab initio gradient calculations at the 4-21G level. MEP has conformational energy minima at 0° and 120° of the C—C—C=O torsion, while the 60-90° range and 180° are energy maxima. For MEG there are two minima (at 0° and 180°) and one barrier to N—C—C=O rotation in the 60-90° range. The N—C—C=O barrier height is about twice as high (4 kcal/mol) as the C—C—C=O barrier. The 180° N—C—C=O minimum is characteristically wide and flat allowing for considerable flexibility of the N—C—C=O torsion in the 150-210° range. This flexibility could be of potential importance for polypeptide systems, since the N—C—C=O angles of helical forms are usually found in this region. The molecular structures of the methyl ester group CH3OC(=O)CHRR′ in several systems are compared and found to be rather constant when R = H and R′ = H, CH3, CH3CH2; or when R = NH2 and R′ = H, CH3, or CH(CH3)2.
Zusätzliches Material:
4 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jcc.540040407
Permalink
