ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Theoretical and experimental studies were performed on a series of 1,4- and 1,6-dihydronicotinic acid derivatives to investigate their relative stabilities and factors contributing thereto. Ferricyanide-mediated oxidation studies indicated that not only did the 1,4-dihydropyridine derivatives oxidize more slowly than the 1,6-isomers, a finding consistent with previously published literature, but also that the ratio of the rates of reaction was constant. Thus, the 1,4-dihydropyridines oxidized 23-fold more slowly than did the 1,6-derivatives. Theoretical studies also indicated that the 1,4-dihydropyridines were more stable than the 1,6-isomers, as illustrated by lower calculated heats of formation, and were also more resistant to oxidation, as demonstrated by larger HOMO-LUMO energy gaps. An examination of the HOMO for the dihydropyridines showed that the 1,4-isomers were associated with a greater degree of homoaromatic and hyperconjugative stabilization as compared to the 1,6-dihydropyridines and that these factors did not appear to be significantly affected by substitution. These data suggest that the stabilizing properties associated with the 1,4-dihydropyridine system (i.e., greater contributions from the sp3 ring carbon and attached hydrogens) are systematically expressed providing an explanation for the constant difference in experimental reaction rates. © 1995 John Wiley & Sons, Inc.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560560717
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