The Effect of Solvent on Spectra. VII. The “Methyl Effect” in the Spectra of Dihydropyridines

Dieter Hofmann, Edward M. Kosower, Kurt Wallenfels

Research output: Contribution to journalArticlepeer-review


The puzzling difference in ultraviolet maximum between the “Hantzsch compounds,” 2,6-dimethyl-3,5;dicarbethoxy-1,4-dihydropyridine (λmax 3690 Å.) and 2,4,6-trimethyl-3,5-dicarbethoxy-1,4-dihydropyridine (λmax 3490 Å.) is now explained as resulting from the relative increase in non-bonded repulsion between the carbethoxy group and the 4-methvl group in the excited state as compared with the compound lacking the 4-methyl group. The explanation is supported by the decrease in the effect when the carbethoxy groups are replaced by cyano groups in which the charge increment in the excited state is farther away from the 4-methyl group. The validity of the comparisons between the carbethoxy and cyano-substituted dihydropyridines is established by the parallelism in solvent effects upon the observed transitions. Data for the model compounds ethyl β-aminocrotonate and β-aminocrotononitrile are also reported.

Original languageEnglish
Pages (from-to)3314-3319
Number of pages6
JournalJournal of the American Chemical Society
Issue number15
StatePublished - 5 Aug 1961
Externally publishedYes


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