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Reactive Sites in Isophorone Isomers: H/D‐Exchange Studies and Quantum‐Chemical Calculations
Author(s) -
Murphy Eamonn F.,
Bürgi Thomas,
Baiker Alfons
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20011017)84:10<2884::aid-hlca2884>3.0.co;2-8
Subject(s) - isophorone , chemistry , reactivity (psychology) , proton , quantum chemical , computational chemistry , chemical shift , photochemistry , catalysis , molecule , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics
Base‐catalyzed H/D‐exchange for α ‐ and β ‐isophorone ( 1 and 2 , resp.) was monitored by NMR spectroscopy to identify the number and nature of reactive sites. Results show that α ‐isophorone ( 1 ) undergoes H/D exchange at up to four different sites depending on reaction conditions. β ‐Isophorone ( 2 ), on the other hand, exhibits activity at two sites, predominantly at the α ‐position, under comparable conditions. Quantum‐chemical calculations indicate that the thermodynamically more‐stable anions formed upon proton abstraction from isophorone are not favored kinetically in all cases. Thermodynamically unfavorable H/D‐exchange at the α ‐position in 1 , which is observed experimentally, is explained via intermediate formation of γ ‐isophorone ( 3 ) with subsequent conjugation to the α ‐isomer. Differences observed in the reactivities of the two isomers and differences in reactivity of 1 under various conditions in reactions involving proton abstraction as an initial step may be partly explained on the basis of these results.