期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 132, 期 34, 页码 12145-12149出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja105331g
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资金
- NSF [CHE07-42801, CHE-0741968]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [0741968] Funding Source: National Science Foundation
Secondary isotope effects (IEs) on basicities of various deuterated pyridine isotopologues and of 2,6-lutidine-2,6-(CD3)(2) have been accurately measured in aqueous solution by an NMR titration method applicable to a mixture. Deuteration at any position of pyridine increases the basicity, but the IE per deuterium is largest for substitution at the 3-position and smallest for the 2-position, which is closest to the site of N-protonation, smaller even than that for 2-CD3 substitution. Computations at the B3LYP/cc-pVTZ level overestimate the magnitude of the measured IEs but largely reproduce the variability with isotopic position. Because the calculated IEs are based on changes in vibrational frequencies on N-protonation, the correspondence between calculated and experimental IEs implies that they arise from zero-point energies, rather than from inductive effects.
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