Enthalpy/Entropy Contributions to Conformational KIEs: Theoretical Predictions and Comparison with Experiment
AbstractPrevious theoretical studies of Mislow’s doubly-bridged biphenyl ketone 1 and dihydrodimethylphenanthrene 2 have determined significant entropic contributions to their normal (1) and inverse (2) conformational kinetic isotope effects (CKIEs). To broaden our investigation, we have used density functional methods to characterize the potential energy surfaces and vibrational frequencies for ground and transition structures of additional systems with measured CKIEs, including [2.2]-metaparacyclophane-d (3), 1,1'-binaphthyl (4), 2,2'-dibromo-[1,1'-biphenyl]-4,4'-dicarboxylic acid (5), and the 2-(N,N,N-trimethyl)-2'-(N,N-dimethyl)-diaminobiphenyl cation (6). We have also computed CKIEs in a number of systems whose experimental CKIEs are unknown. These include analogs of 1 in which the C=O groups have been replaced with CH2 (7), O (8), and S (9) atoms and ring-expanded variants of 2 containing CH2 (10), O (11), S (12), or C=O (13) groups. Vibrational entropy contributes to the CKIEs in all of these systems with the exception of cyclophane 3, whose isotope effect is predicted to be purely enthalpic in origin and whose Bigeleisen-Mayer ZPE term is equivalent to ΔΔ H‡. There is variable correspondence between these terms in the other molecules studied, thus identifying additional examples of systems in which the Bigeleisen-Mayer formalism does not correlate with ΔH/ΔS dissections. View Full-Text
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Fong, A.; Meyer, M.P.; O'Leary, D.J. Enthalpy/Entropy Contributions to Conformational KIEs: Theoretical Predictions and Comparison with Experiment. Molecules 2013, 18, 2281-2296.
Fong A, Meyer MP, O'Leary DJ. Enthalpy/Entropy Contributions to Conformational KIEs: Theoretical Predictions and Comparison with Experiment. Molecules. 2013; 18(2):2281-2296.Chicago/Turabian Style
Fong, Aaron; Meyer, Matthew P.; O'Leary, Daniel J. 2013. "Enthalpy/Entropy Contributions to Conformational KIEs: Theoretical Predictions and Comparison with Experiment." Molecules 18, no. 2: 2281-2296.