Hydride-abstraction reactions from cycloheptatriene and 1-carbamoylcycloheptatriene. Effect of the CONH2 group orientation on the reactivity difference of the exo and endo hydrogen toward hydride abstraction. A quantum-chemical study

R.H.A.M. Brounts, H.M. Buck

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Abstract

Quantum chemical calculations (MIND0/3 and ab initio (STO-3G)) for the enzyme-catalyzed stereospecific hydride transfer equilibrium RH + NAD' 8 R+ + NADH have shown that it seems possible to relate the stereospecificity with an out-of-plane orientation of the CONHz group in the transition state. To generalize this model reaction for cyclic (4n + 2) aromatic cations, we focus our attention on the intermolecular hydride transfer from 1-carbamoylcycloheptatriene to the cyclopropenium cation. The enthalpy of activation for exo-hydride abstraction from cycloheptatriene was found to be 26 kJ mol-' higher than for endo-hydride transfer. For 1 -carbamoylcycloheptatriene the calculations showed clearly that the difference in enthalpy of activation for endo- and exo-hydrogen transfer is more favored for endo abstraction by orientation of the carbonyl dipole toward the endo hydrogen. Orientation toward the exo hydrogen does not result in an increased selection with respect to the parent hydrocarbon.
Original languageEnglish
Pages (from-to)1284-1288
JournalJournal of the American Chemical Society
Volume105
Issue number5
DOIs
Publication statusPublished - 1983

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