Hammerum S, Jensen LB, Mohr M. Isotope Effects on the Unimolecular Dissociation of Ionized 3-Methyl-2-butanol: Reactions via a Long-Lived C−H−C Hydrogen-Bridged Ion-Neutral Complex.
J Phys Chem A 2005;
109:3159-65. [PMID:
16833644 DOI:
10.1021/jp0407425]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A pronounced isotope effect causes metastable CD3CHOHCH(CH3)2+* ions to expell C3H6D2 in preference to C3H7D in a ratio of approximately 33:1; a number of related compounds show similar effects. High-level ab initio calculations suggest that the reactant alcohol molecular ion possesses an extraordinarily long alpha-carbon-carbon bond and that the reaction proceeds via the formation of an intermediate hydrogen-bridged complex of propane and ionized vinyl alcohol, in which the bridging hydrogen atom is almost midway between the two carbon termini. The isotopic preference reflects the difference between the zero-point vibrational energies of the isotopically different product pairs rather than kinetic isotope effects on the hydrogen atom transfer reactions that precede dissociation.
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