Theoretical Study of the Stability of β-Hydroxy Carbonium Ion as an Intermediate of Pinacol Rearrangement

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  • NAKAMURA Kensuke
    Department of Chemistry, Faculty of Science and Technology, Keio University;
  • OSAMURA Yoshihiro
    Department of Chemistry, Faculty of Science and Technology, Keio University;

Bibliographic Information

Other Title
  • β-ヒドロキシカルボニウムイオンの構造と安定性ピナコール転位反応中問体は存在するか?
  • Theoretical study of the stability of .BETA.-hydroxy carbonium ion as an intermediate of pinacol rearrangement.

Description

Pinacol rearrangement is one of the typical reactions via carbonium ion. The molecular structure and stability of intermediate species of pinacol rearrangement are examined with ab initio molecular orbital theory. The stability of β-hydroxy carbonium ion depends on the substituents and the migrating group, while 2-hydroxyethyl cation[11]is known to be unstable and to automatically isomerize to protonated acetaldehyde[12]. By carrying out the geometry optimization for various methyl substituted p-hydroxy carbonium ions, we have found that both methyl group and hydrogen atom spontaneously migrate to form protonated aldehyde or ketone for primary cation. The secondary carbonium ion is also found to rearrange with a very low energy barrier. Although β-hydroxy tertiary carbonium ion is possible to locate at an energy minimum on the potential energy surface, the present calculation suggests that the carbonium ion is not necessary to be formed as an intermediate of the pinacol rearrangement.

Journal

  • NIPPON KAGAKU KAISHI

    NIPPON KAGAKU KAISHI 1989 (8), 1392-1399, 1989-08-10

    The Chemical Society of Japan

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