L-shaped three-center two-electron (C-C-C)+ bonding array.
The structures and reactivities of the complexes between carbenium ions (R(+)) and acetylene or propyne have been investigated with the aid of electron-correlated quantum mechanical calculations (hybrid density functional, perturbation theory, and coupled cluster methods). Depending on the R group, the acetylene/carbenium ion interaction can produce either an "open" 3c-2e structure or the conventional vinyl cation structure. The "open" 3c-2e C-C-C bonding geometry exists as a minimum for R = methyl and primary/secondary/tertiary alkyl, and hence is the most notable. The alignment of three carbon centers is neither bridged nor linear, but L-shaped, and represents a new type of "open" 3c-2e bonding that has so far escaped proper attention.
Yoshikai
Naohiko
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Contribution from the Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
Ammal
Salai Cheettu
SC
Nakamura
Eiichi
E