Structures and energies of isomeric C5H42+ and C6H42+ dications

Koop Lammertsma, Paul Von Ragué Schleyer

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15 Citations (Scopus)


The geometries of various C5H42+ and C6H42+ isomers with acetylene, cumulene, vinyl, propargyl, and three- and four-membered ring structures were optimized by ab initio molecular orbital theory employing the 3-21G basis set. Comparison of the Hartree-Fock (for C6H42+) and MP2/6-31G* (for C5H42+) relative energies shows clearly that there is no common minimum energy CnH42+ structure of the CH3-Cn-1-H2+ type as has been suggested from mass spectroscopic investigations. Thus, both 25 (n = 4) and 26 (n = 5) are quite high in energy relative to most other isomers examined. In addition, the cumulene dications, H2C(Cn)CH22+ (n = 3 and 4), which favor anti-van't Hoff geometries (11a and 12a), are less stable than structures with cyclopropenium ion moieties. The vinylidenecyclopropenium dication (15a) and the triafulvene dication (18a) are the lowest energy C5H42+ and C6H42+ dications investigated; heats of formation of 630 ± 5 (15a) and 617 ± 5 kcal/mol (18a) are estimated.

Original languageEnglish
Pages (from-to)881-886
Number of pages6
JournalJournal of Physical Chemistry
Issue number4
Publication statusPublished - 1988
Externally publishedYes

ASJC Scopus subject areas

  • General Engineering
  • Physical and Theoretical Chemistry


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