Structures and Energies of C4H22+1

Koop Lammertsma, John A. Pople, Paul von Rague Schleyer

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)


At the MP3/6-31G*//HF/6-31G* level of ab initio theory, the lowest energy C4H22+ dication is indicated to have a linear (D∞h) structure; the four-membered-ring (D2h) alternative is 13.3 kcal/mol less stable. At MP4SDQ/6-31G*//3-21G the linear C4H+(C∞h) monocation is only 3.6 kcal/mol more stable than its four-membered-ring (C2v) isomer. These stability orders differ from those of the C4 structures where the cyclic isomer (D2h) is 0.7 kcal/mol (MP4SDQ/6-31G*//6-31G*) more stable than the linear (D∞h) structure. Despite the estimated very large heat of formation of C4H22+ of 733 kcal/mol, all the modes of dissociation explored are calculated to be endothermic. In particular, the surprisingly large proton affinity of C4H+, 63.1 kcal/mol, may be attributed to the diminution of electrostatic repulsion in the long, linear structure. In agreement with gas-phase studies, we find the most favorable C4H22+ dissociations to be into C3H++ CH+(endothermic by 36.7 kcal/mol for 1) and into C3H2+ + C+ (endothermic by 14.7 kcal/mol for 2). All the four-membered-ring structures, C4H22+, C4H+, and C4, show σ-deficient character for the bridging carbons. In these cases the HOMO’s are σ orbitals of nonbonding nature with the significant stabilization resulting from 4-center, 2-electron aromatic π bonding. This result is contrary to intuition, which suggests double bond character between the bridging carbons as allowed for by an inverted geometry of the two sp12-hybridized carbons.

Original languageEnglish
Pages (from-to)7-10
Number of pages4
JournalJournal of the American Chemical Society
Issue number1
Publication statusPublished - 1986
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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