A piece of the C₆H₉⁺ potential energy surface: Rearrangement of spiropentylmethyl cation and an elegant nonclassical spiro[2.3]hex‐5‐yl cation

Abstract

Stationary points in a region of the C6H9+ potential energy surface was explored using the CBS‐QB3 method. The region includes the spiropentylmethyl cation and all three bicyclohexyl bridgehead cations. The relative energies of these bicyclohexyl cations are −54 kJ/mol for bicyclo[2.2.0]hex‐1‐yl cation and −75 kJ/mol for bicyclo[2.1.1]hex‐1‐yl cation, with spiropentylmethyl cation being 0 kJ/mol. Bicyclo[2.1.1]hex‐1‐yl cation is a transition state, while bicyclo[3.1.0]hex‐1‐yl cation is not a stationary point after all, but rearranges without barrier to 2‐methylenecyclopentyl cation. Although spiropentylmethyl cation and spiro[2.3]hex‐4‐yl cation are local minima on the CBS‐QB3 potential energy surface, their existence is questioned. Spiro[2.3]hex‐5‐yl cation has an unusual structure, with the central carbon having five nearest neighbors with interatomic distances between 1.5 and 1.7 Å. The results for rearrangement of the spiropentylmethyl cation are in general agreement with previous solvolysis studies.

Kinetics of reactions of NH4+ with some biogenic organic molecules and monoterpenes in helium and nitrogen carrier gases: A potential reagent ion for selected ion flow tube mass spectrometry

“…The transfer of a proton from an ion to complex compounds can result in a marked change in the structure of the molecule. This could be especially so for the C 10 H 17 + carbocations, which are known to undergo facile rearrangement 38,39 . Such a change could depend on the amount of energy released on protonation and therefore depend on the nature of the donating ion and the PA of its neutral molecule.…”

“…This could be especially so for the C 10 H 17 + carbocations, which are known to undergo facile rearrangement. 38,39 Such a change could depend on the amount of energy released on protonation and therefore depend on the nature of the donating ion and the PA of its neutral molecule. Our calculations of the PA, which do not consider rearrangement of the C-C bonds in the ions, as described above, do not account for possible structural changes and so may not be as appropriate for real proton transfer reactions as those for simpler molecules.…”