ISSN:
0030-493X
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The structures and energies for 16 different [C5H3]+ isomers were geometry optimized from ab initio molecular orbital calculations. The global minimum on the [C5H3]+ surface at the MP3/6-31G* level was found to be the ethynyl cyclopropenylium cation (a), with a penta-1,3-diynylium structure (b) and a penta-1,4-diynylium structure (c) being 90 and 100 kJ mol-1 higher in energy, respectively. An isodesmic reaction was used to calculate a value of 1339 kJ mol-1 for the enthylpy of formation of b. Photoinization appearance energies were measured for the [C5H3]+ ions from penta-1,3-diyne, hexa-2,4-diyne and hexa-1,5-diyne as 11.66, 12.25 and 11.8 eV respectively The penta-1,3-diyne fragmentation was used to estimate an experimental enthalpy of formation for b of 1315 ± 2 kJ mol-1. There is some theoretical evidence that the penta-1,3-diyne fragmentation occurs without any significant reverse activation energy whereas both the hexa-2,4-diyne and hexa-1,5-diyne fragmentations involve excess energy.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/oms.1210281042
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