ISSN:
0894-3230
Schlagwort(e):
Organic Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
The relatively high stability and the structure of the simplest homoaromatic carbocation, the cyclobutenyl cation 1, was established ab initio by using correlated wave functions at HF 6-31G*, MP2(full)/6-31G*, MP2(full)/6-311G** and MP4(SDQ,full)/6-31G* geometries. The stability of 1 was estimated using homodesmotic and isodesmic reactions. The heat of formation of 1 was estimated to be 244 kcal mol-1 (1 kcal = 4·184 kJ). Chemical shift calculations were carried out at correlated levels and are in good agreement with the experimental values. At all levels of theory chemical shift calculations confirm the bent structure of 1. The MP4(SDTQ,fc)/6-311G**//MP2(full)/6-311G** + ZPE(MP2/(full)6-31G*), QCISD(T,fc)/6-31 + G*//MP2(full)/6-31G* + ZPE(MP2(full)/6-31G*) and MP4(SDQ,full)/6-31G*//MP4(SDQ,full)/6-31G* + ZPE(MP2(full)/6-31G*) ring inversion energies of 9·1, 9·3 and 9·0 kcal mol-1, respectively, agree with experiment (8·4 ± 0·5 kcal mol-1). Triplet electronic states are not competitive energetically. The homoaromatic character of the cyclobutenyl cation is shown by the nearly equal charges on C-1, C-2 and C-3, the considerable 1,3-bond order, the short 1·74 Å C-1—C-3 distance and the large stabilization energy relative to the allyl cation.
Zusätzliches Material:
8 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/poc.610060803
Permalink
