ISSN:
0947-6539
Keywords:
ab initio calculations
;
carbenes
;
cyclopropenes
;
matrix isolation
;
rearrangements
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The photochemical rearrangement of 4,4-dimethylcyclogexa-2,5-dienylidene (3) to 4,4-dimethylbicyclo-[3.1.0]hexa-1(6),2-diene (5) was investigated by means of the matrix isolation technique. Carbene 3 was generated in argon matrices at 10 K by photolysis of the corresponding diazop compound γ 〉550 nm) and was characterized by IR and UV/Vis spectroscopy and its characteristic thermal reaction with triplet oxygen. Long-wavelength irradiation (γ 〉 515 nm) induced an irreversible rearrangement of carbene 3 to the highly strained cyclopropene 5. This is in contrast to the previously investigated 1 H-bicyclo[3.1.0]hexa-3,5-dien-2-one (1), which is thermally labile even at 10 K and rearranges back to 4-oxo-2,5-cyclohexa-dienylidene. The experimental findings were confirmed by ab initio calculations at the MP 2/6-31 G(d) level. MP 2 and experimental IR frequencies are in good agreement. The strain energies of 5 and 1 are 75 and 78 kcalmol-1, more than 20 kcal mol-1 larger than that of cyclopropene. The somewhat greater stability of 5 than 1 is a consequence of better π delocalization in the diene unit of the bicyclic system.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.1460020809
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