ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Fully optimized transition states for hydrogen transfer from methane and propene to substituted 2-adamantyl radicals were calculated using the AM1 molecular orbital method. Methane and propene were chosen to provide an early (propene) and a late (methane) transition state. For 5-substituted radicals (F, Cl, Ph, CH3, CF3) the enthalpic differences between syn and anti reactions was found to be small [〈0·1 kcal mol-1 (1 kcal = 4·184 kJ)]. Other radicals with nitrogen or boron included directly in the adamantyl fragment showed greater selectivities, with aza substitution favoring syn and bora substitution favouring anti attack, as did the 4,9-difluoro derivative. The calculated selectivities are all in qualitative agreement with experimental results (where available) on bromine atom transfer. PPFMO calculations showed the polarization of the SOMO to be generally in accord with the AM1 results, whereas the polarization of the LUMO's was less indicative. The bond orders for the bonds syn and anti to the incipient C—H bond in the adamantyl fragments indicated that the anti bonds were always weaker than those syn, in agreement with the suggestion by Cieplak that has been used to explain the experimental selectivities. However, the bond lengths of the incipient C—H bonds are always shorter for the side of preferred attack, in apparent agreement with the suggestion by Anh.
Additional Material:
4 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610061206
