Perturbations by phenyl on the 1,5-hydrogen shift in 1,3(Z)-pentadiene. Another chameleonic transition region?
The acyclic 1,5-dienyl hydrogen shift is accelerated by radical-stabilizing phenyl substituents without regard to the type of position occupied in the 1,3(Z)-pentadiene system. 1-Phenyl-5-p-tolyl-1,3(Z)-pentadiene has a corrected energy of activation 5.8 kcal mol(-)(1) lower than that of the parent, while the 2- and 3-phenyl analogues, examined in cyclic systems specifically designed to obviate the otherwise general need for a thermochemical correction to the immediately precursory s-cis conformation, reveal stabilizing effects of 3.6 and 3.4 kcal mol(-)(1), respectively. These relatively small effects are consistent with a chameleonic conceptual scheme for the transition region.
Doering
William von E
Wv
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138-2902, USA. doering@chemistry.harvard.edu
Keliher
Edmund J
EJ
Zhao
Xin
X