Showing papers on "Protoporphyrins published in 1988"
TL;DR: The potential surfaces for the vinyl torsion in 2,4-divinyl porphyrins are calculated by using semi-empirical [INDO (intermediate neglect of differential overlap) and INDO•PSDCI (partial single and double excitation configuration interaction)] molecular orbital theory as discussed by the authors.
Abstract: The potential surfaces for the vinyl torsion in 2,4‐divinyl porphyrins are calculated by using semiempirical [INDO (intermediate neglect of differential overlap) and INDO‐PSDCI (partial single and double excitation configuration interaction)] molecular orbital theory. Calculations are carried out on the two pyrrole hydrogen tautomers of the free base porphyrin as well as on the porphyrin dianion. The calculated potential surfaces are predicted to have energy maxima at 0° and 180° due to steric hindrance. A third maximum near 70° (approximately perpendicular) is predicted due to electronic destabilization associated with the loss of conjugation and a decrease in dispersive stabilization energy. The torsional surface associated with the porphyrin dianion is qualitatively different from that calculated for the free base porphyrin due primarily to more effective conjugation of the vinyl group into the porphyrin macrocycle in the dianion. Neither pyrrole hydrogen tautomerization nor internal rotation of the se...
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