On the selenepin/benzene selenide valence tautomerizations: electronic and steric effects at theoretical levels

Tautomerization in selenepin (1) benzenea double dagger OE selenide (2) binary system is found to favor, 2, at HF, MP2, and B3LYP levels, using 6-311G* basis set. Electronic effects appear to have small effects on 1a double dagger OE 2 equilibria and show little impact on the conformational ring inversions of 1, at the same levels. In contrast, steric effects effectively decrease a dagger H values in an order inversely proportional to the size of the substituents employed (Me > Et > i-Pr). A possible Se extrusion is suggested to be the main reason why no 2 has ever been detected experimentally.