The stabilization of thiepin by substitution

Resonance energies of 430 substituted thiepins have been calculated using a simple Hückel method described before. The results predict that thiepins substituted with electron-withdrawing groups (methoxycarbonyl and fluorine) will be less antiaromatic than the parent thiepin. Thus the calculated REPE of the only known type of monocyclic thiepin viz. 3,4 - bis(methoxycarbonyl) - 5 pyrrolidinothiepin (-0.007β) is less negative than that of the parent thiepin