ELECTRONIC INTERACTIONS STUDIES OF TRANS-3-(2'-CHLOROCYCLOPENTYLTHIO)-THIOCHROMONES AND E-3-(2'-CHLORO-1'-METHYLPROPEN-1'-YL-THIO)-THIOCHROMONES AND THEIR 3-SULFINYL AND 3-SULFONYL DERIVATIVES

The analysis of the nu(CO) bands in the IR spectra of the 3-(2'-chlorocyclopentylthio)- and 3-(2'-chloro-1'-methylpropen-1'-ylthio)-thiochromones and their 3-sulfinyl and 3-sulfonyl derivatives. supported by molecular mechanics calculations of 3-methylthio-, 3-methylsulfinyl- and 3-methylsulfonyl-thiochromones, taken as model compounds, indicates the existence of a single conformer for the whole series except for the case of the 3-(2'-chloro-1'-methylpropen-1'-ylsulfinyl)-thiochromone where three conformers can be observed. The negative carbonyl frequency shifts (DELTA(nu)) for the 3-sulfinyl- and 3-thiothiochromone derivatives and the positive carbonyl shifts for the 3-sulfonyl-thiochromone derivatives are interpreted on the grounds of an interplay of the pi(CO) --> 3d(SO(n)) orbital interaction with the inductive and field effects of the 3-substituents. The orbital interaction is responsible for the shorter S . . . O intramolecular contact observed previously from X-ray data of some 3-thio-thiochromone derivatives. The bathochromically shifted n --> pi(CO)* band for the 3-thio-and 3-sulfinyl-thiochromone derivatives and the slight hypsochromic effect for the 3-sulfonyl-thiochromone derivatives are discussed in terms of the relative energy level stabilization of the pi(CO)* orbital (due to the pi(CO)*/3d(SO(n)) orbital interaction) and the n(O(CO)) lone pair (due to the electron-attracting inductive effect of the 3-sulfur-substituent). The IR and UV spectra of thiochroman-4-one show the existence of a mixture of two conformers, the twist-boat being the one where the transannular interaction between the 3p(s) --> pi(CO)* orbitals takes place.824173072