Experimental and Computed Chiroptical Properties of Thioketones

Article abstract of DOI:10.1021/ja00316a019

(+)-(1S,3R)-4S(a)-Methyladamantane-2-thione (1), (+)-(1S,3R)-4R(e)-methyladamantane-2-thione (3), and (+)-(1S,3R)-4,4-dideuterioadamantane-2-thione (5) were prepared and their circular dichroism (CD) spectra measured and compared with those of the corresponding ketones.The long-wavelength n-?^* CD transitions of the thiones and parent ketones agree in sign and magnitude.Ab initio calculations on thioacetone and methyl ethyl thioketone in the random-phase approximation (RPA) in several basis sets lead to assignment of the two lowest energy observed bands as n-?^* and ?-?^* and a third band composed of closely spaced and n-4s and ?-?^* excitations.Similar calculations on 1 and 3 and their keto analogues yield n-?^* rotatory strengths (R) in excellent agreement with experimental and support the applicability of the ketone octant rule to thioketones.An origin-independent analysis of the computed R values suggests that the same mechanism for n-?^* optical activity operates in both classes of compounds.