Determination of the Group Electronegativity of CF<sub>3</sub>Group in 3′-<i>O</i>-CF<sub>3</sub>-Thymidine by<sup>1</sup>-NMR
作者:C. Thibaudeau、N. Nishizono、Y. Sumita、A. Matsuda、J. Chattopadhyaya
DOI:10.1080/15257779908041642
日期:1999.4
The interplay of enthalpy of the gauche effect (Delta H degrees(GE)) Of the [X3'-C3'-C4'-O4'] fragment in various 3'-substituted (X) 2',3'-dideoxythymidine derivatives 1 - 7 and the inherent anomeric effect drives the two-state North reversible arrow South equilibrium in the constituent sugar moiety. The group electronegativity of 3'-OCF3 substituent in Marriott's, Inamoto's and Mullay's scales has been determined from simple calibration graphs correlating the group electronegativity of various 3'-substituents (X) in 2',3'-dideoxythymidine derivatives 1 - 7 with the experimental strength (Delta H degrees(GE)) Of the [X3'-C3'-C4'-O4'] gauche effect. Delta H degrees(GE) has been experimentally determined from pseudorotationaI analyses of temperature-dependent (3)J(HH) coupling constants, and can be used as an unambiguous tool for direct experimental estimation of the group electronegativity of a specific substituent covalently attached to 3'-carbon of 2',3'-dideoxythymidine, which can be compared, in turn, with the theoretical estimation carried out according to Marriott's or Inamotols procedure. Inconsistency found between theoretical values in Marriott's and Inamoto's scales, on the one hand, and between our experimental estimate and the theoretical value in Marriott's scale, on the other, have been solved by refining the electronegativity scale using our experimental data for 1 - 7.