Effect of the Leaving Group and Solvent Combination on the LFER Reaction Constants

International Journal of Molecular Sciences

Mirela Matić²  Sandra Jurić²  Bernard Denegri¹ 

[1] Faculty of Pharmacy and Biochemistry, University of Zagreb, 10000 Zagreb, Ante Kovačića 1, Croatia;

关键词: reaction constant;    nucleofuge specific parameter;    nucleofugality;    electrofugality;    solvation;    solvolysis;   

DOI  :  10.3390/ijms13022012

来源: mdpi

【 摘 要 】

Fine effects that influence the variations of the reaction constants s_f in LFER log k = s_f(N_f + E_f) have been summarized here. Increasing solvent polarity in the series of binary mixtures increases the solvolysis rates for the same factor for all benzhydryl derivatives in which the solvation of the leaving group moiety in the transition state is substantial, i.e., log k vs. E_f correlation lines are parallel (same s_f). For the substrates in which the demand for solvation of the leaving groups moiety is reduced, (e.g., carbonates) s_f parameters decrease as the fraction of the water in a given solvent/water mixture increases (log k vs. E_f plots converge), due to decreasing solvation of the electrofuge moiety toward bigger electrofugality. The abscissa of the intersection of the converging plots might indicate the critical electrofugality above which the solvolysis rates should not depend of the water fraction. Larger reaction constant s_f indicate later transition state for structurally related substrates only, while s_f parameters for structurally different substrates cannot be compared likely due to different intrinsic barriers. Inversion in relative abilities of leaving groups is possible if they have similar reactivities and are characterized with different reaction constants.

【 授权许可】

CC BY   
© 2012 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.