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Solvolytic Behavior of Aliphatic Carboxylates
Author(s) -
Matić Mirela,
Denegri Bernard,
Kronja Olga
Publication year - 2014
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201301574
Subject(s) - chemistry , solvolysis , taft equation , carbocation , leaving group , solvation , free energy relationship , alkyl , inductive effect , reaction rate constant , carboxylate , medicinal chemistry , hammett equation , aqueous solution , delocalized electron , alcohol , computational chemistry , solvent effects , substituent , solvent , organic chemistry , catalysis , hydrolysis , kinetics , physics , quantum mechanics
The leaving group abilities (nucleofugalities) of a series of aliphatic carboxylates have been obtained by determining the nucleofuge‐specific parameters ( N f and s f ) from solvolysis rate constants of X,Y‐substituted benzhydryl carboxylates in a series of aqueous ethanol mixtures by applyication of the linear free energy relationship (LFER) equation: log k = s f ( E f + N f ). These values can be employed to compare reactivities of carboxylates with those of other leaving groups previously included in the nucleofugality scale, and also to estimate the solvolysis rates of various carboxylates. It is confirmed that the inductive effect is the most important variable governing the reactivities of halogenated carboxylates in solution. Moreover, both the Hammett correlation and the solvolytic activation parameters have revealed a strong influence of the inductive effect on the nucleofugality of alkyl‐substituted carboxylates. The reaction constants ( s f ) indicate that carboxylate substrates with weaker leaving groups solvolyze via later, more carbocation‐like, transition states, which is in accord with the Hammond postulate. In addition, due to the weaker demand for solvation of transition states that produce more strongly stabilized benzhydrylium ions, in which more efficient charge delocalization occurs, the reaction constants ( s f ) obtained with most of the leaving groups investigated here increase as the polarity of the solvent decreases.