TY - JOUR
T1 - Tautomeric conjugate acids of 2-aminopyrroles
T2 - Effect of substituents, solvation and cosolute
AU - Fradera, Xavier
AU - De Rosa, Michael
AU - Orozco, Modesto
AU - Luque, F. Javier
PY - 2004/3
Y1 - 2004/3
N2 - The tautomeric preferences of the conjugated acids of 2-aminopyrrole derivatives have been examined both in the gas phase and in aqueous solution by using a combination of quantum mechanical, self-consistent reaction field and Monte Carlo-free-energy perturbation methods. The results show that the nature of substituents, the solvent and the presence of cosolute are relevant factors in modulating the relative stability between the tautomeric conjugate acids protonated at the heterocyclic ring and at the exocyclic amino nitrogen. Thus, attachment of electron-withdrawing groups to the ring, solvation in polar solvents, and the presence of negatively charged cosolutes tend to favor protonation at the exocyclic amino nitrogen. Nevertheless, none of these factors alone suffice to change the tautomeric preference for the ring-protonated forms. The results point out that the concerted occurrence of the three factors is necessary to shift the tautomeric preference towards the conjugated species protonated at the exocyclic nitrogen.
AB - The tautomeric preferences of the conjugated acids of 2-aminopyrrole derivatives have been examined both in the gas phase and in aqueous solution by using a combination of quantum mechanical, self-consistent reaction field and Monte Carlo-free-energy perturbation methods. The results show that the nature of substituents, the solvent and the presence of cosolute are relevant factors in modulating the relative stability between the tautomeric conjugate acids protonated at the heterocyclic ring and at the exocyclic amino nitrogen. Thus, attachment of electron-withdrawing groups to the ring, solvation in polar solvents, and the presence of negatively charged cosolutes tend to favor protonation at the exocyclic amino nitrogen. Nevertheless, none of these factors alone suffice to change the tautomeric preference for the ring-protonated forms. The results point out that the concerted occurrence of the three factors is necessary to shift the tautomeric preference towards the conjugated species protonated at the exocyclic nitrogen.
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U2 - 10.1007/s00214-003-0508-5
DO - 10.1007/s00214-003-0508-5
M3 - Article
AN - SCOPUS:84962374184
VL - 111
SP - 223
EP - 230
JO - Theoretical Chemistry Accounts
JF - Theoretical Chemistry Accounts
SN - 1432-881X
IS - 2-6
ER -