The influence of substituent field and resonance effects on the ease of N-heterocyclic carbene formation from imidazolium rings

摘要

Using a set of twelve selected substituents, the influence of substituent properties on the ease of deprotonation of imidazolium cations and mesoionic imidazolium-4-olates measured by the CREF index has been investigated. Significant correlations between CREF values and the Swain and Lupton field ( F ) and resonance ( R ) substituent constants have been found. In all cases the field effect has the greatest influence but resonance effects are also significant.