SEARCH Articles Figures Tables 2-substituted thiophenes Electrophiles reactivity Electrophilic Substitution Reactivity Electrophilic reactivity Electrophilic substitution relative reactivities Reactive electrophiles Reactivity electrophilicity Reactivity relative reactivities Reactivity substitution Relative reactivities Substitution thiophene Thiophenes electrophilic substitutions Thiophenes reactivity Thiophenes substitution