The quantitative electrophilic reactivity of annulenes. Part 2. Partial rate factors for hydrogen exchange of azulene, cycl[3,2,2]azine, indolizine, N-methylisoindole, indole, and pyrrolo[2,1-b]thiazole, and attempted exchange in trans-9,10-dimethyldihydropyrene: the dramatic effect of creating aromaticity in the transition state for electrophilic substitution, and the importance of valence bond theory