Application of Semi-Quantitative Theory of Resonance for Comparative Study of the Reactivity of the Like Positions in Some Hydrozycoumarins in Electrophilic Substitution

With the help of Bartell's equation the difference in resonance energy of the metastable intermediate states leading to substitutions (electrophilic) in positions 8 and 6 of 7-hydroxycoumarin, in positions 5 and 7 of 6-hydroxycoumarin and in positions 6 and 8 of 5-hydroxycoumarin have been calculated. On this basis it has been concluded that the position 8 should be more reactive than 6 in 7-hydroxycoumarin, position 5 should be more reactive than 7 in 6-hydroxycoumarin and positions 6 and 8 should have equal reactivity in 5-hydroxycoumarin in electrophilic substitution. These deductions have been compared with the experimental observations made in the literature.