Sulphuryl chloride as an electrophile. Part 5. Chlorination of some anthracene derivatives; molecular orbital modelling of substituent effects

Abstract

The rates of electrophilic attack at C-10 of some 9-substituted anthracenes (9-H, Br, CHO, CN, NO₂, OMe, or Bz) by sulphuryl chloride have been measured (in PhCl 298 K). The substituent effects roughly parallel those expected from considering the simpler p-XC₆H₄ system (ρ–1.51; r 0.975); better agreement (ρ–1.23 ± 0.05; r 0.994) comes by using Dewar's FMMF treatment. MNDO calculations of the energy and optimised geometry of the intermediate σ-complex show a folded structure which allows a degree of sp³ character of the C-10 atom while maintaining sufficient delocalisation of the extended π-system in the anthracenium ion. The Bell–Eyring–Polyani principle is followed with a linear correlation between the difference in the calculated energy between each reactant and its σ-complex and the experimentally observed change in free energy during attack by Cl^δ+.