Molecular orbital calculations for the reactions of 2,5-dimethyl pyrrole with phenylsulfonyl chloride

Electrophilic substitutions on beta-position of 2,5-dimethyl pyrrole have b een investigated theoretically. The electron donating methyl groups enrich electron densities on C-3, C-4 positions and pi* interactions with methyl g roups substituted on C-2 and C-5 positions pushed up the HOMO level of the pyrroles consequently induce rapid substitutions on C-3, C-4 sites. Substit ution of phenylsulfonyl group on nitrogen stabilized LUMO levels through we ak pi bonding interactions. Unexpected deoxidation reaction underwent on th e sulfonyl group substituted at C-3 position. The structures were solved by X-ray crystallography. Meanwhile, gas phase HF/6-31G* and density function al method (B3LYP/6-31G*) calculations gave favorable energies for 1-phenyls ulfinyl pyrrole (6) over 3-phenylsulfinyl pyrrole (5) by 3.6-4.7 kcal/mol w hich is contrary to the experimental result. However the methods involve th e effects of molecular polarizability and solvent, molecular dynamics (MD) and ab-initio self consistent reaction field (SCRF) calculations showed sam e trend as experiments. According to MD calculations, compound 5 is more st able than compound 6 by 4.15 kcal/mol and the SCRF, HF/6-31G* calculations gave more stable energy value for structure 5 than 6 by 0.03 kcal/mol.