Methyl–Methyl Proton Spin–Spin Coupling Constants in Some Six-membered Ring Compounds. A Test for Delocalization in Borazine

Abstract

Spin–spin coupling constants over five, six, and seven bonds between protons in different methyl groups are reported for the xylenes, derivatives of benzene, pyridine, pyrimidine, pyridinium salts, p-benzoquinone, and borazine. The coupling magnitudes are characteristic of the substitution pattern in the delocalized systems. Calculations at the INDO-MO-FPT level of methyl proton couplings in N- and B-methylborazines are in agreement with the available experimental evidence in indicating a relatively weak transmission of spin density information via the presumed π electron system of borazine.