Negative Nuclear Spin-Spin Coupling Constants for Aromatic Protons

Valence bond theory and observed hyperfine splitting data are used to calculate proton-proton spin-spin couplings that arise through long range correlation of π-electron spins in even alternate aromatic hydrocarbons. In benzene and naphthalene calculated spin coupling constants are positive for protons separated by an odd number of carbon-carbon bonds and are negative for protons separated by an even number of carbon-carbon bonds.