The ring proton and fluorine nuclear magnetic resonance spectra of para fluoro acetophenone, para fluoro ethyl benzoate and para fluoro benzonitrile have been studied as an A2B2X system at 40 Mc/sec and 56·445 Mc/sec. As the AB chemical shift is large, the secular equation has been solved in the first approximation. The two meta H-H coupling constants are found to be different. With the values obtained in the first approximation the roots of the involved 4 × 4 determinants have been calculated by an iteration method and it has been found that the values of the parameters are not affected appreciably by the approximation.