By making use of specific solvent interaction effects it has been found possible to vary the relative chemical shift between ortho and meta protons in p-fluorotoluene continuously from about 0.2 p.p.m. to zero. The values of the HF coupling constants were found to be [Formula: see text] and [Formula: see text]. As the internal chemical shift goes to zero the ring proton spectrum collapses to two lines with a separation of 7.3 c/s. This splitting is interpreted as equal to [Formula: see text]. Corresponding changes observed in the CH 3 proton spectrum are consistent with this interpretation.
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Schaefer et al. (1959) studied this question.