Double long-range spin-spin couplings between aldehydic and aromatic protons in the N.M.R. spectra of salicylaldehydes

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Abstract
A detailed method of analysis of the N.M.R. spectra of some salicylaldehydes, which makes use of the splittings of the combination lines, shows that in some of them there is more than one long-range interaction between the formyl and the ring protons. It is shown that the splittings of the combination lines are equal if the aldehyde proton is coupled to the proton in position three only, and are different if there is another coupling present. In this way, the magnitudes and relative signs of the J OCH-3 and J OCH-4 or J OCH-6 are determined in the 5-bromo, 5-chloro, 5-hydroxy and 4-hydroxysalicylaldehydes. These couplings are of the order of 0·10 c.p.s., J OCH-4 being positive and J OCH-6 being negative with respect to J OCH-3.