A strong correlation is found between the electronegativity,Ex, and the three proton coupling constant of the vinyl group in over a hundred compounds of the type CH2 = CHX. This correlation extends over the rangeEx = 4 to 1 and over the rangeJgem + Jcis + Jtrans = 14 to 50 c.p.s. Simple implications and some useful applications of this correlation are discussed.