Determination of conformation of halomethyl ketones from the temperature dependence of Geminal H,H coupling constants

The temperature dependence of the geminal H,H coupling constant in solutions of α‐chloroacetophenone, α‐bromoacetophenone, 1‐bromo‐3‐chloro‐1‐phenylpropan‐2‐one and 1,3‐dibromo‐1‐phenylpropan‐2‐one has been determined at temperatures between 230 and 404 K. The values indicate that in the chloromethyl ketones the conformer with halogen and oxygen eclipsed is favored over that with hydrogen and oxygen eclipsed, while in the bromomethyl ketones the two conformers are of more nearly equal energy. The use of geminal coupling constants to indicate conformational preferences in substituted ketones appears promising.