NMR Experiments on Acetalsl XXVI. Influence of β‐Substitution on Geminal Coupling Values in 1,3‐Dioxanes

The influences of β‐substituents–either in equatorial or in axial positions–on the numerical value of 2J(H‐2) (the geminal coupling J(OCH2O)) in 1,3‐dioxanes, have been scrutinized. Influences on 2J(H‐2) by the nature and electronegativity of the substituents seem to depend on the orientation of these substituents. Equatorial substituents cause composite influences, alkyl groups leading to an almost independent constant value for 2J(H‐2) = −6.2 cps. Suitable equatorial ρ‐substituted phenyl derivatives show a numerical decrease with increasing electrodonating capacity (range 6.2‐6.5 cps) however. The same, but more pronounced trend is found for the axial substituents.