Geminal carbon‐proton spin‐spin coupling constants in ethyl, isopropyl and tert‐butyl compounds

The geminal 13 C 1 H coupling constants in ethyl, isopropyl and tert ‐butyl compounds having elements of the first row of the Periodic Table and halogens as substituents are determined by single resonance 13 C FT NMR spectroscopy. In addition, the values of directly bonded 13 C 13 C coupling constants are given. The substituent electronegativity dependence of the geminal 13 C 1 H coupling constant is discussed. It is concluded that the influence exerted by a β‐methyl substituent on the geminal 13 C 1 H coupling constant of 13C α ‐C β ‐ 1 H fragments is not constant and hence no simple additivity relation can be established for this coupling constant.