Vibrations de valence C?H dans les hydrocarbures et les halogénures de butyle

The valence vibrations C? H and C? D of a number of alkanes and of (CH₃)₃CX are studied using compounds deuterated in specific positions. For the methyl and the methylene groups an experimental model of group frequencies is proposed, which allows some general conclusions to be drawn concerning the assignation of the frequencies. The methyl group always shows a Fermi resonance between ν_s and 2δ_as in the region of 2930–2870 cm^?1. In consequence the unperturbed ν_sCH₃ frequency may be situated at ∽2915 cm^?1 and the absence of a coupling with other groups can be checked. The vibrations of the methylene group adjacent to a methyl group have higher frequencies than those of CH₂ groups further removed. The coupling of the methylene group with other groups is always strong and may amount to 10 cm^?1. For a chain of methylene groups, the coupling is the larger the longer the chain; being relatively small for symmetrical modes (∽3 cm^?1) for the antisymmetric mode. A correlation is found between protonated and deuterated groups which leads to isotope effects comparing well with recorded values.