Frequency Assignments for Normal Aliphatic Compounds: I. The Normal Paraffins in the Range 1450 cm—1 to 650 cm—1

It is assumed that the normal aliphatic hydrocarbons in their crystalline forms belong to the symmetry groups C2v (odd number of carbon atoms) or C2h (even number of carbon atoms), and that the selection rules for these symmetry groups hold exactly. It is then possible to work out a ``theoretical distribution pattern'' for the carbon-stretching modes, and for most types of the hydrogen deformation modes. Comparison of these patterns with available experimental data leads to a complete assignment of frequencies of these types in all the normal hydrocarbons for which data are available, and accounts satisfactorily for all spectral features for these materials in the solid and liquid state. The results might evidently be extended to other aliphatic series.