Gas phase dipole moments of a series of terminal bromoalkanes

The dipole moments of ethyl, n-propyl, n-butyl, n-amyl, and n-hexyl bromide have been measured in the gas phase at 35°. The dipole moments were found to increase with increasing chain length up to and including the hexyl derivative. The increase in dipole moment up to such high members of the homologous series was explained as due to conformations in which the tail of the molecule comes quite close to the C-Br group. Calculations for a highly simplified model gave increases of dipole moment with chain length of the right order of magnitude.