Carbon-Halogen Distance in the Methyl Halides

IN attempting to correlate the data on interatomic distances in polyatomic molecules, certain serious discrepancies have come to light between the spectroscopic method and the diffraction method as regards the carbon-halogen distances in the methyl halides. The differences are tabulated in Table 1. The reason that this had not been noticed earlier is that certain mistakes have been present in the deductions from the spectroscopic data and also that many new data are available. These results are particularly interesting when compared with the corresponding distances in the carbon tetrahalides, which are given in the last column. Thus it will be seen that, according to the diffraction method, in the methyl halides the carbon-halogen distance is always greater than, or equal to, the corresponding distance in the tetrahalides, whereas the spectro-scopic method would seem to indicate that exactly the opposite is the case. The latter seems much more likely from consideration of the mutual repulsion of the halogen atoms in the tetrahalides.