Acetylenes and other compounds with C sp —F bonds

A very limited number of compounds which contain C(sp)—F bonds has been studied in the gas phase (Table 18). In the MW analyses for bromo- and chlorofluoroacetylene, the length of the C=C bond had to be assumed, because only two rotational constants were measured. This bond length was varied within a reasonable range and the experimental uncertainties for the C—F bond distances include a possible systematic error due to this assumption. The C—F bond lengths in the four acetylenes are equal within their experimental error limits. The value derived for FCN is somewhat shorter, that for FCP slightly longer, but the differences are within the experimental uncertainties which are rather large for molecules of this size. 

TABLE 19. Typical C—F bond distances (in pm) in crystals, standard deviations a and number of observations n in various substructures 

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