Neutron Diffraction Study of Significant sp 3 and sp 2 C–H Bond Shortening in a Fluorinated Pyridinium Saccharinate

We have experimentally shown by neutron diffraction significant shortening of both sp 3- and sp 2-hybridized C–H bonds to 1.092(2) and 1.081(1) Å in a hydrogen-bonded crystal of a difluorinated compound, 4-((2,2-difluoro­ethoxy)­methyl)­pyridinium saccharinate. Both MP2 and DFT calculations affirmed the C–H bond shrinkages. Sanderson’s electronegativity equalization principle provides insight into the shortening of the C–H covalent bond lengths for both sp 3- and sp 2-hybridized carbon atoms. To the best of our knowledge, this neutron diffraction study has revealed the largest extents of sp 3 and sp 2 C–H bond shrinkages with a 3-sigma rule being satisfied.