Neutron Diffraction Study of Significant sp³ and sp² C-H Bond Shortening in a Fluorinated Pyridinium Saccharinate

We have experimentally shown by neutron diffraction significant shortening of both sp³- and sp²-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 sp³- and sp²-hybridized carbon atoms. To the best of our knowledge, this neutron diffraction study has revealed the largest extents of sp³ and sp² C-H bond shrinkages with a 3-sigma rule being satisfied.