Not all short C–H···O contacts are hydrogen bonds: the prototypical example of contacts to CO+–H

Abstract

Intermolecular contacts between C–H groups and the charged moiety XO⁺–H show a pronounced negative directionality, i.e. short contacts are associated with strongly bent angles; this indicates that these interactions do not represent hydrogen bonds, although they are occasionally short with H⋯O distances down to 2.5 Å.