Competition between weak hydrogen bonds: C–H⋯Cl is preferred to C–H⋯F in CH2ClF–H2CO, as revealed by rotational spectroscopy†,10.1039/C4CP00919C

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Competition between weak hydrogen bonds: C–H⋯Cl is preferred to C–H⋯F in CH2ClF–H2CO, as revealed by rotational spectroscopy†

Gang Feng,Qian Gou,Luca Evangelisti,Montserrat Vallejo-López,Alberto Lesarri,Emilio J. Cocinero,Walther Caminati

Physical Chemistry Chemical Physics Pub Date : 04/28/2014 00:00:00 , DOI:10.1039/C4CP00919C

Abstract

We recorded the pulsed jet Fourier transform microwave spectrum of the 1 : 1 adduct of CH₂ClF with formaldehyde. Formaldehyde is linked to CH₂ClF through a C–H⋯Cl bond rather than a weak C–H⋯F hydrogen bond, with a H⋯Cl “bond length” of 2.918 Å. Two additional equivalent C–H⋯O contacts, with a H⋯O distance of 2.821 Å, characterize the complex. Tunnelling splittings due to the internal rotation of the formaldehyde moiety have been observed, which allowed estimating the barrier to the internal rotation of formaldehyde to be 125(10) cm⁻¹. The ³⁵Cl quadrupole coupling constants have been determined to be χ_aa = 31.131(7) MHz and χ_bb–χ_cc = −105.82(1) MHz.