The C-F⋅⋅⋅H-C “Anti-Hydrogen Bond” in the Gas Phase: Microwave Structure of the Difluoromethane Dimer

Abstract

A shortening of the C-H bond lengths and a blue shift of the C-H stretching frequencies for the C-F small middle dot small middle dot small middle dotH-C groups indicates that anti-hydrogen bonds are present the difluoromethane dimer. The most stable conformer has three such interactions (shown schematically).

Blue-Shifting Hydrogen Bonds

“…This increase in electron density weakens the O (1) -H (3) bond, resulting in its elongation and a concomitant red shift of its O-H stretch frequency, in full agreement with what is known about the origin of the H-bond. 53 The situation with the fluoroform‚‚‚water complex ( Figure 10) is, however, different. There is not any EDT to the C-H antibonding σ* orbital of Figure 9.…”

Reduced bandwidth chirped-pulse microwave spectroscopy for analysis of weakly bound dimers: Rotational spectrum and structural analysis of CH2ClF⋯FHCCH2

“…Weakly bound dimers serve as prototype systems for weak CAHÁ Á ÁX interactions, where the polarity of the CAH bond can be tuned by varying the number and type of electronegative substituents to the carbon atom. While many studies have focused on complexes of CH 3 F [1][2][3], CH 2 F 2 [4][5][6][7][8][9][10][11], and CHF 3 (for example: [2,[12][13][14][15][16][17][18][19]) as the proton donor, more recent investigations have examined a variety of hydrochlorofluorocarbons as CAH donors [20][21][22][23][24][25]. In most of the halogenated methane complexes, cyclic structures have been observed in which a halogen atom also acts as a weak hydrogen bond acceptor.…”

Rotational Spectroscopic Studies of C–H···F Interactions in the Vinyl Fluoride···Difluoromethane Complex

“…The C−H···F contact distances are very close to those observed in the similar complexes VF···CFM 30 and TFE··· DFM 6 (in which the DFM binds on the side), and even DFE··· DFM, 6 where the DFM binds on top. Comparison with DFM dimer 39,40 and trimer 41 structures also shows a relatively narrow range of C−H···F contact distances in these different complexes. The structure observed experimentally for VF··· DFM is consistent with the lowest energy geometry predicted by ab initio calculations at the MP2/6-311++G(2d,2p) level.…”