Molecular Tuning of the Closed Shell C–H···F–C Hydrogen Bond

Abstract

The existence of the rare six-membered and intramolecular C-H···F-C hydrogen-bond has been experimentally proven in the gas phase and in the solid state recently. However, the effect of the substituents on this C-H···F-C hydrogen-bond system has never been reported. In view of the importance of this type of C-H···F-C H-bonding whose weak interaction has been found critical in nanotechnology and biological systems, the nine functional groups composed of electron donating and electron withdrawing groups are inserted into this C-H···F-C interaction to study the group effect on the hydrogen bonding. Group effects on this C-H···F-C H-bonding system have been found, and their effects on the H-bonding system have been found to be tunable.

Organic Fluorine as a Hydrogen-Bond Acceptor: Recent Examples and Applications

“…Lectka and co-workers then studied slightly different tricycles 26 (Figure 25) bearing various substituents. 62 Similar to the above study from Lu, Francisco, and Negishi, 59 variations of the X moiety altered the properties of the observed C-H•••F bond. In this system, with the hydrogen bond being so short, the magnitude of the 1h J (H,F) coupling constant (up to 30.7 Hz) correlates with the increased frequency of the C-H bond stretching and therefore with the strength of the interaction.…”

“…In another computational study, Lu, Francisco, Negishi, and co-workers analyzed the six-membered hydrogen bond in model substrate 25 ( Figure 24) bearing a variety of electron-donating and -withdrawing X and Y groups. 59 Analyzing the three X-modified series independently, the authors showed that the C-H•••F hydrogen bond becomes stronger with increasing electron-donating ability of Y substituent, as expected in such a system, and they observed this by measuring an increase in the C-H vibration frequency. Associated with the strengthening of the interaction were a shorter H•••F distance, longer C-F bonds, and shorter C-H bonds.…”

Structure and emission studies of dimorphic crystals of [PtBr2(5,5′-bis(CF3CH2OCH2)-2,2′-bpy)] (1)

“…The structure of 1o in the solid state is best described as the infinitely connected dimer pairs, so we call it as a double belt (whose better pictorial view is highlighted and shown as Fig. S1 in ESI †) in this study, resulting from (1) a vertical Pt⋯Pt interaction with a short distance of 3.590 Å at 295 K (3.579 Å at 250 K), creating a dimer-pair with two bpyPtBr 2 molecular planes facing each other in a head to tail fashion, (2) the fluorinated side chains 17 on bpy running vertically towards the molecular plane of the partner, with two methylene C-H⋯O interactions 18 linking adjacent ponytails within the dimer-pair, (3) two extra methylene C-H⋯Br short contact interactions, also inside the dimer-pair, (4) for connective dimer-pairs, horizontal Br⋯H3-C3 and Br′⋯H4′-C4′ interactions on both the top belt and the bottom belt running antiparallel, and (5) additionally for connective dimer-pairs, two terminal C-F⋯H4-C4 interactions. 17,18 The molecular structure of 1o is shown in Fig.…”

Microsolvation of anions by molecules forming CH··X− hydrogen bonds

“…Water interacts with the ionic species via its strong H-bonding capacity as well as charge-dipole interactions. On the other hand, a great deal of recent work has shown that the CH group can serve as a potent proton donor in H-bonds (HBs) in parallel fashion to OH and NH donors [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. CH••X HBs are quite prevalent in nature, in biological [27][28][29][30][31][32][33][34][35] as well as chemical [36][37][38][39][40][41][42][43][44] contexts.…”