Hydrogen bonding, structure, and dynamics of benzonitrile–water

Abstract

Rotational transitions with high quantum numbers J and K of the 1:1 complex of benzonitrile with H2O and D2O have been investigated in the frequency range 60–78 GHz with the free jet absorption microwave technique to get detailed information on the unusual hydrogen bond and on the dynamics of the large amplitude motions of the water moiety. With respect to previous microwave studies [V. Storm, D. Consalvo, and H. Dreizler, Z. Naturforsch. A 52, 293 (1997); R. M. Helm, H.-P. Vogel, H. J. Neusser, V. Storm, D. Consalvo, and H. Dreizler, 52, 655 (1997); V. Storm, H. Dreizler, and D. Consalvo, Chem. Phys. 239, 109 (1998)] the position of the water oxygen has been confirmed and the planar configuration of the complex has been determined. The distance of the oxygen atom to the ortho hydrogen is 2.48 Å, the angle to the ortho C–H bond is 144° and the angle between the free hydrogen atom of water with the same C–H bond is 164°. A coupled analysis of the 0+ and 0− states observed for the normal species was performed and the experimental data were reproduced by a flexible model which allowed the determination of the barrier to internal rotation of water [V2=287(20) cm−1] and the structural relaxation associated with the dynamic process.

Noncovalent Interactions and Internal Dynamics in Dimethoxymethane–Water

“…The water moiety is linked in an asymmetric way to DMM, forming both strong O···HÀO and weak O···HÀC hydrogen bonds. The barriers to internal rotation of the two methyl groups (V 3 A C H T U N G T R E N N U N G (Me1) = 6.83 (8) ). [20] Surprisingly, the V 3 value for the methyl group (Me1 of Figure 1), which interacts with the water molecule, is even closer to that of bare DMM.…”

“…[36] The complex was formed by means of the pulsed supersonic expansion of a gas mixture composed of approximately 1 % DMM FMS in He at a total backing pressure of 2 bar, flowed over a water reservoir at room temperature. Molecular pulses of approximately 0.40 ms duration followed by a MW polarization pulse of 10-20 mW for the m a and m c type [8] 37.9(3) 38.0 58.7 a(ci) [8] 68.4(3) 72.9 36.0 angles aA C H T U N G T R E N N U N G (g i) of Me2 a(ai) [8] 71.2(1) 75.8 88.5 a(bi) [8] 48.9(4) 49.5 2.7 a(ci) [8] 47 Figure 2). …”

“…The j b j coordinate of the hydrogen-bonded hydrogen atom and the j c j coordinate of the oxygen atom have, indeed, imaginary values. Caution is needed in considering the r s position of a hydrogen atom involved in a hydrogen bond, because the H!D isotopic substitution produces a shrinking of the distance between the heavy atoms involved in the hydrogen 2.8(2) aA C H T U N G T R E N N U N G (a i) [8] 60.5(2) 51(3) 57.1 (9) 63 (2) 57(4) aA C H T U N G T R E N N U N G (b i) [8] 37.9 (3) 48 (4) 41 (1) 36 (2) 42(4) aA C H T U N G T R E N N U N G (c i) [8] 68.4 (3) 67 (3) 69 (1) 3.4(1) aA C H T U N G T R E N N U N G (a i) [8] 71.2(1) 71 (6) 66 (1) 68 (3) 66(6) aA C H T U N G T R E N N U N G (b i) [8] 48.9(4) 53 (3) 54 (1) 52 (2) 51(3) aA C H T U N G T R E N N U N G (c i) [8] 47.0(4) 44 (3) 46 (1) 46 (2) 48 ( bond (Ubbelhode effect [30] ). As for the imaginary j c j value for the water oxygen atom, this is plausibly due to the large amplitude motion that the water moiety undergoes in the complex.…”

“…As a consequence, splittings are observable in the pure rotational spectra, [1,3] from which information on the potential-energy surface is obtained. When water acts as a proton donor towards weak proton acceptors, such as a fluorine or chlorine atom, or a p system, the water moiety has a considerable dynamic freedom, which still produces features in the microwave (MW) spectrum, as in the cases of difluoromethane-W, [6] chlorofluoromethane-W, [7] and benzonitrile-W. [8] Finally, when water acts as a proton donor and forms strong hydrogen bonds, such as OÀH···O, [9][10][11][12] OÀH···N, [5,[13][14][15][16] or O À H···S, [17] the water moiety is blocked and no splitting due to its internal dynamics is observed. Some exceptions have been observed, however: 1) in the case of dimethylether-W, [18] the W molecule tunnels between the two lone pairs of the ether oxygen, generating large tunnelling splittings; 2) in anisole-W, [19] the W moiety is delocalized while forming secondary interactions with the adjacent methyl or phenyl hydrogen atoms, allowing tunnelling of the water hydrogen atoms.…”

Structures, charge distributions, and dynamical properties of weakly bound complexes of aromatic molecules in their ground and electronically excited states

“…Concerning the pDFBW, the magnitude of its inertial defects are relatively small (ΔI″ = -0. 68 It is interesting to compare the results for pDFBW to those for the analogous benzonitrilewater (BNW) complex [62][63][64][65]. In both complexes, the oxygen is bound to an ortho hydrogen and one hydroxy hydrogen is bound to the fluorine or the cyano group.…”