Blue-shifting hydrogen bond in the benzene–benzene and benzene–naphthalene complexes

Characteristics of nonconventional hydrogen bonds and stability of dimers of chalcogenoaldehyde derivatives: a noticeable role of oxygen compared to other chalcogens

In this work, twenty-four stable dimers of RCHZ with R = H, F, Cl, Br, CH3 or NH2 and Z = O, S, Se or Te were determined. It was found that the stability of most dimers is primarily contributed by the electrostatic force, except for the dominant role of the induction term in those involving a Te atom, which has been rarely observed. Both electron-donating and -withdrawing groups in substituted formaldehyde cause an increase in the strength of nonconventional Csp2-H⋯Z hydrogen bonds, as well as the dimers, in which the electron donating effect plays a more crucial role. The strength of nonconventional hydrogen bonds decreases in the following order: Csp2-H⋯O ≫ Csp2-H⋯S > Csp2-H⋯Se > Csp2-H⋯Te. Remarkably, a highly significant role of the O atom compared to S, Se and Te in increasing the Csp2-H stretching frequency and strength of the nonconventional hydrogen bonds and dimers is found. A Csp2-H stretching frequency red-shift is observed in Csp2-H⋯S/Se/Te, while a blue-shift is obtained in Csp2-H⋯O. When Z changes from O to S to Se and to Te, the Csp2-H blue-shift tends to decrease and eventually turns to a red-shift, in agreement with the increasing order of the proton affinity at Z in the isolated monomer. The magnitude of the Csp2-H stretching frequency red-shift is larger for Csp2-H⋯Te than Csp2-H⋯S/Se, consistent with the rising trend of proton affinity at the Z site and the polarity of the Csp2-H bond in the substituted chalcogenoaldehydes. The Csp2-H blue-shifting of the Csp2-H⋯O hydrogen bonds is observed in all dimers regardless of the electron effect of the substituents. Following complexation, the electron-donating derivatives exhibit a stronger Csp2-H blue-shift compared to the electron-withdrawing ones. Notably, the stronger Csp2-H blue-shift turns out to involve a less polarized Csp2-H bond and a decrease in the occupation at the σ*(Csp2-H) antibonding orbital in the isolated monomer.

Remarkable shifts of Csp2 -H and O-H stretching frequencies and stability of complexes of formic acid with formaldehydes and thioformaldehydes

Thirty-six stable complexes of formic acid with formaldehydes and thioformaldehydes were determined on the potential energy surface, in which the XCHO···HCOOH complexes are found to be more stable than the XCHS···HCOOH counterparts, with X = H, F, Cl, Br, CH₃ , NH₂ . All complexes are stabilized by hydrogen bonds, and their contribution to the total stabilization energy of the complexes increases in going from C-H···S to C-H···O to O-H···S and finally to O-H···O. Remarkably, a significant blueshift of C_sp2 -H bond by 81-96 cm^-1 in the C_sp2 -H···O hydrogen bond has hardly ever been reported, and a considerable redshift of O-H stretching frequency by 206-544 cm^-1 in the O-H···O/S hydrogen bonds is also predicted. The obtained results in our present work and previous literatures support that a distance contraction and a stretching frequency blueshift of C-H bond involving hydrogen bond depend mainly on its polarity and gas phase basicity of proton acceptor, besides the rearrangement of electron density due to complex formation. Markedly, we suggest the ratio of deprotonation enthalpy to proton affinity (R _c ) as an indicator to prospect for classification of hydrogen bonds. The symmetry adapted perturbation theory results show a larger role of attractive electrostatic term in XO-n as compared to that in XS-n and the electrostatic interaction is overwhelming dispersion or induction counterparts in stabilizing XO-n and XS-n, with n = 1, 2, 3. © 2019 Wiley Periodicals, Inc.

Behavior of interactions between hydrogen chalcogenides and an anthracene π-system elucidated by QTAIM dual functional analysis with QC calculations

The nature of the interactions between chalcogenides and the anthracene p-system, EH₂-*-p(C₁₄H₁₀), is predicted to be close to that of EH₂-*-p(C₁₀H₈), although the partial structures around the central rings can be found in EH₂-*-p(C₆H₆).

Quantum chemical calculations with the AIM approach applied to the π-interactions between hydrogen chalcogenides and naphthalene

The nature of π-interactions in (EH₂)n–*–π(C₁₀H₈) (n = 1 and 2: E = O, S, Se and Te) is elucidated with QTAIM-DFA. They have the character of the vdW-nature of the pure-CS interactions, except for HHTe–*–π(C₁₀H₈), which seems stronger than others.

Strong orbital deformation due to CH-π interaction in the benzene-methane complex

The orbital distribution and composition of the benzene-methane complex have been investigated systemically using ab initio calculations for the first time. Surprisingly, we find strong deformation in the HOMO-4 and LUMO+2 induced by CH-π interaction, extending the general view that nonbonding interaction does not cause orbital change of molecules.

In the pursuit of small "red shift" of C-H stretching vibrational frequency of C-H...pi interactions for benzene dimer: How to amend MP2 calculations to reproduce the experimental results

For the bent T-shaped benzene dimer, the vibrational frequencies at the MP2/aug-cc-pVDZ level with counterpoise correction reproduce experimental results of the small "red shifts" of C-H stretching, while those without counterpoise correction yield considerable "blue shift." Counterpoise correction also affects the C-H bond distances of C-H...pi interactions as well as intermoiety distances.

Raman spectrum of [Ru(CNBu t)(CO)(eta2-C6H4-2-CHO)(PPh3)2][BF4].2CDCl3 shows that the crystallographically determined bifurcated hydrogen-bonding interaction Cl3CD...F2BF2- is an example of a blue-shifting hydrogen bond

Raman data suggest that a crystallographically determined Cl3CD...F2BF2- interaction in the solid-state structure of [Ru(CNBut)(CO)(eta2-C6H4-2-CHO)(PPh3)2][BF4].2CDCl3 is an example of a blue-shifting bifurcated hydrogen bond. The nu(C-D) band blue-shifts 5 cm-1 to 2269 cm-1 compared to 2264 cm-1 for CDCl3 in the gas phase and 20 cm-1 from frozen CDCl3 at 2249 cm-1. A conventional interpretation of these band shifts would suggest that the CCl2 fragment of DCCl3 is a stronger hydrogen-bond acceptor than the BF2 fragment of a BF4- group.