Electronic properties of multifurcated bent hydrogen bonds CH3⋯Y and CH2⋯Y

Abstract

H-bonding angle angleYHX has an important effect on the electronic properties of the H-bond Y...HX, such as intra- and intermolecular hyperconjugations and rehybridization, and topological properties of electron density. We studied the multifurcated bent H-bonds of the proton donors H3CZ (Z = F, Cl, Br), H2CO and H2CF2 with the proton acceptors Cl(-) and Br(-) at the four high levels of theory: MP2/6-311++G(d,p), MP2/6-311++G(2df,2p), MP2/6-311++G(3df,3pd) and QCISD/6-311++G(d,p), and found that they are all blue-shifted. These complexes have large interaction energies, 7-12 kcal mol(-1), and large blue shifts, delta r(HC) = -0.0025 --0.006 A and delta v(HC) = 30-90 cm(-1). The natural bond orbital analysis shows that the blue shifts of these H-bonds Y...HnCZ are mainly caused by three factors: rehybridization; indirect intermolecular hyperconjugation n(Y) -->sigma*(CZ), in that the electron density from n(Y) of the proton acceptor is transferred not to sigma*(CH), but to sigma*(CZ) of the donor; intramolecular hyperconjugation n(Z) -->sigma*(CH), in that the electron density in sigma*(CH) comes back to n(Z) of the donor such that the occupancy in sigma*(CH) decreases. The topological properties of the electron density of the bifurcated H-bonds Y...H2CZ are similar to those of the usual linear H-bonds, there is a bond critical point between Y and each hydrogen, and a ring critical point inside the tetragon YHCH. However, the topological properties of electron density of the trifurcated H-bonds Y...H3CZ are essentially different from those of linear H-bonds, in that the intermolecular bond critical point, which represents a closed-shell interaction, is not between Y and hydrogen, but between Y and carbon.

A theoretical investigation on the excited state intramolecular single or double proton transfer mechanism of a salicyladazine system

“…Generally, the theoretical investigations provide direct approaches to solve this problem in recent years. [35][36][37][38][39][40] The overall ESIPT reaction is complicated, and unraveling the detailed mechanism of ESIPT seems to be more and more important experimentally and theoretically.…”

Me3SiBr/InCl3 catalyzed allylation of alcohols: Identifying the combined Lewis structure and investigating the reaction mechanism

“…DFT is the most powerful method for understanding the compound structures and reaction mechanism. [22][23][24][25][26][27][28] All the geometries including reactants, intermediates, transition states, and products were obtained at ωB97XD/def2-SVP theory level. [29][30][31] ωB97XD is range-separated functional, which can obtain satisfactory accuracy for thermochemistry, kinetics, and noncovalent interactions and be used for reaction mechanism research [32][33][34][35][36] with def2-SVP basis set.…”

A theoretical perspective of the nature of hydrogen-bond types – the atoms in molecules approach

“…The 15 molecules ( Figure 1) were optimised at the MP2 and M052X levels of theory, and their respective geometrical parameters are summarised in Table S1 (available as supplemental data in the online version). Almost all the molecules considered here were investigated earlier by experimentally and/or theoretically [7][8][9][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. To obtain a reliable comparison, we optimised the chosen molecules at the above levels of theory, and the results of the accurate MP2 level calculations were considered (see Table S1 Table 1.…”

“…Even though the strength of an HB is an intermediate between a covalent bond and a van der Waals interaction, in few other molecules the HB is stronger than the weakest covalent bond [3]. HBs may be classified based on various criteria, such as the presence of donor and acceptor atoms [4], the strength [5], the charge-transfer mechanism [6], the position of the proton upon hydrogenbond formation [7], chemical leitmotifs [8], multifurcation [9], cooperativity [10] and unconventionality present [11] in the HB. Although a great deal of research work has been carried out on classification of HBs, the presence of common factors in the overall chameleon bond is little explored.…”