Relating Environmental Effects and Structures, IR, and NMR Properties of Hydrogen-Bonded Complexes:  ClH:Pyridine

Abstract

MP2/aug′-cc-pVDZ potential surfaces for the hydrogen-bonded complex ClH:pyridine have been generated without and with external electric fields. The zero-field, gas-phase structure of this complex is stabilized by a traditional Cl-H‚‚‚N hydrogen bond. As the field strength increases, the equilibrium structure changes to that of a proton-shared hydrogen-bonded complex, which is close to quasi-symmetric at a field of 0.0040 au, and then an ion-pair complex at higher fields. Anharmonic dimer-and proton-stretching frequencies have been computed from each surface, and compared to experimental frequencies in Ar and N 2 matrices. The computed results suggest that the hydrogen bond in ClH:pyridine is on the traditional side of quasi-symmetric in an Ar matrix, and on the ion-pair side in an N 2 matrix. EOM-CCSD and MP2 calculations have been performed on the equilibrium structure at each field strength to obtain the 35 Cl-15 N spin-spin coupling constant across the hydrogen bond, and the chemical shift of the hydrogen-bonded proton, respectively. As a function of field strength, the Cl-N distance, the proton-stretching frequency, and the Cl-N coupling constant exhibit extrema for the quasi-symmetric complex found at a field of 0.0040 au. These IR and NMR properties are fingerprints of hydrogen bond type from which the intermolecular distance in a complex may be determined. The chemical shift of the hydrogen-bonded proton is also a maximum at a field of 0.0040 au, but it does not decrease dramatically at higher fields, and may not be as useful for structure determination. Deuteration of HCl lowers the proton-stretching frequency, as expected. The two-dimensional anharmonic proton-stretching frequencies for ClD:pyridine, as a function of field strength, show the same pattern as the ClH:pyridine frequencies.

Intermolecular interactions in mixtures of 1-n-butyl-3-methylimidazolium acetate and water: Insights from IR, Raman, NMR spectroscopy and quantum chemistry calculations

“…When water is added to BmimAc, they decrease with a larger extent for the C (2,4,5) -H, indicating an increase of the electron density. This behavior of the 1 H and 13 C chemical shifts of the ring atoms correlates well with the blue shift of the corresponding vibrational modes [41,80,81,[83][84][85][86][87][88][89][90]. The blue shift of the ν(C (2,4,5) -H) as a function of decreasing X BmimAc as well as the decrease of the corresponding 1 H and 13 C chemical shift is compatible with the physical picture that the interactions between the acetate anion and the Bmim + are gradually weakened because of the concomitant increasing predominance of the interactions between water molecules and the COO − moiety of the Ac − over both those between water molecules and between water and the Bmim + .…”

High-Field Chlorine NMR Spectroscopy of Solid Organic Hydrochloride Salts: A Sensitive Probe of Hydrogen Bonding Environment

“…Recently, Chapman et al have investigated some other NMR properties of N-H‚‚‚Cl hydrogen bonds, e.g., the across hydrogen bond indirect nuclear spin-spin coupling constant, 2h J iso ( 35 Cl, 15 N), in NH 4 Cl and pyridine hydrochloride using equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculations. 75 Halide ions represent some of the strongest hydrogen bond acceptors. 76 It is generally thought that a chloride ion has the ability to bind to a maximum of four strong donors, e.g., O-H and N-H donors.…”

Review on DFT and ab initio Calculations of Scalar Coupling Constants

“…In cases were the proton is shared between A and B the distinction between 1 J AH and 1h J B···H disappears; finally, when the proton is completely transferred, the situation again becomes "classical", with The contribution of the Bartlett, Perera and Del Bene's group to this topic is so significant that we have decided to divide this section in three parts: a) Other groups [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]; b) Bartlett-Perera-Del Bene [25][26][27][28][29][30][31][32][33][34][35][36]; c) Data analysis [37][38][39][40][41].…”

“…The next problem they tackled concerns the hydrogen chloride:pyridine complex (26) [32]. Pyridine is a very good HBA because the positive charge can be delocalized over the ring.…”