An Exploration of the Hydrogen Bond Donor Ability of Ammonia.

Ammonia is an important molecule due to its wide use in the fertiliser industry. It is also used in aminolysis reactions. Theoretical studies of the reaction mechanism predict that in reactive complexes and transition states, ammonia acts as a hydrogen bond donor forming N-H⋅⋅⋅O hydrogen bond. Experimental reports of N-H⋅⋅⋅O hydrogen bond, where ammonia acts as a hydrogen bond donor are scarce. Herein, the hydrogen bond donor ability of ammonia is investigated with three chalcogen atoms i. e. O, S, and Se using matrix isolation infrared spectroscopy and electronic structure calculations. In addition, the chalcogen bond acceptor ability of ammonia has also been investigated. The hydrogen bond acceptor molecules used here are O(CH3 )2 , S(CH3 )2 , and Se(CH3 )2 . The formation of the 1 : 1 complex has been monitored in the N-H symmetric and anti-symmetric stretching modes of ammonia. The nature of the complex has been delineated using Atoms in Molecules analysis, Natural Bond Orbital analysis, and Energy Decomposition Analysis. This work presents the first comparison of the hydrogen bond donor ability of ammonia with O, S, and Se.

An Experimental Exploration of C-H⋠⋠⋠X Hydrogen Bond in [CHCl3 -X(CH3 )2 ] Complexes (X=O, S, and Se).

Among the conglomeration of hydrogen bond donors, the C-H group is prevalent in chemistry and biology. In the present work, CHCl3 has been selected as the hydrogen bond donor and are X(CH3 )2 are the hydrogen bond acceptors. Formation of C-H⋅⋅⋅X hydrogen bond under the matrix isolation condition is confirmed by the observation of red-shift in the C-H stretching frequency of CHCl3 and comparison with the simulated spectra. Stabilisation energy of all the three complexes is almost equal although the observed red-shift for the C-H⋅⋅⋅O complex is less compared to the C-H⋅⋅⋅S/Se complexes. The nature and origin of the hydrogen bond have been delineated using Natural Bond Orbital, Atoms in Molecules, Non-Covalent Interaction analyses, and Energy Decomposition Analysis. Charge transfer is found to be proportional to the observed red-shift. This work provides the first impression of C-H⋅⋅⋅Se hydrogen bond and its comparison with C-H⋅⋅⋅O/S hydrogen bond interaction under experimental condition.

Hydrogen bond properties of Se in [ROH-Se(CH3)2] complexes (R = H, CH3, C2H5): matrix-isolation infrared spectroscopy and theoretical calculations.

Se is now considered as a potential centre for hydrogen bond interactions. The hydrogen bond acceptor ability of Se has been investigated in [ROH-Se(CH3)2] complexes (R = H, CH3, and C2H5) using matrix-isolation infrared spectroscopy and electronic structure calculations. The first impression of the IR spectra of the hydrogen bond complexes of [ROH-Se(CH3)2] in N2 and Ar matrices is presented here. Moreover, no spectroscopic data are available for the [HOH-Se(CH3)2] complex. Vibrational spectra in the OH stretching region indicate the formation of the [ROH-Se(CH3)2] complex under the matrix-isolation conditions. Comparison of the experimental spectra with the simulated vibrational frequencies at different levels of theory confirms the formation of the 1 : 1 cluster of [ROH-Se(CH3)2] stabilised by O-H⋯Se hydrogen bond interactions. Multiple conformers of the [CH3OH-Se(CH3)2] complex having marginally different stabilisation energies have been predicted from electronic structure calculations and signatures of the same have been observed under the cold conditions of matrix isolation. Conformer specific assignment of the 1 : 1 cluster of [C2H5OH-Se(CH3)2] (anti and gauche forms) has been carried out in both the matrices. Concentration dependent experiments indicate the formation of higher order clusters and/or mixed clusters along with the formation of a 1 : 1 cluster for CH3OH and C2H5OH. The nature of the selenium centred hydrogen bond has been delineated using AIM, NBO and energy decomposition analysis. A comparison of similar complexes of H2O, CH3OH, and C2H5OH with O, S and Se indicates that Se is not far away in hydrogen bond acceptor ability compared to O and S.

Competition between the hydrogen bond and the halogen bond in a [CH3OH-CCl4] complex: a matrix isolation IR spectroscopy and computational study.

Methanol (CH3OH) is the simplest alcohol and carbon tetrachloride (CCl4) is widely used as a solvent in the chemical industry. CH3OH and CCl4 are both important volatile substances in the atmosphere and CCl4 is an important precursor for atmospheric ozone depletion. Moreover, mixtures of CH3OH and CCl4 are an important class of non-aqueous mixtures as they exhibit a large deviation from Raoult's law. The specific interaction between CH3OH and CCl4 is not yet investigated experimentally. The interaction between CH3OH and CCl4 at the molecular level can be twofold: hydrogen bond (O-HCl) and halogen bond (C-ClO) interaction. One halogen bonded minimum and two hydrogen bonded minima are identified in the dimer potential energy surface. Herein, the 1 : 1 complex of [CH3OH-CCl4] has been characterised using matrix-isolation infrared spectroscopy and electronic structure calculations to investigate the competition between hydrogen bonded and halogen bonded complexes. Vibrational spectra have been monitored in the C-Cl, C-O, and O-H stretching regions. The exclusive formation of halogen bonded 1 : 1 complexes in argon and nitrogen matrices is confirmed by a combination of experimental and simulated vibrational frequency, stabilisation energy, energy decomposition analysis, and natural bond orbital and atoms-in-molecules analyses. This investigation helps to understand the specific interactions in the [CH3OH-CCl4] mixture and also the possibilities of formation of halogen bonded atmospheric complexes that may influence the atmospheric chemical activities, and enhance aerosol formation and deposition of CCl4.