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Highlights: [•] Intramolecular hydrogen bond of MS is strengthened upon photoexcitation. [•] Experimental peak at 310nm in UV absorption spectrum corresponds to the S1. [•] The S3 state is the main state of the low-lying excited states. [•] The S1 and S3 are predicted to be the π → π ∗ transition mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Conformations of dimethyl carbonate (DMC) were studied using matrix isolation infrared spectroscopy. Infrared spectra of DMC trapped in inert gas matrixes, using an effusive source at 298 and 423K, showed evidence of both the ground state (cis–cis), and higher energy (cis–trans) conformers. Experiments were also performed using a supersonic jet source to deposit the matrix, to look for conformational cooling in the expansion process. The structures and vibrational frequencies of these conformers were computed at the B3LYP/6-31++G** level of theory. Natural bond orbital analyses were performed to understand the role of the delocalization interactions in conformational preferences. Complexes of DMC with H2O were also studied. A 1:1 DMC–H2O complex was identified in the matrix isolation experiments, where the carbonyl oxygen of DMC served as the proton acceptor for the hydrogen bonded complex. This observation was corroborated by computations performed on the complex at the B3LYP/6-31++G** level. Our computations also indicated another minimum, corresponding to an alkoxy bonded DMC–H2O complex, which was less exothermic; however, this complex was not identified in our experiments. Atoms-in-molecules theory was also performed to understand the nature of the intermolecular interaction in the DMC–H2O complex. [Copyright &y& Elsevier]

Abstract: The present work entails a comparative photophysical study of two structurally similar donor–acceptor dyes. In one of the dyes (DN2) twisting about C–N bond is permissible, while twisting is strategically restricted in the other (N2). Optical responses of both the dyes have been monitored in pure and mixed binary solvents comprising of mainly aprotic+protic systems. Results indicate that the nature of emitting states in protic and aprotic microenvironments is different for the two dyes. In aprotic media the solvated dye molecule is the emitting species while emission mainly takes place, supposedly, from the dye-solvent hydrogen bonded complex in protic media. The parallel behaviour of the two dyes indicates that twisting about C–N bond in the excited state is not an important photophysical process. Further, the effect of addition of strong acid to the dye solution and the corresponding existence of equilibrium between two tautomeric forms for both the dye has been studied. [Copyright &y& Elsevier]

Abstract: The isotropic part of the Raman bands corresponding to NH2 bending and ν(Ching modes of formamide (HCONH2) at ∼1593 and 1668cm−1, respectively, in neat HCONH2 as well as in binary mixtures with methanol (CH3OH) were reinvestigated. Variations of their linewidths exclusively with mole fractions of HCONH2, in the range C =0.1–0.9 were studied. The linewidth variation of the NH2 bending mode shows a departure from the trend expected on the basis of concentration fluctuation model and this has been explained using a recently suggested empirical model by invoking the concept of microviscosities of the solute, HCONH2 and the solvent, CH3OH. The other peak at ∼1668cm−1 shows a peculiar variation of the linewidth with concentration having two minima at C =0.8 and 0.4, which have been explained in terms of formation of hydrogen bonded complexes, NH2HCO⋯HOCH3, and NH2HCO⋯(HOCH3)2 and the two phenomena, namely motional narrowing and diffusion dynamics being simultaneously operative. The equilibrium constants have been evaluated from the spectral data and their variation with total molar concentration has been presented. [Copyright &y& Elsevier]

The changes in the structural parameters and vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) arising from the hydrogen bonding between NO2 and HONO2 have been studied employing ab initio 6-31G(d, p)/UHF and 6-31+G(d, p)/UHF, and B3LYP/6-31G(d, p) calculations. The charge rearrangement upon hydrogen bonding have been, estimated using the Mulliken population analyses. It was established that the complexation between NO2 and HONO2 leads to changes in the structural parameters and the vibrational characteristics of the monomers. The most sensitive to the hydrogen bond formation are the vibrational characteristics of the normal modes of the monomer bonds participating in the hydrogen bonding. The predicted shifts in the vibrational frequencies by ab initio and B3LYP/6-31G(d, p) calculations are in very good agreement with the experimentally observed, which is an evidence for the reliance of the studied structure. [Copyright &y& Elsevier]

• Formation of four amines and ethers H-bonded complexes is established through acoustic method. • UV-Vis. Spectral data support the existence of such complexes in n-hexane. • Thermodynamic parameters K, ΔG, ΔH and ΔS obtained by acoustical and optical methods are reported. • ΔG values reveal thermodynamic stability and ΔH data show exothermic nature of complexes. • Structure of amine and ether influences the formation of these complexes. The present work deals with experimental determination of acoustical parameters to investigate the influence of structure of amines and ethers on thermodynamic properties of four hydrogen bonded complexes in n-hexane solvent at four different temperatures in the range 294.15 K-310.15 K. Benzyl amine (BA) and n-propyl amine (NPA) are used as H-donors while anisole (ANI) and diphenyl ether (DPE) act as H-acceptors. The existence of these H-bonded complexes in solution is also supported by UV spectral data. The formation constants (K) of the complexes determined by ultrasonic and UV-Vis. spectral methods at 303.15 K are comparable. Further, it is observed that the interactions in the aliphatic amine - aromatic ether systems are stronger than aralkyl amine (BA) – ether systems. The thermodynamic parameters confirm that all the four complexes are thermodynamically stable and formation of these complexes is exothermic. The sign of ΔS shows there are strong intermolecular interactions between amines and ethers in n-hexane medium. [Display omitted] [ABSTRACT FROM AUTHOR]

The crystal and molecular structure of lamotrigine isethionate, C9H8Cl2N5 + .HOC2H4SO3 − has been determined by direct methods. The compound crystallizes in the tetragonal space group I41/ a. The isethionate moiety forms multiple hydrogen bonds to the lamotrigine nucleus, three from one isethionate, two from a symmetry related isethionate and a further two from two different symmetry related molecules. Protonation of N(2′) in the triazine ring, not observed in the native lamotrigine structure is presumably associated with the interaction of the isethionate moiety. Both rings in the lamotrigine moiety are essentially planar, with a dihedral angle of 66.08(7)° compared to 80.70° in native lamotrigine. The connecting bond length C(1)—C(6′) = 1.493(3) Å also correlates well with values in related compounds (1.480(3) Å) in the native structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Infrared spectrum of the adduct of H 2 S and NH 3 measured in solid argon matrices. • Anharmonic frequency calculations agreed well with the experimental values. • Binding energy of 8.6 kJ mol−1 (720 cm−1) calculated for the complex. Hydrogen bonding in S H⋯N systems has received little attention compared to other hydrogen bond motifs. To characterise S H⋯N bonding, infrared spectra of the most fundamental S H⋯N system—the H 2 S·NH 3 complex—were recorded in solid argon. These experiments were complemented by high level ab initio and density functional theory calculations. The H 2 S symmetric stretch was observed to shift by −155.3 cm−1 when mixed with NH 3 , while the NH 3 umbrella mode was found to shift by +31.8 cm−1. These, as well as deuterium and 15 N isotopologue studies indicated the formation of a complex. The structure of the H 2 S·NH 3 complex was determined to be almost identical to that of the H 2 O·NH 3 complex, with a nearly linear S H⋯N bond. A binding energy of 8.6 kJ mol−1 (720 cm−1) was calculated at the CCSD(T) level of theory extrapolated to the complete basis set limit. Anharmonic frequency calculations at the DSD-PBEP86-D3BJ/aug-cc-pV(D+d)Z level of theory produced frequencies with a RMSD of 13 cm−1 for the complex, relative to the experimental values. Comparison with previous work showed that the S H⋯N bond is weaker in H 2 S·NH 3 than the O H⋯N bond in the H 2 O·NH 3 system. [ABSTRACT FROM AUTHOR]