Solvent dependent study of carbonyl vibrations of 3‐phenoxybenzaldehyde and 4‐ethoxybenzaldehyde by Raman spectroscopy and ab initio calculations

A Raman spectroscopy investigation of the carbonyl stretching vibrations of 3‐phenoxybenzaldehye (3Phbz) and 4‐ethoxybenzaldeheyde (4Etob) was carried out in binary mixtures with different polar and nonpolar solvents. The purpose of this study was twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. Changes in wavenumber position, variation in the anisotropic shift and full width half maximum were investigated for binary mixtures with different mole fractions of the reference systems. In binary mixtures, the observed increase in wavenumber with solvent concentration does not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self‐association of the solute. In all the solvents, a gradual decrease in the anisotropic shift reflects the progressive separation of the coupled oscillators with dilution. Γ_i(η_c), 3Phbz—solvent mixtures, exhibit a gradual decrease with decrease in the concentration of the solute which is an evidence on the influence of micro viscosity on linewidth. For 4Etob, the carbonyl stretching vibration shows two well‐resolved components in the Raman spectra, attributed to the presence of two distinct carbonyl groups: hydrogen‐bonded and free carbonyl groups. The intensity ratio of the carbonyl stretching vibration of these two types of carbonyl groups is studied to understand the dynamics of solute/solvent molecules owing to hydrogen bond interactions. Ab initio calculations were employed for predicting relevant molecular structures in the binary mixtures arising from intermolecular interactions, and are related to the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Absorption, fluorescence studies and ab initio calculations on binary mixture of p-dimethylaminobenzaldehyde

Absorption as well as fluorescence emission studies of p-dimethylaminobenzaldehyde (DMABA) in solvents with different polarity have been reported by varying the concentration of the solute. Dual fluorescence corresponding to the non-polar (NP) and twisted intramolecular charge transfer (TICT) states has been observed. The optimized geometry of DMABA was evaluated using ab-initio theory at various levels. The optimized geometries of the hydrogen bonded complexes with the solvent molecules were also calculated with the theory Hartree Fock at the basis set 6-31+G (HF/6-31+G). The results have been used to understand the structure of the molecule and the spectral changes in terms of hydrogen bonding and solute–solvent interaction.     

Changes in spectral features with varying mole fractions of anisaldehyde in binary mixtures

Raman and IR spectra of neat anisaldehyde (4‐methoxybenzaldehyde (4MeOBz)) and its binary mixtures (in polar and nonpolar solvents) with varying mole fraction of 4MeOBz were investigated. The concentration dependence of the wavenumber position and line width (full width at half maximum, FWHM) was analyzed to study the interaction of the solute vibrational modes with the microscopic solvent environment. The wavenumbers of Raman modes of 4MeOBz, namely, the carbonyl stretching, aldehydic δ (C H) and ring‐breathing modes, showed a linear variation in the peak position for varying concentrations of 4MeOBz in the different solvents. The dependence of Raman line width with concentration of 4MeOBz of these modes was also taken into account. The solute–solvent interaction is stronger in 2‐propanol and acetonitrile because of the formation of hydrogen bonds between them, whereas in benzene the interaction is too weak to affect the Raman modes. The modes, ν (CO) in 2‐propanol and aldehydic δ (C H) in acetonitrile, gave a Gaussian‐type line width variation, which was explained by the concentration fluctuation model, and the linear variation of the line widths was also interpreted by solute–solvent interactions. IR spectra were taken for these binary mixtures, which also give further support to these data. Copyright © 2006 John Wiley & Sons, Ltd.     

激发态分子内质子转移分子2-羟基-1-萘甲醛半碳酰腙的光谱特性

通过考察2-羟基-1-萘甲醛半碳酰腙(HNLSC)在不同极性溶剂中的吸收光谱和荧光光谱,详细研究了HNLSC分子在不同溶剂及酸、碱条件下的不同构型,证实了HNLSC具有典型的ESIPT特性。在非极性溶剂中分子主要以分子内氢键的闭式构型存在,这种闭式构型使分子具有ESIPT特性,在环己烷溶剂和高酸度极性溶剂中分子均表现出～415nm的正常荧光和～435nm处的反常ESIPT荧光。在极性质子溶剂中,因溶质和溶剂之间形成了分子间的氢键以及进一步去质子化,HNLSC形成了基态的溶剂化开式构型和离子构型,在吸收光谱中表现出～395nm的离子构型特征吸收。开式构型和离子构型阻断了分子内质子转移途径,因而在荧光光谱中仅表现出一个特征峰。实验进一步通过三乙胺和稀硫酸调节溶液体系的极性和酸度环境,证明在不同溶剂极性和酸度环境下,HNLSC分子不仅存在萘环上羟基变化引起的多种互变异构体间的转化平衡,同时存在—CHN—NH—CO—NH2结构域的烯醇式和酮式结构的相互转化。     

Time‐dependent density functional theory study on the excited‐state hydrogen bonding strengthening of photoexcited 4‐amino‐1,8‐naphthalimide in hydrogen‐donating solvents

The time‐dependent density functional theory (TDDFT) method was performed to investigate the excited‐state hydrogen bonding dynamics of 4‐amino‐1,8‐naphthalimide (4ANI) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground‐state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low‐lying electronically excited states for the isolated 4ANi and hydrogen‐bonded 4ANi‐(MeOH)_1,4 complexes were calculated by the DFT and TDDFT methods, respectively. We demonstrated that the intermolecular hydrogen bond C═O···H–O and N–H···O–H in the hydrogen‐bonded 4ANi‐(MeOH)_1,4 is strengthened in the electronically excited state, because the electronic excitation energies of the hydrogen‐bonded complex are correspondingly decreased compared with that of the isolated 4ANi. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electronically excited state of fluorescent dye in hydrogen‐donating solvents exists in many other systems in solution. Copyright © 2013 John Wiley & Sons, Ltd.     

Improper hydrogen bonding and motional narrowing in binary mixtures of 2‐ and 3‐bromopyridine in methanol probed by polarized Raman study and DFT calculations

A concentration‐dependent Raman study of the ν(C Br) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH₃OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm⁻¹in the case of 2Br‐p and at ∼618 cm⁻¹ in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.     

Spectroscopic Studies of Intra- and Inter-Molecular Hydrogen Bonding of Some O-Hydroxylbenzenesulfonanilides in Solutions

The effect of solvent on the electronic spectra of some fasciolici-dal o–-hydroxylbenzenesulfonanilides is examined and discussed. It is revealed that in solution these compounds exist in both intramolecular hydrogen bond form and intermolecular hydrogen bond form occurring between solute and solvent molecule. In solutions containing large amount of apolar aprotic solvents such as dioxane, compounds studied are mainly intramolecular hydrogen bond form and exhibit a weak transition band which is presumably attributed to the transition of n-electrons of oxygen atom in the intramolecular hydrogen bonded six-membered ring of the compounds.     

乙二醇分子间氢键结构与溶剂效应

采用密度泛函理论在B3LYP/6-311++G** (范德华校正)水平上研究乙二醇在气相中分别与乙腈、丙酮、四氢呋喃、水、乙二醇形成氢键二聚体的结构性质,根据PCM 极化统一场模型讨论氢键溶剂效应。结果表明,五种氢键二聚体分子中的氢键属于红移氢键,溶剂使氢键二聚体分子的偶极矩变大,并对OH振动频率的影响不大。     

乙二醇分子间氢键结构与溶剂效应

采用密度泛函理论在B3LYP/6-311++G~(**)水平上研究乙二醇在气相中分别与乙腈、丙酮、四氢呋喃、水、乙二醇形成氢键二聚体的结构性质,根据PCM(polarized continuum model)极化统一场模型讨论氢键溶剂效应.结果表明,五种氢键二聚体分子中的氢键属于红移氢键,溶剂使氢键二聚体分子的偶极矩变大,并对OH振动频率的影响不大.     

Intra‐ and intermolecular N?H···O hydrogen bonds in pyrrolyl derivatives of indane‐1,3‐dione – experimental and theoretical study

2‐(Pyrrol‐2‐ylmethylene)‐1,3‐indandione ( 4 ) and 2‐(pyrrol‐2‐ylmethylene)‐3‐dicyanomethylidene‐1‐indanone ( 5 ) were synthesized. Multinuclear and 2D‐NMR, IR, UV spectroscopic investigations as well as quantum chemical calculations showed the presence of strong hydrogen bonding in these molecules. For both molecules, the presence of two conformers, with and without H‐bond, was experimentally detected in the basic solvents (DMSO, acetone, pyridine) and the solvate complexes were theoretically calculated. Specific behavior of the intramolecular H‐bonded complexes different from that of the intermolecular H‐complexes is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Binary mixture of p‐methylbenzaldehyde with polar and nonpolar solvents

In this work, a combined theoretical and experimental study of binary mixture of liquid p‐methylbenzaldehyde (PMBz) is reported using ab initio calculations as well as Raman and IR spectroscopies. The purpose of this study was twofold: firstly, to describe the interaction of PMBz in terms of bonding energies and preferred geometries; and secondly, to characterize the spectroscopic effects on the vibrational modes of PMBz in the binary mixture of different polar and nonpolar solvents. The three vibrational modes, namely, carbonyl stretching, ν(C CH₃) and aldehydic (C H) vibrations have been analyzed in all the three solvents in different concentrations. The dependence of Raman linewidth on the concentration of PMBz of these modes was also taken into account. By analyzing the peak position and linewidth of these modes, it is seen that the solute–solvent interaction is stronger in BuOH and 1,2 dichloroethane (DCE) because of the hydrogen‐bonding interaction between these molecules. The formation of C H···O hydrogen bonds in liquid p‐methylbenzaldehyde is also investigated by Gaussian fitting. The ab initio calculations suggest several possible dimer configurations. Copyright © 2008 John Wiley & Sons, Ltd.     

Direct NMR measurement of rotation rates: solvent effects on rotation barriers

2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐dialkoxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. The IR spectra of the solids display a broad OH absorption at 3320 cm^?1, corresponding to an intermolecularly hydrogen‐bonded syn rotamer, probably a dimer, as well as absorptions around 3500 cm^?1 of the intramolecularly hydrogen‐bonded anti form. Well‐crystallized samples of these derivatives go into solution in the syn form but undergo rotation to the anti rotamer at a rate which can be measured directly by proton Nuclear Magnetic Resonance (NMR) spectroscopy. The diethoxy derivative was studied in a wide variety of solvents. The activation energy for syn→anti rotation is practically solvent‐independent, whereas that of the reverse reaction falls in hydrogen‐bonding solvents, by more than 2 kcal mol^?1 on going from chloroform or benzene to dimethylsulfoxide (DMSO). By combining direct measurements at low temperature and Dynamic Nuclear Magnetic Resonance (DNMR) results at high temperature, rotation rates were evaluated over a range of more than 100 K, and significantly large negative activation entropies determined. Copyright © 2007 John Wiley & Sons, Ltd.     

氢键对2-(N-甲基)氨基-5-硝基吡啶分子非线性光学性质的影响

本文在杂化密度泛函理论水平上研究了溶剂对2-(N-甲基)氨基-5-硝基吡啶分子非线性光学性质的影响.在溶剂中,构造了包括氢键作用的超分子体系,在优化结构的基础上分别研究了由极化连续模型模拟的溶剂与该分子的长程相互作用、溶剂与该分子的氢键相互作用以及溶剂与包括氢键作用的超分子体系整体的相互作用对分子的几何结构、非线性光学性质、紫外吸收光谱和电荷分布等特性的影响.结果表明,溶剂中分子电偶极矩、线性极化率和第一超极化率都增大,而溶剂与溶质分子通过氢键形成的超分子结构与单体有着明显区别.因此,氢键对分子结构和性质的影响较大,从而将明显的影响该类分子的非线性光学性质.     

Distinctive thermodynamic properties of solute–solvent hydrogen bonds in self‐associated solvents

Solute–solvent hydrogen bonding affects reactivity and other properties of dissolved species. In self‐associated media, because of cooperativity and solvent reorganization, the thermodynamic functions of solute bonding with bulk solvent can be different from those of bimolecular solute–solvent complexes. Using available experimental data on the Gibbs free energies of solvation in aliphatic alcohols and water, we have determined the energies of solute–solvent hydrogen bonding for various proton accepting solutes. We show that the increase in the strength of hydrogen bonds because of the cooperative effect is strong for bonding with bulk water and significantly less so with bulk aliphatic alcohols. The hydrogen bonding Gibbs free energies for the same solute with bulk water and alcohol are correlated, but they correlate poorly with the energies of formation of the corresponding bimolecular solute–solvent complexes. Thus, the traditional hydrogen bond basicity scales, based on data for bimolecular complexes, do not correctly describe the thermodynamics of hydrogen bonding with self‐associated solvents. Our results may help to define a separate solute basicity scale for associated media. Copyright © 2012 John Wiley & Sons, Ltd.     

用激光拉曼光谱研究液态乙醇的水合作用过程

为研究室温下乙醇-水二元混合物内部的分子间缔合情形,测得了不同体积配比溶液的拉曼光谱,发现位于2 800~3 050 cm-1波数区间的C—H伸缩振动频率随乙醇中加入水量的增加整体呈现蓝移趋势,而位于1 048 cm-1附近的CO伸缩振动频率的变化规律却与此相反。分析认为,这种现象主要由溶液内部分子间发生的不同水合作用所致,并据此阐明了液态乙醇的水合作用过程:水分子首先与纯乙醇中的自缔合短链发生氢键缔合作用,形成了含有较多乙醇分子数的乙醇水合团簇,直到溶液中水的体积含量达到50%时,乙醇的水合作用达到暂时饱和;而当水的体积含量继续增加到70%以后,水分子致使原有乙醇水合团簇解离形成较小尺寸的团簇,并与解离点位上的乙醇分子羟基发生进一步水合作用;而后,当水体积含量增至一定程度后,还会导致乙醇分子疏水基CH基团与水分子间形成弱氢键C—H…O。     

Self‐association and hydrogen bonding of propionaldehyde in binary mixtures with water and methanol investigated by concentration‐dependent polarized Raman study and DFT calculations

The Raman spectra of neat propionaldehyde [CH₃CH₂CHO or propanal (Pr)] and its binary mixtures with hydrogen‐donor solvents, water (W) and methanol (M), [CH₃CH₂CHO + H₂O] and CH₃CH₂CHO + CH₃OH] with different mole fractions of the reference system, Pr varying from 0.1 to 0.9 at a regular interval of 0.1, were recorded in the ν(CO) stretching region, 1600–1800 cm⁻¹. The isotropic parts of the Raman spectra were analyzed for both the cases. The wavenumber positions and line widths of the component bands were determined by a rigorous line‐shape analysis, and the peaks corresponding to self‐associated and hydrogen‐bonded species were identified. Raman peak at ∼1721 cm⁻¹ in neat Pr, which has been attributed to the self‐associated species, downshifts slightly (∼1 cm⁻¹) in going from mole fraction 0.9 to 0.6 in (Pr + W) binary mixture, but on further dilution it shows a sudden downshift of ∼7 cm⁻¹. This has been attributed to the low solubility of Pr in W (∼30%), which does not permit a hydrogen‐bonded network to form at higher concentrations of Pr. A significant decrease in the intensity of this peak in the Raman spectra of Pr in a nonpolar solvent, n‐heptane, at high dilution (C = 0.05) further confirms that this peak corresponds to the self‐associated species. In case of the (Pr + M) binary mixture, however, the spectral changes with concentration show a rather regular trend and no special features were observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Self‐association,tautomerism and E–Z isomerization of isatin–phenylsemicarbazones – spectral study and theoretical calculations

The self‐association and tautomerism of (E)‐isatin‐3‐4‐phenyl(semicarbazone) Ia and (E)‐N‐methylisatin‐3‐4‐phenyl(semicarbazone) IIa were investigated in solvents of various polarity. In weakly interacting non‐polar solvents, such as CHCl₃ and benzene, phenylsemicarbazone concentrations above 1×10^?5 mol dm^?3 result in the formation of dimers or higher aggregates of E‐isomers Ia and IIa . This aggregate formation prevents room temperature E–Z isomerization of Ia and IIa to more stable Z‐isomers. In contrast to the situation in non‐polar solvents, E–Z isomerization from the monomeric form of phenylsemicarbazone Ia and IIa E‐isomers occurs in highly interactive polar solvents including MeOH and DMF only at temperatures above 70 °C. Moreover, decrease in phenylsemicarbazone concentration below 1×10^?4 mol dm^?3 in these highly solute–solvent interacting systems leads to aggregate dissociation, and a new hydrazonol tautomeric form with a high degree of conjugation predominates in these solutions. Theoretical calculations confirm obtained experimental results. Copyright © 2013 John Wiley & Sons, Ltd.     

Excited‐state hydrogen bonding dynamics of pyruvic acid and geminal‐diol, 2,2‐dihydroxypropanoic acid in aqueous solution: a DFT/TDDFT study

In this work, we present the optimized ground state geometrical structures, electronic excitation energies and corresponding oscillation strengths of the low‐lying electronically excited states for the isolated Tce‐CH3COCOOH and Tce‐CH3C(OH)2COOH as well as their corresponding hydrogen‐bonded dimers Tce‐CH3COCOOH‐H2O and Tce‐CH3C(OH)2COOH‐H2O through time‐dependent density functional theory method. It is found that the intermolecular hydrogen bonds C=O···H‐O are strengthened in the electronically excited states of the hydrogen‐bonded dimers Tce‐CH3COCOOH‐H2O and Tce‐CH3C(OH)2COOH‐H2O, in that the excitation energies of the related excited states for the hydrogen‐bonded dimers are decreased compared with those of the corresponding monomers. The calculated results are consistent with the rules that are first demonstrated by Zhao on the excited‐state hydrogen bonding dynamics. Copyright © 2012 John Wiley & Sons, Ltd.     

Solution calorimetry of organic nonelectrolytes as a tool for investigation of intermolecular interactions

The paper is mainly the review and generalization of the previous publications of the authors. It demonstrates that solution calorimetry method gives the opportunities of more detailed understanding of various aspects of intermolecular interactions in solution. We are assured that prerequisite to such an understanding is the successive analysis of various solute–solvent systems from the simplest ones which include alkanes as a solute or as a solvent to the most complex systems with solvent self‐association via hydrogen bonding. Particular findings discussed in this paper are (i) an inconspicuous contribution of electrostatic solute–solvent interaction to the solvation enthalpy and, accordingly, the dominating contribution of dispersion interactions for nonspecifically solvated solutes; (ii) new, very general method for the extraction of specific interaction enthalpy from the enthalpy of solvation; (iii) new method of determination of self‐association enthalpies for the solvents associated via hydrogen bonding; (iv) new method for determination of cooperative hydrogen bonding enthalpies of proton acceptors with associated species of alcohols; (v) the unique method of experimental determination of the hydrophobic effect enthalpy. Copyright © 2007 John Wiley & Sons, Ltd.     

Origin of significant solvent effects on 1J(CC) spin–spin coupling in some acetylenes: hydrogen bonding and solvent polarity

It is demonstrated that some acetylenes, those of the R? C?CH structure, display anomalously high sensitivity to solvent effects of their ¹J(C?C) coupling while R? C?CR acetylenes fail to show that. The solvent‐induced variation in the latter coupling does not exceed 3 Hz; this seems to be the upper limit of variation of any J(CC) and J(CH) coupling in the molecular system studied which included: acetylene (in 13 solvents), phenylacetylene (in 12 solvents), 1‐phenylpropyne, and 2‐hexyne (two solvents each), and the only exceptions are ¹J(C?C) in acetylene, which is shown to vary within about 13 Hz, and that in phenylacetylene where the range amounts to about 8 Hz. These apparent anomalies are explained in the present study in terms of two effects of prime importance, solvent polarity and the solute‐to‐solvent hydrogen bonds where the CH moiety in R? C?CH acetylenes acts as a donor of hydrogen bonds to acceptor sites in the solvent concerned. Copyright © 2009 John Wiley & Sons, Ltd.