Infrared and Raman study of the interaction between methyl acetate and phenol derivatives

In previous publications [1–3], we have been concerned with the influence of hydrogen bond formation on the Raman intensity of the carbonyl stretching vibration. It has been shown that hydrogen bond association of simple carbonyl bases (cyclohexanone, acetone, acetophenone) with proton donors such as phenol derivatives, hydrochlorid or hydrobromic acid brings about an intensity increase of the ν_CO Raman band; moreover, the intensity enhancement is linearly related to the enthalpy of complex formation. In the present work, these measurements are extended to the complexes formed between methyl acetate (MeAc) and phenol derivatives.

As suggested by the frequency lowering of the ν_CO vibration and the frequency increase of the ν_CO band, complex formation in solution takes place on the carbonyl function.From NMR [4–5] and UV data [6] it can also be concluded that protonation via hydrogen-bonded attachment occurs in solution predominantly at the carbonyl oxygen atom.Literature data for the thermodynamic quantities referring to esters with hydroxylic compounds are scarce. Consequently in this work, we have determined the equilibrium constants and the enthalpy of formation for complexes between MeAc and phenol derivatives. We also report the absolute intensity of the ν_CO Raman band in the free ester molecule and in the complexes, all measurements been made in a solvent of low polarity : carbontetrachloride.     

Structural and thermochemical studies on CH3SCH2CHO,CH3CH2SCHO,CH3SC(═O)CH3, and radicals corresponding to loss of H atom

CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are intermediates during the partial oxidation of CH₃SCH₂CH₃ in the atmosphere and in combustion processes. Thermochemical properties (ΔH_f^o, S^o and C_p(T)), structures, internal rotor potentials, and C─H bond dissociation energies of the parent molecules and their radicals formed after loss of a hydrogen atom are of value in understanding the oxidation processes of methyl ethyl sulfide. The lowest energy molecular structures were initially determined using the density functional B3LYP/6‐311G/(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods using isodesmic reactions. Internal rotation potential energy diagrams and internal rotation barriers were investigated using B3LYP/6‐31 + G(d,p) level calculations. The contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation on the basis of the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions from the method of Pitzer‐Gwinn. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are ?34.6 ± 0.8, ?42.4 ± 1.2, and ‐49.7 ± 0.8 kcal/mol, respectively. The structural and thermochemical data presented for CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ and their radicals are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures. Group additivity values are developed for estimating properties of structurally similar, larger sulfur‐containing compounds.     

A quantum-chemical study of the effect of complexation on the spectral and luminescent properties and photolysis of cresol

The effects of methyl substitution and complexation on the spectral and luminescent properties of the phenol molecule and on the photodissociation of its OH bond are studied by methods of quantum chemistry. It is shown that methyl substitution at the ortho or para positions of phenol does not affect markedly the electronic spectrum or photophysical processes in the phenol molecule. The reasons for the dependence of the quantum yield of fluorescence γ on the excitation energy and the type of solvent are ascertained. Thus, the decrease in γ with increasing energy of excitation is associated with a higher efficiency of the photodissociation of the OH bond, whereas the increase in γ in proton-donating solvents is attributed to the increase by ～2000 cm^?1 of the activation energy of photoreaction upon formation of an H bond with solvent molecules. The mechanism of the photoreaction is established.     

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH,and radicals corresponding to loss of H atom

Sulfide alkoxy radicals are important intermediates during the partial oxidation of alkyl sulfides in atmospheric chemistry and in combustion. The atmospheric reaction sequence to formation of the alkoxy radicals includes (1) initial reaction with OH to create a radical on a carbon site, (2) the carbon radical then associates with ³O₂ to form a peroxy radical, and (3) an NO radical reacts with the peroxy radical to form an alkoxy radical (RO?) plus NO₂. This study determines structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (Δ_fH°, S°, and C_p(T)) of 3 corresponding alcohols HOCH₂SCH₂CH₃, CH₃SCH(OH)CH₃, and CH₃SCH₂CH₂OH of methyl ethyl sulfides studied in order to characterize the thermochemistry of the respective alkoxy radicals. The lowest energy molecular structures were calculated using the B3LYP density functional level of theory with the 6‐311G(2d,d,p) basis set. Standard enthalpies of formation (Δ_fH°₂₉₈) for the radicals and their parent molecules were calculated using B3LYP/6‐31 + G(2d,p), CBS‐QB3, M062x/6‐311 + g(2d,p), and G3MP2B3 methods. Isodesmic reactions were used to determine ?_fH° values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31 + G(d,p) level theory. The contributions for S°₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by CBS‐QB3 calculations, with contributions from torsion frequencies replaced by internal rotor contributions. Group additivity and hydrogen bond increment values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxide molecules and their radicals.     

位阻效应对受阻酚杂化体系阻尼机理的影响

针对尚未解决的受阻酚结构变化与杂化体系阻尼机理间关系的问题,本文采用分子动力学模拟方法构建了三种受阻程度不同的受阻酚/聚合物杂化体系,从理论上探讨了位阻效应对阻尼机理的影响.对体系氢键相互作用、结合能、相对自由体积及扩散系数进行模拟分析表明,位阻效应对受阻酚分子内氢键相互作用有显著的弱化效果,可减少小分子团聚倾向,有利于小分子与聚合物分子间氢键相互作用的形成.但是,过高的位阻对小分子运动有阻碍作用,不利于小分子与聚合物形成强烈的氢键键合,也即不利于杂化体系阻尼性能的提高.因此,如何选择受阻程度适中的受阻酚是制备高阻尼杂化材料的一关键要素.     

Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH2SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH,and radicals

Hydroperoxides and the corresponding peroxy radicals are important intermediates during the partial oxidation of methyl ethyl sulfide (CH₃SCH₂CH₃) in both atmospheric chemistry and in combustion. Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔH_f^o, S^o and C_p(T)) of 3 corresponding hydroperoxides CH₂(OOH)SCH₂CH₃, CH₃SCH(OOH)CH₃, CH₃SCH₂CH₂OOH of methyl ethyl sulfides, and the radicals formed via loss of a hydrogen atom are important to understanding the oxidation reactions of MES. The lowest energy molecular structures were identified using the density functional B3LYP/6‐311G(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods. Isodesmic reactions were used to determine ?H_f^o values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31G(d,p) level theory. Contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CH_2, CH₂(OOH)SCH₂CH₃, CH₃SCH(OOH)CH₃, and CH₃SCH₂CH₂OOH are ?14.0, ?33.0, ?37.2, and ?32.7 kcal/mol, respectively. Group additivity values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxides. Groups for use in group additivity estimation of sulfur peroxide thermochemical properties were developed.     

Manifestation of intramolecular hydrogen bonds in the IR spectra of bioactive aminophenols

The intermolecular interactions in solutions of aminophenols in CCl₄ are studied by the methods of IR Fourier spectroscopy. If the hydroxyl groups of aminophenol molecules occupy the ortho positions with respect to the amino groups of the molecules, the hydroxyl and amino groups are involved in intramolecular interactions with the formation of hydrogen bonds O-H...N and N-H...O. The introduction of two additional tert-butyl groups into the structure of the aminophenol molecule facilitates the formation of O-H...N bonds and impedes the formation of N-H...O bonds. The occurrence of the carbonyl group in the structure of aminophenols leads to the formation of intramolecular hydrogen bonds O-H...O=C. The introduction of the methyl groups into carbonyl-containing aminophenols transforms the O-H...O=C bond into the hydrogen bond N-H...O=C.     

The effect of complexation on the spectral and luminescent properties and photolysis of methyl[(4-aminophenyl)sulfonyl]carbamate

The spectral and luminescent properties and the photolysis of 1: 3 hydrogen bonded complexes of methyl[(4-aminophenyl)sulfonyl]carbamate (asulam) with water are studied with the aid of methods of quantum chemistry using the theory of intramolecular photophysical processes. It is shown that the formation of hydrogen bonds does not have a large effect on the spectral and luminescent properties of asulam. The breaking of the C-S and N-S bonds occurs according to the predissociation mechanism in electronically excited states localized on the bonds to be broken. In singlet photodissociative states, the N-S bond is more likely to break than the C-S bond, with the bond breaking being independent of the excitation energy. The formation of hydrogen bonded complexes increases the rate of population of photodissociative states, and, therefore, one can assume that the photoreaction efficiency increases.     

Structure and reaction pathways of methyl lactate on Pd(1 1 1)

The adsorption and reaction of methyl lactate (CH₃CH(OH)COOCH₃) is studied in ultrahigh vacuum on a Pd(1 1 1) surface using temperature-programmed desorption (TPD) and reflection–absorption infrared spectroscopy (RAIRS). Methyl lactate reacts at relatively low temperatures (220 K) by O–H bond scission. This intermediate can either react with hydrogen to reform methyl lactate at 280–300 K or undergo β-hydride elimination to form flat-lying methyl pyruvate. This decomposes to form acetyl and methoxy carbonyl species as found previously following methyl pyruvate adsorption on Pd(1 1 1). These species predominantly react to form carbon monoxide, methane and hydrogen.     

计算饱和醇异构体标准生成焓的新方法

基于极性叠加原理,在成功设计烷烃异构体和多氯代烷烃生成焓计算新方法的基础上,设计了一种计算多元醇异构体生成焓的新方法,并合理地假定任一异构体的原子化焓等于三种键（C-C、C-H和C-O-H键）的键能、极性叠加能项以及氢键能项的加和。用这一模型拟合24种原子化粹数据,得到了标准生成焓的估算公式。为了检验预测的精确性,又设计了一种预测方法,使用在排除液预测的化合物条件下回归得到的参数,预测该化合物的生成焓。按这种方法,预测了24种异构体的生成焓。通过该5参数预测的相对于实验值的各种误差（平均绝对误差、均方根误差和最大绝对误差）不仅比7参数的基团法预测的对应误差小得多,而且比相应实验数据的误差还要小。与键加和法比较,该方法的模型包含了极性叠加能和氢键能量,该两项代表了主要的非键相互作用能,表征了不同异构体的结构差异,并大大减少了参数。     

Solvent Effect on the Isotopic Ratios vo OH/vOD and AOH/AOD in a Tetrachlorosubstituted Mannich Base

Mannich bases are compounds formed from phenols and amines, characterized by intramolecular hydrogen bonds whose strength depends on the substituent implanted on the phenol ring; moreover, as shown by uv measurements, the strength of the interaction for a given phenol derivative depends strongly on the solvent In this work, we have studied the ir spectra of 2,3,4,5-tetrachloro-6-[(diethylamino)methyl]phenol (TCMBH)     

Intra- and intermolecular proton transfer in methyl-2-hydroxynicotinate

Spectral characteristics of methyl 2-hydroxynicotinate (MEHNA) have been studied using absorption, fluorescence excitation and fluorescence spectroscopy, as well as, using single photon counting nanosecond spectrofluorimeter. MEHNA is present as enol in less polar solvents and keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to phototautomer, formed by excited state intramolecular proton transfer (ESIPT), whereas fluorescence is only observed from keto form in polar solvents. In aqueous and polar solvents monocation (MC) is formed by protonating the exo carbonyl oxygen atom in the ground state (S₀) and in the first excited singlet state (S₁), MC is obtained by protonating carbonyl oxygen atom of the ester. It is formed by ESIPT from exo carbonyl proton to carbonyl oxygen atom of the ester. Dication is formed by protonating both the oxygen atoms. Two kinds of monoanions formed by deprotonating phenolic proton or >N-H proton of keto suggest the presence of enol and keto in aqueous solution. In cyclohexane MC is formed by protonating carbonyl oxygen in both S₀ and S₁ states. The electronic structure calculations were performed on each species using semi-empirical quantum mechanical AM1 method and density functional theory B3LYP with 6-31G^** basis set using Gaussian 98 program, along with potential energy mapping, to characterize the particular species.     

Raman signatures of strong and weak hydrogen bonds in binary mixtures of phenol with acetonitrile,benzene and orthodichlorobenzene

The present study aims at investigating the effect of hydrogen bonds of phenol in binary mixtures of phenol with three solvents viz. acetonitrile, orthodichlorobenzene and benzene respectively in order of decreasing hydrogen bond strength. Raman spectroscopy in correlation with density functional theory (DFT) calculations has led to a profound understanding of changes in structure, energy, dipole moment and other physical and chemical properties of phenol pertaining to hydrogen bond formation in solution. The spectral variation in wavenumber and linewidth of ring deformation, ring stretching, C≡N stretching and C―H stretching modes have been analyzed in detail. The breaking of self association of phenol in solution and formation of strong or weak hydrogen bonds depending on the nature of the solvent has been discussed by comparing the Raman and DFT results for three different solvents. Copyright © 2016 John Wiley & Sons, Ltd.     

Vibrational Spectra of Hydrogen Bonded Complexes Between Acetophenone and Some Phenol Derivatives

The hydrogen bonded complexes between hydroxylic derivatives and carbonyl bases have been extensively studied by infrared spectroscopy but meager Raman spectroscopic results are available for such complexes. This work reports on a study of the Raman intensity of the v_C[dbnd]0 stretching vibration of hydrogen bonded complexes formed between acetophenone and some phenol derivatives. The formation constants of these complexes are calculated from infrared spectroscopy.     

Raman Intensity of the v C=O Band in Hydrogen Bonded Complexes Involving Ethylformate and Phenol Derivatives

The hydrogen bonded complexes between carbonyl bases and hydroxylic derivatives have been extensively studied by infrared spectrometry; by comparison very little Raman data have been reported in the literature. Some qualitative measurements on the v _C=O band of acetone dissolved in water-tetrachloride mixtures have been performed by Singurel¹. Quantitative data on the absolute Raman intensity have been obtained for complexes involving cyclohexanone², acetone, acetophenone³ and methylacetate⁴. For these systems, hydrogen bond formation brings about a moderate intensity enhancement of the v _C=O band. In this work the Raman intensity of the v _C=O band of ethylformate (EtFo) complexed with phenol derivatives is investigated.     

Calculation of electronic spectra for intermolecular complexes of 3-aminophthalimide by a modified Hückel molecular orbital method

Calculation of the spectra of intermolecular complexes of 3-aminophthalimide is used as an example to show that when hydrogen bonds are present, the resonance integrals for the proton donor and acceptor atoms are different from zero. Theoretical analysis of strained 3-aminophthalimide complexes allowed us to establish the determining role of hydrogen bonds in their formation. Using an intramolecular peptide hydrogen bond as an example, we studied the effect of the solvent on its parameters. In particular, we showed that hydrogen bond formation with a proton-acceptor group of the chelate ring leads to a decrease in the resonance integral, and consequently a decrease in the enthalpy of formation of the intramolecular hydrogen bond, to a significantly greater degree than formation of a hydrogen bond at a proton-donor group. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 735–740, November–December, 2006.     

Mechanistic study of the reaction of methyl peroxy radical (CH3O2) with formaldehyde (CH2O)

ABSTRACT

A direct dynamic study on the reactions of CH₃O₂?+?CH₂O was carried out over the temperature range of 300–1500?K. All stationary points were calculated with the M06-2X/6-311++G(d,p) level of theory and identified for local minimum. The energetic parameters were refined at QCISD (T)/cc-pVTZ and CCSD (T)/cc-pVTZ levels of theory. Three channels were explored and a reaction of hydrogen abstraction from CH₂O by CH₃O₂ was identified as dominant channel which involves the formation of a prereactive complex in the entrance channel. The rate coefficient of the dominant channel was calculated with TST and TST/Eck and the Eckart tunnelling effect is only important over the lower temperature region. The calculated rate coefficient of the dominant channel has positive temperature dependence and agrees reasonably with the available literature data.     

The chemistry of iodomethane on MoAl alloy thin films formed on dehydroxylated alumina: Formation and reaction of surface methyl species

The surface chemistry of iodomethane is studied in ultrahigh vacuum using X-ray and Auger spectroscopies and temperature-programmed desorption, on a MoAl alloy film formed by reacting molybdenum hexacarbonyl with dehydroxylated alumina. The alloy is grown by reacting Mo(CO)₆ with a thin alumina film on a molybdenum substrate at 700 K and heating to 1500 K. A portion of the iodomethane dissociates following adsorption at 150 K. Heating to 220 K desorbs molecular iodomethane from the surface leaving adsorbed methyl species and iodine, where the iodine appears to adsorb preferentially on the aluminum. The resulting methyl species can either decompose to deposit carbon and evolve hydrogen, hydrogenate to yield methane or oligomerize yielding predominantly ethylene and propylene, and a small amount of ethane is formed. Both methyl and ethyl radicals are found to desorb from the surface suggesting that the ethylene is formed by methylene insertion into the methyl surface bond to form an ethyl intermediate, which forms ethylene by β-hydride elimination, or hydrogenates to yield ethane. Propylene is likely to form by further methylene insertion into the ethyl-surface bond.     

The prominent enhancing effect and mechanism of the methyl group in the X···Y (X=O,S, H3CO,H3CS, (H3C)2O, (H3C)2S; Y=HCN,HNC) hydrogen-bonded complex

An ab initio computational study of the enhancing role of the methyl group in the M···H (M=S and O) hydrogen bond has been carried out at the QCISD/6-311++G(2df,2p) level. The bond lengths, frequency shifts, and interaction energies were analysed. The methyl group of the electron donor plays a positive role in the formation of the hydrogen bond. Its enhancing role is stronger in the O···H hydrogen bond than in the S···H hydrogen bond. The results show that the methyl group has a prominent effect on the strength of the hydrogen bond. The interaction energy is increased by 347% for the Me₂O–HCN complex relative to that for the O–HCN complex. The enhancing mechanism of the methyl group has been analysed by means of natural bond orbital (NBO) theory. The electrostatic interaction is of more importance to the O···H hydrogen bond, whereas dispersion and charge-transfer interactions play a more significant role in the S···H hydrogen bond.     

Ultrasonic waste-water treatment: incidence of ultrasonic frequency on the rate of phenol and carbon tetrachloride degradation

Organic compounds in aqueous solution submitted to an ultrasonic irradiation behave differently according to their physical and chemical properties. In this work, hydrogen peroxide formation and the degradation rate of phenol and carbon tetrachloride have been studied at different frequencies: 20, 200, 500 and 800 kHz. Whatever the frequency, it is easier to decompose CCl₄ than phenol by means of ultrasonic wave. It is shown that the rates of reactions involving hydroxyl radicals (hydrogen peroxide formation and phenol degradation) have a maximum value at 200 kHz. The best yield observed at 200 kHz for the phenol degradation may be the result of better HO radicals availability outside of the bubble of cavitation. The degradation rate for carbon tetrachloride which decomposes into the bubble of cavitation increases with frequency. Calculating the reaction rate for one ultrasonic period shows that the efficiency of one ultrasonic cycle decreases as frequency increases.