Solvent effects on C?O stretching frequencies of some 1-substituted 2-pyrrolidinones

Anomalous Infrared Absorbance of S═O: A Perturbation Study of α-C-H/D

Solvatochromic shifts of S═O vibrational probes describe the strength of the surrounding electric fields and the hydrogen bonding status. Herein, we demonstrated how the solvents alter the infrared (IR) spectra of the S═O vibrating mode. The experimental measurement of the involvement of α-H/D isotopic interactions with different solvents and their effects on the IR absorbance spectra of the vibrational probe provides detailed knowledge of the microsolvation environment despite the complexity of overlapping bands in the spectra. Herein, we discover how the solvents interact differently with DMSO and DMSO-d6, while being electronically and structurally the same. Interestingly, the IR spectrum of the S═O mode remains unaltered during α-isotopic replacement in the presence of aprotic solvents (acetone, acetonitrile, and dichloromethane), but in strongly coordinating polar solvents (D2O), it is altered remarkably. There is a lack of quantitative information about the influence of the α-H atom or α-isotopic substitution on the vibrational probe in the literature. Our experiments provide a detailed molecular understanding of the structure of DMSO in DMSO-solvent binary mixtures. As DMSO plays an important role in virtually all subdisciplines of chemistry and biology, we believe that our work will be of interest to a large diversity of studies in these fields.

A QSPR study on the solvent-induced frequency shifts of acetone and dimethyl sulfoxide in organic solvents

In this study, solvent-induced frequency shifts (SIFS) in the infrared spectrum of acetone and dimethyl sulfoxide in organic solvents were investigated by using four types of quantum-chemical reactivity descriptors. The results showed that the SIFS of acetone is mainly affected by the electron-acceptance chemical potential and the maximum nucleophilic condensed local softness of organic solvents, which represent the electron flow and the polarization between acetone and solvent molecules. On the other hand, the SIFS of dimethyl sulfoxide changes with the maximum positive charge of hydrogen atom and the inverse of apolar surface area of solvent molecules, showing that the electrostatic and hydrophilic interactions are main mechanisms between dimethyl sulfoxide and solvent molecules. The introduction of the four-element theory model-based quantitative structure-property relationship approach improved the assessing quality and provided a basis for interpreting the solute-solvent interactions.

A quantitative structure-activity relationship approach for assessing toxicity of mixture of organic compounds

Four types of reactivity indices were employed to construct quantitative structure-activity relationships for the assessment of toxicity of organic chemical mixtures. Results of analysis indicated that the maximum positive charge of the hydrogen atom and the inverse of the apolar surface area are the most important descriptors for the toxicity of mixture of benzene and its derivatives to Vibrio fischeri. The toxicity of mixture of aromatic compounds to green alga Scenedesmus obliquus is mainly affected by the electron flow and electrostatic interactions. The electron-acceptance chemical potential and the maximum positive charge of the hydrogen atom are found to be the most important descriptors for the joint toxicity of aromatic compounds.

Microwave-assisted ionothermal synthesis of SnSex nanodots: a facile precursor approach towards SnSe2 nanodots/graphene nanocomposites

Presented is a facile approach towards spherical SnSe₂ nanodots/graphene nanocomposites based on a microwave-assisted ionothermally synthesized nanodot precursor.

Combined IR/NIR and density functional theory calculations analysis of the solvent effects on frequencies and intensities of the fundamental and overtones of the C ═ O stretching vibrations of acetone and 2-hexanone

Vibrational overtone studies primarily focus on X-H stretching overtone transitions, where X is an atom like C, O, N, or S. In contrast, the studies on the C ═ O stretching overtones are very scattered. To advance the research in this field, we measured the fundamental, first, and second overtones of the C ═ O stretching vibration of acetone and 2-hexanone in n-hexane, CCl4, and CHCl3, as well as in the vapor phase using FT-IR/FT-NIR spectroscopy. Density functional theory (DFT) calculations have also been performed to help the assignment of the C ═ O stretching bands and to guide interpretation of the experimental results. It was found that the wavenumbers, absorption intensities, and oscillator strengths of the C ═ O stretching bands show marked solvent dependence. In the fundamental and the first overtone regions, the intensities of the C ═ O stretching vibration were found to be pronouncedly more intense than those of the C-H stretching vibration. In the second overtone region, the intensities of the C-H stretching vibration are comparable to those of the C ═ O stretching vibration. The theoretical and observed decrease in integrated intensity upon going from the fundamental to the first overtone of the C ═ O stretching vibration is around 50, which is significantly larger than those of the O-H, C-H, and S-H stretching vibration. Both the calculated and experimental results suggest that excessive weakness in the C ═ O stretching overtone was shown to be a result of both a low anharmonicity and a substantial reduction in the oscillator strength. These results provide new insight into our understanding of the C ═ O stretching vibration.

The conformational analysis of push-pull enaminones using Fourier transform IR and NMR spectroscopy, and quantum chemical calculations. IV. 4-(N,N-dimethylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one and 4-(N,N-dimethyl-amino)-1,1,1-trifluoropropen-3-en-2-one

IR Fourier spectra of two enaminoketones with general formula (CH(3))(2)NCR(1)CR(2)C(O)CF(3), R(1)H, R(2)CH(3) (2); R(1)CH(3), R(2)H (3) were investigated in various pure solvents. For comparison results of earlier investigated enaminoketone R(1)H, R(2)H (1) were also presented. On the basis of NMR and IR spectra it was shown that enaminoketones 1 and 2 presented in solutions as an equilibrium of two conformers, (E-s-Z)⇌(E-s-E), whereas the enaminoketone 3 presented as equilibrium of two isomers, (E-s-Z)⇌(Z-s-Z). Quantum chemical calculations by the DFT methods were carried out to evaluate relative energy and dipole moment of each spatial form. For both (E-s-Z) and (E-s-E) conformer of the 1 and 2 the main influence on the ν(C=O) vibrations has the solvent's hydrogen bond donor (HBD) acidity whereas for the 3 influence of the solvent's polarity/polarizability dominated. Both the solvent's polarity/polarizability and solvent's hydrogen bond donor (HBD) acidity influenced on the ν(C=C) mode of the conformers of the 1 and 2. Solvent influence on the ν(C=C) vibrations of the 3 depended substantially whether the solvent is aprotic or an alcohol. In the former case the main contribution made the solvent's hydrogen bond acceptor (HBA) basicity [(E-s-Z) isomer] or the solvent's polarity/polarizability with solvent's hydrogen bond donor (HBD) acidity [(Z-s-Z) isomer]. Alcohols influenced on the ν(C=C) vibrations of both isomers predominantly due to the solvent's polarity/polarizability. In aprotic solvents the greatest contribution in solvent influence on thermodynamic parameters of both (E-s-Z)⇌(E-s-E) and (E-s-Z)⇌(Z-s-Z) equilibrium made the solvent's hydrogen bond acceptor (HBA) basicity. Rotation around double C=C bond is characterized by higher sensitivity to the solvent's hydrogen bond acceptor (HBA) basicity compared to the rotation around formally single C-C=O bond.

Vibrational solvatochromism in Vaska's complex adducts

The vibrational solvatochromism of bis(triphenylphosphine) iridium(I) carbonyl chloride (Vaska's complex, VC) was investigated by FTIR spectroscopy. The carbonyl stretching frequency (ν(CO)) was measured in 16 different organic solvents with a wide range of Lewis acidities for VC and its dioxygen (VC-O(2)), hydride (VC-H(2)), iodide (VC-I(2)), bromide (VC-Br(2)), and sulfide (VC-S(X)) adducts. The ν(CO) of the VC-O(2) complex was sensitive to the solvent electrophilicity, whereas minimal correlation was found for VC and the other adducts. The stretching frequency of the trans-O(2) ligand on VC-O(2) was measured to be anticorrelated with ν(CO), supporting a model in which this ligand indirectly affects the carbonyl frequency by modulating the extent of metal-to-CO back-bonding. The ν(CO) values obtained from DFT calculations on VC adducts with solvent continua and explicit hydrogen bonds were used to aid the interpretations of the experimental results. The O(2) ligand is more susceptible to stronger specific solvent interactions and it binds in a fundamentally different mode from the monatomic ligands, providing a more direct communication channel with those metal d-orbitals that have the appropriate symmetry to back-bond into the carbonyl π*-orbital.

Solvent effects on the infrared spectra of beta-alkoxyvinyl methyl ketones I. Carbonyl and vinyl stretching vibrations

Infrared spectroscopy studies of six beta-alkoxyvinyl methyl ketones, with common structure R(1)O-CR(2)CH-COR(3), where R(1)=R(3)=CH(3), R(2)=H (1); R(1)=C(2)H(5), R(2)=H (2); R(3)=CF(3); R(1)=R(2)=CH(3), R(3)=CF(3) (3); R(1)=C(2)H(5), R(2)=C(6)H(5), R(3)=CF(3) (4); R(1)=C(2)H(5), R(2)=4-O(2)NC(6)H(4), R(3)=CF(3) (5); R(1)=C(2)H(5), R(2)=C(CH(3))(3), R(3)=CF(3) (6) in 11 pure organic solvents of different polarity were undertaken to investigate the solute-solvent interactions and to correlate solvent properties by means of linear solvation energy relationships (LSER) with the carbonyl and vinyl stretching vibrations of existing stereoisomeric forms. It was shown that contrary to simple carbonyl-containing compounds where solvent HBD acidity (alpha) has the largest influence on the nu (CO) band shift to lower wavenumbers, the dipolarity/polarizability (pi) term plays the main role in the interactions of conjugated enones with solvent molecules leading to the nu (CO) and nu (CC) bathochromic band shifts. The trifluoroacetyl group possesses a reduced ability to form hydrogen bonds with solvents. For the nu (CC) band of non-fluorinated enone 1 solvent HBD acidity (alpha) and solvent HBA basicity term (beta) play a perceptible role, whereas for 2 these terms are not significant. beta-Substituents in fluorinated enones such as R(2)=H, C(6)H(5), and C(CH(3))(3) assist in the intermolecular hydrogen bond formation of the carbonyl moiety with HBD solvents, while beta-substituents such as CH(3) and 4-NO(2)C(6)H(4) prevent the CO group to form the H-bonds with HBD solvents (the solvent HBD acidity term (alpha) is not significant). The comparison of four conformers of the enone 1 reveals that (EEE) form is the most polarizable conformer; the influences of the solvent dipolarity/polarizability (pi) and solvent HBD acidity (alpha) term on the bathochromic nu (CO) band shift are opposite to one another.

Application of artificial neural networks for predicting the aqueous acidity of various phenols using QSAR

Artificial neural networks (ANNs) have been successfully trained to model and predict the acidity constants (pK(a)) of 128 various phenols with diverse chemical structures using a quantitative structure-activity relationship. An ANN with 6-14-1 architecture was generated using six molecular descriptors that appear in the multi-parameter linear regression (MLR) model. The polarizability term (pi (I)), most positive charge of acidic hydrogen atom (q+), molecular weight (MW), most negative charge of the phenolic oxygen atom (q-), the hydrogen-bond accepting ability (epsilon(B)) and partial-charge weighted topological electronic (PCWTE) descriptors are inputs and its output is pK(a). It was found that a properly selected and trained neural network with 106 phenols could represent the dependence of the acidity constant on molecular descriptors fairly well. For evaluation of the predictive power of the ANN, an optimized network was used to predict the pK(a)s of 22 compounds in the prediction set, which were not used in the optimization procedure. A squared correlation coefficient (R2) and root mean square error (RMSE) of 0.8950 and 0.5621 for the prediction set by the MLR model should be compared with the values of 0.99996 and 0.0114 by the ANN model. These improvements are due to the fact that the pK(a) of phenols shows non-linear correlations with the molecular descriptors. [Figure: see text].