Hybrid-Density Functional Theory Study and Natural Bond Orbital Interpretation of the Conformational Behavior of 1,3-Dioxanyl, 1,3-Dithianyl,and 1,3-Diselenanyl Carbanions

Abstract

The effective factors on the conformational properties of 1,3-dioxanyl (1), -dithianyl (2), and -diselenanyl (3) carbanions have been investigated by means of the hybrid-density functional theory (DFT) (B3LYP/6-311+G**)-based method and natural bond orbital (NBO) interpretation. The results obtained showed that the axial conformation (i.e., the axial H atom attached to C₂) of carbanion 1 is more stable than its equatorial conformation. Contrary to the carbanion 1, the equatorial conformations of carbanions 2 and 3 are more stable than their corresponding axial conformations. The instability of the axial conformations of carbanions 1–3 increases from carbanion 1 to carbanion 2 but decreases from carbanion 2 to carbanion 3. The NBO analysis showed that the anomeric effect (AE) associated with the electron delocalization increases from carbanion 1 to carbanion 2, but decreases from carbanion 2 to carbanion 3. The calculated total dipole moment values of the axial conformations of carbanions 1–3 are greater than those of their corresponding equatorial conformations, but the calculated total dipole moment difference values between the axial and equatorial conformations decreases from carbanion 1 to carbanion 3. Consequently, the AE associated with the electron delocalization, but not the total dipole moment changes (i.e., Δμ_ax–eq), thus explaining the total energy differences between the axial and equatorial conformations of carbanions 1–3. The correlations between the AE, dipole moments, ΔG_ax–eq, structural parameters, and conformational behaviors of carbanions 1–3 have been investigated.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

ELECTRON-DONOR PROPERTIES OF SULFUR COMPOUNDS WITH A FEW DONOR SITES

Abstract

The structure and the coordination properties of sulfur compounds such as RS-(CH₂)n-SR, (I), n=1-10 and RS-(CH₂)nCOOR' (II), n=1,2 have been investigated by dipole moment, calorimetrie, IR-spectroscopy and cryoscopy methods.     

Rotamere 2-Phenyl-1,3-dioxane

By means of dipole moment measurements, NMR-spectroscopical methods and force field calculations of o-, m- and p-substituted 2-phenyl-1,3-dioxanes a systematic study concerning the rotameric behaviour of the phenyl group was performed.In o-substituted 2-phenyl-1,3-dioxanes the preferred conformation of the phenyl ligand was found to be displaced about 60 degs. from thecisoid-bisectional conformer. Introduction of an additional substituent in the second o-position gives rise to a change in the rotameric state, the preferred conformation now being bisectional. In contrast, the barriers resisting rotation about the C_ar–C-2-bond in 2-phenyl-1,3-dioxane and its m- and p-substituted derivates turn out to be much lower. Thus at room temperature an ensemble of approximately bisectional rotamers exists.The conformations and rotational barriers determined are discussed in terms of non bonded and dipole-dipole interactions.

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6. Mitt.:H. Lehner, Mh. Chem.107, 565 (1976).     

Random-Coil configurations of the polymormals [CH2?O?(CH2)y?O?]. II. Dipole moments of poly(1,3–dioxepane) [CH2?O?(CH2)4?O?;]

Dielectric constant measurements were carried out on a sample of poly(1,3–dioxepane) [CH₂? O? (CH₂)₄? O? ], in benzene over the range 25—60°C. This chain molecule was found to be very similar to poly(1,3–dioxolane) [CH₂? O? (CH₂)₂? O? ] in having a relatively small dipole moment, which increases markedly with increasing temperature. Rotational isomeric-state calculations show that these two characteristics are due to very strong preferences for gauche states in the two central bonds in the sequence CH₂? O? CH₂? O? CH₂. Such pairs of gauche states, necessarily of the same sign, place neighboring-group dipoles in essentially antiparallel orientations. The resulting attenuation of dipole vectors is the origin of the small dipole moment, and the disruption of these preferred conformations with increasing temperature gives rise to the large positive temperature coefficient of the dipole moment.     

Structure and Basicities of Aliphatic Organophosphorus Compounds

Abstract

As an extension of our previous works concerning the basicities of aliphatic phosphoric amides and phosphinoxides, the influence of structure is studied for some series of parent compounds, such as :

XP(tBu)₃ with X=lone pair; O; S; NH ˙ OP[N(CH₂)_X]₃ with x=2; 3; 4; 5.

The techniques used here are mainly:

determination of gas phase basicities by ion cyclotron resonance mass spectrometry

determination of Broensted basicities by titration in an non-aqueous solvent system

dipole moment measurements     

The effect of molecular polarity on nem/catic phase stability in 12-vertex carboranes

Weakly polar–polar isosteric pairs of 12-vertex p-carborane [closo-1,12-C₂B₁₀H₁₂] (1[12]) and monocarbaborate [closo-1-CB₁₁H₁₂]^? (2[12]) nematic liquid crystals, in which the difference in the calculated molecular dipole moment is 11.3 D, were synthesised, and the effect of the dipole moment on nematic phase stability was investigated. The trend observed for the 12-vertex series ([12]) was identical to that of the previously investigated 10-vertex series ([10]) containing [closo-1,10-C₂B₈H₁₀] (1[10]) and [closo-1-CB₉H₁₀]^? (2[10]): the uniform increase in the molecular dipole moment in the pairs of mesogens does not correspond to a uniform change in the clearing temperature, T_NI. This demonstrates the role of a remote substituent in modulating the intermolecular dipole–dipole interactions. The magnitude of such interactions was calculated (using density functional theory methods) for a pair of polar (2[12]d–2[12]d) and an analogous pair of weakly polar (1[12]d–1[12]d) molecules. All results for the 12-vertex series ([12]) were analysed relative to the 10-vertex analogues ([10]).     

On the conformational structure of cyclohexadecane,the corresponding ketone,the 1,9-dione and the corresponding ketals

The title compounds have been prepared, and their structures have been studied using molecular mechanics calculations, together with dipole moment measurements, and thermodynamic and spectroscopic data reported in the literature. It is concluded that the parent hydrocarbon exists to a very large extent in a “square” diamondoid conformation (D_2d symmetry). Other conformations (rectangular, nearly D₂, and puckered, (D_2d) are considerably higher in energy. The ketone consists of a mixture of both square and rectangular conformations with the CO group in several different positions. The monoethylene ketal exists primarily in a conformation which is square, with the ketal group on a corner. The diketone, diketal, and monoketal of the dione are considered in the light of the above, and conclusions are drawn regarding their conformations. The dipole moments of the difunctional compounds are in agreement with the conformational conclusions reached by the calculations.     

Solvatochromic and Quantum-Mechanical Characterization of Methyl Red

ABSTRACT

Quantum-mechanical characterization for methyl red was performed using density function theory. The dipole moment and polarizability in the ground state of methyl red were theoretically calculated. The contribution of intermolecular interactions to spectral shifts in solution and the limits in which the excited states’ dipole moment vary in the neutral form were established by a solvatochromic study. The solvatochromism of the acid and alkaline forms of methyl red was experimentally measured and compared with calculated spectra.     

In situ measurements of emission transition dipole moment of individual ordered microdomain of diprotonated tetraphenylporphine aggregate formed at dodecane/aqueous H<Subscript>2</Subscript>SO<Subscript>4</Subscript> interface

Rhombic-ordered microdomains of diprotonated 5,10,15,20-tetraphenylporphine aggregate, whose sizes were 10–200 μm, were formed at dodecane/aqueous H₂SO₄ interfaces. The light excitation of their two absorption bands (410 and 473 nm for H- and J-bands, respectively) led to one fluorescence band at longer wavelength (723 nm). The direction of the emission transition dipole moment (μ _e) of individual rhombic microdomains, determined with an in situ optical microscope and a linear polarizer, was almost parallel to the major axis, which was also almost parallel to the direction of the absorption transition dipole moment of their J-bands. Their absorption and emission transition scheme was proposed.     

Dipole Moment Studies of n-butanol,i-butanol and t-butanol with Chlorobenzene Complexes

Abstract

The dipole moments of H-bonded complexes of n-butanol, i-butanol and t-butanol with chlorobenzene in benzene were investigated from dielectric measurements at 455 kHz and at temperature 303.16 K. The dipole moment of the complex (μab), interaction dipole moment (Δμ) and induced polarization (Pab) for thermodynamically most favoured geometry of 1:1 complexes in these systems were determined. The results shows that the complexation is due to charge redistribution effect in all cases studied and the tendency of complex formation is maximum in n-butanol system.     

Complete basis set,hybrid-DFT study,and NBO interpretations of the conformational behavior of 1,2-dihaloethanes

The conformational behavior of 1,2-difluoroethane (1), 1,2-dichloroethane (2), 1,2-dibromoethane (3), and 1,2-diiodoethane (4) have been analyzed by means of complete basis set CBS-QB3, hybrid-density functional theory (B3LYP/Def2-TZVPP) based methods and natural bond orbital (NBO) interpretation. Both methods showed the expected greater stability of the gauche conformation of compound 1 compared to its anti conformation. Contrary to compound 1, the anti conformations of compounds 2–4 are more stable than their gauche conformation. The stability of the anti conformation compared to the gauche conformation increases from compound 1 to compound 4. The NBO analysis of donor–acceptor (σ → σ*) interactions showed that the generalized anomeric effect (GAE) is in favor of the gauche conformation of compound 1. Contrary to compound 1, GAE is in favor of the anti conformations of compounds 2–4. The GAE values calculated (i.e., GAE_anti − GAE_gauche) increase from compound 1 to compound 4. On the other hand, the calculated dipole moment values for the gauche conformations decrease from compound 1 to compound 4. In the conflict between the GAE and dipole moments, the former succeeded in accounting for the increase of the anti conformation stability from compound 1 to compound 4. There is a direct correlation between the calculated GAE, ∆[r _c–c(G) − r _c–c(A)] and ∆[r _c–x(A) − r _c–x(G)] parameters. The correlations between the GAE, bond orders, total steric exchange energies (TSEEs), ΔG _{Anti–Gauche}, ΔG ^‡(Gauche → Gauche′, C _2v), ΔG ^‡(Anti → Gauche, C ₂), dipole–dipole interactions, structural parameters, and conformational behaviors of compounds 1–4 have been investigated.     

DFT study of ferroelectric properties of the copolymers: Poly(vinylideneflouride‐trifluoroethylene) and poly(vinylidene fluoride‐chlorotrifluoroethylene)

A theoretical study of poly(vinylidene flouride‐trifluoroethylene) and poly(vinylidene fluoride‐chlorotrifluoroethylene, is presented. By density functional theory calculations, some of the properties of these materials have been obtained. Among such properties, the dipolar moment and the energies associated to the structural changes. The B3LYP functional and 6311+G(d,p) bases set were used with Gaussian program. Calculations associated to different conformations were carried out to get insight about the involved phase changes. The energetic, charges, and dipole moment were calculated. The conformations, namely, I = T_p, II = TG_a, and III = TG_p, where T means trans and G means gauche, for the two polymers aforementioned were compared with the poly(vinilydene fluoride) studies previously obtained. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2411–2417, 2010     

Influence of heteroelement on dipole and quadrupole moments of a series of three-membered rings containing a second,third, fourth,or fifth-row atom: a theoretical investigation

The influence of heteroelements on the molecular dipole and traceless quadrupole moments of a series of twenty-two three-membered rings (1–22) was theoretically estimated employing levels of theory such as MP2, CCSD, and PBE1PBE in combination with standard Pople’s basis set. To an accurate evaluation of these properties, additional calculations on the optimized geometries were performed using the correlation-consistent cc-pVDZ and aug-cc-pVDZ basis sets on the three mentioned methods. In particular, the dipole and quadrupole moments from MP2 and CCSD approaches are comparable to each other for the studied molecules, while PBE1PBE calculations were significantly deviated compared to MP2 and CCSD levels. High level of theory and large basis sets seemed to be needed to obtain reliable electrical properties in the heterocycles containing heavy atoms. Results demonstrated that the dipole and quadrupole moments are strongly determined by the nature of the heteroatom into ring skeleton, and its magnitude depends on the polarity of C-heteroelement bond. Dipole moment of these molecules 1–22 showed a clear increase with the increase of electronegativity and the atomic size of heteroatom into ring skeleton. Then, high relative dipole moment was found for three-membered rings containing II, IIIA, VIA, and VIIA elements, which is associated to the high polarization of the C-heteroatom bond. A similar behavior was observed for the quadrupole moments of these three-membered rings.

     

Conformational properties of polar polymers. I. Poly(vinyl chloride)

A recently developed method for including polar bonds in conformational energy calculations is applied to poly(vinyl chloride). Inductive effects on dipole moments and the effects of intervening atoms on electrostatic interaction energies are represented by polarizability centers in conjunction with bond centered dipoles. Solvation energies are estimated by means of a continuum dipole–quadrupole electrostatic model. Calculated energies of a number of conformations of meso and racemic 2,4-dichloropentane and the iso, syndio, and hetero forms of 2,4,6-trichloroheptane give satisfactory representations of isomer and conformer populations. Electrostatic effects are found to be quite important. However they appear to be effectively of sufficiently short range that the calculated conformer energies are found to be fit well by a linear combination of interaction parameters (consisting of gauche, skew chlorine, four-bond CH₂…CH₂, CH₂…Cl, and Cl…Cl interactions) conventional to vinyl polymers and a special four-bond interaction that arises when the bond sequence Cl? CH? CH²? CH? Cl is (nearly) coplanar. These interaction parameters when assembled into statistical weight matrices lead to calculated values of both the characteristic ratio and the dipole moment ratio in satisfactory agreement with experiment. Least energy paths for transitions between the most stable conformations are also calculated.     

Structure Features of 1,3,5-Tris(Diphenylphosphinoxidemethylene)Ben zene in Crystal and Solution on the Base of X-Ray,Dipole Moments and Quantum Chemical Analysis

Abstract

The molecular structure, polarity and conformations in solution of 1,3,5-tris(diphenylphosphinoxidemethy1ene)benzene 1,3,5-[Ph₂P(0)CH₂]₃C₆H₃ have been studied by X-ray, dipole moments and quantum chemistry methods. It have been shown, that in crystal molecule has the conformation in which two diphenylphosphinoxide fragments dispose on one and the same side, but the third - on the other side of central benzene ring plane with torsion angles C_SP2-C_SP2-C_SP3-P 60–80° and C_SP2-C_SP3-P=O about 50–70°. In solution conformational picture is more rich: side by side with the structures realized in crystal, conformations with all three diphenylphosphinoxide fragments disposed on one and the same side of central benzene ring plane with torsion angles C_SP2-C_SP2-C_SP3-P 70-90° and C_SP2-C_SP3-P=O about 70–75° become preferable.     

Quantum-Mechanical and Solvatochromic Characterization of Quercetin

ABSTRACT

Quercetin was subjected to a quantum-mechanical analysis and energetic and electro-optic parameters were evaluated. A solvatochromic study was used to estimate the dipole moment of quercetin in the excited state and to determine the angle between the dipole moments of this molecule in the electronic states responsible for the visible absorption band. The contribution of each type of intermolecular interactions to the total spectral shift experimentally recorded in quercetin solution was also established in this study.     

Construction of half-sandwich rhodium- and iridium-based metallamacrocycles with different space conformations via isomeric pyridyl-substituted ligands

Abstract

Herein, we describe the utilization of isomeric pyridyl-substituted ligands featuring different coordination vectors to rationally design and construct a series of discrete organometallic assemblies with specific space conformations. In the case of tetranuclear macrocycles constructed from the ligand 3-bpb, different conformations of these assemblies with C_2v and C_2 h point symmetry were revealed by single-crystal X-ray diffraction. These complexes were further characterized by X-ray crystallography, ¹H NMR, DOSY NMR, IR spectroscopy, and elemental analyses.     

New approximate formulae for the retardation factors of nematic liquid crystals with simple uniaxial anisotropy

Abstract

Simple formulae which yield a close approximation to the exact analytic solution for the longitudinal and transverse relaxation times T _|| and T _⊥ of the components of the dipole moment of a nematic liquid crystal with simple uniaxial anisotropy are presented. The new formula for T _|| yields a substantial correction to the Meier-Saupe formula [1966, Molec. Crystals, 1, 515]. It appears that both the longitudinal and transverse relaxation processes may be accurately described by a single Debye type relaxation mechanism with relaxation times T _|| and T _⊥.     

Dielectric Study of Charge-transfer Complexes in Binary and Ternary Systems at 35°C

Abstract

The measurements of dielectric constant of a number of binary and ternary mixtures of butyl acetate, butyl alcohol, quinoline, pyridine and o-cresol in carbon tetrachloride and benzene have been made at 35°C. Molecular interaction of these aromatic compounds have been studied in terms of variations in parameters; ‘dipole moment’ (μ), ‘interaction dielectric constant’ (δ?), ‘molecular polarisation’ (P) and ‘excess polarisation’ (P_E ). The dipole moment has been calculated using Hysken's method, the interaction dielectric constant utilizing the equation of ideal mole fraction law and excess polarisation using the theory of Erap and Glasstone. The positive values of δ?₁₂ for binary mixtures of quinoline and butyl acetate in carbon tetrachloride and benzene have been attributed to the formation of charge transfer complexes. The negative values of δ?₁₂ and δ?₁₂₃ with pyridine suggest that charge transfer interaction is weakened by pyridine in its binary and ternary mixtures. The plot between the excess polarisation value and the product of mole fractions yielded a straight line passing through the origin showing the formation of charge transfer complexes.