Microwave spectrum,centrifugal perturbation,dipole moment,and conformation of 5-methyl-1,3-dioxane

The microwave spectrum of 5-methyl-1,3-dioxane was studied in the frequency range 12–35 GHz. The a and c type rotation transitions with J≤30 were identified. The rotational constants A = 4658.5244(33) MHz, B = 2383.3930(12) MHz, and C = 1724.28907(88) MHz and the quartic constants of the centrifugal distortion of the molecule in the ground vibrational state were determined. The components of the dipole moment were found, μ _a = 1.76 ± 0.01 D and μ _c = 1.10 ± 0.01 D; the net dipole moment of the molecule is μ = 2.08 ± 0.01 D. 5-Methyl-1,3-dioxane was calculated by the B3PW91/aug-cc-pVDZ density functional theory method. The calculated data are compared with the experimental data. The most stable conformation is the chair conformation with an equatorial orientation of the methyl group.     

Microwave spectrum, centrifugal distortion, dipole moment and conformation of 2-methyl-1,3-dioxane

Microwave spectrum of 2-methyl-1,3-dioxane has been investigated in the frequency range 8–40 GHz. Rotational a-type and c-type transitions with J≤40 have been identified. Rotational constants A = 4658.122(2) MHz, B = 2503.221(1) MHz, C = 1783.950(1) MHz and centrifugal distortion constants for the ground vibrational state have been found. Dipole moment components μ_a = 1.43 ± 0.01 D, μ_c = 1.15±0.01 D and overall dipole moment μ = 1.84±0.02 D have been determined. The data obtained are in accord with the chair conformation of the molecule having equatorial arrangement of the methyl group. Original Russian Text Copyright ? 2006 by A. Kh. Mamleev, R. V. Galeev, L. N. Gunderova, M. G. Faizullin, and A. A. Shapkin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No.2, pp. 373–375, March–April, 2006.     

Structure and spectra of 1,3-dioxanes. II. Microwave spectrum, structural parameters, and ab initio calculations of 2-methyl-1,3-dioxane

The microwave spectra of five isotopomers with the ¹³C and ¹⁸O natural abundance isotopes of the 2-methyl-1,3-dioxane molecule (22–50 GHz) were studied. Rotational transitions of a and c types with 4 ≤ J ≤ 12 were identified. The rotational constants and the substitution r _s and effective r _o structural parameters of the molecule were determined. Ab initio calculations on 2-methyl-1,3-dioxane were performed with molecular structure optimization. The results of quantum-chemical calculations at different levels are compared with experimental data.     

Microwave spectrum,centrifugal perturbation,and dipole moment of acetyl chloride

An analysis of the microwave spectrum of acetyl chloride (¹²CH₃ ¹²C¹⁶O³⁵Cl) in the ground vibrational state allowed us to determine the quartic constants of centrifugal distortion and to refine the rotational constants and the constants of quadrupole coupling of³⁵Cl nuclei in this compound. The Stark effect of the 0–1₁₁ transition has been measured and analyzed. The components of the dipole moment have been determined: μ_a=1.047(10) D and μ_b=2.503(4) D. The total dipole moment of the moment of the molecule is 2.713(8) D. Ufa Scientific Center of Russian Academy of Sciences, Physics Department. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 3, pp. 424–429, May–June, 1995. Translated by I. Izvekova     

Microwave spectrum,conformation, dipole moment and centrifugal distortion of glyoxylic acid

Microwave spectra of CHO-COOH and CHO-COOD are reported. The molecule has a planar equilibrium conformation with the two carbonyl groups trans to each other. A weak five-member intramolecular hydrogen bond is formed between the hydroxyl proton of the carboxyl group and the oxygen atom of the carbonyl group thus stabilizing the trans planar form. Other conformations having a statistical weight of 1 (cis and trans) are at least 1.3 kcal mol^?1 less stable, and rotamers with a statistical weight of 2 (e.g., gauche and skew) have at least 1.7 kcal mol^?1 higher energy. Four vibrationally excited states of CHO-COOH have been analyzed and relative intensity measurements yielded 167 ± 12 cm^?1 for the C-C torsional mode and 288 ± 26 cm^?1 for the lowest in-plane bending mode. The dipole moment was determined to be μ_a = 1.85 ± 0.03 D, μ_b = 0.20 ± 0.10 D, and μ_tot = 1.86 ± 0.04 D. A seven-parameter centrifugal distortion analysis has been carried out for the ground vibrational state of CHO-COOD and for the ground and three vibrationally excited states of CHO-COOH.     

Relative thermodynamic stabilities of 2-substituted 4-methylene-1,3-dioxolanes and 4-methyl-1,3-dioxoles

The relative thermodynamic stabilities of 24 pairs of carbon-carbon double-bondexo-endo isomeric 2-substituted 4-methylene-1,3-dioxolanes (a) and 4-methyl-1,3-dioxoles (b) have been determined by base-catalyzed chemical equilibration in DMSO solution. In all cases, theendo isomer (b) is the favored species at thermodynamic equilibrium. A single alkyl substitutent on C-2 gives only a negligible contribution to the relative stability of the isomeric forms, but the presence of two alkyl groups on C-2 increases the relative stability of theendo isomer by 2–3 kL mol^–1. A still higher effect in favor of theendo isomer is produced by introduction of a single alkoxy group on C-2; this effect is further slightly accentuated by 2,2-dialkoxy substitution at C-2. The origin of the favorable effect of 2-alkoxy substitution on the relative stability of theendo isomer is not clear, but it seems to arise from an unexpected stability of theendo isomer rather than from an enhanced destabilization of theexo form.     

Structure and spectra of 1,3-dioxanes. microwave spectrum,structural parameters and <Emphasis Type="Italic">ab initio</Emphasis> calculations of 1,3-dioxane

Microwave spectra of the 1,3-dioxane molecule (C₄H₈O₂) with the main isotopic composition and four its isotopomers (¹³C(2)¹²C₃H₈ ¹⁶O₂, ¹³C(4)¹²C₃H₈ ¹⁶O₂, ¹³C(5)¹²C₃H₈ ¹⁶O₂, ¹⁸O(1)¹²C₄H₈ ¹⁶O) are investigated in a frequency range of 28–44 GHz. Rotational transitions of b-and c-types with 2 ≤ J ≤ 5 are identified. Rotational constants, quartic constants of centrifugal distortion, isotope-substituted r _s-and effective r ₀-structures of the molecule ring are determined. Experimental data are compared to the results of quantum chemical calculations of different levels.     

Microwave spectrum,conformation, barrier to internal rotation,centrifugal distortion,and dipole moment of methylpropargyl ether

The microwave spectrum of methylpropargyl ether, CH₃OCH₂CCH, has been investigated in the 11.9–26.5 GHz region. Only the gauche rotamer with a dihedral angle of 68° ± 2° from the syn position was assigned. Other forms are not present in concentrations exceeding 10 % of the total. The barrier to internal rotation of the methyl group was determined to be 2512 ± 75 cal mol^?1. The dipole moment components are μ_a = 0.290 ± 0.003 D, μ_b = 0.505 ± 0.012 D, and μ_c = 1.016 ± 0.003 D. The total dipole moment is 1.171 ± 0.013 D. Extensive centrifugal distortion analyses have been carried out for the ground as well as for two vibrationally excited states. For the ground state, transitions up to J = 77 were assigned and a large centrifugal distortion exceeding 9 GHz enabled the determination of accurate quartic and significant sextic distortion coefficients.     

白藜芦醇分子的转动惯量和电偶极矩

通过分子轨道理论和杂化轨道理论推断出较稳定的白藜芦醇分子是平面型分子,然后根据白藜芦醇分子结构特点计算了该化合物的一种稳定异构体的转动惯量,用矢量合成法计算了其电偶极矩,为微波辅助白藜芦醇萃取理论研究提供转动惯量和电偶极矩的数据.     

Synthesis of 2-Aryl and 2-Hetaryl Derivatives of 2'-Aminospiro[(1,3-dioxane)-5,5'-thiazolin]-4'-one and Spiro[(1,3-dioxane)-5,5'-thiazolidine]2',4'-dione

2-(Het)aryl derivatives of 2'-aminospiro[(1,3-dioxane)-5,5'-thiazolin]-4'-one or spiro[(1,3-dioxane)-5,5'-thiazolidine]-2',4'-dione are formed by the acid catalyzed interaction of 2-amino-5,5-bis(hydroxymethyl)-4-thiazolinone or its oxo analog 5,5-bis(hydroxymethyl)thiazolidine-2,4-dione with (hetero)aromatic aldehydes.     

Microwave Spectrum of 1,3-Dioxolane in the v=4-8 States of Hindered Pseudorotation

The microwave spectrum of 1,3-dioxolane (C₃H₆O₂) (8 GHz - 53 GHz) has been studied. We identified 247 b type transitions in the v=4, 5, 6, 7, 8 states of excited pseudorotation: rotational transition; vibration-rotation transitions between the v=5 and v=6 states and between the v=7 and v=8 states. Rotational constants, centrifugal distortion constants, and coupling constants between general rotation and hindered pseudorotation have been determined. The intervals _{v v'} between the pseudorotational energy levels have been evaluated: ₅₆=298,618 MHz and ₇₈=201,078 MHz.     

Microwave spectrum,centrifugal distortion constants,dipole moment and quadrupole coupling constants of pentafluoropyridine

Pentafluoropyridine has been analysed in the frequency range of 8 to 18 GHz at dry ice temperature, using a conventional 100 kHz Stark modulated microwave spectrometer. The rotational constants and centrifugal distortion constants are A = 1481.539 ± 0.003 MHz, B = 1075.348 ± 0.004 MHz and C = 623.101 ± 0.001 MHz; and d_J = ?0.39 ± 0.06 kHz, d_JK = 1.86 ± 0.27 kHz, d_K = 0.70 ± 0.1 kHz, d_EJ = (0.3 ± 0.03) × 10^?6 and d_EK = (?1.5 ± 0.2) × 10^?6. The electric dipole moment has been found to be 0.98 ± 0.08 D and the values of the quadrupole coupling constants are x_aa = 1.94 ± 0.22 MHz, x_bb = ?4.08 ± 0.06 MHz and x_cc = 2.14 ± 0.22 MHz. A simple analysis based on Townes and Dailey theory points to a considerable increase in the π-electron density and excess charge on the nitrogen site.     

Microwave spectrum,conformation, barrier to internal rotation and dipole moment of pyruvic acid

Microwave spectra of CH₃COCOOH and CH₃COCOOD are reported. The preferred conformation of the molecule is demonstrated to possess a planar HCCOCOOH skeleton with two out-of-plane hydrogens. The two carbonyl groups are trans to each other and a weak five-membered hydrogen bond is formed between the carboxyl group hydrogen atom and the carbonyl group oxygen atom. The methyl group conformation is discussed. A computer programme based on “the principal axis method” is described in some detail and the results of a least squares analysis of the observed spectra are outlined. The barrier to internal rotation was determined as V₃ = 965±40 cal mol^?1 for both isotopic species. Stark effect measurements yielded μ_a = 2.27±0.02 D, μ_b = 0.35±0.02 D and μ_tot = 2.30±0.03 D for the dipole moment and its components along the principal axes.     

Microwave spectrum,conformation, intramolecular hydrogen bond,and dipole moment of pyrrole-2-carboxaldehyde

Microwave spectra of C₄H₃NH-CHO, C₄H₃ND-CHO, and C₄H₃NH-CH¹⁸O are reported. The stable form of the molecule is demonstrated to be planar with the N-H and C-O bonds in a cis conformation. Other forms of the molecule are at least 1 kcal mol^?1 less stable. The H(1) · O distance is 2.592±0.006 Å. Six vibrationally excited states were attributed to the C-C torsional mode, the symmetrical, and the antisymmetrical aldehyde group deformation vibrations. Relative intensity measurements yielded 151±11 cm^?1, for the first frequency, 210±17 cm^?1 for the second, and 270±38 cm^?1 for the last mode. The dipole moment was determined to be μ_a = 2.47 ±0.02 D, μ_b = 0.16±0.06 D, and μ_tot = 2.48 ±0.02 D, respectively.     

Investigation in the Area of Furan Acetal Compounds. 13. Synthesis and Structure of 1,3-Dioxacyclanes Based on Furfural and Glycerol

The optimum conditions were found for the condensation of glycerol with furfural. It was shown that the reaction of glycerol with furfural gives a mixture of the cis and trans isomers of five- and six-membered furan 1,3-dioxacyclanes. The cis- and trans-5-hydroxy-2-furyl-1,3-dioxanes were isolated by column chromatography, and their stereochemical structure was established by IR and NMR spectroscopy.     

Microwave spectrum,structure and dipole moment of trimethylamine-borane

The ground state rotational spectra often isotopic species of trimethylamineborane, (CH₃)₃N¹⁰BH₃, (CH₃)₃N¹¹BH₃, (CH₃)₃N¹⁰BD₃, (CH₃)₃N¹¹BD₃, (CH₃)₃N¹¹BD₂H, (CD₃)₃N¹⁰BH₃, (CD₃)₃N¹¹BH₃, (CD₃)₃N¹⁰BD₃, (CD₃)₃N¹¹BD₃ and (¹³CH₃)(¹²CH₃)₂N¹¹BH₃, have been measured and the effective moments of inertia obtained. The utilization of Kraitchman's equations leads to an r_s value of the B-H distance of 1.211±0.003 Å and a NBH angle of 105.32±0.16°. By a least squares fit of the rotational constants the following structural parameters were obtained: r(NC) = 1.495 Å, r(BN) = 1.609 Å, and ∠BNC = 110.9°. The value of the dipole moment was found to be 4.59±0.13 D. A lower limit to the barrier to internal rotation of the BH₃ group was determined to be 3.4 kcal/mole.     

Freezing points and enthalpies of dilute aqueous solutions of tetrahydropyran, 1,3-dioxane, 1,4-dioxane,and 1,3,5-trioxane. Free energies and enthalpies of solute-solute interactions

The enthalpies of dilute aqueous solutions of tetrahydropyran, 1,3-dioxane, 1,4-dioxane, 1,2,5-trioxane, and an equimolal mixture of tetrahydropyran and 1,3,5-trioxane were measured at 25°C and at molalities from about 0.1 to 1.0 mol kg¹. The freezing points of the same aqueous solutions (except for 1,3-dioxane) were measured over a similar molality range. The results were used to calculate the enthalpies and Gibbs free energies of the pair-wise interactions of the above solutes in dilute aqueous solutions at 25°C. From these results, the additivity principle proposed by Savage and Wood was used to get the Gibbs free energy and enthalpies of interaction for the ether-ether and ether-methylene groups. Because of the limited number of measurements, the interaction parameters were not determined with great precision. Nevertheless, the standard errors for the predicted enthalpies and Gibbs free energies are quite reasonable. The signs and magnitudes are similiar to those determined for other polar groups.