Microwave Spectrum of 1,3-Dioxolane. Potential Function of Hindered Pseudorotation and Molecular Conformation

Vibrational and rotational transitions of c type with 24 ≥ J ≥ 18 between the pseudorotational states v = 4 and v = 5 have been identified in the range 23 GHz–39 GHz of the microwave spectrum of 1,3-dioxolane (C₃H₆O₂); their frequencies have been measured. Spectrum analysis was performed using numerical diagonalization of the effective rotational Hamiltonian for three states: v = 4, 5, and 6 of hindered pseudorotation, and it gave the intervals ΔE ₄₅ = 331,023 MHz and ΔE ₅₆ = 298,771 MHz. The potential function of hindered pseudorotation was determined from the values of ΔE ₄₅ and Δ E ₅₆ and from the values of ΔE ₀₁, ΔE ₁₂, ΔE ₂₃, and ΔE ₇₈ found previously for the molecule; the molecular conformation has been established.Original Russian Text Copyright © 2004 by A. Kh. Mamleev, L. N. Gunderova, R. V. Galeev, and A. A. Shapkin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1008–1012, November–December, 2004.     

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.     

含抗氧化受阻胺的三聚芴有机半导体的合成及其光谱稳定性的研究

芴基电致蓝光材料低能绿光带(LEEB)的起源仍没有结论,其中芴酮诱导LEEB是重要机制之一,基于此我们提出通过引入含抗氧化的受阻胺来抑制LEEB的策略.通过复杂二芳基芴(CDAF)方式构建了一个共价键联接的含四甲基哌啶(TMP)的蓝光三聚芴有机半导体材料DF-PTMPF,并通过退火实验研究对其光谱稳定性的影响.研究结果表明DF-PTMPF的光谱稳定性有了很大提高,退火120h时的绿光指数φ为1.4(φ=IGreen/IBlue),而相同条件下的三聚芴TDHF的绿光指数φ为2.4.同时,由于受阻胺可以除掉体系中微量的氧,而DF-PTMPF在起初的氮气气氛下退火24h仍产生绿光带,这一结果暗示了聚集诱导LEEB仍不能忽视.     

烷氧基磷烷的合成及假旋转

氢膦烷２与苯基次磺酸酯３反应，制得几种带有取代基的螺双环烷氧基磷烷４。变温＾３１Ｐ ＮＭＲ谱监测，观察到化合物４的假旋转，并计算出了假旋转的活化自由能。     

Microwave Activation of Reaction between 1,3,5-Trisubstituted Pyrazole-4-carbaldehydes and Sterically Hindered Aminoalcohols

Structure of products of reaction between 1,3,5-trisubstituted pyrazole-4-carbaldehydes and 2-aminoalkan-1-oles is determined by the structure of the alkyl chain of aminoalcohol. The reaction with 2-aminobutan-1-ol proceeds for 2 h in conditions of microwave activation at 150°C with the formation of 2-hydroxyalkylimines of pyrazole-4-carbaldehyde. At reaction of 1,3,5-trisubstituted pyrazole-4-carbaldehydes with 2-amino-2-methylpropan-1-ol mixtures form of the corresponding 2-hydroxyalkylimines and pyrazol-4-yl-1,3-oxazolidines in ratios 66 : 33–80 : 20. Heating of 2-hydroxyalkylimines of pyrazole-4-carbaldehyde in the presence of dehydrating agents, in particular, trimethylchlorosilane, does not result in 1,3-oxazolidines.     

微波作用下大位阻氨基酸与H-Pro-CTC树脂的高效缩合

微波反应下, 运用新型固相肽合成反应器, 深入研究了五种大位阻氨基酸与H-Pro-CTC树脂(CTC树脂, 2-氯三苯甲基氯树脂)的缩合反应. 使用三次缩合的策略, 分别在DMF/NMP/THF (V∶V∶V＝1∶1∶1), NMP/DMSO/THF (V∶V∶V＝4∶1∶1), DMF/DMSO/THF (V∶V∶V＝4∶1∶1)混合溶剂中缩合一次, 每次缩合反应的最优条件为: 缩合试剂HBTU、氨基酸浓度7 mmol/L、微波辐射3 min、反应温度35 ℃、维持时间3 min, 与传统方法相比, 氨基酸的用量大大减少, 其过量倍数从5倍降低为2倍, 缩合反应速率提高了16倍以上. 五种大位阻氨基酸与H-Pro-CTC树脂的缩合率都提高到80%以上.     

Syntheses of Metallaphosphorane Complexes and Berry Pseudorotation

Iron-, ruthenium-phosphoranes Cp'(CO) 2 M{P(OC 7 H 6 O) 2 }(Cp' = m 5 -C 5 H 5 , m 5 -C 5 Me 5 ; M = Ru, Fe), and cobalt-phosphoranes L(CO) 3 Co-{P(OC 7 H 6 O) 2 }(L = PPh 3 , PPh 2 Me) were prepared. From the variable-temperature 31 P NMR studies, the activation parameters for Berry pseudorotation were determined.     

Pseudorotation and Barriers to Inversion of 1,3,2-Dioxaborinane Rings

It has been shown by empirical, semiempirical, and nonempirical methods that the interconversion of the rings of 1,3,2-dioxaborinanes goes via transition state with the 2,5-twist form and differs from the monotypic substituted 1,3-dioxanes in having a lower potential barrier.     

Microwave Spectrum and Structure of 2-(Trifluoromethyl)pyridine

The high resolution rotational spectrum of 2-(trifluoromethyl)pyridine in 2\begin{document}$ - $\end{document}20 GHz was recorded and analyzed. Spectroscopic parameters including rotational constants, nuclear quadrupole coupling constants of \begin{document}$ ^{14} $\end{document}N as well as the centrifugal distortion constants were determined. The rotational spectra of five mono-substituted \begin{document}$ ^{13} $\end{document}C and one \begin{document}$ ^{15} $\end{document}N isotopologues were also measured and assigned in natural abundance. Experimental results complemented by ab initio calculations lead to an accurate determination of the skeleton structure. The values of the planar moment inertia \begin{document}$ P_{cc} $\end{document} were determined to be 44.46 u?\begin{document}$ ^2 $\end{document} for all the measured isotopologues, indicating a C\begin{document}$ _ \rm{s} $\end{document} symmetry of this molecule. The molecular electrostatic surface potential was calculated to illustrate the trifluoromethyl substitution effects on the electron distribution.     

Pseudorotation and Conformational Transmission in Pentacoordinated Phosphorus Compounds

Abstract

This poster reviews our recent work on conformational transmission and pseudorotation in the pentacoordinated phosphorus (P^v) compounds 1a-d and 2a-d (1,2).     

Pseudorotation and the environmental effects of the phosphorescence lifetime of benzene

The strong temperature dependence of the phosphorescent decay rate of benzene is attributed to pseudorotational motion of benzene which has the lowered D_2h symmetry in the triplet state. This model accounts for the unusual deuterium effect of the activation energy, the very large pre-exponential factor, the low onset temperature, and the solvent effects.     

Microwave Spectrum of Two-Top Molecule: 2-Acetyl-3-Methylthiophene

The microwave spectrum of 2-acetyl-3-methylthiophene (2A3MT) was recorded in the frequency range from 2 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer and could be fully assigned to the anti-conformer of the molecule, while the syn-conformer was not observable. Torsional splittings of all rotational transitions in quintets due to internal rotations of the acetyl methyl and the ring methyl groups were resolved and analyzed, yielding barriers to internal rotation of 306.184(46) cm⁻¹ and 321.813(64) cm⁻¹, respectively. The rotational and centrifugal distortion constants were determined with high accuracy, and the experimental values are compared to those derived from quantum chemical calculations. The experimentally determined inertial defect supports the conclusion that anti-2A3MT is planar, even though a number of MP2 calculations predicted the contrary.     

Vibrational Satellites and Pseudorotation in 2-Methyl-1,3-dioxolane

Vibrational satellites caused by pseudorotation are identified in the microwave spectrum of 2-methyl-1,3-dioxolane. The rotational constants of the satellites are determined up to state v = 6. Splittings between lower pseudorotational energy levels are determined by measuring the relative intensities of rotational transitions. An attempt is made to determine the form of the pseudorotation function of the molecule using the obtained data.     

Two Equivalent Internal Rotations in the Microwave Spectrum of 2,6-Dimethylfluorobenzene

Large amplitude motion of methyl groups in isolated molecules is a fundamental phenomenon in molecular physics. The methyl torsional barrier is sensitive to the steric and electronic environment in the surrounding of the methyl group, making the methyl group a detector of the molecular structure. To probe this effect, the microwave spectrum of 2,6-dimethylfluorobenzene, one of the six isomers of dimethylfluorobenzene, was measured using two pulsed molecular jet Fourier transform microwave spectrometers operating in the frequency range from 2 to 40 GHz. Due to internal rotations of two equivalent methyl groups with relatively low torsional barriers, all rotational transitions split into quartets with separations of up to several hundreds of MHz. The splittings were analyzed and modeled to deduce a torsional barrier of 236.7922 (21) cm⁻¹. The results are compared to those obtained from quantum chemical calculations and with other fluorine substituted toluene derivatives of the current literature where the methyl group is adjacent to a fluorine atom.     

Hindered rotation and exchange in trimethylsilylanilides

A series of trimethylsilylanilides were prepared and characterized as amide—imidate mixtures. Low temperature NMR spectra reveal both hindered rotation and exchange processes for the formanilides and benzanilides and exchange for the acetanilides. Isomer ratios and free energies of activation are reported and used to postulate a mechanism for the exchange process.