The infrared spectra of 3-pentyn-2-ol, CH3CCCH(OH)CH3, have been recorded as a vapour and liquid at ambient temperature, as a solid at 78 K in the 4000–50 cm−1 range and isolated in an argon matrix at ca. 5 K. Infrared spectra of the solid phase at 78 K were obtained before and after annealing to temperatures of 120 and 130 K. The IR spectra of the solid were quite similar to that of the liquid.
Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of an amorphous and annealed solid were recorded at 78 K. In the variable temperature Raman spectra, some bands changed in relative intensity and were interpreted in terms of conformational equilibria between the three possible conformers. Complete assignments were made for all the bands of the most stable conformer in which OH is oriented anti to C1(aMe). From various bands assigned to a second conformer in which OH is oriented anti to Hgem(aH), the conformational enthalpy differences was found to be between 0.4 and 0.8 kJ mol−1. The highest energy conformer with OH anti to C3(aC) was not detected.
Quantum-chemical calculations have been carried out at the MP2 and B3LYP levels with a variety of basis sets. Except for small basis set calculations for which the aH conformer had slightly lower energy, all the calculations revealed that aMe was the low energy conformer. The B3LYP/cc-pVTZ calculations suggested the aMe conformer as more stable by 0.8 and 8.3 kJ mol−1 relative to aH an aC, respectively. Vibrational wavenumbers and infrared and Raman band intensities for two of the three conformers are reported from B3LYP/cc-pVTZ calculations. 相似文献
Summary. ESR and ENDOR spectra are reported of several symmetrical substituted N,N,N,N-tetraalkyl-p-phenylenediamine radical cations in solution. Different N,N-alkyl substituted para-phenylenediamines, like the ethyl, n-propyl, and iso-propyl derivative are compared with the parent N,N,N,N-tetramethyl-p-phenylenediamine (Wursters Blue Cation). N,N,N,N-Tetrabenzyl-p-phenylenediamine, 1,4-dipyrrolidinylbenzene, and N,N-bis[4-(dimethylamino)phenyl]piperazine are additionally investigated. Experimental and calculated hyperfine coupling constants are compared. Characteristic UV-VIS data and redox potentials in acetonitrile are reported, together with the syntheses of the compounds. 相似文献
A new potential energy surface (PES) for the atmospheric formation of sulfuric acid from OH+SO2 is investigated using density functional theory and high-level ab initio molecular orbital theory. A pathway focused on the new PES assumes the reaction to take place between the radical complex SO3·HO2 and H2O. The unusual stability of SO3·HO2 is the principal basis of the new pathway, which has the same final outcome as the current reaction mechanism in the literature but it avoids the production and complete release of SO3. The entire reaction pathway is composed of three consecutive elementary steps:(1) HOSO2+O2→SO3·HO2, (2) SO3·HO2+H2O→SO3·H2O·HO2, (3) SO3·H2O·HO2→H2SO4+HO2. All three steps have small energy barriers, under 10 kcal/mol, and are exothermic, and the new pathway is therefore favorable both kinetically and thermodynamically. As a key step of the reactions, step (3), HO2 serves as a bridge molecule for low-barrier hydrogen transfer in the hydrolysis of SO3. Two significant atmospheric implications are expected from the present study. First, SO3 is not released from the oxidation of SO2 by OH radical in the atmosphere. Second, the conversion of SO2 into sulfuric acid is weakly dependent on the humidity of air. 相似文献
We report sufficient theoretical evidence of the energy stability of the e+?H22? molecule, formed by two H? anions and one positron. Analysis of the electronic and positronic densities of the latter compound undoubtedly points out the formation of a positronic covalent bond between the otherwise repelling hydride anions. The lower limit for the bonding energy of the e+?H22? molecule is 74 kJ mol?1 (0.77 eV), accounting for the zero‐point vibrational correction. The formation of a non electronic covalent bond is fundamentally distinct from positron attachment to stable molecules, as the latter process is characterized by a positron affinity, analogous to the electron affinity. 相似文献
Summary TheZ-expansion theory of Atomic Structure is supplemented with the inclusion of the external screening concept, calculated from
a simplified version of the works of M. Kregar, where the two-body potential energy operators are split into the sum of effective
one-body operators. The use ofZ- andN-dependent screening parameters instead of screening constants, gives a simplified Screened Hydrogenic Model which compares
favourably with more sophisticated methods, specially for ionized atoms.
The author of this paper has agreed to not receive the proofs for correction.
Member of the Consejo Nacional de Investigaciones Cientificas y Tecnicas, Argentina, and Associate Member ICTP (Trieste, Italy). 相似文献
The possibility for nitroso-oxime tautomerism in symmetric monooximes of 1,2,3-phenalenetrione and 1,2,3-indantrione is studied by means of ab initio quantum chemical methods and NMR spectroscopy. For both compounds, ab initio calculations with different basis sets predict the oxime tautomer as most stable in agreement with the 1H- and 13C-NMR results in CDCl3 and DMSO-d6 solutions. A coalescence of the signals for the carbon atoms from carbonyl groups of 1,2,3-phenalenetrione monooxime in DMSO-d6 solution at temperature 360 K is observed. This coalescence may be attributed to rotation of the hydrogen atom from the hydroxyl group around the N---O bond. The rotational transition structures for both compounds at different computational levels were located in the gas phase and in solution. 相似文献
A theoretical analysis of the interaction between formaldehyde, CH2O, and the MgO (100) surface is reported. Ab initio Hartree-Fock calculations are carried out using an embedded cluster approach in which the environment is described by both total ion potentials and point charges. The cluster selected to describe the CH2O-surface interaction is CH2O[MgO5]8−, in which the formaldehyde oxygen is coordinated to the Mg2+ ion. The effect of the addition of metallic cations to the catalyst is analysed by replacing the cluster Mg2+ ion by Na+, Al3+, Sc3+ and Ti4+ so as to modify the Lewis acid properties of the surface. The different contributions to the adsorbate-surface interaction are analysed, and the theoretical vibrational frequencies are discussed. 相似文献