Multichannel decomposition and isomerization of octyl radicals

The thermal cracking patterns from the decomposition and isomerization of octyl-1 radicals have been determined from the pyrolysis of n-octyl iodide in single pulse shock tube experiments at temperatures in the 850-1000 K range and pressures near 2 bar. Rate constants for the six beta bond scission and five of the six isomerization processes have been derived over all combustion conditions [0.1-100 bar, 700-1900 K]. Comparisons are made with previous studies on the decomposition of other primary radicals. Results are consistent with similar types of reactions having equal rate constants. The larger size of the octyl radicals makes contributions from secondary to secondary radical isomerization increasingly important. The results confirm that the 1-3 H-transfer process (involving a seven member cyclic transition state) have rate constants that are within a factor of 2 of those for the 1-4 process (six member cyclic transition state) It appears that rate constants for 1-2 H-transfer isomerization, involving an eight member cyclic transition state is unimportant in comparison to contributions from other isomerization processes. The strain energy does not appear to play an important role for these larger transition states. The implications of these results to larger fuel radicals will be discussed.     

Energetics, structures, bonding, and kinetics of the HSCl–HClS system

The [H,S,Cl] potential-energy surface has been investigated at the self-consistent field (SCF), complete active space self-consistent field (CASSCF), second-order M?ller–Plesset, coupled-cluster single-double and perturbative triple excitation, [CCSD(T)]/6-31G(d,p), 6-31G(2df,2pd), and correlation-consistent polarized valence triple zeta (cc-pVTZ) levels of theory. CCSD(T)/ cc-pVTZ results predict a very stable HSCl species, an isomer HClS, 51.84 kcal/mol higher in energy, and a transition state 57.68 kcal/mol above HSCl. Independent of the level of theory, results with the smaller 6-31G(d,p) basis set turned out to be poor, especially for HClS. Vibrational analysis indicates that both species can be easily differentiated if isolated. Bonding differences between these molecules are illustrated by contour plots of valence orbitals. Viewed classically, bonding in HClS involves a dative bond. Transition-state rate constants, and equilibrium constants for the HSCl ↔ HClS isomerization have been estimated for various temperatures (200–1000 K). At 298.15 K, the forward rate is predicted to be 7.95 × 10⁻²⁹ s⁻¹, and the equilibrium constant to be 2.31 × 10⁻³⁸. Tunneling corrections vary from 1.57 at 298.15 K to 1.05 at 1000 K. Activation energies have been obtained by a two-points linear fit to the Arrhenius equation. Received: 7 May 1999 / Accepted: 22 July 1999 / Published online: 4 October 1999     

苯并氧化呋咱稳定性和异构化的DFT和ab initio研究

运用B3LYP/6-31G(d)密度泛函理论（DFT）方法对苯并氧化呋咱、邻二亚硝基苯及其间的异构化反应进行了计算研究。结果表明,苯并氧化呋咱的分子总能量比邻二亚硝基苯的低;由苯并氧化呋咱异构为邻二亚硝基苯的正向反应活化能（Ea+=51.0kJ/mol）,与文献实测值（58.6kJ/mol）较接近,而其逆向反应活化能（Ea-=4.6kJ/mol）很小,从而揭示了苯并氧化呋咱比邻二亚硝基苯更稳定·此外,进行了HF/3-21G、HF/6-31G(d)和MP2/6-31G(d)//6-31G(d)水平下相应的计算,发现B3LYP-DFT的结果较abinitio为优。谐振动频率的B3LYP/6-31G(d)计算还支持了邻二亚硝基苯为苯并氧化呋咱“自-自”互变重排反应的中间体。     

The deviating behavior of thiols in nucleophilic trapping reactions of chromiumcarbonyl phenyl complex substituted propargyl cation

The (phenyl)Cr(CO)₃-complex substituted propargyl cation 4 significantly deviates in the chemoselectivity of the nucleophilic attack of thiols from the previously reported planar chiral ortho-substituted arene complexes and furnishes allenyl thioethers 5. This peculiar behavior can be rationalized assuming a subsequent base catalyzed propargyl–allenyl isomerization in acidic medium (!). An X-ray structure analysis of allenyl thioether 5c recrystallized from acetonitrile over weeks reveals that the [2+2] cyclodimer 10 has been formed. Thiolate adds to 5c to give a single diastereomer of the allyl compound 15 in good yield.     

Cyclization and Isomerization Reactionsin Silylhydrazine Chemistry

Summary.  This review describes the synthesis and isomerization reactions of cyclic silylhydrazines. Topics of discussion are the ring expansion of the three-membered Si(SiN₂) to the four-membered (SiN)₂ ring by lithiation of the (SiN₂) ring and by thermal silyl group insertion into the N*N bond, the ring expansion of a three-membered (SiN₂) to a five-membered (CSi₂N₂) ring by SiCH₂ insertion into the Si*N bond, the formation of isomeric four- and six-membered (SiN₂)₂ rings, the synthesis of five- and six-membered silylhydrazine rings, and the expansion of a five-membered (N₂Si₂N)N ring to the isomeric six-membered (SiNN)₂ ring. The mechanisms of the isomerizations are explained by quantum chemical calculations, and the results are verified by crystal structure determinations. Received February 23, 2001. Accepted (revised) April 24, 2001     

S-烷基-O-多氯苯基硫代磷(膦)酸衍生物的合成及杀菌活性研究

O,O-二烷基硫代磷(膦)酸酯与三氯氧磷发生异构化氯化反应生成S-烷基硫代磷(膦)酰氯,后者在缚酸剂存在下与多氯酚反应得到标题化合物。此类化合物也可以用传统方法,从S-烷基硫代磷酰二氯先后与多氯酚及其它亲核试剂反应得到。对所合成的28个新化合物的平碟试验表明,在0.005%浓度下对小麦赤霉等12种植物病菌均表现了明显的抑制活性。     

Large variations in acidity of terminal amide bonds in histamine-containing peptides as measured by proton DNMR

The main objective of these studies is to quantitatively estimate pK variations of individual amide bonds as a function of the ionization state of end groups in peptides, determined on measuring macro- and micro- (if any) ionization constants. ¹H NMR spectra of aqueous solutions of eight model substrates were consequently recorded using a water suppression sequence, within large pH ranges. A set of programs was devised to treat NMR data over the entirety of pH-dependent NMR patterns, in order to smooth out errors arising in handling individual spectra. Rates of amide proton abstraction by hydroxide ions were obtained from the coalescence of methylene coupled protons and the decrease of NH bond signal intensities, allowing us to estimate and discuss peptide pKs on assuming back reprotonation at a diffusion-limited rate. Cis–trans isomerization rates in two substrates bearing a tert-Butyloxycarbonyl terminal group were put in parallel with the acidity of carbamic protons.     

Monte-Carlo simulations of rotating clusters

A new scheme for estimating densities of states at non zero angular momentum is proposed, using the Monte-Carlo (MC) and multiple histogram methods. It is based on a rigorous expression of the classical density of states for a rotating system. Two features appear: the centrifugal energy ( angular momentum and I the instantaneous inertia tensor in the center of mass reference frame) is added to the potential energy and the configurational densities of states is weighted by . Comparing the MC results for the 13-atom Lennard-Jones cluster and a calculation based on molecular dynamics (MD) shows that this weight is important if the rotation induces a structural change at a finite temperature. The MC algorithm proves to be much more efficient than MD, even at finite . Received: 27 January 1998 / Received in final form: 15 June 1998 / Accepted: 18 June 1998     

水溶性钌膦配合物催化1-己烯异构化反应的研究

配位催化有催化剂和产物不易分离、溶剂污染环境等问题．而使用水溶性催化体系是克服这些缺点的有效方法之一，并且催化剂还可以循环使用．1984年德国鲁尔化学工业公司用水溶性铑-膦配合物为催化丙烯氢甲酰化生产取得了成功．在众多的水溶性配体中，三-间磺酸钠-三苯基膦[trisodi-     

A Study of the Cis-Trans Isomerization of a Square Planar pt Ylide Complex

The isomerization of cis-Pt(PPh₃)₂(I)(CH₂P(O)(OCH₃)₂), 1 , was studied by an NMR technique. An Arrhenius plot for the isomerization gives an activation energy of 99.2 KJ/mol, ΔH^≠ = 97 KJ/mol and ΔS^≠ = ?8.3 J/mol-K. Under a CO atmosphere the cis isomer catalytically isomerized to its trans form. Free PPh₃ did not catalyze the cis-trans isomerization. In the proposed isomerization mechanism the reaction goes through an intramolecular assisted phosphine dissociation, followed by dimer formation. The addition of phosphine to the dimer then completes the isomerization of the original monomer from cis to trans.