Theoretical Study of the NH2+ C2H2Reaction

Theoretical Study of the Kinetics of the Gas-Phase Reaction between Phenyl and Amino Radicals

The potential energy surface (PES) of the C₆H₅ + NH₂ reaction has been investigated by using ab initio CCSD(T)//B3LYP/6-311++G(3df,2p) calculations. The conventional transition-state theory (TST) and the variable reaction coordinate-TST (VRC-TST) have been used to predict the rate constants for the channels possessing tight and barrierless transition states, respectively. The Rice-Ramsperger-Kassel-Marcus/Master equation (RRKM/ME) theory has been utilized to determine the pressure-dependent rate constants for these reactions. The PES shows that the reaction begins with an exothermic barrierless addition of NH₂ to C₆H₅ producing the vital intermediate state, namely, aniline (C₆H₅NH₂, IS1). Once IS1 is generated, it can further isomerize to various intermediate states, which can give rise to different products, including PR4 (4,5,6-trihydro-1-amino phenyl + H₂), PR5 (3,4,5,6-tetrahydro phenyl + NH₃), PR6 (2,3,5,6-tetrahydro-1-imidogen phenyl + H₂), PR9 (3,4,5,6-tetrahydro-1-imidogen phenyl + H₂), and PR10 (2,5,6-trihydro-1-amino phenyl + H₂), of which the most stable product, PR5, was formed by the most favorable channel going through the two advantageous transition states T1/11 (-28.9 kcal/mol) and T11P5 (-21.5 kcal/mol). The calculated rate constants for the low-energy channel, 1.37 × 10^-9 and 2.16 × 10^-11 cm³ molecule^-1 s^-1 at T = 300, P = 1 Torr and T = 2000 K, P = 760 Torr, respectively, show that the title reaction is almost pressure- and temperature-dependent. The negative temperature-dependent rate coefficients can be expressed in the modified Arrhenius form of k ₁ = 8.54 × 10¹³ T ^-7.20 exp (-7.07 kcal·mol^-1/RT) and k ₂ = 2.42 × 10¹⁵ T ^-7.61 exp (-7.75 kcal·mol^-1/RT) at 1 and 10 Torr, respectively, and in the temperature range of 300-2000 K. The forward and reverse rate coefficients as well as the high-pressure equilibrium constants of the C₆H₅ + NH₂ ↔ IS1 process were also predicted; their values revealed that its kinetics do not depend on pressure at low temperature but strongly depend on pressure at high temperature. Moreover, the predicted formation enthalpies of reactants and the enthalpy changes of some channels are in good agreement with the experimental results.

Ab initio kinetics of the C2H2 + NH2 reaction: a revisited study

This work provides a rigorous detailed kinetic study on the C₂H₂ + NH₂ reaction in a wide range of conditions (T = 250-2000 K & P = 1-76000 Torr). In particular, the composite method W1U was used to construct the potential energy surface on which the kinetic behaviors were characterized within the state-of-the-art master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) framework. Corrections of the hindered internal rotation (HIR) treatment and quantum tunneling effect were included. A clear reaction mechanism shift with respect to both temperature and pressure was revealed via detailed kinetic and species analyses. In particular, bimolecular products (i.e., CH₂[double bond, length as m-dash]C[double bond, length as m-dash]NH + H, CH[triple bond, length as m-dash]CNH₂ + H, CH₃CN + H, CH[triple bond, length as m-dash]C· + NH₃ in the decreasing mole fraction order) can be formed directly from the reactants at high temperature and/or low pressure while they can be produced indirectly via intermediates (e.g., ·CH[double bond, length as m-dash]CHNH₂(cis), ·CH[double bond, length as m-dash]CHNH₂(trans), CH₂[double bond, length as m-dash]C·NH₂,…) at low temperature and/or high pressure. The calculated rate constants are in good agreement with the literature data from ab initio calculations without any adjustment; thus, the proposed temperature- and pressure-dependent rate constants, together with the thermodynamic data of the species involved, can be confidently used for modeling NH₂-related systems under atmospheric and combustion conditions.

On the abundance of non-cometary HCN on Jupiter

Using one-dimensional thermochemical/photochemical kinetics and transport models, we examine the chemistry of nitrogen-bearing species in the Jovian troposphere in an attempt to explain the low observational upper limit for HCN. We track the dominant mechanisms for interconversion of N2-NH3 and HCN-NH3 in the deep, high-temperature troposphere and predict the rate-limiting step for the quenching of HCN at cooler tropospheric altitudes. Consistent with some other investigations that were based solely on time-scale arguments, our models suggest that transport-induced quenching of thermochemically derived HCN leads to very small predicted mole fractions of hydrogen cyanide in Jupiter's upper troposphere. By the same token, photochemical production of HCN is ineffective in Jupiter's troposphere: CH4-NH3 coupling is inhibited by the physical separation of the CH4 photolysis region in the upper stratosphere from the NH3 photolysis and condensation region in the troposphere, and C2H2-NH3 coupling is inhibited by the low tropospheric abundance of C2H2. The upper limits from infrared and submillimetre observations can be used to place constraints on the production of HCN and other species from lightning and thundershock sources.

Prognostic factors associated with resectable carcinoma of the esophagus

A retrospective review of esophagectomy for esophageal carcinoma between 1982 and 1999 was performed. Two hundred twenty-two patients (mean age 61.7 years) underwent esophagectomy: 128 transhiatal, 74 Ivor Lewis, and 20 abdominal. Most tumors were adenocarcinoma (65%); the majority were in the lower third or cardia (78%). Excluding operative mortality the one-, 3-, and 5-year survival rates were 67, 39, and 31 per cent (median survival, 16.3 months) respectively. The hospital mortality rate was 6.8 per cent. Through univariate analysis race other than white, history of weight loss, poor or moderate differentiation (P = 0.05), full-thickness invasion (P = 0.02), positive lymph nodes (P < 0.01), Ivor Lewis esophagectomy (P = 0.02), intraoperative blood transfusion (P = 0.01), and tumor location in the upper or middle third in node-positive patients (P = 0.02) were associated with a poorer survival. Adjuvant therapy improved survival for patients with positive lymph nodes (P < 0.01). In multivariate analysis positive lymph nodes, tumor location, intraoperative blood transfusion, and adjuvant therapy were independent predictors of survival. To optimize survival esophagectomy for esophageal carcinoma should be performed without blood transfusion, and node-positive patients should receive multimodal therapy.