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[3+2] Cycloadditions of nitrones as three-atom components to alkenes yield isoxazolidine cycloadducts, which on chemical transformations can be converted to bioactive compounds. The [3+2] cycloadditions route thus provides conversion of simple natural products to more complex naturally occurring bioactive nitrogen heterocycles, and close analogues. As α,β-unsaturated amides abundantly occur as natural products, [3+2] cycloadditions of nitrones with simpler α,β-unsaturated amides were studied to get information about reactivity profiles. The reactions of C-(4-chlorophenyl)-N-methyl nitrone as three-atom component to cinnamic acid anilides were investigated. The 3,4-trans-4,5-trans-4- carboxanilido-2-methyl-3,5-diaryl isoxazolidines were the major cycloadducts; the diastereoisomeric 3,4-cis-4,5-trans-4-carboxanilido-2-methyl-3,5-diaryl isoxazolidines and regioisomeric 3,4-trans-4,5- trans-5-carboxanilido-2-methyl-3,4-diaryl isoxazolidines were obtained as minor cycloadducts. The cycloadducts were characterized by NMR studies and XRD analysis.

Investigations of [3+2] cycloadditions of C,N-diaryl and C-aryl-N-methyl nitrones as three atom components (TAC) to substituted methyl E-cinnamates and diethyl arylidene malonates have been further investigated. [3+2] Cycloadditions of cinnamates yielded mixtures of cycloadducts, the major products being the 3,4-trans-4,5-trans-2,3,5-triaryl-4-carbomethoxy products originating from the endo-carbonyl-exo-aryl meta channel approach of the cinnamate component. [3+2] Cycloadditions to diethyl arylidene malonates furnished single cycloadducts-3,5-trans-2-methyl-3,5-diaryl-4,4- dicarbethoxy isoxazolidines by a endo-aryl meta channel approach of the 2π-component.

Trifluoroacetic acid (TFA) is released in the atmosphere through its use in the chemical industry and as degradation product of chlorofluorocarbon (CFC) alternatives like hydrofluorocarbons and hydrochlorofluorocarbons. In the present study, we have investigated the OH formation dynamics in the photodissociation of TFA at 193 nm by Laser Photolysis-Laser Induced Fluorescence (LP-LIF) method, as well as stable product formation by GC MS and FTIR. It was found that, ∼26% of the available energy is partitioned into the relative translation of the photoproducts (f(T) = 0.26), which could be explained by presence of an exit barrier of ∼13 kcal/mol in OH formation channel. This result is very similar to OH formation from acetic acid (AA) and difluoroacetic acid (DFA), indicating fluorination at the side chain of aliphatic carboxylic acids does not significantly change the mechanism of C OH bond scission. Our experimental results tallied with the theoretical studies, which suggested that the major OH formation channel in acetic acid and fluoroacetic acid is direct dissociation from the optically excited S1 state through an exit barrier, with some competition from the T1 state. However, quantum yield of OH formation from TFA (0.4) was found to be much smaller than AA (0.8), which is probably caused by higher reaction barrier in T1 state of TFA, compared to AA. CHF3, C2F4, C2F6, CO2, CO, CF3CFO, CF2O and hexafluoropropylene oxide (HFPO) were detected as the stable products of the photolysis of TFA. The theoretically optimized ground state dissociation channels showed significant difference between TFA and AA.

The rate coefficient for the gas phase reaction of the OH radical with 1,2-propylene oxide (PPO) has been measured at 298 K using a relative rate method, employing Gas Chromatography (GC) technique, using ethane and 1,2-dichloroethane as reference compounds. Temperature dependence of the above reaction is also studied using an absolute rate method, employing Laser Photolysis-Laser Induced Fluorescence (LP-LIF) technique, over a range of 261–335 K. The measured bimolecular rate coefficients were fitted into the Arrhenius plot, which yielded a straight line roughly parallel to the x-axis and implies no or very weak temperature dependence. Within the experimental error limits, rate coefficients obtained at various temperatures, are found to vary within a narrow range from (4.65 ± 0.24) × 10−13 to (4.80 ± 0.24) × 10−13 cm3 molecule−1 s−1. Room temperature rate coefficient of the reaction of PPO with the OH radical was found to be (4.65 ± 0.24) × 10−13 cm3 molecule−1 s−1, using LP-LIF technique. These results have been discussed with available literature to unveil the probable mechanism. An average tropospheric lifetime of PPO has been estimated to be about two weeks for degradation by the OH radical. In addition, atmospheric parameters such as Radiative Efficiency (RE) and Global Warming Potential (GWP) for PPO are determined. Stable products formed are characterized using GC-MS and FT-IR techniques. Theoretical calculations are performed to understand the energetics and mechanism of H atom abstraction by OH, and also to complement the experimental observations.

The photodissociation dynamics of benzoyl chloride at 235 nm has been investigated and compared with that of 2-furoyl chloride. Atomic Cl and molecular HCl channels have been detected in benzoyl chloride by employing resonance-enhanced multiphoton ionization technique and time-of-flight mass spectrometry. Both the Cl fragments, Cl((2)PJ=3/2, relative quantum yield 0.70 ± 0.15) and Cl*((2)PJ=1/2), show isotropic angular distribution and bimodal translational energy distributions. The predominant high kinetic energy channel contributes 72% to the C-Cl bond scission and arises from the S1 state having nπ* character of benzoyl chloride. However, the low-energy Cl and HCl channels originate from the ground electronic state. The most plausible mechanism of HCl formation is proposed based on molecular orbital calculations. In contrast to benzoyl chloride, the HCl channel is not observed in 2-furoyl chloride on excitation at 235 nm, and this is attributed to an energy constraint.

The rate coefficients for the reactions of OH radicals with three fluoroalcohols, CF 3 CH 2 OH ( k 1 ), CF 3 CF 2 CF 2 CH 2 OH ( k 2 ), and CHF 2 CF 2 CH 2 OH ( k 3 ), have been measured in the temperature range of 298–363 K, at a total pressure of ∼55 torr, using LP-LIF method. The kinetic parameters measured for CF 3 CH 2 OH, which is well studied, matches with the previous reports within error limits. The rate expression for k 2 is (1.54 ± 0.80) × 10 −12 exp (−765 ± 170)/ T ), and for k 3 is (1.12 ± 0.26) × 10 −12 exp (−560 ± 80)/ T ). Based on the above values of the rate coefficients, the tropospheric lifetimes with respect to removal by reaction with OH have been estimated to be 0.38 and 0.26 years for CF 3 CF 2 CF 2 CH 2 OH and CHF 2 CF 2 CH 2 OH respectively, supporting their potential use as HFC alternatives. The results are discussed along with the literature data on other fluoroalcohols. The present study is aimed to assess the effect of additional CF 2 groups and H atoms on tropospheric lifetime and global warming potential of fluoroalcohols. The results confirm that the rate coefficients at room temperature and activation energy parameters are independent of n, for the reaction of OH with fluoroalcohols of general formula CF 3 (CF 2 ) n CH 2 OH, which are potential CFC/HFC alternatives.

Kinetics of reaction of OH radical with morpholine, a heterocyclic molecule with both oxygen and nitrogen atoms, has been investigated using laser photolysis-laser-induced fluorescence technique, in the temperature range of 298-363 K. The rate constant at room temperature (k(298)) is (8.0 +/- 0.1) x 10(-11) molecule(-1) cm(3) s(-1). The rate constant decreases with temperature in the range studied, with the approximate dependence given by k(T) = (1.1 +/- 0.1) x 10(-11) exp[(590 +/- 20)/T] cm(3) molecule(-1) s(-1). The rate constants are high compared with those of similar heterocyclic molecules with oxygen atom but comparable to those reported for aliphatic amines. Ab initio molecular orbital calculations show that prereactive complexes, 5-7 kcal mol(-1) lower in energy as compared with the reactants, are formed because of hydrogen bond interaction between OH and the N/O atom of morpholine. The stability of the complex involving the nitrogen atom is found to be more than that involving the oxygen atom. The optimized transition-state structures and energies for the different pathways of hydrogen abstraction from these prereactive complexes explain the observation of negative activation energy.

Dynamics of formation of electronically excited NO2 and formation of OH fragment, during photo dissociation of 2-nitropropane (NP) and 2-methyl-2-nitropropane (MNP), were investigated at 193 and 248 nm. The radiative lifetime of the electronically excited NO2 fragment, observed at 193 nm, was measured to be 1.2 ( 0.1 micros and the rate coefficient of quenching of its emission by MNP was measured as (2.7 ( 0.1) x 10(-10) molecule(-1) cm3 s(-1). Formation of the ground electronic state of OH was confirmed in both molecules. State selective laser induced fluorescence technique was used to detect the nascent OH (X 2Pi, v'', J'') fragments in different ro-vibrational states, and to obtain information on energy partitioning. Though MNP and NP differ in the types of the available H atoms, the dynamics of OH formation is found to be the same in both. The relative population in different rotational states does not follow Boltzmann equilibrium distribution in both the molecules at 193 and 248 nm. The translational energies of the OH fragments, calculated from the Doppler width, are 21.2 ( 7.2 and 25.0 ( 2.5 kcal mol-1 for NP at 248 and 193 nm, respectively. The translational energies of the OH fragments, in the case of MNP, are found to be lower, 17.5 ( 4.1 and 22.0 ( 3.2 kcal mol-1,respectively, at 248 nm 193 nm. These results are compared with the earlier reports on photodissociation of nitromethane (NM), nitroethane (NE), and other nitroalkanes. All possible dissociation pathways of these molecules--NM, NE, NP, and MNPs leading to the formation of the OH fragment were investigated computationally, with geometry optimization at the B3LYP/6-311+G(d,p) level and energy calculation at the MP4(SDQ)/6-311+G (d,p) level. The results suggest that in NM, OH is formed after isomerization to CH2N(OH)O, whereas in all other cases OH is formed from HONO, a primary product of molecular elimination of nitroalkanes, formed with sufficient internal energy.

on in urticaria pigmentosa are discussed.