Makroni Lily

Theoretical investigation of atmospheric chemistry of volatile anaesthetic sevoflurane: reactions with the OH radicals and atmospheric fate of the alkoxy radical (CF3)2CHOCHFO: thermal decomposition vs. oxidation†

A theoretical study on the mechanism and kinetics of the gas phase reactions of a volatile anaesthetic compound (CF3)2CHOCH2F (Sevoflurane) with the OH radicals has been carried out using the hybrid HF–density functional M06-2X/6-31+G(d,p) method. Three conformations are predicted for the Sevoflurane molecule. Among the three conformers, the most stable one is considered for a detailed study. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Single point energy calculations have been performed by using the 6-311++G(d,p) basis set. The hydrogen abstraction from the –CH2F group is found to be the dominant reaction channel for hydrogen abstraction by OH radicals. Theoretically the calculated rate constant is found to be in good agreement with the experimentally measured ones. Using group-balanced isodesmic reactions, the standard enthalpies of formation for (CF3)2CHOCH2F, (CF3)2COCH2F and (CF3)2CHOCHF radicals are also reported for the first time. The atmospheric fate of the alkoxy radical, (CF3)2CHOCHFO, is also investigated for the first time using the same level of theory. Out of four prominent plausible decomposition channels including oxidation, our results clearly point out that reaction with O2 is the dominant path for the decomposition of (CF3)2CHOCHFO in the atmosphere involving the lowest energy barrier which is in accord with recent experimental findings.

Synthetic, mechanistic and kinetic studies on the organo-nanocatalyzed synthesis of oxygen and nitrogen containing spiro compounds under ultrasonic conditions

A novel class of organo-nanocatalysts was fabricated by encapsulating magnetic Fe2O3@SiO2 nanoparticles with thiamine hydrochloride. Its catalytic application in the synthesis of oxygen and nitrogen containing spiro heterocycles via ultrasonication was thoroughly investigated. The synthetic protocol was found to be efficient, economical and green. The prepared catalyst was characterised by TEM, SEM, EDS, powder XRD, VSM, FT-IR, TGA, DTA, etc. Mechanistic and kinetic studies for the organic transformations were also carried out to determine the catalytic role of thiamine hydrochloride using a computational method viz. DFT: B3LYP.

Theoretical study of the O···Cl interaction in fluorinated dimethyl ethers complexed with a Cl atom: is it through a two-center-three-electron bond?

Theoretical investigations are carried out on the interaction between fluorinated dimethyl ethers (FDME, nF = 0-4) and the Cl atom. Short intermolecular O···Cl distances between 2.401 and 2.938 Å reveal the formation of a new class of complexes. The interaction energies calculated with the G2(MP2) method range between -9.1 (nF = 4) and -26.0 (nF = 0) kJ/mol. The charge transfer occurring from the ethers to atomic Cl is moderate and ranges between 0.012 e (nF = 4) to 0.188 e (nF = 0). The binding energies are linearly related to the proton affinity, to the charge transfer (CT) occurring in the molecular system and inversely proportional to the ionization potential and electron affinity (IP-EA) values. The CT and spin density data indicate substantial two-center-three-electron O···Cl interaction in CH3OCH3···Cl and CH3OCH2F···Cl systems, whereas for highly fluorinated ethers the interaction is predominantly electrostatic in nature. The formation of the complex results in a contraction of the CH bonds, especially in the gauche position. The blue shifts of the C-H stretching vibrations calculated in the partially deuterated isotopomers range between 2 and 54 cm(-1) and are correlated to the variation of the CH distances.

Theoretical investigation on gas-phase reaction of CF3CH2OCH3 with OH radicals and fate of alkoxy radicals (CF3CH(O•)OCH3/CF3CH2OCH2O•).

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF3CH2OCH3 (HFE-263fb2) with OH radicals using ab-initio and DFT methods. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels, respectively. Our calculations reveal that hydrogen abstraction from the CH2 group is thermodynamically and kinetically more facile than that from the CH3 group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CF3CH2OCH3 and radicals (CF3CHOCH3 and CF3CH2OCH2) are also reported for the first time. The calculated bond dissociation energies for the CH bonds are in good agreement with experimental results. At 298K, the calculated total rate coefficient for CF3CH2OCH3+OH reactions is found to be in good agreement with the experimental results. The atmospheric fate of the alkoxy radicals, CF3CH(O)OCH3 and CF3CH2OCH2O are also investigated for the first time using the same level of theory. Out of three plausible decomposition channels, our results clearly point out that reaction with O2 is not the dominant path leading to the formation of CF3C(O)OCH3 for the decomposition of CF3CH(O)OCH3 radical in the atmosphere. This is in accord with the recent report of Osterstrom et al. [CPL 524 (2012) 32] but found to be in contradiction with experimental finding of Oyaro et al. [JPCA 109 (2005) 337].

A theoretical insight into atmospheric chemistry of HFE-7100 and perfluoro-butyl formate: reactions with OH radicals and Cl atoms and the fate of alkoxy radicals

A mechanistic study on the hydrogen abstraction reaction of HFE-7100 (n-C4F9OCH3) with atmospheric oxidants has been carried out in the gas-phase by performing DFT-based M06-2X/6-31+G(d,p) calculations. We observe a complex mechanism due to the presence of the pre-reactive and post-reactive complexes at the entrance and exit channels, respectively. The standard enthalpies of formation for species and bond dissociation energy for C–H bonds are also reported. The rate expressions were determined for reaction channels in the broad temperature range of 250–1000 K. The rate coefficients over the studied temperature range yield the following Arrhenius expressions (cm3 molecule−1 s−1): kOH = 2.87 × 10−24·T3.66 exp(527/T) and kCl = 1.68 × 10−19·T2.71 exp(207/T). At 298 K, the results were found to agree comparatively well with modest differences in rates for reactions. Finally, the atmospheric lifetime and global warming potential of HFE-7100 are computed to be 2.12 years and 155.3, respectively. We also investigated the reactivity of the alkoxy radical (C4F9OCH2O˙), considering three decomposition channels including oxidative pathways. Based on thermochemical data, we can speculate that oxidative pathways are dominant for the decomposition of C4F9OCH2O˙ radicals, which is in concurrence with experimental observations. The radiative efficiency and global warming potential of fluoroesters (C4F9OC(O)H) are also calculated and compared with parent species.

Theoretical investigation on kinetics and thermochemistry of reaction of CHF2CF2OCH2CF3 with OH radicals and global warming potentials

Theoretical investigation has been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CHF2CF2OCH2CF3 and OH radical using a new hybrid density functional M06-2X/6-31+G(d,p) and G2(MP2)//M06-2X/6-31+G(d,p) methods. The most stable conformer of CHF2CF2OCH2CF3 is considered in our study and the possible H-abstraction reaction channels are identified. Each reaction channel shows an indirect H-abstraction reaction mechanism via the formation of pre-reactive complex. The rate coefficients are determined for the first time over a wide range of temperature 250–1000 K. At 298 K, the calculated total rate coefficient of kOH = 1.01×10−14 cm3 molecule−1 s−1 is in good agreement with the experimental results. The heats of formation for CHF2CF2OCH2CF3 and CF2CF2OCH2CF3 and CHF2CF2OCHCF3 radicals are estimated to be -1739.25, -1512.93 and -1523.94 kJ mol−1, respectively. The bond dissociation energies of the two C-H bonds are C(-H)F2CF2OCH2CF3: 423.34 kJ mol−1 and CHF2CF2OC(-H)HCF3: 411.87 kJ mol−1. The atmospheric lifetime of CHF2CF2OCH2CF3 is estimated to be around 4.5 years and the 100-year time horizon global warming potentials of CHF2CF2OCH2CF3 relative to CO2 is estimated to be 601.