CHF(X 1 A′) radical kinetics. Part 1.—Reaction with NO and O 2

The radical-molecule reaction mechanism of CH3 with NOx (x = 1, 2) has been explored theoretically at the B3LYP/6-311Gd,p and MC-QCISD (single-point) levels of theory. For the singlet potential energy surface (PES) of the CH3 + NO2 reaction, it is found that the carbon to middle nitrogen attack between CH3 and NO2 can form energy-rich adduct a (H3CNO2) with no barrier followed by isomerization to b1 (CH3ONO-trans), which can easily convert to b2 (CH3ONO-cis). Subsequently, starting from b (b1, b2), the most feasible pathway is the direct N-O bond cleavage of b (b1, b2) leading to P1 (CH3O + NO) or the 1,3-H-shift and N-O bond rupture of b1 to form P2 (CH2O + HNO), both of which may have comparable contribution to the reaction CH3 + NO2. Much less competitively, b2 can take a concerted H-shift and N-O bond cleavage to form product P3 (CH2O + HON). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CH3 + NO2 reaction is expected to be rapid, as is consistent with the experimental measurement in quality. For the singlet PES of the CH3 + NO reaction, the major product is found to be P1 (HCN + H2O), whereas the minor products are P2 (HNCO + H2) and P3 (HNC +H2O). The CH3 + NO reaction is predicted to be only of significance at high temperatures because the transition states involved in the most feasible pathways lie almost above the reactants. Compared with the singlet pathways, the triplet pathways may have less contributions to both reactions. The present study may be helpful for further experimental investigation of the title reactions.

Section: The Singlet Potential Energy Surfacementioning

confidence: 97%

Section: The Singlet Potential Energy Surfacementioning

confidence: 99%

Theoretical study on the reaction mechanism of the methyl radical with nitrogen oxides

Zhang

Liu

et al. 2005

“…The pathway is associated with the direct Cl-extrusion of the HClCNO isomer a 2 via TSa 2 P 9 , which is 25.4 kcal/mol lower than the reactants R. Path P13 (I) R 3 a1 (a2) 3 d 3 f1 3 g1 3 Now we consider the products P 4 CO ϩ NClH (Ϫ71.1 kcal/mol), P 5 OH ϩ ClCN (Ϫ54.6 kcal/mol), P 8 HCl ϩ CNO (Ϫ27.5 kcal/mol), P 10 ClO ϩ HNC (Ϫ17.4 kcal/mol), P 11 3 NH ϩ ClCO (Ϫ19.5 kcal/mol), P 12 HCl ϩ c-CNO (Ϫ13.9 kcal/mol), P 15 CN ϩ HOCl (Ϫ4.8 kcal/mol), P 16 H ϩ ClOCN (0.8 kcal/mol), and P 17 H ϩ ClCNO (7.4 kcal/mol). Except for P 16 and P 17 , the products are lower in energy than the reactants and are thus thermodynamically accessible.…”

Section: P 9 CL ϩ Hcnomentioning

confidence: 99%

“…13 Also, the 1 CHCl ϩ NO reaction is roughly twice as fast as the 1 CHF ϩ NO reaction [(7.0 Ϯ 0.4) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 ]. 10 Thus, the title reaction may be very effective in NO-reduction in atmospheric and combustion chemistry and may thus be considered as an important process, referred to as "reburning." NCO (60%) and F ϩ HNCO (40%), 11 suggesting further experimental studies are necessary.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study on the mechanism of the ¹CHCl + NO reaction

Liu¹,

Ye²,

Tao³

et al. 2002

The complex doublet potential energy surface of the CHClNO system, including 31 minimum isomers and 84 transition states, is investigated at the QCISD(T)/6-311G(d, p)//B3LYP/6-31G(d, p) level in order to explore the possible reaction mechanism of the singlet CHCl with NO. Various possible isomerization and dissociation channels are probed. The initial association between 1CHCl and NO at the terminal N-site can almost barrierlessly lead to the chainlike adducts HClCNO a (a1, a2) followed by the direct Cl-extrusion to product P9 Cl + HCNO, which is the most feasible channel. Much less competitively, a (a1, a2) undergoes a ring-closure leading to the cyclic isomer c-C(HCl)NO d followed by a concerted Cl-shift and N-O cleavage of d to form the branched isomers ClNC(H)O f (f1, f2). Eventually, f (f1, f2) may take a direct H-extrusion to produce P7 H + ClNCO or a concerted 1,2-H-shift and Cl-extrusion to form P1 Cl + HNCO. The low-lying products P2 HCl + NCO, P3 Cl + HOCN, P14 HCO + 3NCl, P6 ClO + HCN, and P13 ClNC + OH may have the lowest yields observed. Our calculations show that the product distributions of the title reaction are quite different from those of the analogous 1CHF + NO reaction, yet are similar to those of another analogous 3CH2 + NO reaction. The similarities and discrepancies among the three reactions are discussed in terms of the substitution effect. The present article may assist in future experimental identification of the product distributions for the title reaction and may be helpful for understanding the halogenated carbene chemistry.

“…[13][14][15][16][17][18] Reliable information on the kinetics of these reactions is of importance for the modeling of combustion processes. Some of the reactions such as CH ϩ NO, 19,20 CH ϩ NO 2 , 14,21,22 CHF ϩ NO, 11,23 and CHCl ϩ NO 2 13,24 have already been the subject of experimental and theoretical investigations. The kinetics of the reaction 1 CHF with NO 2 , which is considered as an important "reburning" process of the NO 2 pollutant, has been studied by Cookson et al 7 The measured rate constant was (7.0 Ϯ 0.4) ϫ 10 Ϫ12 cm 3 mol Ϫ1 s Ϫ1 at 295 K. However, Cookson et al did not further provide the available information on product channels, product identification, and product distributions, although this information may be important in the NO 2 -involved sequential chain processes.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study on reaction mechanism of the fluoromethylene radical with nitrogen dioxide

Zhang

Liu

et al. 2004

The complex doublet potential energy surface for the reaction of 1CHF with NO2, including 14 minimum isomers and 30 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and CCSD(T)/6-311G(d,p) (single-point) levels of theory. The initial association between 1CHF and NO2 is found to be the carbon-to-middle-nitrogen attack forming an energy-rich adduct a (HFCNO2) with no barrier, followed by concerted O-shift and C--N bond rupture leading to product P2 (NO + HFCO), which is the most abundant. In addition, a can take a 1,3-H-shift to isomer b (FCN(O)OH) followed by the dissociation to form the second feasible product P4 (OH + FCNO). The least favorable pathway is that b undergoes a concerted OH-shift to form d (HO(F)CNO), which will dissociate to product P5 (HF+OCNO) via side HF-elimination. The secondary dissociation of P5 may form product P7 (HF+NO+CO) easily. Furthermore, the 1CHF attack at the end-O of NO2 is a barrier-consumed process, and thus may only be of significance at high temperatures. The comparison with the analogous reactions 1CHCl + NO2 is discussed. The present study may be helpful for probing the mechanism of the title reaction and understanding the halogenated carbine chemistry.