Dramatic Conformer-Dependent Reactivity of the Acetaldehyde Oxide Criegee Intermediate with Dimethylamine Via a 1,2-Insertion Mechanism

Abstract

The reactivity of carbonyl oxides has previously been shown to exhibit strong conformer and substituent dependencies. Through a combination of synchrotron-multiplexed photoionization mass spectrometry experiments (298 K and 4 Torr) and high-level theory [CCSD(T)-F12/cc-pVTZ-F12// B2PLYP-D3/cc-pVTZ with an added CCSDT(Q) correction], we explore the conformer dependence of the reaction of acetaldehyde oxide (CH 3 CHOO) with dimethylamine (DMA). The experimental data support the theoretically predicted 1,2insertion mechanism and the formation of an amine-functionalized hydroperoxide reaction product. Tunable-vacuum ultraviolet photoionization probing of anti-or anti-+ syn-CH 3 CHOO reveals a strong conformer dependence of the title reaction. The rate coefficient of DMA with anti-CH 3 CHOO is predicted to exceed that for the reaction with syn-CH 3 CHOO by a factor of ∼34,000, which is attributed to submerged barrier (syn) versus barrierless (anti) mechanisms for energetically downhill reactions.

Quantitative kinetics for the atmospheric reactions of Criegee intermediates with acetonitrile

“…The contribution (0.58 kcal mol −1 ) of post-CCSD(T) calculations for TS1 is close to our previous estimation of around 0.5 kcal mol −1 . 39,47,74…”

“…Previous investigations have shown that post-CCSD(T) calculations are necessary for reliable results because of the strong multireference characters of Criegee intermediates. 39,47,49,50,53,[70][71][72][73][74][75] We consider the contribution of post-CCSD(T) calculations in the reaction of CH 2 OO + CH 3 CN. The contribution of post-CCSD(T) calculations from the difference between W3X-L and W2X is calculated to be 0.58 kcal mol À1 and 1.30 kcal mol À1 for TS1 and M1, respectively (see Table 1).…”

“…The contribution (0.58 kcal mol À1 ) of post-CCSD(T) calculations for TS1 is close to our previous estimation of around 0.5 kcal mol À1 . 39,47,74 The calculated enthalpy of activation at 0 K for the reaction of CH 2 OO + CH 3 CN is À0.36 kcal mol À1 by our best estimate, which is slightly lower than that of the reaction of CH 2 OO + NH 3 /H 2 S. 39 The relative enthalpies of activation at 0 K determined by CCSD(T)-F12a/cc-pVTZ-F12 agree well with the values determined using W2X//CCSD(T)-F12a/cc-pVTZ-F12, as shown in Table 1, which shows that CCSD(T)-F12a/cc-pVTZ-F12 can reach the accuracy of CCSD(T)/CBS. In particular, the MUD of M06CR/MG3S is 0.64 kcal mol À1 , which is slightly smaller than that (0.70 kcal mol À1 ) of W2X//CCSD(T)-F12a/cc-pVTZ-F12.…”

Infrared Characterization of the Products of the Reaction between the Criegee Intermediate CH3CHOO and HCl

“…The estimated rate coefficient is about 17 times the value k HCl syn = (4.77 ± 0.95) × 10 −11 cm 3 molecule −1 s −1 reported by Liu et al for syn-CH 3 CHOO + HCl. 48 The RPS of CH 3 CHOO + HCl is similar to that of CH 3 CHOO + dimethylamine (DMA) 41 formation of a pre-reactive complex and a submerged transition structure for the 1,2-insertion. For the reactions with DMA, Vansco et al predicted rate coefficients of 2.4 × 10 −14 and 8.0 × 10 −10 cm 3 molecule −1 s −1 for syn-CH 3 CHOO and anti-CH 3 CHOO, respectively.…”

“…Similarly, anti-CH 3 CHOO also showed much greater rate coefficients toward reactions with CH 3 OH, 35−38 amino alcohol, 39,40 and dimethylamine (DMA). 41 Hydrogen chloride (HCl) has both biogenic and anthropogenic sources in the atmosphere; its average mixing ratio in the polluted urban atmosphere is (0.53−2.7) ppbv (part per billion by volume) in southern California. 42 The rate coefficient for the reaction CH 2 OO + HCl was reported to be (4.6−4.8) × 10 −11 cm 3 molecule −1 s −1 ; 43,44 the effective first-order rate coefficient 0.6−3.0 s −1 is comparable to that (∼2.4 s −1 ) of CH 2 OO + organic acids, 20 indicating the potential importance of the reaction CH 2 OO + HCl in atmospheric chemistry.…”