Criegee中间体RCHOO(R=H,CH_3)与NCO的反应机理

Theoretical Studies on the Reaction Mechanism of Criegee Intermediates RCHOO( R=H,CH_3) with NCO Radical

采用CCSD(T)/aug-cc-p VTZ//B3LYP/6-311+G(2df,2p)方法对Criegee中间体RCHOO(R=H,CH_3)与NCO反应的机理进行了研究,利用经典过渡态理论(TST)并结合Eckart校正模型计算了标题反应在298~500 K范围内优势通道的速率常数.结果表明,上述反应包含亲核加成、氧化和抽氢3类机理,其中每类又包括NCO中N和O分别进攻的两种形式.亲核加成反应中O端进攻为优势通道,氧化和抽氢反应则是N端进攻为优势通道;甲基取代使CH_3CHOO反应活性高于CH2OO;anti-CH_3CHOO的加成及氧化反应活性高于syn-CH_3CHOO,而抽氢反应则是syn-CH_3CHOO的活性高于anti-CH_3CHOO.anti-构象对总速率常数的贡献大于syn-构象,且总速率常数具有显著的负温度效应.

A comprehensive theoretical study about the reaction of RCHOO（ R = H,CH3） with NCO was performed at the CCSD（ T）/aug-cc-p VTZ//B3LYP/6-311 ＋ G（ 2df,2p） level. The rate coefficients for the dominant reaction channels were determined at 298—500 K via conventional transition state theory（ TST） with a Eckart tunneling. The results show that the detailed mechanism mainly includes addition,oxidation and hydrogen abstraction reactions. N and O atoms of the NCO radical can react to RCHOO（ R = H and CH3） in each reaction mode. Moreover,the end O atom of NCO addition to RCHOO（ R = H and CH3） α-C is favored for the addition reaction,while the reactions involving the end N atom of NCO is advantaged in both oxidation and hydrogen abstraction. The methyl substituents in the CH2 OO produce an increase of the reactivity.Anti-CH3CHOO shows a higher reactivity than syn-CH3CHOO towards addition and oxidation reaction,but for the hydrogen abstraction,syn-CH3CHOO is significantly more reactive than anti-CH3CHOO. The contribution of anti-CH3CHOO to the overall rate constant is greater than that of syn-CH3CHOO,and the total rate constant satisfies a strong negative temperature effect.