双取代铵氧化物(R_2HNO)与双取代羟胺(R_2NOH)的相互转换机制的量子化学研究

A Quantum Chemical Study on the Interconversion Mechanism between Double-substituted Ammonium Oxide and Double-substituted Hydroxylamine

在B3LYP/6-311++G(d,p)水平下,首次对一系列双取代铵氧化物(R2HNO)与双取代羟胺(R2NOH)[R=CH3,NH2,OH,F,CH2CH3,CH(CH3)2,C(CH3)3]同分异构体的相互转换机制进行了理论计算研究,并与已知的H3NO和H2NOH进行了比较.结果表明,相对于双取代羟胺(R2NOH),按照H<CH3<NH2<OH<F的顺序,增加取代基R的电负性有助于提高双取代铵氧化物(R2HNO)的热力学和动力学稳定性.此外,对烷基取代基R[R=CH3,CH2CH3,CH(CH3)2,C(CH3)3],其空间位阻越大越能增加双取代铵氧化物(R2HNO)的热力学稳定性,动力学稳定性也有相应增加,但不显著.对所研究的7种取代基[R=CH3,NH2,OH,F,CH2CH3,CH(CH3)2,C(CH3)3],R2HNO向R2NOH转换的能垒介于27.0～56.3 kcal/mol之间,表明在气相条件下极有可能观测到双取代铵氧化物(R2HNO).

At the B3LYP/6-311 ＋ ＋ G（d,p） level, the first time computational study was performed on the interconversion mechanism between a series of double-substituted ammonium oxide （R2HNO） and double-substituted hydroxylamine （R2NOH） isomers with R=CH3, NH2, OH, F, CH2CH3, CH（CH3）2 and C（CH3）3. Comparisons were made with the mechanism of H3NO and H2NOH. It was shown that relative to the double-substitued hydroxylamine （R2NOH）, the increase of/he electronegativity of R in the order of H〈 CH3〈NH2〈OH〈F could raise both the thermodynamic and kinetic stability of the double-substituted ammonium oxide （R2HNO）. In addition, for the alkyl substituents R [R=CH3, CH2CH3, CH（CH3）2 and C（CH3）3], the greater steric effect would result in the higher thermodynamic stability, and also certainly increased kinetic stability, though not so noticeable. For the newly considered seven substituents [R=CH3, NH2, OH, F, CH2CH3, CH（CH3）2 and C（CH3）3], the conversion barrier from R2HNO to R2NOH is as large as 27.0-56.3 kcal/mol. This indicates that all of them might be probably characterized in gas-phase.