THEORETICAL-MODEL FOR ELECTROPHILIC OXYGEN-ATOM INSERTION INTO HYDROCARBONS
THEORETICAL-MODEL FOR ELECTROPHILIC OXYGEN-ATOM INSERTION INTO HYDROCARBONS
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DOI：
10.1021/ja00066a049
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发表时间：
1993-06-30
影响因子：
15
通讯作者：
MCDOUALL, JJW
中科院分区：
文献类型：
--
作者：
BACH, RD;ANDRES, JL;MCDOUALL, JJW
描述了饱和烷烃氧化成相应的醇和酮的机理模型。采用水氧化物(H2O-O)作为模型单重态氧原子供体。用6-31G*基组在MP2、QCISD、QCISD(T)、CASSCF和MRCI理论水平上进行的分子轨道计算表明，水氧化物的氧插入是通过亲电氧原子与双占据的碳氢化合物碎片轨道相互作用进行的。亲电氧沿着包括pi(CH2)或pi(CHCH3)碎片轨道的碳原子p轨道的轴向接近碳氢化合物，以形成碳-氧西格马键。协同的氢迁移到邻近的氧孤电子对，以立体选择性的方式提供了具有可预测的立体化学的醇插入产物。随后将醇氧化成酮(或醛)的方式与此类似，并且具有较低的活化势垒。计算得到氧原子插入甲烷、乙烷、丙烷、丁烷、异丁烷和甲醇的C-H键的活化势垒(MP4/6-31G*//MP2/6-31G*)分别为10.7、8.2、3.9、4.8、4.5和3.3kcal/mol。我们使用从头算分子轨道计算5来支持前沿的MO理论，该理论为将亲电氧和相关的亲电性插入碳氢键的立体专一性和立体选择性提供了独特的理论基础。
A theoretical model suggesting the mechanistic pathway for the oxidation of saturated alkanes to their corresponding alcohols and ketones is described. Water oxide (H2O-O) is employed as a model singlet oxygen atom donor. Molecular orbital calculations with the 6-31G* basis set at the MP2, QCISD, QCISD(T), CASSCF, and MRCI levels of theory suggest that oxygen insertion by water oxide occurs by the interaction of an electrophilic oxygen atom with a doubly occupied hydrocarbon fragment orbital. The electrophilic oxygen approaches the hydrocarbon along the axis of the atomic carbon p orbital comprising a pi(CH2) or pi(CHCH3) fragment orbital to form a carbon-oxygen sigma bond. A concerted hydrogen migration to an adjacent oxygen lone pair of electrons affords the alcohol insertion product in a stereoselective fashion with predictable stereochemistry. Subsequent oxidation of the alcohol to a ketone (or aldehyde) occurs in a similar fashion and has a lower activation barrier. The calculated (MP4/6-31G*//MP2/6-31G*) activation barriers for oxygen atom insertion into the C-H bonds of methane, ethane, propane, butane, isobutane, and methanol are 10.7, 8.2, 3.9, 4.8, 4.5, and 3.3 kcal/mol, respectively. We use ab initio molecular orbital calculations5 in support of a frontier MO theory that provides a unique rationale for both the stereospecificity and the stereoselectivity of insertion of electrophilic oxygen and related elcectrophiles into the carbon-hydrogen bond.