High level ab initio study of thermal 1,3-sigmatropic shift in CH2=CHCH2X with X = BH2, NH2, and CH3
High level ab initio study of thermal 1,3-sigmatropic shift in CH2=CHCH2X with X = BH2, NH2, and CH3
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DOI：
10.1021/jp025721u
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发表时间：
2002-06-13
影响因子：
2.9
通讯作者：
Lee, I
中科院分区：
文献类型：
--
作者：
Choi, JY;Kim, CK;Lee, I
在RHF，MP2，B3 LYP，G3和CBS-APNO水平上，采用添加了扩散和极化函数的基组，研究了X-CH 2-CHCH 2（X = BH 2，NH 2和CH 3）体系的热1，3-σ迁移.在所有三种情况下，表面允许路径通过TS进行，其中CC π电子离域到迁移X中的2 p AO中。对于2 p空轨道的X = BH ~ 2，活化焓小于1.0 kcal mol ~（-1）（CBS-APNO），因此1，3-位移几乎是无势垒的.对于X = NH 2，有两条表面路径，其中一条（高能路径a）通过N上孤对电子的参与进行。较低能量路径的势垒高度（ΔH = 68.9 kcal mol-1）仅比C−N键的键离解能低1.0 kcal mol-1，因此双自由基路径可以与协同σ迁移竞争。对于X = CH 3，活化能垒（ΔH ε = 76.1 kcal mol-1）更高（约为1.2kcal mol-1）。1 kcal mol-1）比C1−X（CH 3）键的键离解能高，因此有利于双自由基反应路径。的antrafacial 1，3-移位被禁止在所有情况下，证明了二阶鞍点（有两个虚频率）和更高的势垒高度比相应的superfacial移位。
The thermal 1,3-sigmatropic migrations in X-CH2−CHCH2with X = BH2, NH2, and CH3have been investigated at the RHF, MP2, B3LYP, G3, and CBS-APNO levels using basis sets with added diffuse and polarization functions. In all three cases, the suprafacial allowed path proceeds through a TS in which the CC π electron is delocalized into the 2p AO in the migrating X. For X = BH2with a vacant 2p orbital, the activation enthalpy is less than 1.0 kcal mol-1(CBS-APNO) so that the 1,3-shift is almost barrierless. For X = NH2there are two suprafacial pathways, one of which (higher energy path a) proceeds by participation of the lone pair on N. The lower energy pathway has a barrier height (ΔH⧧= 68.9 kcal mol-1) of only 1.0 kcal mol-1below the bond dissociation energy of the C−N bond, so that a diradical pathway can compete with the concerted sigmatropic shift. For X = CH3, the activation barrier (ΔH⧧= 76.1 kcal mol-1) is higher (by ca. 1 kcal mol-1at the CBS-APNO level) than the bond dissociation energy of the C1−X(CH3) bond, so that the diradical reaction path is favored. The antrafacial 1,3-shifts are forbidden in all cases as evidenced by the second-order saddle-points (with two imaginary frequencies) and much higher barrier heights than those for the corresponding suprafacial shifts.