Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI 96822, USA.
Phys Chem Chem Phys. 2014 Jan 21;16(3):989-97. doi: 10.1039/c3cp53930j. Epub 2013 Nov 26.
The crossed molecular beam reaction of boron monoxide ((11)BO; X(2)Σ(+)) with dimethylacetylene (CH3CCCH3; X(1)A(1g)) was investigated at a collision energy of 23.9 ± 1.5 kJ mol(-1). The scattering dynamics were suggested to be indirect (complex forming reaction) and were initiated by the addition of (11)BO(X(2)Σ(+)) with the radical center located at the boron atom to the π electron density at the acetylenic carbon-carbon triple bond without entrance barrier leading to cis-trans(11)BOC4H6 doublet radical intermediates. cis-(11)BOC4H6 underwent cis-trans isomerization followed by unimolecular decomposition via a methyl group (CH3) loss forming 1-propynyl boron monoxide (CH3CC(11)BO) in an overall exoergic reaction (experimental: -91 ± 22 kJ mol(-1); theoretical: -105 ± 9 kJ mol(-1); NIST: -104 ± 12 kJ mol(-1)) via a tight exit transition state; trans-(11)BOC4H6 was found to lose a methyl group instantaneously. Neither atomic nor molecular hydrogen loss pathways were detectable. The experimental finding of an exclusive methyl loss pathway gains full support from our computational study predicting a methyl group versus atomic hydrogen loss branching ratio of 99.99% to 0.01% forming 1-propynyl boron monoxide (CH3CC(11)BO) and 1-methyl-propadienyl boron monoxide (CH3((11)BO)CCCH2), respectively.
一氧化碳（(11)BO；X(2)Σ(+))与二甲基乙炔（CH3CCCH3；X(1)A(1g)）的交叉分子束反应在 23.9±1.5 kJ mol(-1)的碰撞能下进行。该散射动力学被认为是间接的（复合形成反应），由(11)BO(X(2)Σ(+))与自由基中心位于硼原子的位置对乙酰基碳-碳三键上的π电子密度的加成引发，没有进入势垒，导致顺式-反式(11)BOC4H6 双自由基中间体。顺式-(11)BOC4H6 经历顺式-反式异构化，然后通过甲基（CH3）丢失通过单分子分解，形成 1-丙炔基硼氧化物（CH3CC(11)BO），在总放热反应中（实验：-91±22 kJ mol(-1)；理论：-105±9 kJ mol(-1)；NIST：-104±12 kJ mol(-1)）通过紧密的出口过渡态；反式-(11)BOC4H6 被发现立即失去一个甲基。没有检测到原子或分子氢的损失途径。实验上发现的排他性甲基损失途径得到了我们的计算研究的充分支持，该研究预测了甲基与原子氢损失分支比为 99.99%对 0.01%，分别形成 1-丙炔基硼氧化物（CH3CC(11)BO）和 1-甲基-丙二烯基硼氧化物（CH3((11)BO)CCCH2）。
