Department of Chemistry, Purdue University, West Lafayette, IN, 47907, USA.
ExxonMobil Research & Engineering Company, Annandale, NJ, 08801, USA.
Chemistry. 2019 Mar 21;25(17):4472-4477. doi: 10.1002/chem.201806096. Epub 2019 Feb 25.
The reactivity of a carbon-centered σ,σ,σ,σ-type singlet-ground-state tetraradical containing two meta-benzyne moieties was examined in the gas phase. Surprisingly, the tetraradical showed higher reactivity than its individual meta-benzyne counterparts. The reactivity of meta-benzynes is controlled by their (calculated) distortion energy ΔE , singlet-triplet spitting ΔE , and electron affinity (EA ) of the meta-benzyne moiety at the transition state geometry for hydrogen-atom abstraction reactions. The addition of a second meta-benzyne moiety to a meta-benzyne does not significantly change EA . However, ΔE is substantially decreased for both meta-benzyne moieties in the tetraradical, and this explains their higher reactivities. The decrease in ΔE for each meta-benzyne moiety in the tetraradical is rationalized by stabilizing spin-spin coupling between one radical site in each meta-benzyne moiety. Therefore, spin-spin coupling between the meta-benzyne moieties in this tetraradical increases its reactivity, whereas spin-spin coupling within each meta-benzyne moiety decreases its reactivity.
在气相中研究了含有两个间苯炔部分的碳中心σ,σ,σ,σ-型单重基态四自由基的反应性。令人惊讶的是，四自由基的反应性比其单个间苯炔对应物更高。间苯炔的反应性受其（计算）变形能ΔE、单重态-三重态分裂ΔE和间苯炔部分在氢原子攫取反应过渡态几何形状的电子亲合能（EA）控制。在间苯炔上添加第二个间苯炔部分不会显著改变 EA。然而，对于四自由基中的两个间苯炔部分，ΔE 都大大降低，这解释了它们更高的反应性。四自由基中每个间苯炔部分的ΔE 降低可以通过稳定每个间苯炔部分中一个自由基位点之间的自旋-自旋偶合来合理化。因此，该四自由基中两个间苯炔部分之间的自旋-自旋偶合增加了其反应性，而每个间苯炔部分内的自旋-自旋偶合降低了其反应性。
