Coote Michelle L, Lin Ching Yeh, Zavitsas Andreas A
Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
Phys Chem Chem Phys. 2014 May 14;16(18):8686-96. doi: 10.1039/c4cp00537f.
Accurate G3(MP2)-RAD calculations are used to predict 264 R-H, R-CH3, R-Cl and R-R bond dissociation energies for a wide-ranging test set of carbon and non-carbon centred R˙ radicals. The data are used to calculate a set of inherent and transferrable radical stabilization energies, denoted RSEEt, which ranks the inherent stability of the 66 radicals studied on the same relative scale, irrespective of the nature of the radical centre. The Pauling electronegativity parameter for each radical is also calculated from the same data, along with the radical's inherent bonding ability D[R-R]calc. This latter quantity is defined as the R-R bond dissociation energy expected in the absence of direct steric or resonance interactions that are present in R-R but absent in R-CH3 and R-Cl. We show that the differences between D[R-R] and D[R-R]calc are typically very small except when R is sterically bulky, or there is a chain of (hyper)conjugation across the R-R bond. In such cases the difference between D[R-R] and D[R-R]calc provides a convenient means of quantifying the stabilization or destabilization of R-R due to these interactions. The predictability of the scheme is demonstrated by using these radical stabilities to calculate R-R' bond dissociation energies for 234 combinations of the 66 radicals studied, chosen to exclude steric or resonance interactions in the R-R' bond. The predicted bond energies lie within an average of 1.6 kcal mol(-1) from directly measured or calculated literature values.
精确的G3(MP2)-RAD计算用于预测一系列以碳和非碳为中心的R˙自由基测试集中264个R-H、R-CH3、R-Cl和R-R键的解离能。这些数据用于计算一组固有且可转移的自由基稳定能，记为RSEEt，它在相同的相对尺度上对所研究的66个自由基的固有稳定性进行排序，而不考虑自由基中心的性质。每个自由基的鲍林电负性参数也从相同的数据中计算得出，同时还有自由基的固有键合能力D[R-R]calc。后一个量被定义为在不存在R-R中存在但R-CH3和R-Cl中不存在的直接空间或共振相互作用时预期的R-R键解离能。我们表明，除了R在空间上体积较大或R-R键上存在（超）共轭链的情况外，D[R-R]和D[R-R]calc之间的差异通常非常小。在这种情况下，D[R-R]和D[R-R]calc之间的差异提供了一种方便的方法来量化由于这些相互作用导致的R-R的稳定或不稳定。通过使用这些自由基稳定性来计算所研究的66个自由基的234种组合的R-R'键解离能，以排除R-R'键中的空间或共振相互作用，证明了该方案的可预测性。预测的键能与直接测量或计算的文献值平均相差1.6 kcal mol(-1)以内。
