School of Chemistry and ARC Center of Excellence for Free Radical Chemistry and Biotechnology, University of Sydney, Sydney, NSW, Australia.
Org Biomol Chem. 2011 May 21;9(10):3636-57. doi: 10.1039/c1ob05196b. Epub 2011 Mar 31.
The bond dissociation energies (BDEs) and radical stabilization energies (RSEs) which result from 166 reactions that lead to carbon-centered radicals of the type ˙CH(2)X, ˙CHXY and ˙CXYZ, where X, Y and Z are any of the fourteen substituents H, F, Cl, NH(2), OH, SH, CH[double bond, length as m-dash]CH(2), C[triple bond, length as m-dash]CH, BH(2), CHO, COOH, CN, CH(3), and CF(3), were calculated using spin-restricted and -unrestricted variants of the double-hybrid B2-PLYP method with the 6-311+G(3df,2p) basis set. The interactions of substituents X, Y, and Z in both the radicals (˙CXYZ) and in the precursor closed-shell molecules (CHXYZ), as well as the extent of additivity of such interactions, were investigated by calculating radical interaction energies (RIEs), molecule interaction energies (MIEs), and deviations from additivity of RSEs (DARSEs) for a set of 152 reactions that lead to di- (˙CHXY) and tri- (˙CXYZ) substituted carbon-centered radicals. The pairwise quantities describing the effects of pairs of substituents in trisubstituted systems, namely pairwise MIEs (PMIEs), pairwise RIEs (PRIEs) and deviations from pairwise additivity of RSEs (DPARSEs), were also calculated for the set of 61 reactions that lead to trisubstituted radicals (˙CXYZ). Both ROB2-PLYP and UB2-PLYP were found to perform quite well in predicting the quantities related to the stabilities of carbon-centered radicals when compared with available experimental data and with the results obtained from the high-level composite method G3X(MP2)-RAD. Particular selections of substituents or combinations of substituents from the current test set were found to lead to specially stable radicals, increasing the RSEs to a maximum of +68.2 kJ mol(-1) for monosubstituted radicals ˙CH(2)X (X = CH[double bond, length as m-dash]CH(2)), +131.7 kJ mol(-1) for disubstituted radicals ˙CHXY (X = NH(2), Y = CHO), and +177.1 kJ mol(-1) for trisubstituted radicals ˙CXYZ (X = NH2, Y = Z = CHO).
采用自旋限制和非限制双杂化 B2-PLYP 方法与 6-311+G(3df,2p)基组计算了导致类型为˙CH(2)X、˙CHXY 和 ˙CXYZ 的碳中心自由基的 166 个反应的键离解能（BDE）和自由基稳定能（RSE），其中 X、Y 和 Z 是 14 种取代基 H、F、Cl、NH(2)、OH、SH、CH[双键，长度为破折号]CH(2)、C[三重键，长度为破折号]CH、BH(2)、CHO、COOH、CN、CH(3)和 CF(3)中的任意一种。取代基 X、Y 和 Z 在自由基（˙CXYZ）和前体闭壳分子（CHXYZ）中的相互作用以及这种相互作用的加和程度，通过计算一系列导致二取代（˙CHXY）和三取代（˙CXYZ）碳中心自由基的 152 个反应的自由基相互作用能（RIE）、分子相互作用能（MIE）和 RSE 加和偏差（DARSE）来研究。还为导致三取代自由基（˙CXYZ）的 61 个反应计算了描述三取代体系中两个取代基相互作用的成对数量，即成对 MIE（PMIE）、成对 RIE（PRIE）和 RSE 加和偏差（DPARSE）。ROB2-PLYP 和 UB2-PLYP 都被发现能够很好地预测与碳中心自由基稳定性相关的数量，与可用的实验数据和高水准复合方法 G3X(MP2)-RAD 的结果相比。从当前测试集中选择特定的取代基或取代基组合被发现会导致特别稳定的自由基，使单取代自由基˙CH(2)X（X = CH[双键，长度为破折号]CH(2)）的 RSE 增加到最大值+68.2 kJ mol(-1)，二取代自由基˙CHXY（X = NH(2)，Y = CHO）的 RSE 增加到+131.7 kJ mol(-1)，三取代自由基˙CXYZ（X = NH2，Y = Z = CHO）的 RSE 增加到+177.1 kJ mol(-1)。
