Theoretical study on homolytic C(sp2)-O cleavage in ethers and phenolsElectronic supplementary information (ESI) available: The 72 C-O BDEs calculated by 26 DFT methods. See DOI: 10.1039/c5nj01354b

• Main Authors: Ding, Lanlan, Zheng, Wenrui, Wang, Yingxing
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/c5nj01354b

The C-O homolytic bond dissociation enthalpies (BDEs) of many ethers were calculated by high-level ab initio methods including G4, G3, CBS-Q, CBS-4M as well as 26 density function theory (DFT) methods. Among the DFT methods, wB97 provided the most accurate results and the root mean square error (RMSE) is 9.3 kJ mol −1 for 72 C-O BDE calculations. Therefore, extensive C(sp 2 )-O BDEs and the substituent effect of alkenyl ethers, para -position phenyl ethers/phenols as well as several typical heterocyclic ethers were investigated in detail by wB97 methods, which is important for the understanding of the chemical process involved in the cross-coupling reactions. For alkenyl ethers, the different substituents exhibited significant effects on C(sp 2 )-O BDEs, especially, the conjugate effect of the substituents on the O atom can greatly decrease the C(sp 2 )-O BDEs. In addition, the NBO analysis produced good linear correlations between the C(sp 2 )-O BDEs and q C × q O values (the q C and q O values denoted the natural charge of C and O atoms of the C-O bond, respectively). For para -position phenyl ethers and phenols, excellent linear relationships between the C(sp 2 )-O BDEs with substituent constant σ p + are found. Further discussion of the substituent effect separated into the ground effect and the radical effect can further help us to understand the essence. For several five-membered typical heterocyclic ethers, a larger bond angle change will lead to a smaller C-O BDE. The C(sp 2 )-O BDEs and the substituent effect of ethers/phenols were investigated in detail by the wB97 method.