Table 1. Forward and reverse classical barrier heights and classical energies of reaction (kcal mol^–1) for (R1)–(R5) ^a .

Electronic model chemistry//M08-HX/MG3S	Forward barrier height V‡f					Reverse barrier height V‡r					Energy of reaction ΔE (kcal mol–1)					MUE	MUE (w/o (R5))
	(R1)	(R2)	(R3)	(R4)	(R5)	(R1)	(R2)	(R3)	(R4)	(R5)	(R1)	(R2)	(R3)	(R4)	(R5)
M08-HX/aug-cc-pVTZ	20.89	12.09	17.66	17.61	22.07	4.46	4.64	4.37	2.83	2.23	16.44	7.45	13.28	14.78	19.84	0.22	0.21
M08-SO/aug-cc-pVTZ	21.92	13.10	18.56	18.39	21.94	5.06	5.19	5.35	3.00	1.41	16.86	7.90	13.20	15.39	20.52	0.66	0.70
M06-2X/aug-cc-pVTZ	19.02	10.61	15.87	15.71	19.83	3.11	3.36	3.20	1.40	0.43	15.90	7.25	12.67	14.31	19.40	1.14	1.11
M08-HX/maug-cc-pVTZ	21.06	12.34	17.84	17.94	22.29	4.61	4.81	4.50	3.09	2.38	16.45	7.52	13.34	14.85	19.90	0.29	0.26
M08-HX/MG3S	20.63	11.61	17.18	17.31	21.68	3.89	3.94	3.55	2.08	1.64	16.74	7.67	13.62	15.23	20.03	0.50	0.58
CCSD(T)-F12a/jun-cc-pVTZ	20.32	12.38	17.57	17.47	21.72	4.52	4.76	4.43	2.91	1.90	15.80	7.62	13.14	14.56	19.82	0.00	0.00

^aFor consistent comparisons, the same set of geometries (those obtained by M08-HX/MG3S) is used throughout this table. The lowest-energy structures for reactants, conventional transition states, and products are employed. Mean unsigned errors (MUEs) are calculated with respect to the CCSD(T)-F12a/jun-cc-pVTZ method. Barrier heights and energies of reaction are classical, i.e., zero-point-energy exclusive.