Table 1:

Key features for the computed free energy profiles shown in Fig. 2 of the main text; energetics (statistical uncertainty in parentheses) are in kcal/mol, and reaction coordinate values (RX: reactant; TS: transition state; PD: product) are in the unit of Angstrom.

Models	ξRX	ξTS	ΔG‡	${\mathrm{\Phi }}_{C{H}_3}^{‡}$	ξPD	ΔG
M2	−0.88	0.16	10.2(0.2)	46	1.77	−16.3(0.1)
M2+D3	−0.88	0.12	10.5(0.3)	49	1.92	−14.5(0.1)
M3	−0.93	0.20	12.1(0.2)	43	1.90	−12.2(0.1)
M3+D3	−0.88	0.16	11.5(0.2)	48	1.73	−13.2(0.1)
M4	−0.93	0.17	10.4(0.2)	47	1.90	−16.0(0.1)
M4+D3	−0.88	0.21	13.0(0.2)	42	1.68	−11.2(0.1)
M5	−0.92	0.25	11.7(0.2)	44	1.75	−12.5(0.1)
M5+D3	−0.81	0.12	10.1(0.2)	59	1.76	−13.4(0.1)
M5C+D3	−0.92	0.20	12.6(0.2)	42	1.71	−10.7(0.1)

^aThe planarity of the methyl group ${\mathrm{\Phi }}_{C{H}_3}^{‡}$ is given as the average absolute value of the H-C-H-H improper dihedral in degrees from each transition state ensemble with the standard deviation given in parentheses, defined such that 0 is perfectly planar.