Table 1

SN	R₁	R₂	R₃	E_R (kcal/mol)	E_a(kcal/mol)
1	H	H	H	-33.1	22.2
2	Methyl	H	H	-33.1	20.3
3	Methyl	Methyl	H	-27.8	21.2
4	Methyl	Methyl	Methyl	-37.3	25.8
5	Ethyl	H	H	-30.9	20.1
6	Ethyl	CH3	H	-26.7	21.3
7	Ethyl	CH3	CH3	-37.9	26.7
8	Propyl	H	H	-34.2	19.5
9	Propyl	CH3	H	-27.4	9.5b, 48.4c
10	Propyl	CH3	CH3	-32.4	15.8b,29.7c
11	Propyl	Ethyl	H	-22.8	16.4b, 3.6c
12	Ethyl	Ethyl	Ethyl	-33.6	27.0
13	Pentyl	Pentyl	Pentyl	-23.7	26.7
14	Benzyl	H	H	-36.4	19.8
15	Benzyl	Methyl	Methyl	-26.4	26.6
16	Benzyl	Benzyl	Methyl	-14.4	-
17	Benzyl	Benzyl	Benzyl	-9.4	35.4
18	Naphthyl	Benzyl	Benzyl	-8.9	37.4
19	Naphthyl	Naphthyl	Benzyl	-10.3	37.2
20	Naphthyl	Naphthyl	Naphthyl	-9.4	37.0

Table 1: Reaction Energies (E_R) and Activation Barriers (E_a) of the cycloaddition reactions with the various electron-donating substituents on the nitronesa aReactions 9, 10, and 11 are stepwise reactions while the rest are concerted bBarriers of first step in a stepwise mechanism. cBarrier of second step in a stepwise reaction. All energies are calculated relative to the separated reactants (fullerene+nitrone).