SN R1 R2 R3 ER (kcal/mol) Ea(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 (ER) and Activation Barriers (Ea) 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).