Cyclic voltammograms of 2,3,5,6-tetrakis(trimethylsilyl)-1,4-benzoquinone ( 1a), 2,3,5,6-tetrakis(dimethylvinylsilyl)-1,4-benzoquinone ( 1b), 2,3,5,6-tetrakis(dimethylsilyl)-1,4-benzoquinone ( 1c), 4,4,6,6,10,10,12,12-octamethyl-4,6,10,12-tetrasilatricyclo[7.3.0.0 3,7]dodeca-1(9),3(7)-diene-2,8-dione ( 1d), and 5- t-butyl-2-(pentamethyldisilanyl)-1,4-benzoquinone ( 5h) showed that the first reduction step was reversible and that the second step was irreversible. The first half-wave reduction potentials ( E 1 / 2 I s ) of 1a, 1b, 1c, and 1d shifted negatively relative to 1,4-benzoquinone by −0.31, −0.24, −0.03, and −0.18 V, respectively. These results demonstrated that the electron-accepting ability of the chair-form quinones 1a and 1b was lower than that of the planar quinones 1c and 1d. The E 1 / 2 I of 5h (−0.93 V vs. Ag/Ag +) was quite similar to that of 5- t-butyl-2-trimethylsilyl-1,4-benzoquinone ( 5a, −0.94 V). A cyclic voltammogram of dimethylsilylene-bridged 1,4-benzoquinone dimer 7 showed two kinds of E 1 / 2 I (−0.76 and −0.94 V). The electrochemical behavior of 7 would be interpreted in terms of near-neighbor interactions between reduced and non-reduced quinone units. Theoretical calculations of the silyl-1,4-benzoquinones reproduced well the solid state structures of the compounds. Also, the computed vibrational frequencies of the silyl-1,4-benzoquinones were in good agreement with the IR absorption frequencies of the C O units in the compounds. The LUMO energy levels of the silyl-1,4-benzoquinones were quantitatively proportional to the E 1 / 2 I s .