TY - JOUR
T1 - Splitting of degenerate orbitals of dibenzyl and tetrabenzyl adducts of C60
T2 - ESR of the radical anions and the rotation barriers of benzyl groups
AU - Fukuzumi, Shunichi
AU - Suenobu, Tomoyoshi
AU - Gao, Xiang
AU - Kadish, Karl M.
PY - 2000/4/6
Y1 - 2000/4/6
N2 - The degenerate 2E1u ground state and the thermally accessible low-lying 2A2u excited state of C60̇- give a broad ESR signal (δHms1 = 30.9 G at 213 K) which has a smaller g value (1.9984) as compared to the free spin value (2.0023) and linewidth which decreases with decreasing temperature (δHms1 = 6.5 G at 133 K). The Ih, symmetry of the parent C60 is lowered by the introduction of two benzyl groups to C60 to give 1,4(C6H5CH2)2C60, which leads to the larger g value (2.0004) of 1,4-(C6H5CH2)2C60 ̇- than that of C60̇ (g = 1.9984) and a much smaller linewidth (δHms1 = 2.5 G at 213 K) which is independent of temperature. An even smaller δHms1 value (0.17 G) and a larger g value (2.0011) are observed in the tetrabenzyl C60 adduct radical anion, l,4,10,24-(C6H5CH2)4C 60̇- This is ascribed to a large splitting of the degenerate t1u orbitals caused by introduction of four benzyl groups to C60-̇ In this case, a hyperfine structure due to two nonequivalent protons of only one benzyl group (aH1 = 0.31 G, aH2 = 0.11 G) is observed and this is consistent with the predicted localized spin density at the C2 position next to the C1 carbon to which a benzyl group is attached. The observation of two nonequivalent hyperfine coupling constants due to the benzyl methylene protons indicates that rotation of the benzyl group at the C1 position is slow on the ESR time scale. The slow rotation rates of the benzyl groups in 1,4-dibenzyl adducts of Ceo and the activation parameters were determined from a line broadening of the methylene protons in the 1H NMR spectra with increasing temperature.
AB - The degenerate 2E1u ground state and the thermally accessible low-lying 2A2u excited state of C60̇- give a broad ESR signal (δHms1 = 30.9 G at 213 K) which has a smaller g value (1.9984) as compared to the free spin value (2.0023) and linewidth which decreases with decreasing temperature (δHms1 = 6.5 G at 133 K). The Ih, symmetry of the parent C60 is lowered by the introduction of two benzyl groups to C60 to give 1,4(C6H5CH2)2C60, which leads to the larger g value (2.0004) of 1,4-(C6H5CH2)2C60 ̇- than that of C60̇ (g = 1.9984) and a much smaller linewidth (δHms1 = 2.5 G at 213 K) which is independent of temperature. An even smaller δHms1 value (0.17 G) and a larger g value (2.0011) are observed in the tetrabenzyl C60 adduct radical anion, l,4,10,24-(C6H5CH2)4C 60̇- This is ascribed to a large splitting of the degenerate t1u orbitals caused by introduction of four benzyl groups to C60-̇ In this case, a hyperfine structure due to two nonequivalent protons of only one benzyl group (aH1 = 0.31 G, aH2 = 0.11 G) is observed and this is consistent with the predicted localized spin density at the C2 position next to the C1 carbon to which a benzyl group is attached. The observation of two nonequivalent hyperfine coupling constants due to the benzyl methylene protons indicates that rotation of the benzyl group at the C1 position is slow on the ESR time scale. The slow rotation rates of the benzyl groups in 1,4-dibenzyl adducts of Ceo and the activation parameters were determined from a line broadening of the methylene protons in the 1H NMR spectra with increasing temperature.
UR - http://www.scopus.com/inward/record.url?scp=0001269873&partnerID=8YFLogxK
U2 - 10.1021/jp993899j
DO - 10.1021/jp993899j
M3 - Article
AN - SCOPUS:0001269873
SN - 1089-5639
VL - 104
SP - 2908
EP - 2913
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 13
ER -