TY - JOUR
T1 - The conformational distributions and interconversions of partially methylated calix[4]arenes
AU - van Hoorn, Willem P.
AU - Morshuis, Martijn G.H.
AU - van Veggel, Frank C.J.M.
AU - Reinhoudt, David N.
PY - 1998
Y1 - 1998
N2 - The conformational distributions and Cone-Inverted Cone (Cone') interconversions of monomethoxy-, 1,2-dimethoxy-, 1,3-dimethoxy-, and trimethoxycalix[4]arenes 3a-6a were investigated by molecular modeling. The calculated conformational distributions are generally in accordance with NMR data obtained for the p-tert-butyl derivatives 3b-6b. Careful examination of all possible inversion pathways showed that the high inversion barriers of Cone-Cone' interconversion are caused by the cooperative barriers of hydrogen bonds rupture and the steric barrier of rotating a methoxy group through the annulus. This cooperative effect is so strong that the Cone Cone' conversion is blocked at room temperature. The order of the calculated barriers for the Cone-Inverted Cone interconversions is monomethoxy- (35.1 kcal mol-1) > 1,2-dimethoxy- (32.2 kcal mol-1)=1,3-dimethoxy- (30.3 kcal mol-1) > trimethoxycalix[4]arene (27.0 kcal mol-1), values that are in good agreement with the available qualitative experimental results. The rate-limiting step involved in all cases is the rotation of a methoxy-bearing ring.
AB - The conformational distributions and Cone-Inverted Cone (Cone') interconversions of monomethoxy-, 1,2-dimethoxy-, 1,3-dimethoxy-, and trimethoxycalix[4]arenes 3a-6a were investigated by molecular modeling. The calculated conformational distributions are generally in accordance with NMR data obtained for the p-tert-butyl derivatives 3b-6b. Careful examination of all possible inversion pathways showed that the high inversion barriers of Cone-Cone' interconversion are caused by the cooperative barriers of hydrogen bonds rupture and the steric barrier of rotating a methoxy group through the annulus. This cooperative effect is so strong that the Cone Cone' conversion is blocked at room temperature. The order of the calculated barriers for the Cone-Inverted Cone interconversions is monomethoxy- (35.1 kcal mol-1) > 1,2-dimethoxy- (32.2 kcal mol-1)=1,3-dimethoxy- (30.3 kcal mol-1) > trimethoxycalix[4]arene (27.0 kcal mol-1), values that are in good agreement with the available qualitative experimental results. The rate-limiting step involved in all cases is the rotation of a methoxy-bearing ring.
U2 - 10.1021/jp973103l
DO - 10.1021/jp973103l
M3 - Article
SN - 1089-5639
VL - 102
SP - 1130
EP - 1138
JO - The journal of physical chemistry A
JF - The journal of physical chemistry A
IS - 7
ER -