Examination of intramolecular potential surfaces of flexible conjugated molecules by calculation of crystal structures. equilibrium geometries of chalc

Chemistry of the Retinoid (Visual) Cycle

“…The most stable conformation for retinoids is all-trans . 174 , 175 Alternative geometrical isomers introduce some steric hindrance that increases the conformational energy compared to the all-trans isomer. 176 Although some retinal isomers introduce only mild steric clashes, e.g.…”

“…Thus, polyene single bonds display some double-bond characteristics contributing to their preferred planar conformation. The most stable conformation for retinoids is all-trans . , Alternative geometrical isomers introduce some steric hindrance that increases the conformational energy compared to the all-trans isomer . Although some retinal isomers introduce only mild steric clashes, e.g.…”

4′-Methylchalcone

“…The two benzene rings are not coplanar with the enone sytem; there is a 11.0 (4) angle between the C4-benzene ring and the enone system (C2-C3-C4-C5) and a 25.4 (3) angle between the 1-benzene ring and the enone system (C2-C1-C10-C15). This non-linearity is commonly observed in other p 0 -substituted chalcones (Rabinovich & Schmidt, 1970;Rabinovich et al, 1973;Warshel et al, 1974;Toda et al, 1998;Li et al, 1992), and is likely due to the accommodation of the bulky 4substituent within the crystal structure.…”

Optical induction in chiral crystals. II. The crystal and molecular structures of 1-(2,6-dichlorophenyl)-4-phenyl-trans,trans-1,3-butadiene

“…Bond C(3)--C(4) 1-420 1.419 1.397 C(4)--C (5) 1.418 1.417 1.398 C(4)--C (7) 1-480 1-478 1.470 C (7) (7) 118.5 118-5 118.1 C(5)--C(4)--C (7) 122.9 122.8 124.0 C(4)--C(7)--C (8) 125.3 125.2 126-9 C(7)--C(8)--C (9) 120.7 120.6 121.2 C(8)--C(9)--C (10) 122-3 122.3 123.9 C(9)--C(10)-C (11) 123-5 123.7 125.9 C(10)-C(I 1)-C (12) 122.2 122.6 124-8 C (10) sistent Force-Field to n electron system (Warshel & Karplus, 1972). The energy parameters used, involving C and H atoms were those of set A given by Warshel, Huller, Rabinovich & Shakked (1974)and the nonbonded potential parameters of CI... CI, CI... C and CI...H were the refined values of set B given by Bonadeo & D'Alessio (1973). Some of the calculated results are given in Table 6 together with the corresponding experimental values corrected for libration motion.…”