4-(2,3-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-bis(methoxycarbonyl),4-(2,4-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-bis(methoxycarbonyl), and 4-(2,3,5-trichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-bis(methoxycarbonyl): conformational observations in the crystalline state

Hydrogen bonding interactions displayed by three crystalline chloro-substituted 4-phenyl-1,4-dihydropyridine molecules 4-(2,3-Dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine3,5-bis(methoxycarbonyl), 4-(2,4-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-bis (methoxycarbonyl) and 4-(2,3,5-trichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-bis (methoxycarbonyl), suggests that, in contrast to previous observation, sp orientation of the 3 or 5 substituted carbonyl group accomodates hydrogen bonding to the carbonyl oxygen atom when polar orthosubstituents exist on the phenyl ring.