ENANTIOMERIC RECOGNITION BY CHIRAL PYRIDINO-18-CROWN-6 FOR 1-NAPHTHYLETHYLAMINE - THE EFFECT OF ALKYL SUBSTITUENTS ON THE MACROCYCLE RING

Molecular recognition of three chiral pyridino-18-crown-6 macrocycles with various dialkyl substituents for (R)- and (S)-[alpha-(1-naphthyl) ethyl]ammonium perchlorate (NapEt) has been determined by isoperibol t itration calorimetry and compared to values already determined for the chiral di-methyl- and di-tert-butyl-substituted crowns, Possible mech anisms of recognition for these systems are discussed using the thermo dynamic values log K, Delta H, and T Delta S. Macrocycles with the bul ky substituents tert-butyl, isobutyl, and sec-butyl shelved better rec ognition than those with the less bulky isopropyl and methyl substitue nts. In the case of macrocycles with bulky substituents, recognition o f the enantiomers of NapEt was mainly the result of differences in ent ropy value changes, With macrocycles having less bulky substituents, r eognition was mainly the result of differences in enthalpy value chang es.