Isomerization studies of Delta,Lambda-[Ni(1,10-phen)(2)(S-aa)](+) systems

The Delta-Lambda isomerization of partially resolved [Ni(1,10-phen)(2)(S-aa )](+) systems, where Saa is S-phenylalaninate, S-isoleucinate, S-leucinate, S-valinate, or S-alaninate, has been studied at 15, 20 and 25 degrees C in methanol as solvent. Kinetic parameters have been obtained by means of opt ical rotation measurements. The first-order rate constants for the isomeriz ation process follow the order S-leu > S-ala > S-phe > S-ileu > S-val, wher eas Delta H double dagger and Delta S double dagger are in the sequence S-p he > S-ala > S-val > S-ileu > S-leu. These results are discussed in relatio n to the possible influences of intramolecular noncovalent interactions on the activation parameters.