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

Abstract

The Δ-Λ isomerization of partially resolved [Ni(1,10-phen)2(S-aa)]+ systems, where S-aa is S-phenylalaninate, S-isoleucinate, S-leucinate, S-valinate, or S-alaninate, has been studied at 15,20 and 25°C in methanol as solvent. Kinetic parameters have been obtained by means of optical rotation measurements. The first-order rate constants for the isomerization process follow the order S-leu > S-ala > S-phe > S-ileu > S-val, whereas ΔH‡ and ΔS‡ are in the sequence S-phe > S-ala > S-val > S-ileu > S-leu. These results are discussed in relation to the possible influences of intramolecular noncovalent interactions on the activation parameters.