Fluorine-19 nuclear magnetic resonance study of the inclusion of fluoro- and difluoro-trans-cinnamates by α-cyclodextrin

Abstract

¹⁹ F n.m.r. studies of the inclusion of o-, m-, p- and α-fluoro-trans-cinnamates and o, p- and α,p-difluoro-trans-cinnamates by α-cyclodextrin (αCD) have shown that two inclusion equilibria [graphic omitted] are established in D₂O solution at pD = 8.5 ± 0.1. Typically at 294 K, K₁= 111 ± 13 dm³ mol^–1 and K₂= 23 ± 2 dm³ mol^–1 for α,p-difluoro-trans-cinnamate. Chemical-shift and other data indicate that the predominant S·αCD complex is that in which the carboxylate group of the fluorocinnamate enters the wide end of the αCD cavity, delineated by twelve secondary hydroxy groups, first. The S·(αCD)₂ complex probably has a structure in which the fluoro-trans-cinnamate is encapsulated by two αCD with the wide ends of their cavities in close proximity.