Clathrate and Inclusion Compounds. Part 13 [1]. Vibrational and NMR Spectroscopic Studies of Carboxylic Acid Guests in Urea

Infrared, Raman and solid state¹³C NMR spectra have been recorded for arange of inclusion compounds of urea containingstraight chain aliphatic carboxylic acids(butyric – decanoic) as guests. Inclusioncompounds are not formed with formic, acetic andpropionic acids. Thiourea does not forminclusion compounds with any of the C1 to C10acids. The vibrational and NMR data support theconclusion that the acids are present ashydrogen bonded dimers in the channels of thehost. The alkyl chain ¹³C chemical shiftvalues are very different from those of acidguests in the cavities formed in Dianin'scompound. These suggest that the alkyl chainsare present in the all-trans conformation,although weak bands observed in the spectrum ofthe decanoic acid inclusion compound lend somesupport to suggestions based on MM calculationsthat other conformations might be present.