Untitled

Anion‐Induced Urea Deprotonation

“…The logK value for the association equilibrium, as determined through nonlinear leastsquares fitting of the smooth titration profile, is 4.05 AE 0.01. The formation of a hydrogen-bond complex of 1:1 stoichiometry has been confirmed by 1 H NMR titration experiments; recorded spectra are shown in Figure 6. Even on excess addition of [BzEt 3 N]Cl, only a very moderate upfield of H b , which reflects a weak hydrogen-bond interaction and a small through-bond effect, and a moderate downfield shift of H c , which indicates a not too pronounced polarisation, were observed.…”

“…[1][2][3] Such molecules should be able to behave as hydrogen-bond donors towards the envisaged anion, giving rise to a complex that is stable in solution. One of the most frequently employed fragments is urea.…”

“…In fact, urea can donate two hydrogen bonds in a parallel fashion, and so it is complementary to Y-shaped oxoanions such as carboxylates. One of the first examples of anion complexation by urea-based receptors was reported by Wilcox, who characterised the receptor-analyte interaction through 1 H NMR experiments and determined the association constant of the complex by spectrophotometric titrations. [4] A variety of receptors containing one or more urea subunits have been designed and tested for anion recognition and sensing over the past years.…”

“…In this context, we studied the interaction of the urea derivative 1 (1-(7-nitrobenzo [1,2,5]oxadiazol-4-yl)-3-(4-nitrophenyl)urea), with some commonly investigated anions (halides, carboxylates, phosphate). In addition, two electronwithdrawing substituents, 4-nitrophenyl and nitrobenzofurazan, were appended to the 1-and 3-positions of the urea Abstract: The urea-based receptor 1 (1-(7-nitrobenzo [1,2,5] ) was isolated and its crystal and molecular structure determined.…”

“…In addition, two electronwithdrawing substituents, 4-nitrophenyl and nitrobenzofurazan, were appended to the 1-and 3-positions of the urea Abstract: The urea-based receptor 1 (1-(7-nitrobenzo [1,2,5] ) was isolated and its crystal and molecular structure determined. Keywords: acid-base reactions · anions · hydrogen bonds · supramolecular chemistry · urea subunit, in order to enhance both hydrogen-bond donor tendencies and acidity of the receptor.…”