Hydrogen bond acceptor molecules

Wilson KR, Cavalleri M, Rude BS, Schaller RD, Nilsson A, Pettersson LGM, Goldman N, Catalano T, Bozek JD, Saykally RJ (2002) Characterization of hydrogen bond acceptor molecules at the water surface using near-edge X-ray absorption fine structure spectroscopy and density functional theory. J Phys Condens Matter 14 L221-L226... 

In a subsequent study involving substituted benzoic acids as hydrogen bond donors and substituted imidazoles as acceptors, Aakeroy and co-workers demonstrated that the likelihood of co-crystal formation is improved by increasing the p a that is, the basicity of the hydrogen bond acceptor molecules. ... 

This closed-loop behavior is typical of hydrogen-bond acceptor molecules (nicotine is an example), as the balance between effects of enthalpy and entropy leads to higher solubility at lower temperatures, then a drop as hydrogen bonding begins to break down, then a second increase as the entropic forces take control. The use of this type of behavior makes certain functional groups (ethers, esters) most useful for separations in NCW systems. 

Diphenylurea Crystallization. 1,3-hfsphenylurea (13) is the parent compound of a large family of derivatives, most of which do not cocrystallize with guest molecules (Etter et al. 1990). Even when put into solution with strong hydrogen bond acceptors, e.g., dimethyl sulfoxide (DMSO), triphenylphosphineoxide (TPPO) and tetrahydrofuran (THF), most diphenyl ureas crystallize with other molecules of the same kind in a connectivity pattern viewed as is shown below (14), instead of forming cocrystals (e.g., 15). 

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