Double hydrogen bonding interactions

Figure 6.1 Chronological order of milestone achievements toward catalytically active (thio)urea organocatalysts utilizing explicit double hydrogen-bonding interactions for substrate activation.

The authors interpreted the outcome of these Henry reactions with an activation of the aldehyde component through double hydrogen-bonding interactions with the thiourea moiety facilitating the product-forming nucleophilic attack of the in situ generated nitronate (Scheme 6.162) [319]. 

The investigation64,65 on the spectral data of partially deuteriated picramide 11 and 2,6-dicarbomethoxyaniline 12 shows that a double hydrogen bonding interaction is present as illustrated in 13 and 14. 

Colominas et al. [143] published a very detailed study on the dimerization of formic and acetic acids in the gas phase and in aqueous and chloroform solutions. By using quantum mechanical self-consistent reaction field and Monte Carlo calculations, they showed that the dimerization is favored in the gas phase and in a chloroform solution (1M) basically due to double hydrogen-bonded interaction between the monomers. In aqueous solution, the dimerization does not seem to occur due to the competitive solute-solvent intermolecular interactions. The computed dimerization energies are shown in Table VII. 15... 

Burrows. A.D. Mingos. D.M.P. White. A.J.P. Williams. D.J. Crystal engineering of metal complexes based on charge-augmented double hydrogen-bond interactions between thiosemicarbazides and carboxylates. Chem. Commun. 1996, (1). 97-99. 

In each structure the urea molecules have three double hydrogen-bonding interactions, donor bonds by the two endo hydrogen atoms to ether oxygen atoms and two sets of N-H donor and 0 receptor giving eight-membered rings. 

The application of 23 to the enantioselechve [3+2] cycloaddihon of dimethyl maleate with glycinate Schiff bases established a protocol for the preparation of pyrrolidine derivatives in a stereoselective fashion, where the acid-base dual function of the catalyst through the double hydrogen-bonding interaction was crucial for gaining substantial acceleration of the reachon (Scheme 7.42) [66]. 

---