Structure-based evaluation of the regioselectivity in bifurcated hydrogen bonds

Apicophilicity versus Hydrogen Bonding. Intramolecular Coordination and Hydrogen Bonds in N-[(Hydroxydimethylsilyl)methyl]-N,N′-propyleneurea and Its Hydrochloride. DFT and FT-IR Study and QTAIM and NBO Analysis

“…This allows to conclude that in 1a , b we have a rare case of a bifurcated bond with one component represented by a hydrogen bond and the other one by a coordination bond, both being intramolecular. The carbonyl oxygen of urea and its derivatives is known to form bifurcated hydrogen bonds and to stabilize specific conformations as well as to result in regioselective H-bonded packing via self-sorting by recognition between N–H···O(S) and O–H···O intermolecular hydrogen bonds . The CO···H bond angles in 1a , b are equal to 140 and 125°, respectively, which favors the formation of a hydrogen bond because it is much larger than the critical value of 72–80° found for the five- and six-membered rings closed by H bonds .…”

“…The carbonyl oxygen of urea and its derivatives is known to form bifurcated hydrogen bonds and to stabilize specific conformations 19 as well as to result in regioselective H-bonded packing via self-sorting by recognition between N−H•••O(S) and O−H•••O intermolecular hydrogen bonds. 20 The CO•••H bond angles in 1a,b are equal to 140 and 125°, respectively, which favors the formation of a hydrogen bond because it is much larger than the critical value of 72−80°found for the fiveand six-membered rings closed by H bonds. 21 The O•••Si distances are 2.908 (1a) and 3.298 Å (1b), that is, less than the sum of the van der Waals (vdW) radii (3.62 Å), 22 suggesting, at least for 1a, CO→Si coordination in the structure with the electronegative substituent in the equatorial plane of the silicon trigonal bipyramid.…”

Self‐Assembly of n‐Alkyl‐ and Aryl‐Side Chain Ureas and Their Derivatives as Evidenced by SEM and X‐ray Analysis

“…Simple ureas as well as complex molecules incorporating ureido groups have attracted considerable attention as transmembrane ion transporters,1–8 anion receptors,9–12 and transdermal penetration enhancers for drug delivery 13,14. Besides their well‐known ability to form strong intermolecular N–H ··· O=C hydrogen bonds15,16 allowing more efficiently to deliver drugs by amphiphilic block copolymers,17a ureas are of considerable interest for supramolecular polymer chemistry 17b. Recent developments are concerned of hydrogen‐bonded urea based supramolecular polymers,18 which easily undergo intensive intermolecular self‐organization process caused by directional H‐bonding interactions.…”