Hydrogenbond

Investigations of the solubilities of aromatic compounds in concentrated and aqueous sulphuric acids showed the activity coefficients of nitrocompounds to behave unusually when the nitro-compound was dissolved in acid much more dilute than required to effect protonation. This behaviour is thought to arise from changes in the hydrogenbonding of the nitro group with the solvent. 

Hydroboration is the addition of a boron—hydrogenbond across a double or triple carbon—carbon bond to give an organoborane ... 

N-Heterocyclic fragments as active centers of biomolecules with hydrogenbonding receptors 98PAC2371. 

Fig. 1. Fraction of non-hydrogenbonded ( free ) OH-groups in water, methanol and ethanol determined by IR-spectroscopy. xF is the fraction of hole defects for water71...

Mixtures of solvent plus solute that obey Raoult s law are described as ideal. For such solutions, heat of mixing. A// = 0. For systems of similar sized molecules where there are no strong interactions, such as hydrogenbonding, it is found that Mi is close to zero. 

An ab initio MO calculation by Jorgensen revealed enhanced hydrogen bonding of a water molecule to the transition states for the Diels-Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile, which indicates that the observed rate accelerations for Diels-Alder reactions in aqueous solution arise from the hydrogenbonding effect in addition to a relatively constant hydrophobic term.7,76 Ab initio calculation using a self-consistent reaction field continuum model shows that electronic and nuclear polarization effects in solution are crucial to explain the stereoselectivity of nonsymmetrical... 

Model of the DNA double helix. Hydrogenbonding bridges keep the two DNA strands together. Without hydrogen bonds, life would not be possible. 

Stabilizing the folded state also benefits from optimizing hydrogenbonding interactions, with water providing donor and acceptor groups to polar side chains and main chain C=0 and N—H groups left exposed on the surface of the folded structure. Direct evidence for such... 

Fig. 19. The combination of (a) a strong stereospecific hydrogenbonding interaction of the C60 carbonyl of 9-EtG with an en NH in [Ru(r 6-dha)(en)(9-EtG)]+ and (b) a strong ti-ti arene-nucleobase stacking interaction is responsible for the high preference of G over A observed for such ruthenium—arene complexes.

---