Search results for "Hydrogen bond"
showing 10 items of 1310 documents
Light-induced, site-selective isomerization of glyoxylic acid in solid xenon
2014
Abstract The isomerization of glyoxylic acid (GA) and its water complex was studied in a low temperature xenon matrix. The aim of these studies was to understand how xenon environment affects the cis-trans GA interconversion upon near infrared irradiation. In solid xenon, the GA conformers are embedded in two different matrix sites. These show up as different vibrational bands of GA that exhibit different kinetic rates of isomerization. Upon complexation with water, the isomerization process slows down. Xenon matrix appears not to affect energy relaxation process via intramolecular or intermolecular hydrogen bond as compared with previous experiments in an argon.
Azonia spiro polyaza macrocycles containing biphenyl subunits as anion and cation receptors
2011
Abstract The reaction of N-Boc triprotected cyclam with bis(chloromethyl)biphenyl followed by the corresponding deprotection of the nitrogen atoms allows the preparation of receptor 3 containing an azonia spiro subunit. This receptor shows slightly increased basicity than cyclam, in particular for the formation of the appropriate triply charged species as a consequence of the reduced capacity of the structure present in 3 to stabilize the species with lower protonation degrees through the formation of intramolecular hydrogen bonds. The properties of 3 as a receptor for Cu2+ and Zn2+ and the anions derived from PO 4 3 − ( Pi ) , P 2 O 7 4 − ( PPi ) , P 3 O 10 5 − ( TPP ) and ATP have been st…
(Z)-1-Chloro-1-[2-(2-nitrophenyl)hydrazinylidene]propan-2-one
2012
The title molecule, C9H8ClN3O3, lies on a mirror plane. Intramolecular N—H...O and N—H...Cl hydrogen bonds occur. One of the nitro O atoms is disordered (site occupancy ratio = 0.40:0.10).
Cocrystal trimorphism as a consequence of the orthogonality of halogen- and hydrogen-bonds synthons.
2019
True trimorphic cocrystals, i.e. multi-component molecular crystals of identical composition that exhibit three polymorphic structures, are exceedingly rare and so far no halogen-bonded cocrystal system has been reported to exhibit trimorphism. Here we describe a unique example of a trimorphic cocrystal exhibiting both hydrogen and halogen bonds in which the differences between polymorphs reveal their orthogonality, evident by the apparently independent variation of well-defined hydrogen- and halogen-bonded motifs. peerReviewed
The enrichment ratio of atomic contacts in crystals, an indicator derived from the Hirshfeld surface analysis
2014
An enrichment ratio is derived from the decomposition of the crystal contact surface between pairs of interacting chemical species. The propensity of different contact types to form is investigated.
Bis[S-hexyl 3-(thiophen-2-ylmethylidene)dithiocarbazato-κ2N3,S]palladium(II)
2016
In the title complex, [Pd(C12H17N2S3)2], the PdIIatom exhibits a square-planar coordination geometry with theN,S-chelating ligands arranged in atransconfiguration. Intramolecular C—H...S hydrogen bonds are observed. In the crystal, molecules are linked by weak C—H...N hydrogen-bond interactions, forming chains parallel to thebaxis.
Electronic and Steric Effects: How Do They Work in Ionic Liquids? The Case of Benzoic Acid Dissociation
2010
The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydr…
3,4′,5,5′-Tetramethoxy-2′-methylbiphenyl-4-ol
2019
The asymmetric unit of the title compound, C17H20O5, contains two independent molecules, A and B, with similar geometries [dihedral angles between the phenyl rings = 56.19 (8) and 54.98 (7)°, respectively]. Intramolecular O—H...O hydrogen bonds occur in both molecules. In the crystal, the A molecules form [1\overline{1}0] chains linked by O—H...O hydrogen bonds from the hydroxyl group to one of the methoxy O atoms. The B molecules form O—H...O hydrogen bonds to the hydroxyl O atoms of the A molecules and thus act as fixed spacers between the chains of molecule A. Some weak C—H...O contacts are also present.
A DFT study on the NHC catalysed Michael addition of enols to α,β-unsaturated acyl-azoliums. A base catalysed C–C bond-formation step
2013
The NHC catalysed nucleophilic additions of enols to α,β-unsaturated acyl-azolium intermediates have been investigated using DFT methods at the MPWB1K/6-31G** computational level. In the direct and the conjugate additions, formation of a hydrogen bond (HB) with the carboxyl oxygen is not sufficient to favour the C-C bond formation as a consequence of the low nucleophilic character of enols. Interestingly, when enols form a HB with the chloride counterion, the activation energies associated with the conjugate addition decrease as a consequence of the increased nucleophilic character of enols and the increased electrophilic character of the 'acyl-azolium + Cl' ion pair. Analysis of the DFT re…
Bifunctional Acid-Base Catalysis
2011
Acid-base catalysis with bifunctional catalysts is a very prominent catalytic strategy in both small-molecule organocatalysts as well as enzyme catalysis. In both worlds, small-molecule catalysts and enzymatic catalysis, a variety of different general acids or hydrogen bond donors are used. In this chapter, important parallels between small molecule catalysts and enzymes are discussed, and a comparison is also made to the emerging field of frustrated Lewis pair catalysis.