HO Hydrogen Bond Research Articles

Hydrogen-bond mediated transitional adlayer of glycine on Si(111)7×7 at room temperature

The growth of glycine film by thermal evaporation on Si(111)7 x 7 at room temperature has been studied by X-ray photoemission. In contrast to common carboxylic acids, glycine is found to adsorb on Si(111)7 x 7 dissociatively through cleavage of a N-H bond instead of O-H bond. The intricate evolution of the observed N 1s features at 399.1, 401.4, and 402.2 eV with increasing film thickness demonstrates the existence of a transitional adlayer between the first adlayer and the zwitterionic multilayer. This transitional adlayer is estimated to be 1-2 adlayer thick and is characterized by the presence of intermolecular N...HO hydrogen bond. An intramolecular proton transfer mechanism is proposed to account for the adsorption process through the amino group.

X-ray and Hydrogen-bonding Properties of 1-((1H-benzotriazol-1-yl)methyl)naphthalen-2-ol

The solid state structure of 1-((1H-benzotriazol-1-yl)methyl)naphthalen-2-ol, C17H13N3O, shows that this Mannich base crystallizes forming intermolecular N⋯HO hydrogen bonds, rather than intramolecular ones. Factors contributing to this choice of hydrogen-bonding mode are discussed. The compound crystallizes in the monoclinic system, P21/c space group, with lattice constants: a = 11.7934(9) Å, b = 14.3002(14) Å, c = 8.4444(8) Å, β = 106.243(5) deg, V = 1367.3(2) Å3, Z = 4, F(000) = 576, R1 = 6.96%, wR2 = 11.4%.

The intramolecular C–F⋯HO hydrogen bond of 2-fluorophenyldiphenylmethanol

The intramolecular C–F⋯HO hydrogen bond of 2-fluorophenyldiphenylmethanol was observed by X-ray crystallographic analysis and NMR spectroscopy. The features of the spectra were compared to triphenylmethanol (a fluorine-free analog) and 2-fluorophenyldiphenylmethane.

Solvent effect on the role of methyl groups in formation of O···HO hydrogen bond in dimethyl ether–methanol complex

The role of the methyl groups in the formation of the O···HO hydrogen bond between dimethyl ether (DME) and methanol molecules in different solvents has been studied with quantum chemical calculations at the MP2/6-31+G(d,p) and B3LYP/6-311++G(d,p) levels. As indicated in the changes of the O⋯H binding distance, O⋯O distance, OH bond length, OH stretching frequency, and complexation energy, the strength of the O⋯HO hydrogen bond in the complex increases as solvent polarity increases. The enhancing effect of solvent on the interaction is analyzed with the natural bond orbital (NBO) method. The charge changes of the methyl groups show that the methyl groups of DME are electron-donating and the methyl group of methanol is electron-withdrawing, both making positive contributions to the formation of the O⋯HO hydrogen bond. However, these contributions decrease with increasing solvent polarity as indicated in the decrease of the methyl charge transfer. The electron-donating ability of the methyl group in DME is greater than the electron-withdrawing ability of the methyl group in methanol, and such difference increases with increasing solvent polarity. The methyl role and weakening effect of solvent on the methyl role in the formation of hydrogen bond are investigated in views of the orbital interactions.

Lactic acid in solution: Investigations of lactic acid self-aggregation and hydrogen bonding interactions with water and methanol using vibrational absorption and vibrational circular dichroism spectroscopies

The infrared vibrational absorption (VA) and vibrational circular dichroism (VCD) spectral features of L-(+)-lactic acid (LA) in CDCl3 solution are concentration dependent, showing evidence of oligomerization with increasing concentrations. To understand the observed spectra, geometry optimizations, vibrational frequencies, and VA and VCD intensities were evaluated for (LA)n with n=1-4 using density functional theory calculations at the B3LYP6-311++G(d,p), B3LYP/cc-pVTZ, and in some cases, B3LYP/aug-cc-pVTZ levels of theory. Comparisons with the experimental spectra indicate that the lowest energy LA dimer (AA), formed by two C Double Bond O...HO hydrogen bonds, is one of the dominating species in solution at room temperature. Possible contributions from the LA trimer and tetramer are also discussed. To model the VA and VCD spectra of LA in water and in methanol, both implicit polarizable continuum model and explicit hydrogen bonding considerations were used. For explicit hydrogen bonding, geometry optimizations of the AA-(water)n and AA-(methanol)n complexes, with n=2,4,6, were performed, and the corresponding VA and VCD spectra were simulated. Comparisons of the calculated and experimental VA and VCD spectra in the range of 1000-1800 cm(-1) show that AA-(water)n with n=6 best reproduces the experimental spectra in water. On the other hand, AA-(methanol)n with n=2 reproduces well the experimental results taken in methanol solution. In addition, we found evidence of chirality transfer, i.e., some vibrational bands of the achiral water subunits gain VCD strength upon complexation with the chiral LA solute. The study is the first to use VCD spectroscopy to probe the structures of LA aggregates and hydrogen bonding solvation clusters in the solution phase.

Influence of Bond Fixation in Benzo-Annulated N-Salicylideneanilines and Their ortho-C(O)X Derivatives (X = CH3, NH2, OCH3) on Tautomeric Equilibria in Solution

1H, 13C, and 15N NMR spectra show that an ortho-C(=O)X group present in the molecules of N-salicylideneanthranilamide (X = NH2), methyl N-salicylideneanthranilate (X = OCH3), N-salicylidene-o-aminoacetophenone (X = CH3), and their benzo analogues have only a minor effect on the tautomeric OH/NH-equilibrium in solution. Only two of three possible tautomers were detected. Lability of the absent form was proved by theoretical calculations. Calculated energies show that the enolimino form (OH) is less stable than the enaminone (NH) form only for dibenzo-annulated N-salicylideneanilines. The population of each species in the tautomeric mixture was found to be inversely proportional to its energy. Application of the geometry-based aromaticity index HOMA shows that the effectiveness of the pi-electron delocalization in different rings in the molecule depends mostly on the position of benzo-annulation. Both the NH...O and N...HO hydrogen bonds present in the NH and OH tautomers, respectively, increase the aromaticity of the quasirings H-O-C=C-C=N and O=C-C=C-N-H and decrease the aromatic character of the fused benzene ring. These results seem to be reliable when N-salicylideneanilines studied are compared with naphthalene and their benzo-annulated derivatives, i.e., phenanthrene, anthracene, and triphenylene. An analysis of the effectiveness of pi-electron delocalization confirms that in all cases studied, the OH form is more stable. Although the HOMA values and calculated energies are not a criterion that allows determination of the dominating tautomer, both of these parameters correctly show the effect of changes in the molecular topology on tautomeric preferences.

Hybrid Tungstocuprate [Cu(2,2′-bpy) 3] 2 H 4 [CuW 12O 40] · 6H 2 O Based on Keggin Polyoxoanion [CuW 12O 40] 6− with Cu II as Heteroatom

A novel hybrid tungstocuprate(II) [Cu(2,2′-bpy)3]2 H4 [CuW12O40] · 6H2O(2,2′-bpy = 2,2′-bipyridine) was synthesized via hydrothermal method and characterized using elemental analyses, IR, UV, XPS, TG-DSC, EPR, and X-ray single crystal diffraction. The structural analysis shows that the complex consists of an unusual Keggin-type polyoxoanion [CuW12O40]6- and a pair of chiral complex cations [Cu(2,2′-bpy)3]+ together with four protons and six crystallization water molecules, and the Keggin polyoxoanion is connected with [Cu(2,2′-bpy)3]+ via multiple C—HO hydrogen bonds resulting in a dimer.

Conformational and tautomeric eccentricities of 2‐acetyl‐1,8‐dihydroxynaphthalenes

Tautomerism in aromatic systems with oxygen substitutents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen-hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3C==O methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B), each having two intramolecular O...HO hydrogen bonds: one involving an acetyl oxygen and the neighboring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT).DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O-1 and O-8 centers, which is modulated by formation of an OH-1...O-8 or OH-8...O1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH...O...C hydrogen bond are other factors.Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state.

Hydrogen-Bond Interactions of Nicotine and Acetylcholine Salts: A Combined Crystallographic, Spectroscopic, Thermodynamic and Theoretical Study

The hydrogen-bond (HB) interactions of the monocharged active forms of nicotine and acetylcholine (ACh) have been compared theoretically by using density functional theory (DFT) calculations and experimentally on the basis of crystallographic observations and the measurement of equilibrium constants in solution. The 2,4,6-trinitrophenolate (picrate) counterion was used to determine the experimental HB basicity of the cations despite its potential multisite HB acceptor properties. The preferred HB interaction site of the ammonium picrate salts was determined from a survey of crystallographic data found in the Cambridge Structural Database (CSD) and is supported by theoretical calculations. Two distinct classes of ammonium groups were characterised depending on the absence (quaternary ammonium) or presence (tertiary, secondary and primary ammoniums) of an N(+)HO hydrogen bond linking the two ions. The crystal structure of nicotinium picrate was determined and compared with that of ACh. This analysis revealed the peculiar behaviour of the ammonium moiety of nicotinic acetylcholine receptor (nAChR) ligands towards the picrate anion. Dedicated methods have been developed to separate the individual contributions of the anion and cation accepting sites to the overall HB basicity of the ion pairs measured in solution. The HB basicities of the picrate anions associated with the two different ammonium classes were determined in dichloromethane solution by using several model ion pairs with non-basic ammonium cations. The experimental and theoretical studies performed on the nicotine and ACh cations consistently show the significant HB ability of the acceptor site of nAChR agonists in their charged form. Both the greater HB basicity of the pyridinic nitrogen over the carbonyl oxygen and the greater HB acidity of the N(+)H unit relative to N(+)CH could contribute to the higher affinity for nAChRs of nicotine-like ligands relative to ACh-like ligands.

Hydrogen-bonding Interaction of 1,2,3-triazine-waters Complexes

Density functional theory B3LYP method with 6-31++G** basis was used to optimize the geometries of the ground states for 1,2,3-triazine-(H2O)n (n=1,2,3) complexes. All calculations indicate that the 1,2,3-triazine-water complexes in the ground states have strong hydrogen-bonding interaction, and the complex having a N HO hydrogen bond and a chain of water molecules which is terminated by a O HC hydrogen bond is the most stable. The HO stretching modes of complexes are red-shifted relative to that of the monomer. In addition, the Natural bond orbit (NBO) analysis indicates that the intermolecular charge transfer between 1,2,3-triazine and water is 0.0222e, 0.0261e and 0.0273e for the most stable 1:1, 1:2 and 1:3 complexes, respectively. The first singlet (n, *) vertical excitation energy of the monomer 1,2,3-triazine and the hydrogen-bonding complexes of 1,2,3-triazine-(H2O)n were investigated by time-dependent density functional theory.

Two polymorphs of 4-hydroxy-1-methylpiperidine betaine hydrochloride studied by X-ray and DFT methods

Two polymorphic crystals (α and β) of 4-hydroxy-1-methylpiperidine betaine hydrochloride, HO-MPBH +·Cl −, have been synthesized and their structures solved by the X-ray diffraction methods. The piperidine ring adopts the chair conformation and the hydroxy group at C(4) in the α-polymorph is in the axial position, while in the β-polymorph it is in the equatorial one. The CH 2COOH group in both polymorphs is in the equatorial position. Crystals of α-HO-MPBH +·Cl − (ax–eq) are monoclinic with the space group P2 1/ n. The molecules are linked by COOH⋯Cl⋯HO hydrogen bonds of 2.988(2) and 3.158(3) Å into infinite chains antiparallel to each other. Crystals of β-HO-MPBH +·Cl − (eq–eq) are orthorhombic with the space group Pca2 1. There are two non-equivalent chains in the unit cell, formed by β(1) and β(2) molecules, which contain different COOH⋯Cl⋯HO hydrogen bonds; 2.974(2) and 3.147(3) Å in β(1) and 3.011(2) and 3.147(3) Å in β(2). These chains are linked by C–H⋯Cl and van der Waals contacts into polar ribbons. The optimized bond lengths and bond angles at the B3LYP/6-31G(d,p) level of theory are in good agreement with the X-ray data, except position of the hydrogen bonded proton and conformation of the carboxylate group. In the α-polymorph, the H-bonded proton is closer to the chloride atom and the O C–O·H unit is cis, while in the β-polymorph the betaine is protonated with the trans O C–O–H unit. In consequence, the β-polymorph is ca. 9.7 kcal/mol more stable than the α-one. From eight optimized structures of HO-MPBH + cations the most stable is ax–eq- cis conformer and the less stable is eq–eq- trans.

Crystal and molecular structure of the 1:1 complex of 1-piperidineacetic acid with 2,6-dichloro-4-nitrophenol studied by X-ray diffraction and B3LYP calculation

Crystal structure of the 1:1 complex of 1-piperidineacetic acid (PAA) with 2,6-dichloro-4-nitrophenol (DCNP) has been solved by X-ray diffraction. The crystals are triclinic, space group P 1 ¯ with a=7.609(2), b=9.456(2), c=11.206(2) Å, α=103.77(3)°, β=103.21(3)°, γ=96.48(3)°, Z=2 and R=0.0378. PAA is linked with DCNP through the O −⋯HO hydrogen bond of 2.469(2) Å. Two such complexes form a centrosymmetric dimer, (PAA·DCNP) 2, in which the PAA moieties, as zwitterions, are joined by two N +–H⋯O hydrogen bonds of 2.869(2) Å, around the symmetry center. The intermolecular C–H⋯O contacts and the intramolecular N +⋯O electrostatic interactions consolidate the crystal lattice. In the isolated dimer molecule, (PAA·DCNP) 2, as predicted by the B3LYP/6-31G(d,p) method, the O–H⋯O hydrogen bonds are longer, while the N +–H⋯O ones are shorter than in the crystal.

Hydrogen bonding interactions of benzylidene type Schiff bases studied by vibrational spectroscopic and computational methods

The structural features of four benzylidene type Schiff bases [(E)-benzaldehyde-N-phenyl imine, (A) (E)-2-hydroxybenzaldehyde-N-phenyl imine (B) (E)-benzaldehyde-N-2-hydroxyphenyl imine (C) (E)-2-hydroxybenzaldehyde-N-2-hydroxyphenyl imine (D)] were studied by FT-IR spectroscopy in solution, photoacoustic and Raman spectroscopies in the solid state and quantum chemical calculations. It was found that molecule D dimerised in the solid state with concomitant loss of aromaticity in the benzylidene ring. Beside the intermolecular CO⋯HO hydrogen bonds, intramolecular N–H⋯CO hydrogen bonds could be found experimentally as well as computationally. Spectra taken in solution and ab initio quantum chemical calculation helped to identify hydrogen bonding interactions occurring for compounds B and C. Intramolecular OH⋯N hydrogen bond predominated in molecule B, while this interaction, although it existed, was weaker.

Synthesis, spectroscopy, and theoretical studies of platinum(ii) phosphate complexes

A method for the synthesis of [Pt(dpp)2(en)] (dpp = diphenyl phosphato, en = ethane-1,2-diamine) is reported, and the resulting complex characterised spectroscopically. The synthesis involves displacement of chloride ligands using silver(I), and requires non-aqueous media. Density functional studies suggest typical square-planar coordination geometry, with rather weak Pt–O bonds and very strong N–HO hydrogen bonds. Comparison with model complexes suggests that phosphates are weaker ligands to platinum(II) than nitrates, and are therefore likely to be highly reactive.

The structure of liquid methanol by H/D substitution technique of neutron diffraction

Neutron diffraction (ND) measurements on liquid methanol (CD3OD,CD3O(H/D),CD3OH) under ambient conditions have been performed to obtain the total (intra-+intermolecular), Gdist(r) and intermolecular, Ginter(r) radial distribution functions (rdfs) for the three samples. The extent to which intermolecular structure is affected by using two different intramolecular models is discussed. The H/D substitution on hydroxyl–hydrogen (Ho) has been used to extract the partial distribution functions, GXHodist/inter(r) (X=C, O, and H—a methyl hydrogen) and GXXdist/inter(r) from the difference techniques of ND at both the distinct and intermolecular levels. The O–Ho bond length, which has been the subject of controversy in the past, is found purely from the partial distribution function, GXHodist(r) to be 0.98±0.01 Å. The C–H distance obtained from the GXXdist(r) partial is 1.08±0.01 Å. These distances determined by fitting an intramolecular model to the total distinct structure functions are 0.961±0.001 Å and 1.096±0.001 Å, respectively. The GXXinter(r) function, dominated by contributions from the methyl groups, apart from showing broad oscillations extending up to ∼14 Å is featureless, mainly because of cancellation effects from six contributing pairs. The Ho⋯Ho partial pair distribution function (pdf), gHoHo(r), also determined from the second-order difference, shows that only one other Ho atom can be found within a mean Ho⋯Ho separation of 2.36 Å. The average position of the O⋯Ho hydrogen bond determined purely from experimental GXHointer(r) partial distribution function, at 1.75±0.03 Å is found to lie in the range (1.75–1.95 Å) of values reported from computer simulation results.

Intramolecular electric field effect on a1J(C,H) NMR spin-spin coupling constant. an experimental and theoretical study

An experimental study of the effects of intramolecular electric fields on 1J(C,H) coupling constants involving a formyl proton in a series of 5-X-salicylaldehydes is reported. The particularly large electric field component along the CcHf bond, calculated for X=NO2 , leads to a measured substituent effect of 7.36 Hz. For other X substituents a linear correlation was found between the calculated substituent electric field component along the Cc—Hf bond and the substituent effect on 1J(Cc ,Hf). To determine if 5-X substituents affect the intramolecular CO· · ·HO hydrogen bond, NBO analyses were carried out on 5-NO2 − and 5-H-salicylaldehyde, and they were compared with those corresponding to benzaldehyde and phenol. The effects of interactions other than the electrostatic one on 1J(Cc ,Hf) couplings were ruled out. The experimental results are in agreement with theoretical predictions published previously. Copyright © 1999 John Wiley & Sons, Ltd.

Preparation of stable α-(nonamethylmetallocenyl)-α-hydroxycarbocations and their transformations

Abstract It has been shown that the structure of α-(nonamethylmetallocenyl)-α-hydroxycarbocations (M = Fe, Ru, Os), prepared by protonation of formylnonamethylmetallocenes with HBF4 and CF3COOH, depends on the nature of the metal and anion and is determined by the relative basicities. The Fe-containing salts have an open fulvenoid structure with an interionic hydrogen bond O-H … X irrespective of the nature of anion (X = BF4−, CF3COO−). The Ru- and Os-containing salts, in which the metal atoms are more basic than Fe, have, in the case of the weakly basic BF4− anion, a cyclic structure with an intramolecular M … HO hydrogen bond, while in the case of the more basic X = F− or CF3COO− anions they are transformed to the open fulvenoid structure with an interionic hydrogen bond OH … X, the structure of which has been established by an X-ray diffraction study of C 5 Me 5 RuMe 4 C + H − OH … F − . When the Fe-containing salts are kept in polar solvents or stored in the solid state for a long time they are entirely converted into paramagnetic salts of formylnonamethylferrocenium, the structure of which was confirmed by the oxidation of formylnonamethylferrocene using AgBF4.

C–HLO Hydrogen bonded multi-point recognition in molecular assemblies of dibenzylidene ketones and 1,3,5-trinitrobenzenes

Dibenzylideneacetone1a, 2,5-dibenzylidenecyclopentanone 1b, 2,6-dibenzylidenecyclohexanone 1c and 2,5-dibenzylidenecyclopent-3-enone 1d form crystalline stoichiometric complexes with 1,3,5-trinitrobenzene 2a, picryl chloride 2b and picric acid 2c. The structures of these complexes are mediated by multi-point C–HO hydrogen bonds. Some of these patterns of molecular recognition also contain stronger O–HO hydrogen bonds. The C–HO hydrogen bonds within these multi-point supramolecular synthons are generally shorter and more linear than the other C–HO hydrogen bonds found in these complexes.

Preparation and properties of stable protonation products of permethylmetallocenecarbaldehydes (M = Fe, Ru, Os)

The products ofO-protonation of metallocenecarbaldehydes C5Me5MC5Me4CHO (M = Fe, Ru, Os) with HBF4 and CF3COOH were obtained for the first time, the adducts [C5Me5MC5Me4CH(OH)]+BF− being isolated in a pure state. The structures of the adducts depend on the nature of the metal and the anion and are governed by the correlation between their basicities. For example, the Fe-containing adducts have an open fulvenoid structure with an interionic hydrogen bond irrespective of the nature of the anion X (X = BF4−, CF3COO−). In the case of the Ru- and Os-containing adducts in which the metal atoms are more basic than iron, the competition between the metal atom and the anion for the formation of a hydrogen bond with the OH group is clearly manifested in the IR and1H NMR spectra. In the presence of the weakly basic BF4− anion, a cyclic structure with an intramolecular M...HO hydrogen bond is formed, while in the presence of a more basic F− or CF3COO− anion. it transforms to the open fulvenoid structure with an interionic hydrogen bond. The structures of the compounds obtained were determined by IR and1H NMR spectra, and the structure of the (C5Me5RuC5Me4CHOH)+...F− salt was proved by X-ray diffraction analysis.

Electronic and vibrational spectroscopy of phototautomerizing heteroazaaromatics with intramolecular hydrogen bonds

Four phototautomerizing derivatives of bipyridyl with intramolecular single and double hydrogen bonds are studied by IR and electronic spectroscopy. A broad IR band corresponding to the stretching vibration of the OH group engaged in the N⋯HO hydrogen bond is observed in all compounds in solutions, KBr tablets and low-temperature Ar matrices. Variations of excited state behaviour observed among the four molecules are well correlated with the ground state hydrogen bonding characteristics.