Showing papers on "Hydrogen bond published in 1970"
TL;DR: In this paper, the potential of interaction for pairs and triplets of water molecules was investigated, and the most stable pair configuration involves a linear hydrogen bond of length ROO = 3.00 A and strength 4.72 kcal/mole.
Abstract: Accurate SCF calculations have been carried out to investigate the potential of interaction for pairs and triplets of water molecules. The most stable pair configuration involves a linear hydrogen bond of length ROO = 3.00 A and strength 4.72 kcal/mole. Three‐molecule nonadditivities are large in magnitude and vary in sign according to the hydrogen‐bond pattern involved. In both aqueous liquids and solids, the net trimer nonadditivity effect amounts to increased binding energy, decreased neighbor distance, and slightly enhanced tendency toward perfect tetrahedral coordination symmetry. The nonadditivity furthermore is inconsistent with the phenomenology of simple mutual electrostatic polarization between neighboring molecules.
514 citations
TL;DR: The infrared spectra of H2O, D2O and HDO in nitrogen matrices at temperatures from 20 to 4°K reveal no evidence of rotation of the water molecules as discussed by the authors.
Abstract: The infrared spectra of H2O, D2O, and HDO in nitrogen matrices at temperatures from 20 to 4°K reveal no evidence of rotation of the water molecules. Absorption features attributed to water dimers and the vibrational force constants calculated therefrom are indicative of an open structure with a single moderately weak hydrogen bond. The absence of certain HDO absorptions in the observed spectra can be interpreted as the manifestation of a stronger deuterium‐vs‐hydrogen bond.
214 citations
TL;DR: A detailed study of hydrogen bonding in the linear dimers of formamide has been performed in a non-empirical SCF framework as mentioned in this paper, where the stabilization energy was studied as a function of the distance between the monomers and a decomposition of the energy into the coulomb, exchange and polarization and charge transfer contributions.
Abstract: A detailed study of hydrogen bonding in the linear dimers of formamide has been performed in a non-empirical SCF framework. The stabilization energy is studied as a function of the distance between the monomers and a decomposition of the energy into the coulomb, exchange and polarization and charge transfer contributions is given as well as a study of the underlying changes in the electron distribution. The angular displacements around the carbonyl oxygen are studied in the antiparallel dimer and show a very shallow minimum. The effects of hydrogen bonding on the NH stretching are satisfactorily accounted for.
185 citations
TL;DR: In this article, a zigzag structure is predicted for the hydrogen fluoride dimer with a dimerization energy in reasonable agreement with experiment, and a microwave experiment is proposed to determine its exact structure.
Abstract: High‐accuracy molecular orbital calculations have been carried out on different geometries of the hydrogen fluoride dimer and the mixed water–hydrogen fluoride dimer. A zigzag (near linear) structure is predicted for the hydrogen fluoride dimer with a dimerization energy in reasonable agreement with experiment. One geometry of the mixed water–hydrogen fluoride dimer has a very large stabilization energy (10 kcal/mole), and a microwave experiment is proposed to determine its exact structure. Changes in molecular properties and charge distribution upon dimer formation are calculated and a dimer rotational barrier determined.
131 citations
130 citations
128 citations
TL;DR: In this article, the most stable linear dimer was found to have an O −H distance of 1.80 A, with the proton acceptor molecule perpendicular to the donor molecule and bent by 54° trans with respect to the end OH bond of the donor.
Abstract: Ab initio LCAO–MO–SCF calculation for the dimeric H2O system is carried out with a minimal Slater basis set with exponents optimized for H2O. The most stable linear dimer is found to have an O···H distance of 1.80 A, with the proton‐acceptor molecule perpendicular to the donor molecule and bent by 54° trans with respect to the end OH bond of the donor. The stabilization energy calculated is about 6.55 kcal/mole. The changes in the length and the stretching force constant of the donor O–H bond are also discussed. A population analysis shows that the stabilization at a larger O···H distance (>2.3 A) is essentially electrostatic, while at a smaller distance, the charge transfer becomes increasingly important.
120 citations
TL;DR: In this paper, a proposed intramolecular hydrogen bond in the 2−haloethanols has been investigated with analysis of the microwave spectra of 2−chloroethanol and 2−bromo-ethanol, for each moledule, only a form gauche about the CC bond has been observed.
Abstract: A proposed intramolecular hydrogen bond in the 2‐haloethanols has been investigated with analysis of the microwave spectra of 2‐chloroethanol and 2‐bromoethanol. For each moledule, only a form gauche about the CC bond has been observed. For the chloro compound nine isotopic species have been studied to yield the molecular coordinates of the chlorine, oxygen, hydroxyl hydrogen, and carbon atoms, and thus a molecular structure. For bromoethanol a molecular structure has been found based upon the coordinates of the bromine and hydroxyl hydrogen atoms. Principal structural conclusions are that, of the probable rotameric forms, the lowest energy form is the one allowing close approach of hydrogen and halogen—namely, the gauche–gauche for dihedral angles (CCX) (COH) close to 60°. The O–H bond length in chloroethanol is 1.008 A, about 5% longer than in ethanol. The H···X distance is ∼ 0.5 A less than the sum of the atom van der Waals radii for X = Cl, Br. The O···X distance is approximately equal to the sum of t...
107 citations
TL;DR: Results support the hypothesis that exchange of the interchain hydrogens of DNA proceeds via a local, transiently-open (non-hydrogen bonded) conformational state which is maintained (“propped” open) by the presence of two (at acid pH) or no (at alkaline pH) hydrogens at the locus of the NH … N internucleotide hydrogen bond.
96 citations
TL;DR: The crystal structure of [OCr3(CH3COO)6.3H20]-C1 -.6H20 has been determined from three-dimensional diffractometer data using Cu Ke radiation as discussed by the authors.
Abstract: The crystal structure of [OCr3(CH3COO)6.3H20]+C1 -. 6H20 has been determined from three-dimensional diffractometer data using Cu Ke radiation. The configuration of the complex cation consists of three chromium atoms linked to a central oxygen atom in a planar configuration. Each chromium atom is coordinated octahedrally by the central oxygen atom, one from each of four acetate groups and a water molecule. The acetate groups link the vertices of the three octahedra in the complex cation. The anions and those water molecules not included in the cations are disordered and lie in channels along the twofold axes. Their structure is ill-defined, but a reasonable model can be presented in which the cations are linked by a system of hydrogen bonds into zigzag layer3 perpendicular to the c axis.
94 citations
TL;DR: The microwave spectra of two isotopic species of 2-fluoroethanol (FCH2CH2OH and FCH2 CH2OD) have been analyzed to yield some information about a proposed intramolecular hydrogen bond in the molecule as mentioned in this paper.
Abstract: The microwave spectra of two isotopic species of 2‐fluoroethanol (FCH2CH2OH and FCH2CH2OD) have been analyzed to yield some information about a proposed intramolecular hydrogen bond in the molecule A molecular structure has been derived which reveals that the most stable rotamer is that which allows close approach of fluorine and hydrogen atoms The F···H distance is 242 ± 002 A; the dihedral angle FCCO is 62°12′ ± 10°, and the dihedral angle CCOH is 55°30′ ± 3° The dipole moment components are μa = 038 ± 002 D, μb = 147 ± 001 D, and μc ≈ 00 D; these are consistent with bond moment calculations A vibrational state attributed to the CC torsional motion has been assigned and determined to be 152 ± 10 cm−1 above the ground state Our results suggest a hydrogen–fluorine interaction which does not grossly distort the normal molecular charge distribution
TL;DR: In this article, a newly calculated electron density map has allowed a more detailed description of the molecular structure to be given, in relation to the probable existence of hydrogen bonds and the conformations of side chains.
Abstract: A newly calculated electron density map has allowed a more detailed description of the molecular structure to be given. The structure can be described in detail in relation to the probable existence of hydrogen bonds and the conformations of side chains. The discovery of a new buried acid group which is part of a hydrogen bonding system involving the active serine has indicated how this serine can become a powerful nucleophile, by means of a 'charge relay system'. Diffraction studies of the binding of various substituents, coupled with accurate model building, have defined the catalytic binding site.
TL;DR: The secondary structure of the cyclic moiety of oxytocin and deamino-oxytocin has been determined by nuclear magnetic resonance spectroscopy (220 MHz).
Abstract: The secondary structure of the cyclic moiety of oxytocin and deamino-oxytocin has been determined by nuclear magnetic resonance spectroscopy (220 MHz). Oxytocin, in a dimethylsulfoxide-methanol mixture, contains a β-turn involving the sequence -L-tyrosyl-L-isoleucyl-L-glutaminyl-L-asparaginyl-. Deamino-oxytocin, in addition to the β-turn, contains a hydrogen bond involving the amide hydrogen of the tyrosine residue and the peptide carbonyl group of the asparagine residue, resulting in an antiparallel β-type conformation for the ring component. An initial attempt has been made to relate conformational features of the hormonal peptides to their biological activity.
TL;DR: The total energy of hydrogen bonding is divided into electrostatic and delocalization contributions as discussed by the authors, and the total energy can be divided into two types of contributions, i.e.
Abstract: The total energy of hydrogen bonding is divided into electrostatic and delocalization contributions.
TL;DR: A non-empirical SCF calculation on the cyclic dimer of formamide in two different GTF basis sets has been performed and is compared to a similar calculation for the isolated monomer as discussed by the authors.
Abstract: A non-empirical SCF calculation on the cyclic dimer of formamide in two different GTF basis sets has been performed and is compared to a similar calculation for the isolated monomer. The energy gain per H-bond is reasonable. Both the proton-donor and proton-acceptor show a global gain in electrons at the expense of the hydrogen of the bridge and of the C atoms. This gross changes in charge are reflected in the e
1s
values. They cover a σ gain for nitrogen and a σ loss for oxygen which are studied in detail on the difference density maps in the molecular plane. The covalent character of the H bond appears very small. Both basis sets yield similar conclusions.
TL;DR: In this article, extended double zeta Gaussian basis SCF LCAO MO calculations have been performed on various configurations of the linearly hydrogen-bonded water dimer and two of the triplet clusters which occur in both cubic and hexagonal ices.
TL;DR: In the refined structure the 2′ hydroxyl group in the ribose sugar does not form a hydrogen bond within the same molecule, but may form one to a phosphate oxygen atom in the neighbouring molecule.
TL;DR: In this paper, the energy hypersurface of the system NH3 · H2O was investigated for a number of different internuclear geometries and the binding energy was calculated to be 6.28 kcal/mole.
TL;DR: In this paper, an almost linear relationship was found between the strength of weak hydrogen bonds and the amount of charge transfered, and the potential curves for proton transfer were free of the errors mentioned above.
Abstract: CNDO and INDO calculations were performed on numerous structures with hydrogen bonds of different strength. An almost linear relationship is found between the strength of weak hydrogen bonds and the amount of charge transfered.π-electrons and lone pairs are nearly equivalent in hydrogen bonding. The stereochemistry of hydrogen bonds is determined largely by additional interactions betweenσ-bonds of the two molecules. Since proton affinities are calculated too large by the CNDO method, an error is introduced in the potential curves for proton transfer in weak hydrogen bonds. In systems with strong hydrogen bonds both structures with the proton on the right and left have almost the same energy and hence the potential curves for proton transfer are free of the errors mentioned above.
TL;DR: In this article, a structure with a single linear hydrogen bond between the fluorine nuclei was obtained with an equilibrium FF distance of d(FF) = 2.85A (experimental FF distance in the cyclic hexamer 2.53A).
TL;DR: In this article, a weak hydrogen bond between water molecules and perchlorate ions in LiClO•3H2O was confirmed by the high HDO stretching frequencies for this compound.
Abstract: Infrared spectra of undeuterated and partially deuterated NaclO4•H2O, LiClO4•3H2O, and Ba(ClO4)2•3H2O were examined. Crystallographic data point to a weak hydrogen bond between water molecules and the perchlorate ions in LiClO•3H2O. This is confirmed by the high HDO stretching frequencies for this compound. The nearly identical HDO stretching frequencies in LiClO4•3H2O, NaClO4•H2O, Ba(ClO4)2•3H2O, and in aqueous solutions of these salts show that similar weak hydrogen bonds occur in all three hydrates and in solution. The hydrogen bond energy is of the order of 2 kcal/mole. In all three compounds the water molecules are symmetric at room temperature. At −165° the water molecules become highly distorted in the sodium compound, slightly distorted in the barium compound, and remain undistorted in the lithium compound. Very narrow OD stretching bands are observed, showing that the hydrogen atom positions are ordered in all three hydrates.
TL;DR: In this paper, a linear relationship between the chemical shifts of the enolic proton and the chelated carbonyl stretching vibrations has been found for various highly enolized 3-substituted 2,4-pentanediones.
TL;DR: In this paper, the effect of intramolecular hydrogen bonds on the reactivity of organic compounds is reviewed systematically and a bibliography of 200 references is provided, including 200 references from the same authors.
Abstract: Numerous new data on the effect of intramolecular hydrogen bonds on the reactivity of organic compounds are reviewed systematically. The bibliography comprises 200 references.
TL;DR: In this article, two octyl-ammonium vermiculite complexes with different 001 periodicities have been studied by i.r. spectroscopy and the results are discussed in relation to the structural models deduced from X-ray analysis.
Abstract: Two octyl-ammonium vermiculite complexes with different 001 periodicities have been studied by i.r. spectroscopy. In each case i.r. spectroscopy affords information on the orientation of the-NH3 + groups and the strength of the hydrogen bond between these groups and the silicate oxygen surfaces. Also a perturbation of the vibration of the OH groups of the silicate has been observed that seems to be related to the distance from the center of the layer at which the-NH3 + groups are situated. The i.r. results are discussed in relation to the structural models deduced from X-ray analysis.