Showing papers on "Molecule published in 1970"

Clustering of Ions in Organic Polymers. A Theoretical Approach

Abstract: : Clustering of ions in organic polymers is treated from a theoretical point of view. It is shown that ions in organic media of low dielectric constant exist most probably as pairs or higher multiplets, even at relatively high temperatures. The maximum size of a non-crystalline and approximately spherical multiplet is shown to be determined by the surface areas and volumes of the participating chemical species and is of the order of 8 ion pairs or less. At relatively low temperatures, the ionic multiplets can aggregate to form a cluster, the factors involved in cluster formation being the elasticity of the chains and the electrical work of cluster collapse. Several simple geometries are assumed for ethylene-sodium methacrylate clusters, and the average inter-cluster distance for 4.5 mol % of the ionic component ranges from 44A to 95A. The experimentally determined repeat distance is of the order of 83A. (Author)

Molecular Spectroscopy by Means of ESCA III. Carbon compounds

Abstract: Carbon 1s energies are measured by ESCA for a series of aliphatic saturated compounds, carbonyl compounds, and some aromatic compounds. For convenient use in chemical structure analysis the binding energy shifts are correlated with a charge parameter obtained from electronegativity considerations. The shifts are also analyzed in terms of group shifts from which group electronegativities are derived. A comparison is made between the shifts in solid and gaseous samples and it is shown that solid state effects are small for non-ionic compounds. The observed shifts are then compared with results of semi-empirical and ab initio molecular orbital calculations on free molecules. The theoretical calculations are simplified by use of an electrostatic potential model.

Physics and chemistry of spin labels.

Abstract: Biological systems provide the physical chemist with an abundance of interesting, challenging and significant problems. One example is the problem of the molecular basis of co-operative or allosteric interactions between distant ligand or substrate binding sites in hemoglobin and in enzymes. This problem has been discussed recently in This Journal by Eigen (1968) and by Wyman (1968). Another particularly challenging problem is the molecular organization of biological membranes. Such problems tend to be particularly resistant to solution by the straight-forward application of most spectroscopic techniques, in large part because of the enormous chemical and spectroscopic complexity of biological macromolecules. This spectroscopic complexity has stimulated the use of various ‘probes’ that can be introduced into selected sites in complex systems to provide spectroscopic signals that are comparatively free from interference. The use of heavy metal atoms (‘isomorphous replacement’) in X-ray studies of protein crystals (Green, Ingram & Perutz, 1954), and fluorescent dyes in the study of proteins in solutions (Weber, 1953; Steiner & Edelhoch, 1962) are early examples. Spin labels represent a new member of the family of spectroscopic structural probes. A spin label is a synthetic paramagnetic organic free radical, usually having a molecular structure and/or chemical reactivity that results in its attachment or incorporation at some particular target site in a biological macromolecule, or assemblage of macromolecules (Ohnishi & McConnell, 1965; Stone et al. 1965). This type of probe is being used in our laboratory to study allosteric interactions in proteins, and molecular dynamics and organization in membranes.

Crystal structure of ettringite

Abstract: ETTRINGITE (Ca6[Al(OH)6]2(SO4)3.26H2O) occurs as a natural mineral, and is technically important as a hydration product of Portland and supersulphated cements and in its use, as satin white, for coating paper. It forms hexagonal, prismatic crystals which in synthetic material are often highly elongated. Bannister, Hey and Bernal1 obtained unit-cell data (hexagonal: a 11.26, c 21.48 A, space group P63/mmc, Z = 2). No crystal structure determination based on single crystal evidence has been reported, but Welin2 determined the structure of a related mineral, thaumasite (Ca6H4(SiO4)2(SO4)2(CO3)2.26H2O), which he found to be based on chains of Ca2+ and SiO44− ions with the remaining ions and water molecules in between.

Mechanism and Rate Constants of Ion–Molecule Reactions Leading to Formation of H+(H2O)n in Moist Oxygen and Air

Abstract: The formation of H+(H2O)n clusters in moist oxygen is of interest since this process must occur in the troposphere and has been observed to occur in the D region of the ionosphere. The reaction mechanism leading from O2+ to H+(H2O)n was investigated with a pulsed electron‐beam high‐pressure mass spectrometer. At oxygen pressures in the torr range and for [O2]/[H2O]>102 the major reaction proceeds by the sequence O2+→O4+→O2+·H2O→H3O+·OH→H+(H2O)2→H+(H2O)n. The rate constants for all major steps were determined. Rate constants for parallel reactions which may become important at different conditions were also determined.

Failure of Energy Transfer between Identical Aromatic Molecules on Excitation at the Long Wave Edge of the Absorption Spectrum

Abstract: Electronic energy transfer among identical molecules has been followed by the depolarization of the fluorescence in concentrated solutions as well as in dimers, polymers, and micelle systems. In the many aromatic fluorophores examined, unlike a few nonaromatic ones, transfer is much decreased or altogether undetectable on excitation at the red edge of the absorption spectrum. The phenomenon is not due to the transfer taking place during a small fraction of the total fluorescence lifetime, nor is it explainable by a decrease in overlap of absorption and emission upon edge excitation.

Some Ion–Molecule Reactions of H3+ and the Proton Affinity of H2

Abstract: The flowing afterglow technique has been used to study the reactions of H3+ with a number of neutral reactants at thermal energies. Proton transfer was the only primary reaction observed with N2, CO, CO2, N2O, NO, CH4, C2H2, H2O, and NH3. Both proton transfer and dissociative charge transfer were observed with C2H4 and C2H6, while dissociative charge transfer is the exclusive primary process with NO2. Secondary reactions were observed with NO, C2H6, C2H4, and C2H2. Cluster ions were formed between NO+ and NO2 and H2O, between H3O+ and H2O, CO2, and CO, and between NH4+ and NH3 and H2O. Proton transfer was also observed between HN2+ and CO2, N2O, CH4, and H2O, and between HO2+ and H2 and N2. Rate constants were obtained for these reactions and are discussed. Limits could be placed on the proton affinity (P.A.) of H2 from the failure to observe rapid proton transfer to O2 and the observation of proton transfer to N2. These indicate 4.2 < P.A. (H2)< 4.7 eV with a recommended value of 4.4 eV. The technique ca...

Flowing Afterglow Studies of the Reactions of the Rare‐Gas Molecular Ions He2+, Ne2+, and Ar2+ with Molecules and Rare‐Gas Atoms

Abstract: The flowing afterglow technique has been used to measure rate coefficients and product channels for the reactions of He2+, Ne2+, and Ar2+ with the rare‐gas atoms Ne, Ar, and Kr, and with the molecules NO, O2, CO, N2, and CO2 at 200°K. These reactions are found to proceed principally by asymmetric charge transfer. The experimental results for the reactions of the rare‐gas molecular ions with rare‐gas atoms indicate a correlation between reaction probability and reaction exoergicity analogous to that observed for asymmetric atomic ion–atomic neutral charge‐transfer reactions. The reactions with molecules are found to proceed with unit reaction probability with the exception of the reactions Ar2++O2 and Ar2++NO. The reaction probability for the reactions of the molecular rare‐gas ions with molecules is not very sensitive to an energy resonance criterion. Finally, rate coefficients and reaction channels for the reaction of the mixed rare‐gas molecular ions HeNe+, ArKr+, and ArCO+ with Ne, Kr, and CO, respecti...

Carbon-13 chemical shifts of bicyclic compounds

Abstract: 13C NMR absorption spectra of 50 bicyclic hydrocarbons, alcohols and ketones have been measured, in addition to some terpenes. The 13C chemical shifts are approximately additive for similar compounds and can be used for the determination of molecular structure; they differ for endo- and exo-isomers, just as in proton spectra. These quite regular and predictable 13C shift differences are much larger and are caused by the 1,4-nonbonded interaction between atoms heavier than hydrogen, not by magnetic anisotropy effects.

Molecular Orbital Studies of Hydrogen Bonds: Dimeric H2O with the Slater Minimal Basis Set

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.

Chemistry of the bis[.pi.-(3)-1,2-dicarbollyl] metalates of nickel and palladium

Abstract: : The synthesis, reactions, and structures associated with the 'sandwich'-bonded bis(pi-(3)-1,2-dicarbollyl) complexes of nickel and palladium, (M(n+)(1,2-B9C2H11)2(n-4)(M=Ni,Pd), and their carbon-substituted derivatives are discussed. The nickel and palladium bis(dicarbollyl) systems each contain species with the metal atoms in the formal +2 (d8, two unpaired electrons for nickel, diamagnetic for palladium), +3 (d7, one unpaired electron), and +4 (d6, diamagnetic) oxidation states. X-ray diffraction studies coupled with magnetic, spectral, and electrochemical data were obtained for structural information. The uncharged (pi-(3)-1,2-B9C2H11)2M(IV) derivatives are Lewis acids which form addition compounds with a variety of 'soft' Lewis bases, e.g., halide ions, thiocyanate ion, naphthalene, etc. The C, C'-dimethyl-substituted nickel and palladium systems, M(1,2-B9H9C2(CH3)2)2, exhibit facile thermal ligand rearrangement reactions leading to three isomeric series of complexes. In these isomerization reactions, a ligand carbon atom in the icosahedral surface was found to migrate away from the metal atom while remaining adjacent to the carbon atom in the open pentagonal face of the ligand. Similar rearrangements occur in the unsubstituted Ni(1,2-B9C2H11)2 complex at 360-400C in the vapor phase. Cyclic voltammetry, optical resolution studies, kinetic and nmr data and their roles in the structure elucidation of these complexes are presented. (Author)

Microwave Spectra and Intramolecular Hydrogen Bonding in the 2‐Haloethanols: Molecular Structure and Quadrupole Coupling Constants for 2‐Chloroethanol and 2‐Bromoethanol

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...

Crystal‐structure of ruthenium red and stereochemistry of its pectic stain

Abstract: A B S T R A C T A crystal-structure analysis of ruthenium red has indicated a composition of [Ru3Cls (OH)a (NH3)12 (H20)31. Each ruthenium ion is coordinated cubically with at least eight chloride ions, and it is coordinated octahedrally with (1) four ammonia molecules in a square planar configuration and (2) either two water molecules or two hydroxyl ions in the axis perpendicular to that plane. The staining group is composed of the ruthenium ion and the associated square planar complex of four ammonia molecules. The staining site in the host molecule must have two negative charges 4.2 A apart and space to accommodate the staining group, lying with its plane perpendicular to the axis between these charges. It is shown that in pectic acid such a staining site occurs between each monomer unit and its next adjacent neighbor. PECTIC MATERIALS will often take up ruthenium red avidly from a dilute solution and in so doing acquire a pale-to-deep red stain. Mangin (1893) noted that the other components of the cell wall were not stained at all and believed that he had found a specific indicator for pectic substances. The reason for this specificity was not explained and has long remained a puzzle. Later it was found that ruthenium red could stain other compounds, such as volutin, i.e., nucleic acid (Meyer, 1904), and oxidized cellulose (FreyWyssling, 1959). The question then arises: What exactly is being stained by ruthenium red? It seems reasonable to expect that a determination of the structure of this compound could reveal the nature of the grouping which complexes with it. This purpose has underlain the present investigation, the first part of which is a crystal-structure analysis of ruthenium red and the second an interpretation of the structure of the stained complex.

Cu2+ – fulvic acid chelation equilibrium in 0.1 m KCl at 25.0 °C

Abstract: Cu2+ reacts with fulvic acid to form a site-bound chelate on the fulvic acid polymer molecules. It is deduced from literature evidence that this chelate is the same type that Cu2+ forms with salicy...

The crystal structure of a basic chromium acetate compound, [OCr3(CH3COO)6.3H2O]+Cl−.6H2O, having feeble paramagnetism

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.

Microwave Spectrum and Intramolecular Hydrogen Bonding in 2‐Fluoroethanol

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

Inelastic collisions between excited alkali atoms and molecules. VII. Sensitized fluorescence and quenching in mixtures of rubidium with H2, HD, D2, N2, CH4, CD4, C2H4, and C2.H6

Abstract: 52P1/2 ↔ 52P3/2 mixing and 52S1/2 ← 52P1/2, 2P3/2 quenching in rubidium, induced in collisions with ground state H2, HD, D2, N2, CH4, CD4, C2H4, and C2H6 molecules, have been investigated using met...