Normal Coordinate Analysis in Cartesian Space II. Planar Symmetric XYn Molecules

Force constants of planar symmetric XY_n type molecules in the Cartesian space have been derived in terms of the vibrational frequencies. The force constants and normal coordinates of some planar XY₃ molecules with available isotoptic data are worked out. Further study of infrared absorption spectra of square planar XY₄ complex ions will be needed for the present normal coordinate analysis.     

Normal Coordinate Analysis in Cartesian Space I. Planar Symmetric Xn Molecules

Normal coordinate analysis of X_n type molecules can be carried out in the Cartesian space as well as in the internal space. Force constants in Cartesian coordinates for aromatic compounds belonging to D_nh group are calculated. The force constants of benzene are evaluated from vibrational frequencies both in the ground state and the ¹B_1u excited state. The calculated frequencies of planar carbon vibration of annulene of any N are tabulated. The normal coordinates derived from the calculation of 10-annulene are roughly the same of naphthalene derived more elaborated by Scherer. The normal modes in 10-annulene are indeed good approximations to the ones in naphthalene. This conclusion is valid for the other aromatic compounds.     

Force Constant Calculation in Mass-Weighted Cartesian Coordinates. Linear XYX and XYZ Type Molecules

Force constants of simple linear XYX and XYZ types of molecules have been calculated in using the method of mass-weighted cartesian coordinates. Relations and results between force constants in mass-weighted cartesian coordinates and in internal coordinates were also discussed.     

Bridging Carbonyl Groups in Transition Metal Clusters; A Normal Coordinate Analysis

The suggestion that the infrared active (CO) features associated with the bridging carbonyls in transition metal cluster carbonyls may provide structural information is examined by a normal coordinate analysis. The species studied are four tetranuclear clusters, each containing an equilateral triangle of metal atoms, the edges of which are spanned by carbonyl groups. Isotopically enriched species have been prepared and are included in the study so that the problem is well over-determined. Excellent agreement between calculated spectra and those observed under high resolution, including relative intensity data, is obtained. The results confirm that it is reasonable to expect that the features associated with bridging carbonyls in such compounds may provide structural information.     

三羟甲基甲胺的红外和Raman光谱研究和简正坐标分析

在4000—50cm~(-1)波段范围内测定了三羟甲基甲胺晶体分子的红外光谱和Raman光谱。采用简化的普遍价力场(SGVFF)进行了简正坐标分析。振动基频的计算值与观测值符合良好。两者平均偏差小于1.0％,证实了振动谱带的归属,确定了相应的力常数。最后讨论了谱带的归属问题和所得结果的合理性和可靠性。     

Boundary Effects in the Hexagonal Packing of Rod-Like Molecules Inside a Right Circular Cylindrical Domain. III. The Case of Arbitrarily Oriented Spherocylindrical Molecules

We study the organization of spherocylindrical molecules inside a freely rotating right circular cylindrical domain at the gas/liquid interface. The analysis is made under the assumption that the molecules are rigid and close packed, and that they are oriented parallel to each other. The direction and angle of their common orientation are completely arbitrary. We obtain exact analytic expressions for the lattice of molecular centers and its boundaries as a function of molecular dimensions, molecular orientation, and domain size. As a first application, we derive the number of molecules in a domain, and the packing fraction. The results obtained are essential when attempting to analytically model a Langmuir film where the global order of the film is less than the local order of the domains.     

Alkylperoxy and Alkyl Radicals. Part 2. IR Spectra and Normal Coordinate Analysis of CH3O2 and Several Isotopically Labelled Species

The methylperoxy radical has been isolated in matrices of Ar + 10% O₂ and its IR spectrum observed. The following isotopic species were used in the investigation: CH₃, ¹³CH₃, CD₃, ¹⁶O₂, ¹⁸O₂, and ¹⁶O¹⁸O. A total of 64 frequencies were identified for the various isotopically labelled peroxy radicals. A normal coordinate analysis for the methylperoxy radical has been made. Good agreement between the observed and calculated frequencies was obtained.     

Raman and Infrared Spectra, Ab Initio Calculations, Normal Coordinate Analysis, and Conformational Stability of 2-Methoxypropene

The Raman (3500–40 cm^–1) and infrared (3500–70 cm^–1) spectra of gaseous and solid 2-methoxypropene, CH₃O(CH₃)C=CH₂, and the isotopomers, CD₃O(CH₃)C=CH₂ and CH₃O(CD₃)C=CD₂ have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurements. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, which remains in the solid. Assignments are provided for the fundamentals of all three isotopomers for the cis conformer with C_s symmetry. The far-infrared spectra of all three isotopic species have been recorded at a resolution of 0.1 cm^–1 in the gas and 1.0 cm^–1 in the solid. The parameters of the potential function governing the asymmetric torsion are determined to be V₃ = 1485 ± 9 cm^–1 and V₆ = –55 ± 4 cm^–1 for the d₀ compound, where only two terms were determined, since a second conformer was not evident. The barrier to internal rotation for the methyl group attached to the oxygen atom is 1370 ± 8 cm^–1 and the C—CH₃ barrier is 772 ± 5 cm^–1. Ab initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium structural parameters, harmonic force constants, fundamental frequencies, infrared intensities, Raman activities, depolarization values, and conformational stability. The predicted values have been compared to the experimental values where appropriate.     

Normal coordinate analysis of malononitriles: III. The valence force field of malononitrile and its deuterated derivatives

The procedure of Becher and Mattes [1] has been applied to the calculation of the valence force field for malononitrile H₂C(CN)₂ and its deuterated derivatives, HDC(CN)₂ and D₂C(CN)₂. The results have been localized in the space of the real solutions of the inverse vibrational eigenvalue problem. The convergence of the method has been demonstrated. The average deviation between observed and calculated frequencies on isotopic substitution is less than 1 %.     

Theory of Chromatography of Rigid Molecules on Hydroxyapatite Columns with Small Loads: III. Theory on the Basis of the Classical Theory of Adsorption Chromatography for the Case when Molecules are Adsorbed on to a Single Type of Crystal Site

Hydroxyapatite chromatography with small loads carried out with a linear gradient of competing ions has been investigated theoretically on the basis of the classical theory of adsorption chromatography for the case when molecules are adsorbed on to a single type of crystal site. By using this result, the experimental chromatography of lysozyme has been re-examined and the limit of the resolving power of the hydroxyapatite column is discussed.     

Orbital Reactions Through Space. Part III. Rate Enhancement in Epoxidation of an Olefin by a Proximate Hydroxyl Group

As part of a programme directed towards the synthesis of polycyclic systems containing a bicyclo[4.2.0]octa-2,4-diene moiety (or a potential precursor thereof) joined at the 7,8 position, suitable as substrates for the 1,2-photoarmatisation reaction¹, we sought a simple route to the epixide (5). We considered this offered the opening to prepare the 8-oxatricyclo-     

[Cl_3Sb(μ-S)SbCl_3]~(2-)阴离子的红外光谱和简正坐标分析

在500—100cm~(-1)波段范围内测定了[Cl_3Sb(μ-S)SbCl_3]~(2-)阴离子的Fourier变换红外光谱。采用简化的普遍价力场(SGVFF)进行了简正坐标分析,振动基频的计算值与观测值符合良好,两者平均偏差小于1.0％,证实了振动谱带的归属,确定了相应的力常数。最后讨论了谱带归属问题和所得结果的合理性和可靠性。     

Searching for Stable,Five‐Coordinate Aquated Al(III) Species. Water Exchange Mechanism and Effect of pH.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Analysis of nonvolatile oxidation products of polypropylene. III. Photodegradation

The nonvolatile oxidation products of photodegraded polypropylene have been analyzed by infrared spectroscopy and chemical reactions. The major functional group is ester followed by vinyl alkene, then acid. In comparison, thermally oxidized polypropylene contains relatively more aldehyde, ketone, and γ-lactone and much less ester and vinyl alkene. Photodegraded polyethylene contains mostly vinyl alkene followed by carboxylic acid. Gel-permeation chromatography (GPC) determined the decrease in polypropylene molecular weights with exposure time. A calculation determined that there is one functional group formed per chain scission; in thermal oxidation there are two groups formed per scission.     

Six‐Coordinate Lanthanide Complexes: Slow Relaxation of Magnetization in the Dysprosium(III) Complex

A series of six‐coordinate lanthanide complexes {(H₃O)[Ln(NA)₂]?H₂O}_n (H₂NA=5‐hydroxynicotinic acid; Ln=Gd^III ( 1?Gd ); Tb^III ( 2?Tb ); Dy^III ( 3?Dy ); Ho^III ( 4?Ho )) have been synthesized from aqueous solution and fully characterized. Slow relaxation of the magnetization was observed in 3?Dy . To suppress the quantum tunneling of the magnetization, 3?Dy diluted by diamagnetic Y^III ions was also synthesized and magnetically studied. Interesting butterfly‐like hysteresis loops and an enhanced energy barrier for the slow relaxation of magnetization were observed in diluted 3?Dy . The energy barrier (Δ_τ) and pre‐exponential factor (τ₀) of the diluted 3?Dy are 75 K and 4.21×10^?5 s, respectively. This work illustrates a successful way to obtain low‐coordination‐number lanthanide complexes by a framework approach to show single‐ion‐magnet‐like behavior.     

Applications of High Performance Size Exclusion Chromatography To The Analysis of Oligomers and Small Molecules

Abstract

Size exclusion chromatography of small molecules has been investigated with high efficiency columns of crosslinked polystyrene. Performance evaluations and calibrations have been determined in toluene and in tetrahydrofuran, and the effect of the solvents on solute retention is discussed. Oligomer separations of samples obtained in the thermal degradation of several polymeric materials are reported, and the utility of the technique for polymer degradation studies is clearly evidentiated.