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 %.     

Normal coordinate treatment of actinide(IV)-hexabromides

Molecular force field studies of hexabromo-thorates(IV) and-uranates(IV) have been carried out using four different force field models. Weighted least square adjustment has been used to fit the observed frequencies. Mean amplitudes of vibration have also been calculated at 0°K and 298°K. The trends of force constants and mean amplitudes have also been discussed.

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Normal-Koordinaten Berechnungen an Actiniden(IV)-hexabromiden

Zusammenfassung Es wurden für die Rechnungen an Hexabromo-thoraten(IV) und-uranaten(IV) vier verschiedene Modelle herangezogen. Die beobachteten Frequenzen wurden mittels gewichteter Kleinster-Fehlerquadrat-Methode angepaßt. Die Trends bei den Kraftkonstanten und den mittleren Amplituden der einzelnen Verbindungen werden diskutiert.

     

Normal coordinate analysis of 1,4-diethynylbenzene

Normal coordinate analysis has been carried out for the 1,4-diethynyl benzene molecule on the basis of experimental frequencies from the natural compound and its deuterated derivatives. A canonic force field has been set up by transferring force constants from related molecules. This force field has been refined to the experimental frequencies. A reassignment of the vibrational spectrum of 1,4-diethynyl benzene has been carried out.     

Vibrational analysis of methylphosphonic acid and its anions: II. Normal coordinate analysis

Normal coordinate analysis of methylphosphonic acid and its anions, is reported. Symmetry force constants were obtained using the method of Becher and Mattes. The fundamental vibrations are described by the potential energy distribution. An approximate method for the calculation of the errors on the symmetry force constants, due to the uncertainties on the vibrational frequencies, is presented. A discussion on the prediction of the CD₃ rocking mode is given.     

Normal coordinate analysis of the indole ring

Normal coordinate calculations have been performed for indole and 11 deuterated indoles. The set of valence force constants obtained is able to reproduce i.r. and Raman frequencies with an average error of about 6 cm⁻¹. Extension of the force field to skatole has also been made and the calculated frequency shifts on isotopic substitutions are compared with the experimental ones of tryptophan. The general agreement between the calculation and experiment suggests that the vibrational modes obtained here are of practical use in the interpretation of Raman spectra of proteins containing tryptophan residues.     

Normal coordinate analysis of cis-1,4-polybutadiene

The fundamental vibrational frequencies of an isolated chain of cis-1,4-polybutadiene have been calculated. Infrared and polarized Raman data are used in the force constant refinement routine. The assignments of the vibrational frequencies are discussed in terms of the potential energy distribution.     

Normal coordinate analysis of trans-stilbene and tolane

The vibrational frequencies and modes of trans-stilbene and tolane have been calculated using a simplified overlay valence force field previously developed for a series of smaller conjugated molecules. The force constants have been directly transferred assuming that the large molecules can be regarded as weakly coupled systems. Several unexpected changes in frequencies and modes on isotopic substitution are discussed, the most interesting ones occurring in the Raman spectrum of α,α′-¹³C substituted trans-stilbene. On the basis of the calculations many revisions in the assignments have been made. The rms frequency deviations are 8.0 cm⁻¹ and 6.9 cm⁻¹ for trans-stilbene and tolane, respectively.     

Normal coordinate analysis of some uranyl pentafluoride complexes

A normal coordinate analysis of the uranyl Cs₃ pentafluoride complexes, M₃UO₂F₅ (M=K, Rb, NH₄) has been made, neglecting the outer M⁺ ions, in order to check the vibrational assignments so far made experimentally for the observed bands and to obtain the force constants associated with the uranium—oxygen (UO) and uranium—fluorine (UF) bonds.In addition to the analysis, π-bonding energies of the UO bonds in the complexes have been estimated from the UO stretching force constants with an aid of molecular orbital theory.     

Vibrational analysis of flavin derivatives: Normal coordinate treatments of lumiflavin

Normal coordinate calculations were carried out for lumiflavin (Lf) and isotope- or methyl-substituted derivatives of it; [3-ND]Lf, [3-NMe]Lf, [2-¹³C]Lf, [4a-¹³C]Lf, [5-¹⁵N]Lf, [1, 3-¹⁵N]Lf and [1, 3, 5-¹⁵N]Lf. Using 69 force constants of the modified local symmetry force field, the observed resonance Raman bands and i.r. bands of these molecules could be assigned to the normal modes. The vibrational modes are represented in terms of the calculated atomic displacement vectors.     

Normal coordinate analysis of the vibrational spectra of stannatranes

The vibrational spectra of mono-chloro-2,8,9-tricarbastannatrane polycrystalline samples are assigned on the basis of the normal coordinate treatment of the Cl—stannatrane molecule. The initial set of force constants was composed from the force fields of the n-paraffins and the (CH₃)₃SnCl molecule. Within the frame of this force field model the force constant of the transannular Sn⋯N bond was estimated and it was shown that the formation of this bond leads to a significant decrease in the SnCl force constant compared to the reference molecule.     

Normal coordinate analysis of bilirubin vibrational spectra: Effects of intramolecular hydrogen bonding

Normal coordinate analyses are presented for half-bilirubin molecules. Calculations for the AB pyrromethenone include intramolecular hydrogen bonds, while those for the CD chromophore exclude intramolecular hydrogen bonds. Valence force-field parameters have been optimized to correlate closely with the IR and Raman spectra of the target molecules. The results of the calculations are compared with the spectra of bilirubin IXa and various model compounds in the solid state and solution.     

Conformational analysis and electronic structure of monothiodiacetamide: Normal coordinate analysis and molecular orbital study

The infrared spectra of monothiodiacetamide (MTDA, CH₃CONHCSCH₃) and its N-deuterated compound in solution, solid state and at low temperature are measured. Normal coordinate analysis for the planar vibrations ofMTDA-d ₀ and –d ₁ have been performed for the two most probablecis-trans-CONHCS-or-CSNHCO-conformers using a simpleUrey-Bradley force function. The conformation ofMTDA derived from the vibrational spectra is supported by the all valence CNDO/2 molecular orbital method. The vibrational assignments and the electronic structure ofMTDA are also given.

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Konformationsanalyse und elektronische Struktur von Monothiodiacetamid. Normalkoordinatenanalyse und MO-Studie

Zusammenfassung Das Infrarotspektrum von Monothiodiacetamid (MTDA, CH₃CONHCSCH₃) und der entsprechenden N-deuterierten Derivate wurde in Lösung, im Festzustand und bei tiefer Temperatur gemessen. Die Normalkoordinatenanalyse der möglichen planaren Konformeren wurde mittels einer einfachenUrey-Bradley-Funktion durchgeführt. Die dabei abgeleitete Konformation vonMTDA steht im Einklang mit einer semiempirischen quantenchemischen Rechnung (CNDO/2). Die Zuordnung der Schwingungen und die Elektronendichteverteilung inMTDA werden angegeben.

     

Normal coordinate analysis of didmide hydrazine and its protonated species

A normal coordinate analysis has been performed for the molecules N₂H₂, N₂H₄ and ions N₂H₅⁺, N₂H₆²⁺ using vibrational frequencies taken from the literature. A Modified Valence Force Field with identical parameters for all species has been obtained.     

Normal coordinate analysis of H8Si8O12

Normal coordinate analysis of the fundamental vibrations of H₈Si₈O₁₂ has been carried out. Because of the octahedral symmetry, the 78 vibrational degrees of freedom lead to 33 different vibrations, six of which are infrared active, 13 are Raman active and 14 are inactive. From the internal coordinates one gets 116 symmetry coordinates. We describe a straightforward method for determining the internal symmetry coordinates of any molecular system. Internal coordinates, symmetry force constants, the full set of orthonormal symmetry coordinates as well as the 38 redundant orthonormal symmetry coordinates of H₈Si₈O₁₂ are tabulated. The potential energy distribution analysis shows that most of the fundamental vibrations can be very well interpreted in terms of the internal vibrations ν(SiH), ν(SiO), δ(SiH), δ(OSiO) and δ(SiOSi) which makes it easy to compare them with vibrations observed in other silsesquioxanes and similar silicon compounds.     

Normal coordinate analysis and thermodynamic functions of niobium and tantalum pentahalides

Normal coordinate treatment of NbX₅ and TaX₅ (X = F, Cl, Br) in the Urey-Bradley force fields was performed using published vibrational frequencies. The analysis was carried out with Wilson's FG formalism and the force constants were evaluated by a computer program based on the least-squares-fit method. Normal coordinates, potential energy distributions and thermodynamic functions were also determined. The results support the reported assignments of the fundamental frequencies of the pentachlorides and the pentabromides, and suggest that the pentafluoride assignments are incorrect.     

Normal coordinate analysis of lanthanoide oxychlorides and oxybromides with Matlockite-type structure

A normal coordinate and force constant calculation was carried out for lanthanoid oxyhalogenides LnOX with Ln = La, Pr, Nd, Sm, Eu and X = Cl, Br on the basis of a modified valence force field by fitting in the frequencies of the i.r. active vibrations. From the obtained force constants frequencies of the Raman-active lattice vibrations are calculated and compared with experimental determined frequencies.