FOURIER-TRANSFORM RAMAN AND INFRARED SPECTRA AND VIBRATIONAL ASSIGNMENT FOR SOLID GLUTARIMIDE

Abstract

The FT-Raman and FT-IR spectra of crystalline glutarimide and its N-deuterated derivative have been recorded in the range 4000-100 cm^?1. A complete vibrational assignment is given for all internal modes and is supported by normal coordinate analysis based on a general valence force field. The calculated frequencies are in very good agreement with experiment. A close similarity is found for frequencies of the corresponding vibrations of glutarimide and uracils in the solid state. It is concluded that the strength of hydrogen bonding in glutarimide is very similar to that in crystalline pyrimidine nucleic bases.     

Vibrational Analysis of the A3Π0−X1Σ+ and B3Π1−X1Σ+ Subsystems of the GaBr Molecule

Abstract

The emission band spectrum of gallium monobromide has been excited in a dc hollow cathode discharge. bands of the ³Π_0,1?X¹Σ⁺ system, lying in the range from 340 to 370 nm have been recorded at high resolution and measured. The previous vibrational analysis has been revised and corrected. New vibrational assignment has been proposed and improved vibrational constants of the upper and lower electronic states have been determined.     

Vibrational Structure of the B—X System of Isotopic Ago Molecules

Spectra of ¹⁰⁷Ag¹⁸O and ¹⁰⁷Ag¹⁶O molecules have been obtained in a low-pressure arc in oxygen atmosphere, and recorded with medium dispersion. Vibrational assignments for the bands of B ²π —X²π system were verified by the study of the oxygen isotope effect, and the vibrational constants were obtained for the states involved in transitions.     

Interpretation of Polarized Absorption and Emission Spectra of Molecules Incorporated in Stretched Polymer Films

Different methods for the interpretation of linear dichroic spectra of molecules incorporated in uniaxial matrices are discussed. A method based on the combination of both polarized absorption and emission measurements is described for the resolution of absorption and emission spectra into their different polarized components, and for the investigation of molecular distributions in the oriented matrix. The distributions of some planar molecules of different shapes incorporated in stretched polyethylene films are presented.     

Headgroup Mobility in the Low Temperature Phase (Lσ′) of DPPC

The ¹H decoupled Phosphorus NMR lineshape of DPPC-water dispersions shows characteristic changes when passing through the three thermotropic phase transitions: subtransition (Lσ′ - Lβ′), pretransition (Lβ′ - Pβ′) and main transition (Pβ -Lα). At the subtransition the spectrum changes from a non-axial-symmetric powder spectrum (Lσ′) to an axial-symmetric one (Lβ′). The two higher phase transitions are characterized by decreases in the intrinsic ³¹P line widths and the chemical shift anisotropy.

Proton-enhanced ¹³C-spectra of the same compound, with natural isotope abundance, recorded at 76 MHz permit the resolved observation of different carbon-positions in the headgroup. In particular the N-(CH₃)₃-carbon nuclei exhibit a narrow isotropic lineshape throughout the entire observed temperature range (-20°C … 50°C). This implies that rotational motion in this moiety does not cease below the subtransition.

To summarize, the headgroup mobility in the Lσ'-phase can be described as follows: The rotation of the entire choline group about the chemical bonds between the phosphate group and the glycerol-backbone is slow on the ³¹P-NMR timescale, the N-(CH₃)₃ end of the choline moiety, however, still undergoes rapid rotational motion. This picture is in accordance with recent interpretations of our ‘H-NMR second moment analysis.     

Electric field‐induced birefringence,optical rotatory power and conoscopic measurements of a chiral antiferroelectric smectic liquid crystal

Using a photoelastic modulator‐based novel set‐up, the electric field‐induced in‐plane birefringence and the optical rotatory power (ORP) were measured of an antiferroelectric liquid crystalline compound (12OF1M7) in its various phases using 30 µm homeotropic cells. Some specific signatures of the in‐plane birefringence and of the ORP for the various phases are being established. A relatively small threshold field is needed for the unwinding process of the antiferroelectric phase with a unit cell of four layers [SmC_A*(1/2)] compared with that for two layers [SmC_A*(0)]. On application of the electric field on the high temperature side of the SmC_A*(1/2) phase (80.1–81.5°C), a field‐induced phase transition is shown to occur directly to the SmC* phase, whereas on the lower temperature side (79.4–80.1°C) the transition takes place to SmC* via the SmC_A*(1/3) phase. The in‐plane birefringence exhibits a critical power law dependence for the SmC*–SmA transition. The ORP changes sign within the temperature range of the phase with a unit cell of three layers, reflecting a change in the handedness during this phase. Using tilted conoscopy, the results for the biaxiality and the apparent tilt angle for a smectic liquid crystal with a tilt angle greater than 18° in the ferroelectric phase are reported. The biaxiality implies the difference in the refractive indices between the two minor axes of the refractive index ellipsoid. The optical transmittance at visible and IR wavelengths for free‐standing films reveal characteristic reflection bands for these phases. The modulated structures of the reflected bands appear just above the SmC_A* phase and below SmC_A*(1/3); these are possibly due to an easy deformation of the phase by the surfaces.     

Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes

Polycyclic aromatic compounds consisting of four or five fused anthracene units were synthesized by PtCl₂-catalyzed cycloisomerization as novel long expanded helicenes. These compounds have helical structures with significant stacking of the terminal anthracene moieties at 0.33 nm interlayer distance. In the UV-vis and fluorescence spectra, the absorption and emission bands were red-shifted as the number of fused anthracene units was increased. The characteristic broad and long-lived emission bands of the long analogues are explained by the excimer-like stabilization of the excited state. These photophysical data as well as their cyclic voltammetric data are discussed on the basis of the π-conjugation and interlayer π⋅⋅⋅π interactions in the molecular structures and the molecular orbitals. The barrier and mechanism of helical inversion are also reported.     

The Electronic Absorption Spectra of Binuclear Complexes,[Cu(o-phen) (sal)No3 and [Cu2 (sacch)4(im)4] Crystal

The electronic absorption spectra of crystals of the title componds were recorded and the experimental results were explained quantitatively with the ligand field theory and the radial wave function of bound Cu(II) cation. With these spactra, the range of magnetic interactions between two Cu(II) ions of the title compounds are discussed.     

Structures and Spectral Characteristics of Silylborane,Silylaluminum Hydride,Silylphosphine, and Silyl Mercaptan

The vibrational frequencies of several silanes H₃SiX (X=BH₂, AlH₂, PH₂ and SH) are determined. The infrared and Raman spectra are plotted. Several scale procedures were use to improve the theoretical spectra. The geometric parameters in the planar, staggered and eclipsed structures of these species are fully optimized and compared with ab initio calculations. Basis set effects on the calculated structures are discussed. A few thermodynamic parameters, net atomic charges, dipole moment and energy are also computed.