J.A. Faniran

Electronic absorption spectra and structures of aniline and its 4-chloro, pentafluoro and pentachloro derivatives

Abstract The relative sensitivities of oscillator strengths and transition energies in an electronic band system to solvent and substitutent perturbations have allowed the assignment of the electronic bands in pentachloroaniline, pentafluoroaniline, 4-chloroaniline and aniline. While the 1 L b , 1 L a and 1 B b transitions are distinct in pentachloroaniline, the 1 L a and 1 B b transitions appear to be mixed in pentafluoroaniline, 4-chloroaniline or aniline. In all these compounds, except aniline, the 1 L b transition shows vibrational bands which are most distinct in nonpolar solvents. Analysis of the vibrational contours and Franck—Condon envelope showed changes in equilibrium nuclear configuration as the origin of the vibrational bands and that in pentachloroaniline and pentafluoroaniline different vibrational modes are responsible for intensity borrowing characteristic of the 1 L b transition. Determination of excited state dipole moment relative to ground states by solvent shift of the transition energy of an electronic band reveals that the excited states of all transitions have more charged character, the charge transfer character of the 1 L a transition being dominant.

Vibrational spectra and torsional barriers of pentachloro and pentabromophenols

Abstract The i.r. and Raman spectra of pentachloro-(PCP) and pentabromophenols (PBP) have been studied and the fundamental frequencies assigned on the basis of Cs symmetry. Thermodynamic properties—heat capacity, entropy, enthalpy and free energy—have been calculated at several temperatures. Good agreement is obtained between the calculated and experimentally determined thermodynamic functions for pentachlorophenol. The two-fold potential barrier hindering the internal rotation of the  OH group were found to be 1318±9 cm−1 in PCP and 1447±6 cm−1 in PBP.

Physico-chemical studies of metal haloacetates—III. Infrared spectra of crystalline divalent metal dichloroacetates

Abstract The i.r. spectra of Mg, Ca, Sr, Ba, Mn(II), Co(II), Ni(II) and Zn monoiodoacetates have been investigated. Except for the zinc complex, the results conform with a symmetric bridging configuration similar to that found in the chloro- and bromo- analogues.

Physicochemical studies of metal haloacetates—VI Infrared spectra of alkaline-earth metals and lead trifluoroacetates

Abstract The i.r. spectra of crystalline Mg, Ca and Pb trifluoroacetates have been investigated between 400—300 cm − . The trihaloacetate group vibrations are found to be more influenced by the mass and steric hindrance of the CX 3 group as compared to the electron withdrawing ability of the halogens.

The i.r. and Raman spectra of pentafluoroaniline

Abstract The i.r. spectrum of pentafluoroaniline in vapour and solid states and in carbon tetrachloride solution has been recorded between 4000-40 cm − . Raman spectra of the solid and solutions in CS 2 and CCl 4 have also been recorded. From Raman depolarization measurements, the symmetry of C 6 F 5 NH 2 appears to be C s . An assignment of the fundamentals is proposed. Frequencies arising from the C 6 F 5 X group vibrations ( X = NH 2 ) are found to be very similar to those of related C 6 F 5 X molecules ( X = halogen, CN or CH 3 ) and are little affected by the X substituent in the series.

The i.r. and Raman spectra of solid trichloroacetonitrile

Abstract The i.r. and Raman spectra of polycrystalline films of CCl 3 CN have been recorded at liquid nitrogen temperature. Chlorine isotope splitting has been resolved for the v 3 fundamental and crystal splittings have been observed for five of the fundamentals. A possible crystal structure is discussed. Raman wavenumbers and depolarization ratios are included for liquid CCl 3 CN.

Vibrational spectra of mesidine and mesitol

Abstract The i.r. and Raman spectra of 2,4,6-trimethylaniline (mesidine) and 2,4,6-trimethylphenol (mesitol) have been measured in solutions and as solids and the observed frequencies assigned to various normal modes. The barriers to internal rotation of the NH 2 group about the CN bond in mesidine and the OH group about the CO bond in mesitol were found to be 18.6 and 15.6 kJ mol −1 , respectively. By comparison with unsubstituted aniline and phenol, these values suggest an increase in double-bond character of the CN and CO bonds which most likely arises from an inductive interaction of the methyl groups with the aromatic rings.

A vibration assignment of tetrabromothiophene

Abstract The i.r. and Raman spectra of tetrabromothiophene were recorded in the region 4000–40 cm −1 . An assignment of the fundamentals has been proposed on the basis of band intensities and comparison with spectra of related molecules. The molar thermodynamic properties have been obtained at several temperatures for a rigid-rotor harmonic oscillator approximation.

Vibrational spectra and torsional barrier of 2,4,6-triiodophenol

Abstract The i.r. and Raman spectra of 2,4,6-triiodophenol (s-TIP) have been recorded and assignments proposed for the frequencies of the normal modes. Some absorption bands useful for characterizing symmetrically-trisubstituted halophenols have also been identified. In CCl 4 solution, no evidence could be found in favour of self-association of s-TIP molecules. The barrier height hindering the rotation of the OH group about the phenyl-O bond was estimated to be 2068±20 cm −1 .

Infrared spectrum and crystal structure of polycrystalline bromoform

Abstract The i.r. spectra of polycrystalline films of CHBr 3 have been recorded at 77 K between 4000–400 cm −1 . The splittings of the observed fundamentals appear to be consistent with an orthorhombic crystal structure with molecules located on sites of C s symmetry and a probable factor group C 2ν or D 2 h .