Minoru Akiyama

Complete quadratic force-field and absolute band intensities for out-of-plane vibrations of pyridine and its deuterium derivatives in CS2 solution

Abstract Infrared spectra were taken for pyridine and its 2- d -, 3- d -, 4- d -, and d 5 -homologs in CS 2 solution. All the out-of-plane bands were carefully reassigned. In assigning Cue5f8H out-of-plane bands their binary combinations played an important part. The least-squares refinement determined a complete, twenty-one constant, quadratic force-field for the out-of-plane vibrations of pyridine, reproducing the forty assigned frequencies with a root-mean-square difference of 2.1 cm −1 . Out-of-plane absolute band intensities were measured in CS 2 solution. Comparison between the observed and the calculated band intensities determined the effective charges located on the individual atoms of pyridine. The results for both the force constants and the effective-charge distribution of pyridine were found to be quite reasonable when compared with those of benzene.

Conformational analysis of p-terphenyl in solution state by infrared band intensifies

Abstract Infrared absolute band intensities of the nonplanar vibrations were measured for p -terphenyl in CS 2 solution in order to determine the molecular structure in the solution state. The normal coordinate treatments were carried out for the seven representative conformations of p -terphenyl due to the torsions about the two Cue5f8C bonds between phenyl rings. Considering the vibrational modes obtained, the nonplanar band intensities were calculated for both of the fundamentals and their combinations of the seven conformations. Comparison between the calculated and the observed intensities resulted in almost unequivocal assignments of the nonplanar bands and also led to some informative results for understanding the conformation in the solution state.

Infrared band intensities of out-of-plane vibrations for thiophene and its deuterium and methyl derivatives in CS2 solution

Absolute band intensities of the out-of-plane fundamentals and their combinations were measured for thiophene and its deuterium and methyl derivatives in CS2 solution; and they were successfully interpreted by introducing several bond-moment parameters, and then combined with the normal coordinate calculation. Fundamental band intensities for various deuterothiophenes gave the four bond-moment values of thiophene, which were transferable to the Cue5f8H out-of-plane modes of various methylthiophenes. Cue5f8H out-of-plane combination band intensities for various deutero- and methylthiophenes were well explained in terms of the second derivatives of dipole moment with respect to the Cue5f8H deformation. Net-charge distribution on a thiophene molecule was obtained from the bond-moment data and it was in good agreement with the benzene result given by the MO calculations.

Infrared band intensities and the complete quadratic force field for planar vibrations of gaseous benzene

Abstract Infrared absolute band intensities of the planar fundamental modes were measured for benzene and its deuterium homologs in the gas phase, and were successfully interpreted in terms of effective charges and charge flux parameters. The charge flux parameters were determined from the intensities by taking the effective charge on the hydrogen atom of benzene to be 0.125 e, a value which had previously been obtained from the nonplanar modes. The parameters determined were found to be quite consistent with those of other molecules. The complete quadratic planar force field of benzene was also introduced, the 273 assigned frequencies having been reproduced with a root-mean-square difference of 2.9 cm −1 .

Determination of effective-charge distribution on some deuterobenzenes from their out-of-plane gas-band intensities

Abstract Infrared band intensities of the out-of-plane fundamental vibrations were measured for benzene and its deuterium derivatives in the gas phase by using the Wilson-Wells method. The 41 intensity values obtained were successfully interpreted in terms of only one parameter, the effective charge on the hydrogen atom of benzene: ϵ 0 (H) = 0.125 ± 0.001 e . This value was consistent with the results given by the quadrupole-moment measurements and by the MO calculations. The effective charge in the gas phase was also compared with that in the solution state.

A simplified CH out-of-plane force field for methylpyridines and their N-oxides

Abstract Normal coordinate treatments were carried out for Cue5f8H out-of-plane vibrations of pyridine, pyridine-N-oxide, and their methyl-derivatives on the basis of the simplified method presented previously, where the motions of only the ring hydrogen atoms were taken into account. A simplified and transferable force field was introduced and five force constants were refined for each of the two series of methylpyridines and their N-oxides. The assigned frequencies corresponding to the umbrella mode were reproduced with a root-mean-square difference of about 0.5% for each series.

Internal field correction for infrared band intensity measured in solutions

The Polo and Wilson equation has been widely used to eliminate the effect of the internal electric field from the observed infrared absorption intensities in the condensed phase. However, the validity of this equation for solution states has not been confirmed yet. This paper gives a new equation for the internal electric field correction in solution states according to the two kinds of molecular models. The equation obtained is identical to that of Polo and Wilson to the limit of pure liquid.

Infrared combination band intensities of CH out-of-plane vibrations for pyridine and its deuterium derivatives in CS2 solution

Abstract Absolute band intensities of the Cue5f8H(D) out-of-plane binary combinations were measured for pyridine and its 2- d -, 3- d -, and 4- d -derivatives in CS 2 solution. The band assignments and the force field used here were those given in one of our previous papers. The band intensities were calculated by introducing the following two parameters: the Cue5f8H(D) bond moment μ(Cue5f8H) and the second derivative with respect to its out-of-plane deformation, ∂ 2 μ( Cue5f8H ) ∂θ 2 . For both the frequencies and the band intensities, the observed values were in very good agreement with the calculated values, by taking μ(Cue5f8H) = 0.7 D and ∂ 2 μ( Cue5f8H ) ∂θ 2 = −1.38 D/rad 2 at the equilibrium position. These two parameters were remarkably close to those of benzene and thiophene.

Internal field correction on infrared spectra of condensed phases

Infrared spectra observed in condensed phases must be corrected for the effect of the internal electric field. A new equation for such correction was derived by employing the Lorentz internal field model. The previous equation which has been widely used was also derived in order to make clear why the difference occurs, and the validity of the present derivation was pointed out. Moreover, the new equation was applied to the 678 cm−1 band of liquid benzene, and the results were found to be quite reasonable.

Conformational distributions of N-acetyl-L-proline N-methylamide in CDCl3 solution studied by NMR and IR spectra

Abstract The amide proton NMR chemical shifts have been widely used for the determination of the population fractions of hydrogen bonding states in peptides. However, in such works the determination of the limiting chemical shift for each hydrogen bonding state is quite problematic. In our previous paper, we derived the expression for the limiting chemical shift as a function of IR band intensity and chemical shift, and then determined the values of the limiting chemical shifts at various temperatures. In the present study, the method was improved, and was applied to conformational studies of N -acetyl- L -proline N -methylamide (APM) in CDCl 3 solution. The population fractions obtained led to thermodynamic quantities of APM for both intra- and intermolecular hydrogen bondings, and also to the complete interpretation of the temperature dependence of the amide proton resonance.