Laboratory for Structural Chemistry

Research Description

1 : Gas Electron Diffraction.
Geometrical structures of free molecules are determined precisely by means of electron diffraction. The gas sample is effused through a nozzle with an i.d. of 0.5 mm or less into a vacuum chamber. The electron beam with an acceleration voltage of about 40 kV crosses the gas flow just in front of the nozzle tip. The intensities of the electrons diffracted by the sample gas are recorded on photographic plates. By analyzing its angular distribution, the bond lengths of the sample molecules are determined with uncertainties of 0.001-0.006 angstroms and the bond angles are determined with uncertainties of 0.1-1 degree. At the same time, the relative abundance of the conformers (e.g., trans and gauche) can be determined.

In this laboratory, organic compounds such as ethers, amines and esters have been chosen to determine their structures and conformations and consequently, the effect of the factors such as steric repulsion and inductive effect on them have been investigated.

Recently, research efforts were made to apply the experimental method to more difficult cases. That is, the molecular structures of non-volatile compounds (e.g., compounds forming liquid crystals) and short-lived intermediate species were determined. The path of a thermal rearrangement reaction was discussed by using the result of a study of intermediate species.

2 : Infrared Spectroscopy.
(1) Infrared study of mixed fluids at high temperatures and high pressures: Water and hydrocarbon such as hexane or benzene are almost immiscible with each other at room temperature. However, their mutual solubility increases with increasing temperature under pressure, and becomes infinite at around the critical point of water. We measure infrared spectra of these mixed fluids with a high-temperature-pressure cell and examine molecular level structure and dynamics of the mixtures.

(2) Infrared spectroscopy of intermediate species: The study has started very recently to measure the vibrational frequencies and rotational constants of the short-lived intermediate species formed by gas-solid reactions by means of infrared spectroscopy.

3 : Liquid-Crystal NMR.
Molecules in liquid crystal solvents are forced to align by solute-solvent interactions. The NMR spectrum measured for such a system shows very rich lines that do not appear in spectra of isotropic solution or liquid. By analyzing these lines, the geometrical structure and motion of the solute molecule can be studied.

In this laboratory, the geometrical structures and internal rotations of methyl-substituted furane and thiophene, and conjugated esters have been studied mainly. At present, the following projects are in progress: combination use of liquid-crystal NMR and gas electron diffraction to study the geometrical distortion of molecules in liquid crystal solvents; comparison of the interaction tensors of the different solute molecules under the equivalent condition that is obtained by making a mixed solution of multiple solutes; investigation of structure change of molecules adsorbed on the outer surface of zeolite.

4 : Computer Chemistry.
Results of the computational techniques involving molecular orbital (MO) and molecular dynamics (MD) methods are utilized to supplement the experimental methods. The MO calculations are used to fix some of the parameters in the analyses of electron diffraction and liquid-crystal NMR data as well as to interpret the results obtained from these experimental methods. On the other hand, the MD simulations are used to study the origins of solute-solvent interactions in isotropic and liquid-crystal solutions.

Staffs

Professor
Shun-ichi Ikawa (Dr. Sci. sikawa@sci.hokudai.ac.jp) Infrared spectroscopy.

Lecturer
Toru Egawa (Dr. Sci. egawa@sci.hokudai.ac.jp) Gas electron diffraction and infrared spectroscopy.

Instructor
Hiroshi Takeuchi (Dr. Sci. takehi@sci.hokudai.ac.jp) Gas electron diffraction and liquid-crystal NMR.

Recent publications

(1) "Effects of Molecular Structure on the Stability of Thermotropic Liquid Crystal. Gas Electron Diffraction Study of the Molecular Structure of Phenyl Benzoate", T. Tsuji, H. Takeuchi, T. Egawa and S. Konaka, J. Am. Chem. Soc., 123, 6381-6387 (2001).

(2) "Molecular Structure of 2-Butanimine, an Unstable Imine, as Studied by Gas Electron Diffraction Combined with MP2 and DFT Calculations", T. Egawa and S. Konaka, J. Phys. Chem. A, 105, 2085-2090 (2001).

(3) "Torsional potential function of phenyl acetate in the S₁ state as studied by fluorescence excitation spectroscopy in a supersonic free jet", T. Egawa, T. Yamada and S. Konaka, Chem. Phys. Lett., 324, 260-264 (2000).

(4) "Molecular structure of trans-azoxybenzene determined by gas electron diffraction combined with ab initio calculations", T. Tsuji, H. Takashima, H. Takeuchi, T. Egawa and S. Konaka, J. Mol. Struct., 554, 203-210 (2000).

(5) "Gas-Phase Molecular Structure of MBBA (4-Methoxybenzylidene-4'-n-butylaniline), a Mesogen, by Electron Diffraction Combined with ab Initio Calculations", N. kuze, H. Fujiwara, H. Takeuchi, T. Egawa, S. Konaka and G. Fogarasi, J. Phys. Chem. A, 103, 3054-3061 (1999).

(6) "Structural Study of Benzamide by Gas Phase Electron Diffraction Combined With ab Initio Calculations", H. Takeuchi, M. Sato, T. Tsuji, T. Egawa and S. Konaka, J. Mol. Struct., 485-486, 175-181 (1999).

(7) "Molecular Structure of p-Azoxyanisole, a Mesogen, Determined by Gas-Phase Electron Diffraction Augmented by ab Initio Calculations", N. Kuze, M. Ebizuka, H. Fujiwara, H. Takeuchi, T. Egawa, S. Konaka and G. Fogarasi, J. Phys. Chem. A, 102, 2080-2086 (1998).

(8) "Structure Determinaton of Methyl Nicotinate and Methyl Picolinate by Gas Electron Diffraction Combined with ab Initio Caclulations", H. Kiyono, R. Tatsunami, T. Kurai, H. Takeuchi, T. Egawa and S. Konaka, J. Phys. Chem. A, 102, 1405-1411 (1998).

(9) "Investigation of Pyrolysis Products of Propyleneimine by Gas Electron Diffraction Combined with Ab Initio Calculations. Molecular Structures of CH₃-NH-CH=CH₂ and CH₃-N=CH-CH₃", H. Fujiwara, T. Egawa and S. Konaka, J. Am. Chem. Soc., 119, 1346-1353 (1997).

(10) "Structural Study of Methyl Isonicotinate by Gas Electron Diffraction Combined with Ab Initio Calculations", H. Kiyono, N. Kuze, H. Fujiwara, H. Takeuchi, T. Egawa and S. Konaka, J. Mol. Struct., 376, 145-150 (1996).

(11) "Gas-Phase Structure and Conformation of Diethyl Ketone Studied by Molecular Orbital Constrained Electron Diffraction", N. Kuze, E. Kojima, H. Fujiwara, H. Takeuchi, T. Egawa and S. Konaka, J. Mol. Struct., 375, 231-241 (1996).

(12) "Molecular Structure of 2-Methylthiophene Studied by Gas Electron Diffraction Combined with Microwave Spectroscopic Data", M. Tanabe, N. Kuze, H. Fujiwara, H. Takeuchi and S. Konaka, J. Mol. Struct., 372, 173-180 (1995).

(13) "Electron Diffraction Study of Thermal Decomposition Products of Trimethylamine: Molecular Structure of CH₃-N=CH₂", H. Fujiwara, T. Egawa and S. Konaka, J. Mol. Struct., 344, 217-226 (1995).

(14) "Inductive and Steric Effects on the Gas-Phase Structure of tert-Butyl Acetate. Electron Diffraction and ab Initio MO Investigations", H. Takeuchi, J. Enmi, M. Onozaki, T. Egawa and S. Konaka, J. Phys. Chem., 98, 8632-8635 (1994).

(15) "Efficient Method to Analyze NMR Spectra of Solutes in Liquid Crystals: The Use of Genetic Algorithm and Integral Curves", H. Takeuchi, K. Inoue, Y. Ando and S. Konaka, Chem. Lett., 1300-1301 (2000).

(16) "Conformational Studies of ¹H-NMR in a Nematic Solvent: Methyl Isoninicotinate, Methyl Nicotinate, and Methyl Picolinate", H. Kiyono, K. Inoue, H. Takeuchi and S. Konaka, J. Mol. Struct., 476, 73-80 (1999).

(17) "Determination of the Molecular Structure of g-Picoline in the Gas Phase and in Liquid Crystal Solvents", K. Inoue, N. Kuze, M. Tanabe, H. Takeuchi, T. Egawa and S. Konaka, J. Mol. Struct., 413/414, 81-91 (1997).

(18) "Structural Study of Methyl Acrylate in a Nematic Liquid Crystal by ¹H NMR with ¹³C Satellites", H. Takeuchi, R. Watanabe, J. Enmi, T. Egawa and S. Konaka, Struct. Chem., 9, 33-38 (1998).

(19) "Effect of solvent on the cis-trans conformational equilibrium of a proline imide bond of short model peptides in solution", M. Sugawara, K. Tonan and S. Ikawa, Spectrochim. Acta A, 57, 1305-1316 (2001).

(20) "Infrared study of water-benzene mixtures at high temperatures and pressures in the two- and one-phase regions", S. Furutaka and S. Ikawa, J. Chem. Phys., 113, 1942-1949; 8390 (E) (2000).

(21) "Coupling of Intramolecular Hydrogen Bonding to the cis-to-trans Isomerization of a Proline Imide Bond of Small Model Peptides", B. Ishimoto, K. Tonan and S. Ikawa, Spectrochim. Acta A, 56, 201-209 (2000).

(22) "Intramolecular Hydrogen Bonding of the C-Terminal NH₂ Groups of Small Peptide Amides in Solution", B. Ishimoto, K. Tonan and S. Ikawa, Spectrochim. Acta A, 55, 2321-2327 (1999).

(23) "Hydrogen Bonding of Water with Aromatic Hydrocarbons at High Temperature and Pressure", S. Furutaka and S. Ikawa, J. Chem. Phys., 108, 5159-5160 (1998).

(24) "Infrared Study of Water in Benzene at High Temperatures and Pressure", S. Furutaka and S. Ikawa, J. Chem. Phys., 108, 1347-1351 (1998).

(25) "FT-IR Study of Water Desorption from Collagen Films", T. Shibata, K. Tonan, T. Yasuda and S. Ikawa, Applied Spectrosc., 51 337-339 (1997).

(25) "High-Pressure FTIR Study of Intramolecular Hydrogen Bonding and Conformation of a Small Peptide in Solution", K. Tonan and S. Ikawa, Spectrochim. Acta Pt. A, 53, 2695-2700 (1997).

(27) "Intramolecular Hydrogen Bonding and Molecular Conformation Part 5 Gas-Phase Infrared Measurement of Some Hydroxyketones and Methoxyalcohols", T. Yasuda and S. Ikawa, J. Chem. Soc., Faraday Trans., 93, 1869-1874 (1997).

(28) "Intramolecular Hydrogen Bonding and Conformation of Small Peptides: Variable-Temperature FTIR Study on N-Acetyl-L-Pro-L-Leu-Gly-NH₂ and Related Compounds", K. Tonan and S. Ikawa, J. Am. Chem. Soc., 118, 6960-6965 (1996).