Yoshiaki Hamada

Vibrational analysis of ethylamines: Trans and gauche forms

Abstract Starting from force constant values calculated by an ab initio MO method ( 4-31G(N ∗ ) ), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm−1) of the gauche form of the ethylamine CH3CH2NH2 molecule and five isotopic species CH313CH2NH2, CH3CH215NH2, CH3CD2NH2, CH3CH2ND2, and CD3CD2NH2. The F matrix for the trans form of ethylamine was constructed by transferring ab initio 4-31G(N ∗ ) values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm−1. In matrix isolation spectroscopy, two bands assignable to the NH2 wagging vibrations of gauche and trans forms have been found at 775 and 782 cm−1, respectively, for CH3CH2NH2. They are at 768 and 774 cm−1, respectively, for CD3CD2NH2. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm−1.

Ab initio MO calculation of force constants and dipole derivatives for formamide

Abstract Ab initio SCF MO calculations have been carried out for the equilibrium geometry, vibrational frequencies, force constants, dipole moment and its derivatives of formamide. The energy gradient method was employed and the 4-31G basis set was used. For in-plane vibrations: (1) Calculated normal frequencies were 10–20% greater than the observed fundamental frequencies. (2) Isotope shifts (− d 0 , − d 1 , − d 2 , and − d 3 species) were well reproduced. (3) The calculated dipole moment derivatives showed a good correspondence with the infrared intensity pattern. (4) The NH 2 rocking—OCN bending cross term, which should be zero in the Urey—Bradley force field, came out to be as large as −0.18 mdyne A. For out-of-plane vibrations, especially for the NH 2 wagging, it was found to be essential to include polarization functions for N, C and O atoms.

Pyrolysis of amines: Infrared spectrum of vinylamine

Abstract Infrared absorption spectrum of allylimine in the gas phase was measured for the first time. The spectrum consisted of two rotational isomers, cis and trans , around the CC bond. The relative population of the trans form was 70–80%, and the rest was for the cis form at room temperature. This intermediate molecule was produced by the thermal decomposition of diallylamine and by the isomerization of propargylamine. The vibrational assignments were made with the help of an ab initio MO calculation. The half-life in the absorption cell was about 20 min.

Infrared diode laser spectroscopy of the CF radical

Abstract The fundamental bands of the CF radical in the X 2 Π 1 2 and X 2 Π 3 2 electronic states were observed by using an infrared tunable diode laser as a source. Zeeman modulation could be used in detecting lines not only in the 2 Π 3 2 state, but also in 2 Π 1 2 , because the CF radical deviates considerably from Hunds case ( a ). From the least-squares analysis of the observed spectra, the following molecular constants were obtained: B e = 1.416 704 (37) cm −1 , α e = 0.018 419 (50) cm −1 , r e = 1.271 977 (17) A , D e = 6.68 (15) × 10 −6 cm −1 , p 0 = 0.008 580 (21) cm −1 , p 1 = 0.008 52 (11) cm −1 , and ν 0 = 1286.1281 (5) cm −1 , with three standard errors in parentheses.

Amino wagging and inversion in hydrazines: Antisymmetric wagging band of NH2NH2

Abstract The fine structure of the 937 cm−1 band of undeuterated hydrazine in the gaseous state has been observed with a resolving power of 0.3 cm−1. It has been found that every vibration-rotation line splits into four components, and that the amounts of the splittings depend only slightly upon the rotational quantum number K. This fine structure was explained by considering (1) that the band is caused by a vibration in which the wagging motions of the two amino groups take place antisymmetrically with respect to the C2 axis, (2) that along this coordinate an appreciable inversion takes place, (3) that such an inversion results in four equivalent equilibrium conformations of the molecule one after another, and (4) that the barrier height between every two adjacent equilibrium conformations is 2620 cm−1.

Molecular structural of the gauche and trans conformers of ethylamine as studies by gas electron diffraction

Abstract The geometrical parameters for the two conformers, gauche ( g ) and trans ( t ), of ethylamine have been determined by a joint analysis of the electron diffraction intensity measured in the present study and the rotational constants reported in the literature. The optimized geometries estimated by an SCF MO calculation with a 4-31G(N*) basis set were also used in the analysis to complement the experimental data. The bond lengths ( r g ) and the bond angels ( r z ) determined are r (CH) av = 1.107(6) A r (CN) t = 1. 470(10)A, r(CN) g = 1.475(10) A r (CC) t = 1.531(6) A r (CC) g = 1.524(6) A , ∠CCN) t = 115.0(3)°, and ∠CCCN g = 109.7(3)°. The uncertainties represent estimated limits of error. The difference between the CCN g and CCN g angles predicted by a previous ab initio calculation is confirmed. The enthalpy difference,Δ H ( g  t ), is determined to be 306(200) cal mol −1 using the abundance of the trans conformer, 46(10)%.

Infrared spectrum of trans-acrolein

Abstract The gas-phase infrared absorption spectrum of acrolein is observed from 4000 to 400 cm −1 with a resolution of 0.06 or 0.03 cm −1 . The previously unlocated vinyl CH stretching band is observed at 3069 cm −1 and its CH out-of-plane modes whose assignments have been in confusion are investigated in detail. The mode assignments of some other bands are revised on the basis of the calculated frequencies and relative intensities by an ab initio MO method.

Ab initio study on cyanamide and isocyanamide

Abstract Spectroscopic parameters, namely force constants and dipole-moment derivatives of cyanamide and isocyanamide at their equilibrium geometry, are studied by the ab initio MO method. The configuration of the former of the two structural isomers has amide character, and the latter amine character. The assignments of skeletal-deformation vibrations are reinvestigated experimentally as well. This study supports Ogilvies attribution of what he observed to the vibrational spectrum of isocyanamide and explains the anomalous infrared intensity in the spectrum. A special theoretical treatment of amino wagging motion is presented, which includes the inversion effect, and which enables the prediction of the inversion splitting of isocyanamide.

Vibrational and conformational analysis of n-propylamine by means of i.r. spectroscopy and ab initio MO calculations

Abstract The gas-phase i.r. absorption spectra of normal and amino-deuterated n -propylamine were observed. Most of the observed bands were assigned with the help of ab initio MO calculations for the normal frequencies. The ab initio force constants were scaled to fit the observed spectrum by a least squares method. The existence of five rotational isomers is suggested from an analysis of the NH 2 wagging and torsion bands. The gauche -conformers about the CN axis are found to occupy about 70 % of all n -propylamine molecules, and the gauche -conformers about the CC axis are found to be more abundant than the trans -conformers.

Torsional bands of hydroxylamine

Abstract Infrared absorption spectrum of NH 2 OH has been observed in its gaseous state, and the fine structures of the bands at 386 and 751 cm −1 assignable, respectively, to the fundamental and overtone of the torsional vibration of this molecule have been examined. Band center frequencies for the n = 1 ← 0, 2 ← 1, 3 ← 2, 2 ← 0, and 3 ← 1 transitions (where n is the vibrational quantum number of the torsional oscillation) have been determined to be 386.2, 365.1, 346.3, 751.2, and 711.3 cm −1 , respectively. On the basis of these data, a discussion is given on the internal-rotation potential function.