Yoshiyuki Mido

Conformations and steric and stacking interactions of trisubstituted ureas and thioureas with alkyl and phenyl groups

Abstract The monomeric ν(N—H) vibrations of various trisubstituted ureas of the R 2 UPh type and -thioureas of the R 2 TUPh type have been studied. The trans —out isomerism in the former and the trans —out— cis isomerism in the latter are discussed from the point of view of steric effect. The monomeric ν(N—H) vibrations of RPhUPh and RPhTUPh are also examined. The single band appearing in the spectrum of both ureas is characteristic of the cis form; this suggests the existence of phenyl—phenyl interaction (the stacking interaction proposed by Galabov et al. [10]). Behavior of ν(N—H) vibrations at several concentrations is shown to be clearly different in the three forms ( trans , out and cis ). The presence of the cis form is confirmed by solvent effect experiments.

Vibrational spectra and normal coordinate analysis of N-methylthiourea and three deuterated analogues

Abstract IR and Raman spectra of N-methylthiourea and three deuterated analogues, CH3NHCSNH2, CH3NDCSND2, CD3NHCSNH2 and CD3NDCSND2, have been studied in the solid state. A complete interpretation of the spectra has been made for the cis conformation on the basis of the N- and C-deuteration effects and of a normal coordinate analysis using the Urey–Bradley force field. The temperature dependence of the IR spectra has been studied in the 300–100 K range. At low temperatures, the NH2 scissoring vibration gives a well-defined doublet band due to the presence of two asymmetric molecules in the unit cell. Some of the overlapped bands are well separated at low temperatures.

Conformational isomerism of methyl dichloroacetate. An infrared, Raman and 35Cl NQR study

Abstract The IR and Raman spectra of methyl dichloroacetate (M-DCA) have been recorded on the liquid, glassy and crystalline states. The vibrational assignment for M-DCA is proposed on the basis of the spectral comparisons between CCl n H 3  n COOCH 3 and CCl n H 5  n CONHCH 5 ( n = 0–3) in the solid state. The observed spectral data indicate that M-DCA exists as a conformational equilibrium in the liquid and in the glassy state and that the conformation in the crystalline state is entirely different from those in the liquid and glassy states. The 35 Cl NQR spectrum suggests that the conformation of M-DCA in the crystalline state is the cis form in which one of the two chlorine atoms is located in the cis position with respect to the carbonyl group. Examination of vibrational spectra also leads to the same conclusion.

Polymorphism of methyl chloroacetate, a raman, IR and 35Cl NQR spectroscopic study

Abstract From Raman. IR and 35 NQR data and thermal analysis it is concluded that there are two polymorphic phases in solid methyl chloroacetate (M-MCA). The Raman and IR spectra of M-MCA have been studied for each of the two crystalline phases at ca. 80 K. The results of 35 Cl NQR measurements are found to be consistent with the vibrational spectra. Conformational properties of M-MCA are discussed and it is proposed that both cis and (probably) gauche isomers (in relation to the chlorine atom and carbonyl group) exist in the liquid phase and that the cis isomer remains in both crystalline phases.

The N—H stretching vibrations and conformations of trialkylthioureas

Abstract The ν(N-H) vibrations of trialkylthioureas observed in the dilute solutions are interpreted in relation to the trans —out isomerism. Occurrence of the out form is discussed from the point of view of steric hindrance. The two forms are characterized by the behavior of ν(N—H) vibrations at several concentrations. Solid DiPTUtB and DcHTUtB exhibited one sharp band at the same position as the ν(N—H) band in solution. This indicates that they are in the out form in the solid state as well as in solution.

Vibrational spectra, normal vibrations and rotational isomerism of ethyl acetate and three deuterated analogues

Abstract IR and Raman spectra of ethyl acetates, CH3COOC2H5, CD3COOC2H5, CH3COOC2D5 and CD3COOC2D5, in the liquid and crystalline states have been recorded in the 3500-200 cm−1 region. These spectra are analysed on the basis of spectral comparison both among themselves and with spectra of the trichloro analogues CCl3COOC2H5 and CCl3COOC2D5 previously studied. All the ethyl acetates in the crystalline state give two completely separated carbonyl stretching Raman bands, suggesting that two, or an even number of molecules, exist in the crystal unit. Liquid-state spectra exhibit many band pairs arising from the trans-trans and trans-gauche conformers around CX3COOCX2CX3 axes (X = H and D) and the bands of the trans-trans conformer persist in the crystalline state. Normal coordinate calculations for the four species have been carried out on the two isomeric models using an MVIB program. The results explain wavenumber shifts on deuteration and the nature and separation of band pairs satisfactorily, and suggest that a large amount of vibrational coupling exists among skeletal stretching vibrations.

Infrared and Raman spectra of N-methyl-N′-alkylureas

Abstract The i.r. and Raman spectra of solid CH3NHCONH(CH2)nCH3 (n = 0–15), MUR′, are presented. The vibrational assignment is proposed on the basis of the spectral comparison and the results of the normal coordinate analysis for some short chain molecules. MUR′ are concluded to be in the extended trans form including the methylurea part. Analysis of methylene band progressions based on the transfer matrix theory, in which the end group effect is taken into account, proves that the force field for the n-alkyl chain of MUR′ agrees with that for n-alkanes within the limit of experimental error.

Molecular structure of methyl trichloroacetate. An IR, Raman and 35Cl NQR spectroscopic study

Abstract The IR and Raman spectra of liquid and crystalline mehtyl trichloroacetate (M-TCA) and its deutrate (M-TCA-d 3 ) have been recorded. The spectra are analysed on the basis of the spectral comparison with related compounds and also with aid a normal coordinate calculation on M-TCA and M-TCA-d 3 . The vibrational and 35 Cl NQR spectra indicate that the M-TCA molecule exists in the (itcis) form in relation to the chlorine atom and the carbonyl group. Anomalous temperature dependences of the 35 Cl NQR and Raman frequencies observed in crytalline M-TCA are reported and discussed qualitatively.

Infrared and Raman spectra of 1-cyclohexyl-3-methylurea and its related compounds

Abstract The i.r. and Raman spectra (4000—100 cm −1 ) of C 6 H 11 NHCONHCH 3 , and C 6 H 11 NHCONHCD 3 , and their N- d compounds are given in the solid state. Also, the i.r. spectra (4000—400 cm −1 ) of some C 6 H 11 NHCONH R type compounds (cHU R ) are presented. The vibrational assignments are proposed on the basis of comparisons among their vibrational spectra. The solution spectra of cHU R are studied with the aims of confirming the correlation between the NH stretching frequency and the type of R group, and of determining whether or not rotational isomers can coexist by the bulkiness of the R group.

Conformational isomerism of chlorophenylthioureas and intramolecular NH … Cl hydrogen bonds: IR spectra of NH stretching vibrations

Abstract The v NH regions of the IR spectra of thioureas with chlorophenyl (ClPh) groups and those with halophenyl groups were measured in dilute CCl 4 solution. The observed v NH bands were classified into eight groups according to the wavenumbers and the two substituent groups. The suggested conformational states and the formation of intramolecular NH … Cl hydrogen bonds in these compounds were discussed in comparison with those of the urea analogs. It was found that these thiourea derivatives are more stable in the cis form than the urea analogs and that thioureas with o -ClPh groups form fewer intramolecular NH … Cl hydrogen bonds than do the urea analogs.