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A theoretical force field for the molecular vibrations of thiourea has been determined from ab initio calculations at the Hartree-Fock level using the 3-21G* basis set. The reliability of the force field is analyzed by calculating the vibrational frequencies for the deuterated and $^{15}N$ isotopomers. Frequencies calculated from the force field are utilized to critically examine the experimental assignments for thiourea and deuterated thiourea. Theoretical geometry, the calculated IR and Raman band intensifies are analyzed.

The complete harmonic force field and optimized geometry of thiosemicarbazide have been calculated at the ab initio Hartree—Fock level using the 3-21G basis set. On the basis of this, the frequencies of thiosemicarbazide-d0 and -d5 and their 15N isotopic molecules have been calculated. The calculated frequencies and their band assignments are utilized to critically examine our previous experimental assignments which were based on normal coordinate calculations. The theoretical IR and Raman intensities, together with qualitative experimental band intensities, are also presented.

Raman and infrared spectra of imidazoline-2-thione (IMZT) and imidazoline-2-one (IMZO) have been recorded. Normal coordinate analyses have been performed for all the fundamental vibrations of IMZT, IMZT-d2 and IMZO employing a Urey—Bradley potential function supplemented with valence type force constants for the out of plane modes. The results of the vibrational analyses are discussed in relation to the assignments in related molecules. The vibrational assignments for IMZT and IMZO have been compared with those in structurally similar molecules and the need to obtain more reliable band assignments for some of the molecules considered is emphasised.

The i.r. frequencies of ethylthioxanthate complexes of some transition metals have been interpreted on the basis of normal coordinate treatments of the 1:1 molecular models. The band assignments are disscussed in comparison with those in closely related xanthate molecules.

Molecular vibrational analyses of two biochemically important molecules, namely pyridine-2-thione and pyrimidine-2-thione, have been made for all the fundamentals employing the Urey-Bradley potential function supplemented with valence force function for the out-of-plane vibrations. The spectra of N-deuterated molecules have also been utilized. The results of the vibrational analyses are discussed in relation to the assignments in structurally related molecules to note the consistency in the assignments

The normal coordinate analyses of the 16 in-plane vibrations of thiosemicarbazide and selenosemicarbazide and their deutero analogues have been made using Wilson's GF matrix method and the Urey—Bradley force field. A revision of the vibrational assignments has been made for thiosemicarbazide based on force constant calculations. A discussion of the CS stretching bands in the free ligand and their metal complexes is given.

The infrared spectra of 2,4-dithiobiuret(DTB), N-deuterated dithiobiuret(DTB-d5) and the laser Raman spectrum of DTB are reported. Normal coordinate treatments of DTB and DTB-d5 have been carried out to aid the assignment of the vibrational frequencies. A trans—cis conformation is favoured for DTB molecule in the solid state.

The i.r. assignments for monothiobiuret(Mtb)-hydrate and its deuterated compound have been made from normal coordinate analyses carried out for Mtb and Mtb- d 5 using a chosen molecular model containing a trans-cis —CONHCS— group for Mtb (H 2 NCONHCSNH 2 ). The i.r. spectra of anhydrous Mtb in solid and in solution and of Mtb · H 2 O at liquid nitrogen temperature have also been studied.

The 13 C NMR spectra of a series of 1,3-dipyridyl- and pyridylphenylthioureas have been obtained. Complete analyses of the experimental spectra have provided the chemical shifts and coupling constants. The spectra of dipyridylthioureas over a temperature range showed important changes which could be attributed to an intramolecular conversion between the two equivalent E,Z and Z,E conformations. The coalescence temperature of the 13 C signals leads to a Δ G * of ∼ 58.0 kJ mol −1 for the dynamic process involved. The results show that pyridylphenyl thioureas exist in a single conformation at ambient temperature.

Several N,N′ -arylalkyl thioureas were examined with 1 H-NMR and i.r. spectra in order to study the conformation of the -NHCSNH- group. The influence of temperature and substituents on the chemical shift of the NH protons has been investigated. Formation of a strong intramolecular hydrogen bond stabilizes the trans—cis conformation for most systems, while for the others the prevalence of different rotational isomers can be postulated. The influence of the steric effect on hydrogen bonding and molecular conformation is discussed.

Infrared and Raman spectra of N,N-dimethylacetamide (DMA) are recorded and the normal vibrational analysis of the DMA skeleton as well as the entire molecule carried out employing the Urey-Bradley and modified Urey-Bradley force fields. Vibrational frequencies are assigned on the basis of the normal coordinate calculations and are compared with those of related molecules. Infrared spectra of metal complexes are examined to substantiate the band assignments.

Assignments of the infrared frequencies of methyl and ethyl xanthato complexes of nickel(II) have been made with the aid of normal coordinate analyses. The assignments are discussed in relation to those in related molecules.