1.3.4- Thiadiazoles physical properties

Thiadiazole 1 and its derivatives were used as model compounds for the calculation of molecular parameters related to physical properties for their use in quantitative structure-activity relationship (QSAR) and quantitative structure-property relationship (QSPR) studies <1999EJM41, 2003IJB2583, 2005JMT27>. 

Renewed interest in 1,2,4-thiadiazoles is not merely part of the general intensive activity in contemporary heterocyclic chemistry. It is obviously desirable to compare this ring system with closely related important heterocycles (including thiazoles, oxazoles, pyrimidines, etc.), the chemistry of which is known in much greater detail. The iso-steric relationship between pyrimidine and 1,2,4-thiadiazole (but not with any of its isomers) foreshadows similarities in certain physical properties of the two series. The question of the biochemical function and physiological activity of heterocyclic compounds of this general pattern has also served to reinforce interest in the 1,2,4-thiadiazoles. 

A. 1,2,4-Thiadiazole and Homoloqs The parent compound, first obtained in 1955, is a volatile liquid, soluble in polar solvents, less so in non-polar ones. Its physical properties are summarized in Table II. Its I.R. spectrum has been recorded.8... 

D. Amino-1,2,4-thiadiazoles 1. 3- and 5-Amino-1,2,4-thiadiazoles a. Physical Properties. 3-Substituted 5-amino-1,2,4-thiadiazoles are generally stable, colorless, odorless compounds.6,88,86,128 Their thermal stability (as reflected by their melting points), solubility, and resistance to acids are influenced by the nature of the 3-substituent. 5-Alkoxy-3-amino-l,2,4-thiadiazoleB sublime without decomposition.83... 

As may be expected from the isosteric relationship between the two ring-systems, 1,2,4-thiadiazoles and the corresponding pyrimidine derivatives show certain similarities in their physical properties. Thus, the boiling points of the parent compounds are strikingly similar5 (see Table V). 

Physical Properties of 1,2,3-Thiadiazoles. Lanthanide-induced shifts have been used for elucidation of the structure of thermally generated monoxides of 1,2,3-thiadiazoles ( H and C). A calculation has been developed for the evaluation of lanthanide-induced shifts according to the McConnell-Robertson equation. The o and Or parameters of triazoles were also determined by n.m.r. spectroscopy. ... 

Physical Properties of 1,2,4-Thiadiazoles. The X-ray determination of the 1 1 adduct between Hector s Base (274 R = H) and methyl isocyanate shows that it forms without a heterocyclic rearrangement the compound is a 5-(iV-methylthiocarbamoylimino)4-phenyl-3-phenylamino-4//-l,2,4-thia-diazoline [274 R = MeNHC(S)]... 

Physical Properties of 1,3,4-Thiadiazoles. Ultraviolet spectra of some 2-benzylideneamino-5-phenyl-1,3,4-thiadiazoles have been reported. The n.m.r. spectral properties and conformational preferences of some open-chain and cyclic aromatic sulphides that contain 1,3,4-thiadiazole units, spectroscopic data of metal (Mn, Fe, Co, Ni, Cu, or Zn) chelates of iV-(5-phenyl-l,3,4-thiadiazol-2-yl)dithiocarbamic acids, conductometric and i.r. and Raman determinations on thirteen complexes of Zn, Cd, or Hg with 2-methyl-5-mercapto-1,3,4-thiadiazole, and thermogravimetry of some noble- and common-metal chelates of 5-amino-l,3,4-thiadiazole-2-thiol were also described, as well as the mass-spectral fragmentation of 2-phenyl-... 

Physical Properties of 1,2,5-Thiadiazoles. An inversion barrier was theoretically and experimentally investigated for 1,2,5-thiadiazole 1-oxides (pyramidal, SO structure). The crystal and molecular structures of sulfametrole have been determined. ... 

Physical Properties. - Naphtho[2,3-c][1,2,5]thiadiazol-4,9-dione and its selenium analogue have been studied by X-ray crystallography. Both show significant ir interaction of the chalcogen diimide with the it system of the naphthoquinone. ... 

Thiadiazoles 195 Synthesis 195 Physical properties 196 Chemical properties 196... 

In the field of thiadiazole chemistry the study of meso-ionic compounds stimulates interest (75, 98—113). The parent thiadiazoles have been obtained for the first time only in recent years they have now been joined by 1,3,4-selenadiazole (75, 120), whose physical properties have been compared with those of relevant analogues in studies of bonding in these systems. The nature of the products formed in the photolysis of 1,2,3-thiadiazoles is accounted for in terms of a transient thiocarbene intermediate (75, 10). 

Physical Properties.—The spectral properties of a series of 3-amino-4-aryl-5-aryl(or alkyl)-imino-4,5-dihydro-l,2,4-thiadiazoles are in accord with the proposed structures. The n.m.r. spectra indicate the preferred existence of the dihydro- rather than the tautomeric tetrahydro-thiadiazole structure. Mass spectral fragmentation patterns were proposed for these, and for compound (70). ... 

Physical Properties.—A study of the u.v. spectra and acid-base equilibria of a-acylamino-N-heterocycles has included measurements for 2-acylamino-l,3,4-thiadiazoles. The formation of their sodium salts is accompanied by a strong bathochromic displacement in the near-u.v. band. The ionization constants indicate that the stability of the anions depends on both the electron-attracting... 

Pure (192) is a white crystalline solid resembling naphthalene in its physical properties. Its high degree of symmetry is reflected in the simplicity of its i.r. spectrum. Hydrolysis yields successively 3,4-diamino-l,2,5-thiadiazole, oxamide, and sulphur. ... 

Physical Properties. - The X-ray crystal structure for 5-acylimino-1,2,3 thiadiazole has been reported. The thiadiazole ring is planar and almost coplanar with the remaining non-H atoms. 

Pesin and his group have continued their investigation of benzo-2,1,3-thiadiazoles and have provided a summary of their recent work. In their opinion, the quinoid structure of benzo-2,1,3-thiadiazole and its selenium analogue is excluded by the sum of their physical and chemical properties, especially i.r. spectra. However, their preferred heteroaromatic structure... 

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