Triazole molecular structures

Contributions in this section are important because they provide structural information (geometries, dipole moments, and rotational constants) of individual tautomers in the gas phase. The molecular structure and tautomer equilibrium of 1,2,3-triazole (20) has been determined by MW spectroscopy [88ACSA(A)500].This case is paradigmatic since it illustrates one of the limitations of this technique the sensitivity depends on the dipole moment and compounds without a permanent dipole are invisible for MW. In the case of 1,2,3-triazole, the dipole moments are 4.38 and 0.218 D for 20b and 20a, respectively. Hence the signals for 20a are very weak. Nevertheless, the relative abundance of the tautomers, estimated from intensity measurements, is 20b/20a 1 1000 at room temperature. The structural refinement of 20a was carried out based upon the electron diffraction data (Section V,D,4). 

Diazotization of 5-amino[l, 2,3]triazole 692 afforded (88BSB179) triaz-olo[l, 5-i>][l, 2,4]triazine 694 as a result of a Dimroth rearrangement of the initially formed isomeric structure triazolo[5,l-c][l,2,4]triazine 693. Molecular structure of 694 was determined by single X-ray diffraction (Scheme 146). 

An interesting Mossbauer study has been reported on the dinuclear SCO complex [Fe2 (PMAT)2](BF4)4-DMF (PMAT 4-amino-3,5-bis [(2-pyridylmethyl) amino]methyl -4H-1,2,4-triazole), where thermal ST occurs from [HS-HS] to the stable endproduct [HS-LS] [32]. The molecular structure and magnetic behavior of this complex was reported earlier by Brooker et al. [33, 34] (Fig. 8.15). At ca. 225 K, the complex undergoes a sharp half ST from the HS state, T2, to a state containing 50% HS and 50% LS, Af, isomers. The single-crystal structural analysis... 

Jeffrey GA, Ruble JR, Yates JH (1983) Neutron diffraction at 15 K and 120 K and ab-initio molecular orbital studies of the molecular structure of 1,2,4-triazole. Acta Cryst B 39 388—394... 

Fig. 1.7 Molecular structures of 5-nitro-l,2,4-triazol-3-one (NTO), 1,3,3-trinitroazetidine (TNAZ), hexanitrohexaazaisowurtzitane (CL-20), octanitrocubane (ONC) and 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX).

FIGURE 16 Top Molecular structures of cucurbit[6]uril and products and reactants of 1,3-dipolar cycloaddition. Bottom Side and top views of the CAChe transition state structure for the formation of the 1,4-triazole included in the cucurbit[6]uril (55). 

Prusiner, P. and Sundaralingam, M. (1976). The crystal and molecular structures of two polymorphic crystalline forms of virazole (l-JS-D-ribofuranosyl-l,2,4-triazole-3-carboxamide). A new synthetic broad spectrum antiviral agent. Acta Crystallogr. B, 32, 419-26. [159]... 

In turn, from the total energy Et it now follows that 2H- 1,2,3-triazoles are more stable than the IH-tautomers, where ET = E +E - -E +Enwieas- This last calculation was confirmed recently by PES spectra (see Section 4.11.3.2.10) and dipole moment measurements (see Section 4.11.3.2.2), comparing them with the corresponding H-methyl derivatives. A refined and optimized molecular structure has also been given for both the IH-and 2H-tautomers (Figure 2) (81ZN(A)1246). 

Such rearomatization of the cycloaddition product in substituted A-imines is impossible without a considerable change of the molecular structure, and these compounds seldom undergo 1,3-dipolar cycloaddition, with the exception of pyridine,29 30 34 37 isoquinoline,29 30 and 1,2,3-triazole A-arylimines.97,106... 

J. Penninger, K. Wippermann and J.W. Schultze. Molecular structure and efficiency of triazole derivatives and other heterocyclics as corrosion inhibitors for copper. Werkstoffe und Korrosion, 1987, Vol. 38, pp. 649-659. 

Self-association of heterocycles containing NH groups (such as imidazoles, triazoles etc.) produces chains of planar molecules connected by N—H- -N hydrogen bonds. The effects of intermolecular hydrogen bonding on the molecular structures are confirmed also by ab initio molecular orbital calculations . 

The dialkyl(alkyl-A/-1H-1,2,4-triazol-3-ylbenzenecarboximidamidato)-boron compounds of type 30 are prepared in analogy to 29 from the corresponding trialkylboranes by reaction with 5-amino-1,2,4-triazole in refluxing xylene and treating the intermediate with a 3- to 5-fold excess of the corresponding aryl nitrile under reflux. The mass spectrum, the NMR spectrum, and IR data are given for the various species. The crystal and molecular structure of 30a has been determined by X-ray diffraction it resembles that of 29f [22]. 

Figure 384 The molecular structures of mononuclear zinc porphyrin dyes (a), Ru-Ru (b), and Ru-Os (c) binuclear complexes containing the bridging ligand 3,5-bis-(pyridin-2-yl)-1,2,4-triazole.

T) -CsH Pr4) with [W(CO) 5 (thf) ] leads a tetracarbonyl tungsten complex [W(CO)4P2Nl2Cp 2] which can be oxidised with MesSlOOSlHes to give the first example of a complex containing a M3-PO ligand, (Cp Ni-W(CO)4-NiCp (ps-PO)2] The synthesis and molecular structure of a 1,2,4-triazole complex [W(co)sL]... 

The water-soluble NHC iridium(i) complex [lr(trz)(CO)2l]OTf 553 (trz= l,2,4-triazol-2-ium-5-ylidene) and a pyridylimidazolylidene species exhibiting a metallacycle structure 554 were also described.The molecular structures of 554 and its precursor containing an agostic Ir- H- C interaction have been reported and the former is presented in Figure 47. 

While the most obvious coordinatimi sites on the 1,4-disubstituted-l,2,3-triazole unit are the N2 and N3 nitrogen atoms, the acidic nature of the hydrogen on the C5 carbon means that it can be readily deprotmiated to provide anionic 1,4-disubstituted-1,2,3-triazolide Ugands. Straub and coworkers [123] were able to isolate a stable copperOD 1,4-disubstituted-l,2,3-triazolide complex (19a) by reacting the bulky NHC-stabdized copper(T) acetyUde 18a with azidodi-4-tolylmethane in toluene at RT for 24 h (Fig. 7). 19a was stable in air and water, and its molecular structure was confirmed by X-ray crystallography (Fig. 7). The copper(I) 1,2,3-triazolide... 

Figure 9.2 Molecular structure of commercially available l,3,4-triphenyl-4,5-dihydro-l H-l,2-triazol-5-ylidene.

The crystal structure analysis of the parent 1,2,3-triazole in the solid state unambiguously demonstrated that it crystallizes as a 1 1 molecular complex of both possible tautomers 24a and 24b, linked by a N-H - N hydrogen bond [97AX(C)1846]. 

Similarly, the structure of 5-nitro-2,4-dihydro-377-l,2,4-triazol-3-one (NTO) 6 has been scrutinized using molecular orbital calculations using the 6-31+G and 6-311+G basis sets. These calculations examined the various tautomers of NTO and give an insight into the molecular mechanisms involved in its explosive decomposition <1996JA8048>. 

A comprehensive study into the structures and molecular properties of 3-amino-177-l,2,4-triazole 15, 4-amino-477-1,2,4-triazole 16, and 5-amino-177-l,2,4-triazole 17 has been undertaken using ab initio methods, both to predict and confirm data obtained from microwave spectroscopy of these compounds <2004JST(705)177>. 

Perhaps the most important issues to consider now are the application of novel methodologies, molecular diversity, and synthetic convenience. There have been several reports of novel, one-pot procedures for the preparation of 1,2,4-triazoles with diverse structures. Synthesis of 1,2,4-triazoles on polymeric supports, in both solution and solid phase, represents a step toward the combinatorial synthesis of these heterocycles. It is these novel applications of technology to organic synthesis that perhaps lead the way in 1,2,4-triazole chemistry. 

A variety of acyclic and cyclic S-N compounds decompose at moderate temperatures (100-150 °C) with the formal loss of a symmetrical NSN fragment, but this molecule has never been detected. The lowest energy isomer, linear NNS, is generated by flash vacuum pyrolysis of 5-phenyl-l,2,3,4-thia-triazole.40 Ab initio molecular orbital calculations indicate that the resonance structure N = N+-S is dominant.41... 

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