Investigation on the aromaticity of 1,3,4-thiadiazole-2-thione and its oxygen analogs including their tautomeric forms

Erdem, Safiye Sağ; Özpınar, Gül Altınbaş; Saçan, Melek Türker

doi:10.1016/j.theochem.2005.04.019

Cited by 19 publications

(14 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our calculations of the HOMA parameter show, as in the Erdem's studies [50], that the unsubstituted heterocyclic ring is nonaromatic and its substitution alters the geometric aromaticity from zero to ca 0.2. Substitution by the aryl groups in C 2 and C 5 do not change or increase aromaticity while addition of the imino group to C 2 significantly decreases HOMA of the heterocyclic ring.…”

Section: Aromaticitysupporting

confidence: 76%

“…Moreover, in the case of coplanar conformations, the substituent can interact with the -electron system of the oxadiazole. Aromaticity of the unsubstituted 1,3,4-oxadiazole ring have been calculated by Erdem at coworkers [50] in terms of HOMA, ASE (aromatic stabilization energy), differential heat of hydrogenation (ÁÁHH) and NICS. The values obtained by them are as follows: HOMA: 0.124, ASE: 9.789 kcal mol À1 , ÁÁHH: 9.036 kcal mol À1 , NICS: À11.111 ppm.…”

Section: Aromaticitymentioning

confidence: 99%

See 1 more Smart Citation

1,3,4-oxadiazoles: evaluation of aromaticity and atomic charge distribution

Malek¹,

Zborowski²,

Gebski³

et al. 2008

Molecular Physics

View full text Add to dashboard Cite

The aromaticity and atomic charge distribution were investigated for the mono-and disubstituted 1,3,4-oxadiazoles. Using an electron density-based approach (B3LYP), the structures of the molecules were estimated, then the changes of -electron delocalization of the heterocyclic ring were estimated based on geometric (HOMA) as well as magnetic properties (NICS). Aromaticity of the oxadiazole ring varies to some extend depending on the electron character of the substituent, however, the two methods do not correlate well. The HOMA approach suggests a non-aromatic character for the oxadiazole ring, while NICS predicts a relatively high aromaticity. Additionally, two computational methodologies were used for quantitative measures of atomic charges, i.e. AIM and GAPT. Results of these computations reveal accumulation of electron density inside the heterocyclic ring due to substitution by the aryl groups and its significant removal in the presence of the imino group. However, both procedures suggest different explanation of this fact.

show abstract

Section: Aromaticitysupporting

confidence: 76%

Section: Aromaticitymentioning

confidence: 99%

1,3,4-oxadiazoles: evaluation of aromaticity and atomic charge distribution

Malek¹,

Zborowski²,

Gebski³

et al. 2008

Molecular Physics

View full text Add to dashboard Cite

show abstract

“…It is instructive to compare the potentials of the oxidation and reduction onsets for compounds (3) and (4) indices. 49,55 This apparently promotes improved electron communication between the two bithiophene pendants in (4), hence lowering the oxidation potential of this pentaring entity.…”

Section: Redox Properties Of Monomers: Theory Versus Experimentsmentioning

confidence: 99%

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

et al. 2014

View full text Add to dashboard Cite

Electrochemical and spectroelectrochemical properties of a series of new penta-ring donor -acceptor compounds, comprising 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole central ring, symmetrically connected to substituted bithiophenes, were investigated. Aromaticity and electrophilic -nucleophilic traits of the aza-heterocyclic units, fostering inductive and resonance effects that translate to conjugation enhancement and electron (de)localization, were found a major factor determining the key electron properties of ionization potential (IP) and electron affinity (EA) of these molecules. Replacing the alkyl thiophene substituent for an alkoxy one, afforded certain control over the two parameters as well. All studied compounds were found to undergo electrochemical polymerization giving p and n-dopable products, featuring good electrochemical reversibility of their oxidative doping process, as demonstrated by cyclic voltammetry and UV-Vis-NIR, EPR spectroelectrochemistry. While electropolymerisation of entities differing in the heterodiazole unit was found to conserve the EA value, the IP parameter of polymerisation products was found to decrease by 0.6 to 0.7 eV affording an asymmetric narrowing of the frontier energy levels gap. Aided by quantum chemical computations, the effects of structure tailoring of the investigated systems are rationalized, pointing to conscious ways of shaping the electronic properties of thiophene class polymers using synthetically convenient heterodiazole π-conjugated units.

show abstract

“…Tautomeric energy differences also calculated for 515, using the HF/6-31G ÃÃ , B3LYP/6-311G ÃÃ , and B3LYP/6-311 þ þ G ÃÃ levels of approximation, confirm that these compounds are oxo or thione compounds rather than hydroxyl and mercapto tautomers [276]. 2-Amino-1,3,4-thiadiazoles 532 exist in the amino form, in solution and in the solid state, while the presence of the sulfonamido group shifts the equilibrium towards the imido tautomer [256,257].…”

Section: Thermodynamic Aspectsmentioning

confidence: 63%