The influence of aza-substitution on azole aromaticity

Ramsden, Christopher A.

doi:10.1016/j.tet.2010.02.019

Cited by 45 publications

(42 citation statements)

References 21 publications

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“…Thus, the value of "C" is equal to 15 in the case of pyrrole 1 but is incremented as the number of pyridine-type atoms increases, reaching the maximum value of 19 for pentazole 10. Azoles may be classified [4] according to the number (N 2,5 ) of pyridine-type nitrogen atoms neighboring the NH group in the ring. Thus, the "N 2,5 =0" group are pyrrole 1, 1H-imidazole 3 and 4H-1,2,4-triazole 7, the "N 2,5 =1" group are 1H-pyrazole 2, 1H-1,2,3-triazole 4, 1H-1,2,4-triazole 6 and 1H-tetrazole 8, and the "N 2,5 =2" group are 2H-1,2,3-triazole 5, 2H-1,2,3-tetrazole 9 and pentazole 10.…”

Section: Resultsmentioning

confidence: 99%

“…In aza-azoles the aromatic stabilization energy (ASE) depends on the number and location of the pyridine-type nitrogen atoms in the ring, especially how many pyridine-type nitrogen atoms are next to the pyrroletype nitrogen atom [4]. The pyrrole-type nitrogen possesses an electron lone pair perpendicular to the molecular plane and nominally contributes two electrons to the aromatic sextet.…”

Section: Introductionmentioning

confidence: 99%

“…One more interesting symptom of the dependence of -electron structure on the relative locations of pyridine-and pyrrole-type nitrogen atoms is that mean HOMA values for the subgroups [4] "N 2,5 =0", "N 2,5 =1" and "N 2,5 =2" increase as N increases, as shown in Schemes 3. Similarly, mean ASE values (taken from [3]) distinguish between these three subgroups.…”

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Sigma- and pi- electron structure of aza-azoles

2010

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The reasons behind changes of aromaticity in 10 unsubstituted aza-azoles was analysed by employing the Natural Bond Orbital (NBO) approach at the MP2/6-311+G(d,p) level of theory. Sum of occupations of p z orbitals at atoms in the ring correlates well with the magnetism based aromaticity index NICS as well as with the number of nitrogen atoms in the ring. Changes of NICS depend strongly in a linear way on the number of NN bonds.Classification of azoles based on the number of pyridine-type nitrogen atoms vicinal to NH is supported by plotting the relative occupation of  orbitals ( occ ) against the relative occupation of  orbitals ( occ ) for all individual atoms in rings.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sigma- and pi- electron structure of aza-azoles

2010

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“…The first conclusion would be to assign this result to the stronger electron accepting properties and higher aromaticity of thiadiazole compared to the other heterocyles (oxadiazole and triazole. 48,49 ). Optical transitions only provide information about the breadth of frontier orbitals separation.…”

Section: Dft Calculationsmentioning

confidence: 99%

“…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

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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.

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Nitrogen Catenation: Polyazoles and Polyazines

Politzer¹,

Murray²

2017

Patai's Chemistry of Functional Groups

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Polyazoles and polyazines are, respectively, five‐ and six‐membered nitrogen heterocycles. An interesting difference between their geometries is that it is possible in polyazoles (but not in polyazines) to distinguish between formal single and formal double bonds. Our particular focus in this chapter is on those polyazoles and polyazines that feature three or more linked nitrogens in their rings (nitrogen catenation). The presence of ring nitrogens is destabilizing, especially when they are linked. Several possible factors that may be responsible for this effect of catenation are discussed in detail, and it is emphasized that these factors are not mutually exclusive or independent of each other. The electrostatic potentials of the molecules of interest are analyzed and related to their relative stabilities. N‐oxide formation is one means of mitigating the destabilization caused by nitrogen catenation. The acidity/basicity of these polyazoles and polyazines is examined in terms of their electrostatic potentials and local ionization energies. Polyazoles and polyazines have been found to provide good molecular frameworks for energetic materials; this application is briefly mentioned.

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The influence of aza-substitution on azole aromaticity

Cited by 45 publications

References 21 publications

Sigma- and pi- electron structure of aza-azoles

Sigma- and pi- electron structure of aza-azoles

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

Nitrogen Catenation: Polyazoles and Polyazines

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