1.3.5- Triazine, aromaticity estimates

Magnetic susceptibility anisotropy has been used for the estimation of relative aromaticity of some azines in comparison with benzene (77JCS(P2)897). If the extent of ir-electron delocalization for benzene is taken as 1.0, the corresponding values for azines are pyridine 0.7, pyridazine 0.7, pyrimidine 0.5, and 1,3,5-triazine 0.3. 

Therefore, the estimation of rate constants for the PAH (including for anthracene) is now uncertain. For substituted PAH, we can estimate approximately the enhancement of the rate constant over that for the parent PAH by using the correlation between the rate constant and Xa+ discussed above for the monocyclic aromatic compounds (Atkinson, 1987), with the enhancement factor being e134 o+. This approach also may work for heteroatom-containing aromatic compounds, such as pyridines and triazines. 

Magnetic susceptibility anisotropy has been used to estimate relative aromaticities of some azines <1977JOC897>. If the extent of -electron delocalization for benzene is taken as 1.0, the corresponding values for azines are pyridine 0.7, pyridazine 0.7, pyrimidine 0.5, and 1,3,5-triazine 0.3. Another quantitative magnetic index is the exaltation of the total magnetic susceptibility (A). All aromatic systems reveal large A values, whereas for nonaromatic compounds A is close to zero and it is assumed that aromaticity increases with A. For six-membered monocycles the following values of A have been reported (in units of cm3 mol-1 x —106) benzene (17.9), pyridine (18.3), pyridazine (8.7), pyrimidine (18.2), pyrazine (12.7), l-ethyl-2-pyridone (13.0), and 1,3,5-triazine (19.0). 

In 1975 the anion of T was observed in a mass spectrometer, indicating a positive valence-state Ea for T. In 1990 the Ea of AGCUT were predicted using substitution, replacement, and conjugation effects [10-14], In order to estimate the Ea of substituted compounds, that of the parent compounds is required. In 1974 I. Nenner and G. J. Schulz estimated the AEa of quinoline (0.36 eV), pyradazine (0.40 eV), pyrimidine (0.00 eV), pyrazine (0.40 eV), and s-triazine (0.45 eV) from electron transmission spectra and half-wave reduction potentials [15]. No adiabatic electron affinities of aromatic nitrogen heterocyclic compounds were measured in the gas phase before 1989 [16]. 

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