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Mark Nealon

The order of aromaticity of benzene, thiophene, pyrrole, furan, and pyridine

Bryan Michaels-Lex  Follow

The main criteria of aromaticity is resonant or delocalization energy.It is difference between energy contained in bonds if they were localized like in Kekule's formula for benzene and actual energy.For benzene if is about 150 kJ/mol.The more this energy the more stable molecule is.

The approaches for calculating this energy may differ.As for β-values mentioned in paper by @orthocresol it looks like it is Dewar's resonance energy per one π-electron calculated based on modified Hückel's MO method as mentioned in GSE article.

There is a table in this article with the same β-values:β-values

In English it is

Benzene                            0.065     Pentalene                     -0.018Naphthalene                        0.055     Azulene                        0.023Anthracene                         0.047     Fulvene                       -0.002Tetracene                          0.042     Pyridine                       0.058Cyclooctadecanonaene([18]annulene) 0.012     Pyrrole                        0.039Cyclobutadiene                    -0.268     Furan                          0.007Azete (Azacyclobutadiene)         -0.160     Thiophene                      0.032

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