Relatively recent experimental facts indicate that the carbon-carbon distances in the benzene molecule are exactly the same, in contradiction with the Kekule formula showing single and double bonds, whose length is different, in fact we know the following values:
- simple carbon-carbon link: 154 pm (picometer)
- Carbon-Carbon Double bond: 133 pm
- carbon-carbon bonds in benzene: 139 pm
These and other experimental evidence led then to believe that the Kekulé formula is not accurate presentation of the molecule benzene.
This consideration is contemplated in the so-called theory of resonance. This theory suggests that the actual structure of benzene each carbon-carbon bond is neither simple nor double, but an intermediate type link.
In general, the theory of resonance applies to cases that can not be achieved for a compound estrucutural unique formula that agrees well with the experimental facts and with the conventions used to describe these formulas, (rule octet, for example)
The actual presentation of the molecule, it is considered as a hybrid of resoncancia between various structures, called estrucuturas or resonant taxpayers. The resonance between these forms taxpayers are indicated by an arrow with a head on both ends. Thus, for benzene (using simplified formulas), we have the following resonance situation (without highlighting the link diferenteslongitudes)
This can only be described as a hybrid of these structures which are illustrated in the figure by barrra models and spheres.
The real estrucutura benzene molecule is a hybrid between the two estrucutras contrubuynetes illustrated here.
anyway for the great majority of purposes forms just use a single taxpayer.
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