Chemistry > Aromatic Compounds > 1.0 The Structure of Benzene
Aromatic Compounds
1.0 The Structure of Benzene
1.1 A Resonance Picture of Benzene
1.2 The Stability of Benzene
1.3 The Resonance Explanation of the Structure of Benzene
1.4 Bond lengths and angles in benzene
1.5 Hückle’s Rule: The $\left( {4n{\text{ }} + {\text{ }}2} \right)\pi $ Electron Rule
2.0 Electrophilic Aromatic Substitution Reactions
3.0 Nitration
4.0 Sulphonation
5.0 Halogenation
6.0 Friedel-Crafts Alkylation
7.0 Friedel-Crafts Acylation
8.0 Orientation and Reactivity in Electrophilic Aromatic Substitution
8.1 Donation of electrons into a benzene ring by resonance
8.2 Withdrawal of electrons from a benzene ring by resonance
9.0 Ortho / Para Ratio
9.1 Directive influence of the groups during substitutions in benzene ring
9.2 Mechanism of o and p-directing groups
9.3 Mechanism of o- and p-directing groups not have unshared pair of electrons
9.4 Mechanism of o- and p-directing gps having unshared pair of electron(s)
9.5 Mechanism of m-directing groups
9.6 Competitive orienting effect of two substituents
10.0 Reactions of Alkyl Benzenes
1.4 Bond lengths and angles in benzene
1.2 The Stability of Benzene
1.3 The Resonance Explanation of the Structure of Benzene
1.4 Bond lengths and angles in benzene
1.5 Hückle’s Rule: The $\left( {4n{\text{ }} + {\text{ }}2} \right)\pi $ Electron Rule
8.2 Withdrawal of electrons from a benzene ring by resonance
9.2 Mechanism of o and p-directing groups
9.3 Mechanism of o- and p-directing groups not have unshared pair of electrons
9.4 Mechanism of o- and p-directing gps having unshared pair of electron(s)
9.5 Mechanism of m-directing groups
9.6 Competitive orienting effect of two substituents
The hybrid structure is represented by inscribing a circle in the hexagon, and it is this new formula (III) that is most often used for benzene today. There are times, however, when an accounting of the electrons must be made, and for these purposes we may use one or the other of the Kekulé structures. We do this simply because the electron count in a Kekulé structure is obvious, whereas the number of electrons represented by a circle or portion of a circle is ambiguous. With benzene the circle represents the six electrons that are delocalized about the six carbon atoms of the benzene ring. With other systems, however, a circle in a ring may represent numbers of delocalized electrons other than six.
Resonance theory also tells us that whenever equivalent resonance structures can be drawn for a molecule, the molecule (or hybrid) is much more stable than any of the resonance structures would be individually if they could exist. In this way resonance theory accounts for the much greater stability of benzene when compared to the hypothetical 1,3,5-cyclohexatriene. For this reason the extra stability with benzene is called its resonance energy. It is this very large increment of resonance energy that places benzene and related compounds in a separate category that we call aromatic.
Huckel’s Orbitals in benzene’s orbital overlap is indicated by the dashed lines
