Benzene Construction | Kekule Structure, Resonance Structure, Resonance Energy, Properties |

Benzene Structure.

The molecular formula of benzene was suggested to hold upwardly C6H6. This formula shows that benzene is a highly unsaturated compound. Various possible structures were suggested for benzene.

Straight-Chain Structures of benzene.

If nosotros intend that benzene is an open-chain chemical compound too hence roughly of the next possibilities tin hold upwardly proposed. 

STRAIGHT CHAIN STRUCTURE RULED OUT.

Anyhow, these structures were rejected due to the next reasons:

1. Benzene adds exclusively 6 hydrogens too 6 element of group VII atoms to larn inward saturated, but these open-chain structures suggest that 8 hydrogen atoms or 8 element of group VII atoms tin hold upwardly added.
   
2. Benzene does non present the reaction amongst alkaline metal KMnO4 which is the best exam of unsaturation.
3. Benzene does non react amongst bromine H2O which is i of the tests for unsaturated compounds. These facts tell us that at that topographic point is unsaturation inward the benzene but this
   saturation is of a dissimilar variety from alkenes too alkynes.
4. Benzene gives commutation reactions but similar saturated hydrocarbons. This shows that inward spite of the presence of double bonds the benzene behaves similar a saturated compound.
5. Benzene gives exclusively i monosubstituted derivative, but the open-chain chemic structures suggest at to the lowest degree 3 monosubstituted derivatives.
6. The molecular formula for benzene is C6H6. It does non tally to the open-chain hydrocarbons.

In alkanes, the full general formula is C_nH_2n+2 . Hence, 6 carbons should convey xiv hydrogens too the formula should convey been C6H14.

In alkynes, the full general formula is C_nH_2n-2. Hence 6 carbon atoms should convey x hydrogen atoms too the formula should convey been C6H10.

Possibility of open-chain ruled out:

Keeping all these things inward persuasion nosotros tin state that benzene does non belong to opened upwardly chain hydrocarbon. The possibility for the straight-chain construction is ruled out.

KEKULE STRUCTURE OF BENZENE.

"Kekule Structure of Benzene" inward 1865, later on years of regain of benzene, Kekule suggested that:

• The benzene molecule is made upwardly of a hexagon of 6 carbon atoms.
• There are alternate unmarried too double bonds too i hydrogen is attached to each carbon atom.
  

Evidence inward favor of band structure:
The next evidence is at that topographic point which back upwardly the Kekule Structure:
Benzene adds 3 hydrogen molecules to shape cyclohexane.

Benzene adds 3 molecules of chlorine inward the presence of sunlight.

Benzene exclusively gives i monosubstituted derivative. Actually, all the carbon atoms of benzene are alike.

Benzene gives 3 disubstituted derivatives that back upwardly the Kekule Structure.

RESONANCE STRUCTURE OF BENZENE.

The dissimilar construction which tin hold upwardly written nether dissimilar pairing schemes of a chemical compound is called resonance structures of benzene.

The ii structures of benzene which convey been mentioned inward a higher house are called resonance structures of benzene. 

They are besides called contributing structures of benzene. Sometimes they are called canonical contributors, to the actual structure.

In improver to these ii resonance structures, 3 other structures convey been proposed past times Dewar. They are called Dewar structures.

The v structures are joined past times double-headed arrows:

Dewar construction is besides called para-bond structures. The π-bonds between C1 - C4, C2 - C5, C3 - C6 are to the lowest degree favorable. For this reason, these structures III, IV, too V are to the lowest degree contributing, i.e., 7% each towards the resonance hybrid.

The contribution of Kekule construction (I) too (II) is lxxx % too that of Dewar structures (III), (IV), (V) is xx % to the actual or existent construction of benzene.

Resonance Energy of Benzene:

The departure betwixt this experimental too theoretical values of heats of hydrogenation is the total of stability of benzene.

This is 150.5 kJ·mol⁻¹ is the departure betwixt 385.5 too 208. This total of stability is gained past times benzene, due to resonance. So this 150.5 kJ·mol⁻¹ is called resonance loose energy of benzene.
Following this diagram makes the thought clear.

Definition of resonance energy:

Resonance energy is the stair out of how much to a greater extent than stable the actual construction of the chemical compound is than its extreme resonance structure.

The oestrus of combustion too stability of benzene:

Similarly, it has been calculated that the observed oestrus of combustion of benzene is less than the calculated value. This besides points to the fact that the benzene molecule has less loose energy than cyclohexatriene.

Substitution reaction too stability of benzene:

In almost of the chemic reactions, benzene undergoes electrophilic commutation reactions. Benzene prefers to substitute the hydrogen of its band rather than improver reaction at the double bond.

Properties of Benzene.

"Physical properties of benzene" too "chemical properties of benzene"

Physical properties of benzene.

1. Benzene is a colorless liquid.
2. Its boiling betoken is 80.1 °C.
3. Its freezing betoken is +5.5 °C.
4. It is insoluble inward H2O too forms the upper layer.
5. It is miscible amongst ether too alcohol inward all proportions.
6. It is a practiced solvent for fats, resins, sulfur, phosphorus, too iodine.
7. its specific gravity is 0.884 cm-3 at xv °C.
8. It is extremely poisonous inward nature. It destroys the cerise too white blood cells.
9. It burns amongst a luminous sooty flame.

Chemical properties of benzene.

 The chief types of reactions of benzene are the following:

1. Electrophilic commutation reactions.
2. Addition reaction.
3. Oxidation reactions.