CH₃CH₂C(CH₃) = CHCH₃

Arenes are aromatic hydrocarbons.

Acetophenone is formed.

Huckel rule states that a compound is said to be aromatic if it has (4n + 2) \(\pi\) electrons delocalized where n = an integer 0, 1, 2, 3,........

Ethyne is more acidic than ethene because it has 'sp' hybridised 'C' which is more electronegative.

2, 2-Dimethylpropane < 2-methylbutane < pentane.

Paraffins means little affinity. Alkanes due to strong C-C and C-H bonds are relatively chemically inert.

Conformations are spatial arrangements which are obtained by rotation around sigma bonds.

(ii) H-C \(\equiv \) C-H (Linear with bond angle 180°

Anhydrous Ferric Chloride (FeCl₃) is another Lewis acid which can be used.

Boiling points of alkanes
1. The boiling points of alkanes rise as the number of carbons increases.
2. Since nonane has a longer carbon chain than octane, it will have a higher boiling point.
Effect of branching on the boiling point of alkane
1. As an alkane chain branch, the surface area of the molecule decreases.
2. The intermolecular force reduces as a result of this.
3. At a lower temperature, the forces can be readily overcome.
4. Therefore, as the branching increases, the boiling point of an alkane chain decreases.

The structures of cis- and trans-isomer of hex-2-ene are:

The boiling point of a molecule depends upon dipole-dipole interactions. Since cis-isomer has higher dipole moment, therefore, it has higher boiling point.

Alkenes are rich source of loosely held \(\pi \) electrons, due to which they show electrophilic addition reaction. Electrophilic addition reactions of alkenes are accompanied by large energy changes so these are energetically favourable than that of Electrophilic substitution reactions.
In special conditions alkenes also undergo free radical substitution reactions.
In arenes during electrophilic addition reactions aromatic character of benzene ring is destroyed while during electrophilic substitution reactions of areans are enegetically more favourable than that of electrophilic addition reaction.
That's why alkenes prefer to undergo electrophilic addition reaction while arenes prefer electrophilic substitution reactions.

On converting benzene to toluene, there is a fall in the melting point although toluene has the higher molecular mass. This is because the planar molecules of benzene can pack more closely in the crystal lattice and the cohesive forces are strong, whereas the methyl group in toluene prevents such close packing.

Rotation around C-C single bond is not completely free and it is restricted due to repulsions between the electron clouds of C-H bonds in the adjacent carbon atoms. Therefore, ethane exixts in infinate number of conformations. Out of these, two extreme conformations are staggered and eclipsed.