Chapter FRP, Problem 1P

Interpretation Introduction

Interpretation:

The mechanism for each of the given reactions are to be written.

Concept introduction:

舧 Electrophiles are electron-deficient species, which has positive or partially positive charge. Lewis acids are electrophiles, which accept electron pair.

舧 Nucleophiles are electron-rich species, which has negative or partially negative charge. Lewis bases are nucleophiles, which donate electron pair.

舧 The reaction in which there is addition of halogen (F, Cl, Br, and I) to the compound is called halogenation reaction.

舧 A type of halogenation in which alkanes and aromatics, which are alkyl substituted, react chemically in presence of light is known as free radical halogenation. It involves chain initiation, propagation, and termination step in its whole mechanism.

舧 Hydride shift is defined as the rearrangement of hydrogen atoms.

Answer to Problem 1P

Solution:

(a)

(b)

(c)

(d)

Explanation of Solution

a)

In the given reaction, cyclopentanol reacts with sulfuric acid in presence of heat to form the required product. The mechanism of this reaction takes place when the hydroxy group, which is having lone pair of electron, attacks on hydrogen atom (H) and withdraw it. After that equilibrium forms and removal of water takes place, which leads to the formation of secondary carbocation. The secondary carbocations are very unstable so methanide shift takes place and stable tertiary carbocation forms.

The mechanism of the reaction is as follows:

b)

The given reaction take place when cyclopentene ring reacts with bromine in presence of light by the help of free radical halogenation. In the mechanism, the cyclopentene attacks on Br and addition of Br cation takes place at cyclopentene ring. The cyclopentene ring becomes electron deficient after the addition of Br so addition of chlorine atom takes place at cyclopentene ring and this leads to the formation of required product.

The mechanism is as follows:

c) The other products from the reaction given in part (b).

From the above reaction, one more product is formed. When addition of chlorine atom takes place at electron deficient cyclopentene ring then addition of chlorine takes place but the product formed here is an enantiomer of the product formed above. So two products are formed, both are in equimolar amount and are enantiomer of each other.

The second product of the reaction is as follows:

d)

The given reaction takes place, when $1-\text{ethylene}$ cyclopentane reacts with hydrogen bromide then ethylene group attacks on hydrogen atom, Br group is removed and unstable secondary carbocation is formed. To stabilize the unstable secondary carbocation, $1,2-\text{Hydride shift}$ takes place. Hence, the required product is formed.

The mechanism is represented below: