Question

Given The following substrates, determine which of the following will and will not react with NaOMe in an SN2 reaction to form an appreciable amount of product.

CH3CH2CH2Br

(CH3)2CHBr

(CH3)3CBr

(CH3)3CCH2Br

CH3CH2CH2OH

CH3CH2CH2NH2

Answer 1

Concepts and reason

Substitution reaction is also termed as single displacement reaction or also single substitution reaction. In a substitution reaction a functional group from the chemical compound will be replaced by another functional group.

Fundamentals

A nucleophile attacks the electrophilic center of the chemical compound and leads to departure of the leaving group.

Example:

Where, the circled carbon is the electrophilic carbon, is the nucleophile and bromine is the leaving group. attacks the electrophilic carbon of the chemical compound and the bromide ion leaves as leaving group.

indicates “substitution, nucleophilic, bimolecular”

Substrate:

For a reaction mechanism, the attack of the electrophilic center by nucleophile and departure of the leaving group occurs in a concerted manner.

As reaction mechanism occurs in a concerted step, the rate of reaction of alkyl halides depends on the steric hindrance of atoms or groups at the reacting site of the substrate.

Rate of reaction decreases with increasing steric hindrance. The relative rate of reaction of alkyl halides in reaction mechanism is as follows:

Methyl alkyl halide:

The carbon attached to halide is bonded to no other carbon atoms.

Primary alkyl halide:

The carbon attached to halide is bonded to one other carbon atom.

Secondary alkyl halide:

The carbon attached to halide is bonded to two other carbon atoms.

Tertiary alkyl halide:

The carbon attached to halide is bonded to three other carbon atoms.

Leaving group:

The reaction mechanism also depends on the nature of leaving group.

The leaving group that can stabilize its negative charge after leaving the substrate is a better leaving group. The species with low basicity can stabilize its negative charge than species with high basicity. Hence, are good leaving group. But are not good leaving group.

Nucleophile:

Nucleophile is affected by the steric hindrance.

Less hindered anion is more nucleophilic compared to more hindered anion.

The given nucleophile is and it is a strong nucleophile.

ion is a good leaving group.

ions are not good leaving group.

The substrate which contains as leaving groups is as follows:

Ans: