Write equations for the substitution reaction of n...

Write equations for the substitution reaction of $n$ -bromobutane, a typical primary haloalkane, with the following reagents: (a) $\mathrm{NaOH} ;$ (b) $\mathrm{NH}_{3} ;$ (c) $\mathrm{NaCN}$ (d) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{ONa}$.

Key Concepts

Primary Haloalkanes

Primary haloalkanes are alkyl halides in which the halogen atom is attached to a carbon bonded to only one other carbon. Their low steric hindrance favors a backside attack by the nucleophile, making them highly reactive in substitution reactions and predominantly proceeding through an SN2 mechanism.

Nucleophilic Substitution Reaction

A nucleophilic substitution reaction involves the replacement of a leaving group by a nucleophile. In the context of organic chemistry, this reaction allows for the transformation of one functional group into another by the action of a nucleophilic reagent, leading to the formation of new bonds.

SN2 Mechanism

The SN2 mechanism is a bimolecular nucleophilic substitution process where the nucleophile attacks the electrophilic carbon simultaneously as the leaving group departs. This concerted mechanism features a single transition state and results in inversion of stereochemistry at the carbon center, with the reaction rate dependent on the concentrations of both the substrate and the nucleophile.

Nucleophiles

Nucleophiles are electron-rich species that can donate a pair of electrons to an electron-deficient center in a molecule, facilitating bond formation. In substitution reactions, different nucleophiles—ranging from hydroxide, ammonia, cyanide, to alkoxide ions—can be used to replace the leaving group, each imparting different reactivity and selectivity based on their nucleophilicity and basicity.

Leaving Groups

A leaving group is an atom or group of atoms that departs from the substrate during a substitution reaction, taking with it the electron pair originally shared with the carbon. The quality of the leaving group, which includes its ability to stabilize the negative charge after leaving, is a critical factor in determining the feasibility and rate of the substitution reaction.

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