Question

Rank the relative nucleophilicity of halide ions in dimethl sulfoxide solution. How is dimethyl sulfoxide classified?

Rank the relative nucleophilicity of halide ions in dimethyl sulfoxide solution.

Answer 1

Concepts and reason

The problem is based on the concepts of Nucleophile and solvent.

Nucleophile are the electron rich chemical species and have the tendency to donate electron pair. The solvent is the compound which can dissolve other compound. When the nucleophiles come in contact with the solvent, the solvent affects the reactivity of the nucleophiles.

Fundamentals

Nucleophiles are the negatively charged species or the compound with the lone pairs. They have the tendency to donate the electron pairs. The solvent has the effect on the nucleophile. The polar protic solvent has the hydrogen atom. Therefore, polar protic solvent has the ability to form the hydrogen bond with the electronegative element. The polar aprotic solvent do not form the hydrogen bond with the nucleophile. Therefore, they do not affect the nucleophilic nature of the nucleophile.

Part 1

Dimethyl sulfoxide is the polar aprotic solvent. The ${{\rm{F}}^ - }$ ion is the unstable ion and has the most nucleophilic character. The ${{\rm{I}}^ - }$ ion is the most stable ion and therefore, the nucleophilic character is of iodide ion is the least.

The nucleophilic character of the halide ion is as follows:

${{\rm{F}}^ - } > {\rm{C}}{{\rm{l}}^ - } > {\rm{B}}{{\rm{r}}^ - } > {{\rm{I}}^ - }$

Part 2

Consider the structure of dimethyl sulfoxide as follows:

Dimethyl sulfoxide is not a polar solvent.

Polar aprotic solvent do not has the ability to donate the hydrogen atom. Therefore, dimethyl sulfoxide is a polar aprotic solvent.

Ans: Part 1

The nucleophilic character of the halide ion is as follows:

${{\rm{F}}^ - } > {\rm{C}}{{\rm{l}}^ - } > {\rm{B}}{{\rm{r}}^ - } > {{\rm{I}}^ - }$

Part 2

Dimethyl sulfoxide is a polar aprotic solvent.