Question

Which of the following behaves both as a nucleophile and as an electrophile? (a) \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{N}\) (b) \(\mathrm{CH}_{3} \mathrm{OH}\) (c) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\)

Short answer

The correct answer is (a) \\(\mathrm{CH}_3-\mathrm{C} \equiv \mathrm{N}\\).

Step-by-step solution

Understanding Nucleophiles

Nucleophiles are species that donate a pair of electrons to form a new covalent bond. They seek out positively charged or electron-deficient areas in molecules. Common nucleophiles include molecules or ions with lone pairs of electrons or π bonds.

Understanding Electrophiles

Electrophiles are species that accept a pair of electrons to form a new covalent bond. They are electron-deficient and seek electron-rich areas in molecules. Common electrophiles have positive charges or incomplete electron octets.

Analyzing Option (a): \\(\text{CH}_3-\text{C} \equiv \text{N}\\)

Acetonitrile \(\text{CH}_3-\text{C} \equiv \text{N}\) has a carbon-nitrogen triple bond, which gives the carbon a partial positive charge making it electrophilic. The nitrogen has a lone pair of electrons, allowing it to act as a nucleophile. Thus, this compound can function both as a nucleophile and as an electrophile.

Analyzing Option (b): \\(\text{CH}_3\text{OH}\\)

Methanol \(\text{CH}_3\text{OH}\) has a lone pair of electrons on oxygen, making it a nucleophile. However, it lacks a significant positive charge center to act as an electrophile effectively, so it does not behave as both.

Analyzing Option (c): \\(\text{CH}_2=\text{CH}-\text{CH}_3\\)

Propene \(\text{CH}_2=\text{CH}-\text{CH}_3\) is primarily a nucleophile due to its \(\pi \)-bonds, which can donate electrons. It is generally not electrophilic as it lacks a positive charge or electron deficiency necessary to accept electrons.

Analyzing Option (d): \\(\text{CH}_3\text{NH}_2\\)

Methylamine \(\text{CH}_3\text{NH}_2\) acts as a nucleophile because of the lone pair on nitrogen that can donate electrons. It does not have a positive charge or electron-deficient center, thus it generally does not behave as an electrophile.

Concluding the Right Answer

Among all the options, only acetonitrile \(\text{CH}_3-\text{C} \equiv \text{N}\) contains both an electrophilic site (positive carbon in the triple bond) and a nucleophilic site (lone pair on nitrogen).

Key concepts

Acetonitrile

Acetonitrile is a versatile compound with the chemical formula \( ext{CH}_3- ext{C} ext{≡} ext{N}\). It is composed of a methyl group (\( ext{CH}_3\)) bonded to a carbon atom, which in turn is triple-bonded to a nitrogen atom.
One of the intriguing aspects of acetonitrile is its ability to act as both a nucleophile and an electrophile. This duality is rooted in its molecular structure and electronic distribution.

• The triple bond between carbon and nitrogen results in a significant electron density difference. The carbon atom carries a partial positive charge due to its association with the more electronegative nitrogen atom.
• The nitrogen atom, characterized by its lone pair of electrons, provides nucleophilic behavior, ready to donate electrons and form new bonds.

This unique combination of features makes acetonitrile a key player in organic chemistry, participating in various reactions where it can either donate or accept electrons.

Nucleophile behavior

Nucleophiles are fascinating entities that are attracted to positive centers in molecules. These species can be atoms, ions, or molecules rich in electrons such as those with lone pairs or C bonds. Essentially, nucleophiles are electron donors.

In chemical reactions, nucleophiles seek out electron-deficient regions, which are often positively charged or partially positive regions in molecules. Their ability to donate electrons allows them to form covalent bonds with electrophiles.

• Common nucleophiles include water (with its lone pairs on oxygen), hydroxide ions, and ammonia, which similarly possesses lone pairs on nitrogen.
• P C bonds in alkenes and alkynes can also serve as nucleophiles by providing electrons to form new bonds.

Nucleophiles are essential players in a multitude of reactions, from simple acid-base reactions to complex organic transformations, where their electron-pair donation leads to the formation of new chemical bonds and, consequently, new compounds.

Electrophile behavior

Electrophiles are the seekers of electrons, driven by their electron-deficient nature. These species are characterized by their need to accept electrons to form stable covalent bonds.

Their electron deficiency often stems from being positively charged or having incomplete electron octets, rendering them highly reactive towards nucleophiles.

• Many classical electrophiles include positively charged ions like hydrogen ions \(( ext{H}^+)\) and carbocations \(( ext{R}_3 ext{C}^+)\).
• Neutral molecules, such as carbonyl compounds, can also act as electrophiles due to their polarized bonds, where one atom is more electron-withdrawing.

Electrophiles are crucial in drive reactions forward by accepting electron pairs from nucleophiles. This acceptance leads to bond formation and is a fundamental aspect of many chemical processes, including substitution and addition reactions in organic chemistry. The balance between nucleophiles and electrophiles illustrates the intricate dance of electrons, crucial for all chemical transformations.