Question

Match the following \begin{tabular}{ll} \hline Column-1 & Column-II \\ \hline (a) \(\mathrm{Hg}_{2}^{2+}\) & (p) Nucleophile \\ (b) \(\mathrm{AlCl}_{3}\) & (q) Catalyst \\ (c) \(\mathrm{Br}\) & (r) Lewis acid \\ (d) \(\mathrm{H}^{+}\) & (s) Soft acid \\ & (t) Electrophile \end{tabular}

Short answer

(a) \(\mathrm{Hg}_{2}^{2+}\) - Soft acid, (b) \(\mathrm{AlCl}_{3}\) - Lewis acid, (c) \(\mathrm{Br}\) - Nucleophile, (d) \(\mathrm{H}^{+}\) - Electrophile.

Step-by-step solution

Analyzing Options in Column I

Begin by considering the options given in Column-I. Each symbol or formula represents a specific chemical identity or ion with unique chemical properties. We'll examine each one individually and determine their roles or characteristics in reactions.

Characteristics of \(\mathrm{Hg}_{2}^{2+}\)

\(\mathrm{Hg}_{2}^{2+}\) is a dimeric ion of mercury, representing a very stable bonding. Mercury ions are usually considered soft acids, meaning they prefer to interact with 'soft' bases. Thus, we can match \(\mathrm{Hg}_{2}^{2+}\) with 'soft acid' (option s).

Characteristics of \(\mathrm{AlCl}_{3}\)

\(\mathrm{AlCl}_{3}\) commonly acts as a Lewis acid because it can accept electron pairs due to its electron-deficient nature. As a Lewis acid, it often participates in reactions by accepting electrons. Therefore, we match \(\mathrm{AlCl}_{3}\) with 'Lewis acid' (option r).

Characteristics of \(\mathrm{Br}\)

\(\mathrm{Br}\), a halogen element, can act as a nucleophile because it has a lone pair of electrons that can be donated to an electrophile in a chemical reaction. Therefore, \(\mathrm{Br}\) matches with 'nucleophile' (option p).

Characteristics of \(\mathrm{H}^{+}\)

The \(\mathrm{H}^{+}\) ion, also referred to as a proton, is highly electron-deficient. It is known to act as an electrophile because it will readily accept electrons from surrounding entities. Thus, we match \(\mathrm{H}^{+}\) with 'electrophile' (option t).

Confirmation of Matches

After matching each item from Column-I with Column-II, confirm that all possibilities are correctly assigned based on their chemical properties and roles:- (a) \(\mathrm{Hg}_{2}^{2+}\) - (s) Soft acid- (b) \(\mathrm{AlCl}_{3}\) - (r) Lewis acid- (c) \(\mathrm{Br}\) - (p) Nucleophile- (d) \(\mathrm{H}^{+}\) - (t) Electrophile.

Key concepts

Lewis Acid

Lewis acids are molecules or ions that can accept a pair of electrons. They essentially act as electron pair acceptors. This characteristic of Lewis acids is particularly useful in many types of chemical reactions, especially those involving coordination compounds.

One of the classic examples of a Lewis acid is \(\mathrm{AlCl}_3\). It frequently participates in reactions where it seeks to fulfill its octet by accepting electron pairs. This electron-deficient nature makes Lewis acids unique because they can form more stable compounds by accepting electrons from Lewis bases, which are electron pair donors.

• Examples: \(\mathrm{AlCl}_3\), \(\mathrm{BF}_3\), and \(\mathrm{FeCl}_3\) are well-known Lewis acids.
• Applications: Lewis acids are essential in metal-catalyzed reactions and polymerization processes.

Nucleophile

Nucleophiles are chemical species that are rich in electrons and have a tendency to donate these electrons to electrophiles. They are the electron-pair donors in a chemical reaction.
In other words, nucleophiles are attracted to positive charges or positively charged species because they seek to balance their excess electron density. A great example of a nucleophile is \(\mathrm{Br}^-\), as it has electron pairs ready to be shared.

• Characteristics: Nucleophiles possess lone pairs or pi bonds that they are willing to donate.
• Examples: \(\mathrm{Br}^-\), \(\mathrm{OH}^-\), \(\mathrm{CN}^-\), and ammonia \(\mathrm{NH}_3\).

Nucleophiles play a vital role in many organic reactions, including substitution reactions.

Electrophile

Electrophiles are chemical species that are electron deficient and tend to accept electrons from nucleophiles. They act as electron pair acceptors and are usually positively charged or neutral with an electron-deficient area.
A common example of an electrophile is \(\mathrm{H}^+\). Being essentially a proton, it readily attracts electrons to achieve stability. Electrophiles are crucial participants in chemical reactions, often determining the pathway that a reaction will follow.

• Characteristics: Electrophiles are often associated with positive charges or polarized bonds with an electron-poor center.
• Examples: \(\mathrm{H}^+\), \(\mathrm{NO}_2^+\), and \(\mathrm{Br}_2\).

Electrophiles are central to many reaction mechanisms, including addition reactions.

Soft Acid

"Soft acid" is a term from Pearson's hard-soft acid-base (HSAB) theory, which categorizes acids and bases based on their polarizability. Soft acids are ions or molecules that are large, have a low charge to size ratio, and are highly polarizable. They tend to interact with soft bases, which share similar characteristics.
An example of a soft acid is \(\mathrm{Hg}_{2}^{2+}\), known for its ability to form soft acid-base compounds due to its polarizable electron cloud.

• Characteristics: Soft acids are often heavy metal ions with partially filled d orbitals.
• Examples: \(\mathrm{Hg}_{2}^{2+}\), \(\mathrm{Pd}^{2+}\), and \(\mathrm{Pt}^{2+}\).

Soft acids frequently participate in organometallic chemistry and complex formation reactions.