Question

Pick the strongest nucleophile. (a) \(\mathrm{X}\) (b) \(\stackrel{\ominus}{\mathrm{N}} \mathrm{H}_{2}\) (c) \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}\) : (d) \(\mathrm{H}\)

Short answer

The strongest nucleophile is \(\stackrel{\ominus}{\mathrm{N}} \mathrm{H}_{2}\).

Step-by-step solution

Define a Nucleophile

A nucleophile is a chemical species that donates an electron pair to form a chemical bond in reaction. Nucleophiles are characterized by their ability to attack a positively charged atom, usually a carbon, due to available electron pairs.

Identify Strong Nucleophiles

Strong nucleophiles are typically negatively charged ions or species with lone pairs ready to donate. They tend to react faster in substitution reactions. Examples include ions like hydroxide (\(\mathrm{OH}^{-}\)) and amide (\(\mathrm{NH}_2^{-}\)).

Analyze Each Option

Let's list and analyze the given options. (a) \(\mathrm{X}\) is unspecified, (b) \(\stackrel{\ominus}{\mathrm{N}} \mathrm{H}_{2}\) has a negatively charged nitrogen, making it a strong nucleophile, (c) \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}:\) is a neutral alkyne, and (d) \(\mathrm{H}\) is a hydrogen atom, which is not generally considered a nucleophile.

Compare Their Nucleophilicity

Among the given species, \(\stackrel{\ominus}{\mathrm{N}} \mathrm{H}_{2}\) is a negatively charged species with a lone pair on nitrogen, which is typically very nucleophilic. Neutral molecules or atoms without charge like \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}\): and \(\mathrm{H}\) are weaker nucleophiles compared to charged ions.

Choose the Strongest Nucleophile

Based on our analysis, the strongest nucleophile is the one with a high electron density and a negative charge. Therefore, \(\stackrel{\ominus}{\mathrm{N}} \mathrm{H}_{2}\) is the strongest nucleophile among the given options.

Key concepts

Nucleophile

Simply put, a nucleophile is a chemical species that loves to engage with positively charged regions of other molecules. They do this by donating a pair of electrons to form a new chemical bond. This ability to donate electrons makes nucleophiles key players in many chemical reactions, particularly in substitution reactions, where they replace another group or atom in a molecule.

Nucleophiles often have extra electrons to share:

• They can be ions, like hydroxide (\( \mathrm{OH}^{-} \)), that possess a negative charge.
• They may also be neutral molecules with lone pairs of electrons, like water (\( \mathrm{H}_{2}\mathrm{O} \)).
• Even though neutral nucleophiles have no charge, their lone pairs allow them to act similarly to their negatively charged counterparts.

Their effectiveness in a reaction depends largely on their electron availability, which is often influenced by their charge.

Electron Donor

In chemistry, an electron donor is a species that has the capacity to offer an electron pair to another atom or ion. This results in the formation of a new chemical bond. Nucleophiles are typical examples of electron donors because they possess extra electrons they are willing to share with an electron-deficient atom.

Several factors influence the strength of an electron donor:

• Charge: A negatively charged species has an increased electron density, making it a more effective electron donor.
• Electronegativity: Atoms that hold their electrons loosely (are less electronegative) are more likely to donate electron pairs.
• Solvent Effect: Polar solvents can stabilize charged species, affecting their donation ability.

Understanding the concept of electron donation is crucial for predicting how substances will interact in a chemical reaction.

Chemical Bond Formation

Chemical bond formation is a fundamental concept in chemistry where two or more atoms or ions combine to form a stable chemical structure. This process involves the sharing or transfer of electrons between participating species. In the case of nucleophiles, they donate an electron pair to a positively charged region of another molecule during a reaction, resulting in bond formation.

Several types of bonds can form:

• Ionic Bonds: Formed through the transfer of electrons from one atom to another, creating ions with opposite charges that attract each other.
• Covalent Bonds: Involve sharing electron pairs between atoms, where nucleophiles play a crucial role.

The role of nucleophiles in bond formation is vital as they initiate the process by attacking electron-poor areas of molecules, emphasizing their importance in diverse chemical reactions.

Negatively Charged Ions

Negatively charged ions, or anions, are ions that have gained one or more electrons, giving them a net negative charge. This additional electron enhances their ability to act as nucleophiles by increasing electron density, making them effective electron donors.

Key characteristics of negatively charged ions include:

• Increased Reactivity: Their negative charge often makes them highly reactive, particularly towards positively charged or electron-deficient species.
• Common Examples: Hydroxide (\( \mathrm{OH}^{-} \)) and amide (\( \mathrm{NH}_2^{-} \)) ions are classic examples that frequently participate in substitution reactions.
• Stability in Solutions: The behavior of these ions can vary depending on the solvent, as polar solvents stabilize ions effectively.

Understanding their behavior helps predict their roles and effectiveness in facilitating chemical transformations.