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Magazine Chapter 11: Problem 4
Pick the strongest nucleophile. (a) : \(\mathrm{CH}_{3}\) (b) \(\mathrm{NH}_{2}\) (c) \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}:\) (d) \(\mathrm{H}^{\ominus{\ominus}}\)
Short Answer
Expert verified
The strongest nucleophile is \(\mathrm{NH}_2\).
Step by step solution
01
Define a Nucleophile
A nucleophile is a species that donates a pair of electrons to an electrophile to form a chemical bond in a reaction. Nucleophiles are electron-rich and seek positively charged or electron-deficient centers.
02
Analyze Available Options
Examine each given species based on their capability to donate electrons and form bonds.(a) \(\mathrm{CH}_3\) - Methyl radical, not negatively charged.(b) \( \mathrm{NH}_2 \) - Has a lone pair and a negative charge, making it a strong nucleophile.(c) \( \mathrm{H}-\mathrm{C} \equiv \mathrm{C}: \) - The acetylide ion is strong but less nucleophilic than \(\mathrm{NH}_2\).(d) \( \mathrm{H}^{\ominus} \) - Hydride ion, not typically acting as a nucleophile, more of a base.
03
Compare Electronegativity and Charge
Nucleophilicity typically increases with the decrease in electronegativity and increasing negative charge. Here, \(\mathrm{NH}_2\) has a high nucleophilicity due to its negative charge and less electronegative nitrogen atom compared to \(\mathrm{H}^{\ominus}\) and \(\mathrm{C}\) in \( \mathrm{H}-\mathrm{C} \equiv \mathrm{C}: \).
04
Identify the Strongest Nucleophile
Based on the evaluation, \( \mathrm{NH}_2 \) is the strongest nucleophile among the given options due to its negative charge and availability of a lone pair for donation.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Electron Donation
In chemistry, electron donation is a crucial process where an electron-rich species, like a nucleophile, donates electrons to an electron-poor species, known as an electrophile. This donation forms a chemical bond during a reaction. Electron-rich species have a surplus of electrons, typically found in their lone pairs or multiple bonds, making them ready donors.
- Electron-Rich Species: Typically, nucleophiles are rich in electrons. They could be ions with negative charges or neutral molecules with free electron pairs.
- Effect of Charge: Negative charges can enhance the electron-donating ability, increasing nucleophilicity.
- Mechanism: The electrons from the nucleophile are transferred to form a stable chemical bond with the electrophile, facilitating reactions such as nucleophilic substitution.
Chemical Bond
A chemical bond is a force that holds atoms or ions together in a molecule or compound. It is the result of electron sharing (in covalent bonds) or electron transfer (in ionic bonds) between atoms, providing stability and releasing energy during formation.
- Covalent Bonds: Formed by sharing electron pairs between atoms, often occurring in organic compounds. These shared pairs come from electron donation by nucleophiles to electrophiles.
- Ionic Bonds: Result from electron transfer, typically between metals and non-metals, creating ions held together by electrostatic forces.
- Bond Formation: Stabilizes involved atoms, releasing energy to achieve lower energy states.
Nucleophilicity
Nucleophilicity refers to the ability of a nucleophile to donate electrons and form a chemical bond with an electrophile. It often depends on several factors, including charge, electronegativity, and the solvent used.
- Charge: Negatively charged species are generally more nucleophilic due to the increased electron density that can be donated.
- Electronegativity: Lower electronegativity usually correlates with higher nucleophilicity, as such atoms are less likely to hold onto their electrons.
- Solvent Effects: Polar protic solvents can hinder nucleophilicity by forming solvation shells around nucleophiles, whereas aprotic solvents often enhance nucleophilicity.
Electronegativity
Electronegativity is a measure of an atom's ability to attract and hold onto electrons within a bond. It's a pivotal concept affecting both the nucleophilicity and reactivity of molecules.
- Trend: Electronegativity increases across a period and decreases down a group in the periodic table.
- Impact on Nucleophiles: Atoms with lower electronegativity often make stronger nucleophiles, as they do not tightly hold their electrons.
- Role in Chemical Reactions: Determines the polarity of bonds and the direction of electron flow, influencing reaction mechanisms.
