Textbook Question
Predict the product that results from the following 'pushed electrons.'
(c)
3. Acids and Bases
Reaction Mechanism
3:17 minutesProblem 1
Textbook Question
Why are NH3 and CH3NH2 no longer nucleophiles when they are protonated?
Verified step by step guidance1
Understand the concept of nucleophilicity: Nucleophiles are species that donate a pair of electrons to form a bond with an electrophile. They must have a lone pair of electrons available for donation.
Examine the structure of NH3 (ammonia) and CH3NH2 (methylamine): Both molecules have lone pairs of electrons on the nitrogen atom, making them nucleophiles in their neutral forms.
Consider what happens during protonation: When NH3 or CH3NH2 is protonated, a hydrogen ion (H⁺) is added to the molecule. This results in the formation of NH4⁺ (ammonium ion) and CH3NH3⁺ (methylammonium ion), respectively.
Analyze the electron availability after protonation: In the protonated forms, the nitrogen atom no longer has a lone pair of electrons available for donation because the lone pair is now involved in bonding with the added hydrogen ion.
Conclude why they are no longer nucleophiles: Since nucleophilicity depends on the availability of a lone pair of electrons for donation, NH4⁺ and CH3NH3⁺ cannot act as nucleophiles because their nitrogen atoms lack free lone pairs after protonation.
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Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilicity
Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, forming a chemical bond. Nucleophiles are typically electron-rich species, such as amines like NH3 and CH3NH2, which have lone pairs of electrons that can be used for bonding. When these nucleophiles are protonated, they become positively charged, which significantly reduces their electron density and ability to donate electrons.
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Nucleophilic Addition
Protonation
Protonation is the addition of a proton (H+) to a molecule, resulting in the formation of a positively charged species. In the case of NH3 and CH3NH2, protonation leads to the formation of NH4+ and CH3NH3+, respectively. This process alters the electronic structure of the molecules, making them less capable of acting as nucleophiles due to the increased positive charge that repels electron donation.
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03:Proton Splitting
Charge and Reactivity
The charge of a molecule significantly influences its reactivity and ability to participate in chemical reactions. Neutral nucleophiles, like NH3 and CH3NH2, can readily attack electrophiles due to their electron-rich nature. However, once protonated, the resulting cations (NH4+ and CH3NH3+) are stabilized by their positive charge, which makes them less reactive towards electrophiles, effectively rendering them non-nucleophilic.
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01:34Calculating formal and net charge.
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