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Chapter 25: Problem 21

Which compound in each pair is more basic: (a) (CH\(_3\))\(_2\)NH and NH\(_3\); (b) CH\(_3\)CH\(_2\)NH\(_2\) and CICH\(_2\)CH\(_2\)NH\(_2\) ?

Short Answer

Expert verified
(a) (CH\(_3\))\(_2\)NH is more basic; (b) CH\(_3\)CH\(_2\)NH\(_2\) is more basic.

Step by step solution

01

Determine Basicity of Each Compound

Basicity in organic compounds is often linked to the availability of a lone pair of electrons for protonation. Amines, like (CH\(_3\))\(_2\)NH and NH\(_3\), can donate their nitrogen's lone pair to a proton, making them basic. Substituents affecting electron dominance or withdrawal around these nitrogens play a key role.
02

Analyze the Effect of Substituents (a)

For (CH\(_3\))\(_2\)NH vs NH\(_3\), the (CH\(_3\))\(_2\) is an electron-donating group, which increases electron density on nitrogen, enhancing basicity compared to NH\(_3\), which has no such electron-donating substituents.
03

Analyze the Effect of Substituents (b)

In the pair CH\(_3\)CH\(_2\)NH\(_2\) and ClCH\(_2\)CH\(_2\)NH\(_2\), Cl in ClCH\(_2\)CH\(_2\)NH\(_2\) is an electron-withdrawing group. It decreases electron density on nitrogen, reducing basicity. CH\(_3\)CH\(_2\)NH\(_2\) lacks such withdrawal and therefore is more basic.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lone Pair of Electrons
The basicity of organic compounds is largely determined by the presence of a lone pair of electrons, especially on nitrogen atoms found in amines. A lone pair of electrons is an unshared pair of electrons that can be donated to an acid, such as a proton (H鈦�), making the compound basic. The availability and accessibility of this lone pair dictate how easily the compound can accept a proton, influencing its overall basicity.
  • Compounds like ammonia (NH鈧�) and amines possess a lone pair on nitrogen, making them capable of forming bonds with protons.
  • The ease with which this lone pair can be donated plays a crucial role in determining the compound's basic strength.
Understanding how lone pairs increase the electron density on a molecule and their role in proton acceptance helps clarify why certain compounds are more basic than others.
Substituents Effect
The basicity of an organic compound can be significantly affected by the substituents attached to it. Substituents are groups of atoms that are attached to a molecule, and they can either release or withdraw electrons from a neighboring atom.
  • Electron-donating groups (EDGs) increase the electron density on the nitrogen atom, enhancing the lone pair's availability for bonding with protons, thus increasing basicity.
  • Conversely, electron-withdrawing groups (EWGs) reduce the electron density on the nitrogen atom, making the lone pair less available for protonation, thus decreasing basicity.
In the pair (CH鈧�)鈧侼H vs NH鈧�, the methyl groups (CH鈧�) are EDGs that increase basicity by enhancing electron density on the nitrogen atom compared to NH鈧�, which lacks such electron-donating substituents.
Electron Donating and Withdrawing Groups
Understanding the influence of electron donating and withdrawing groups is crucial in determining the basicity of compounds.
  • Electron donating groups, such as alkyl groups, increase basicity by enhancing the electron density on the nitrogen atom, making the lone pairs more reactive and available for donation.
  • In contrast, electron withdrawing groups, such as halogens like chlorine, decrease basicity by reducing electron density on the nitrogen atom, making the lone pairs less willing to interact with protons.
When comparing CH鈧僀H鈧侼H鈧� and ClCH鈧侰H鈧侼H鈧�, the methyl group in CH鈧僀H鈧侼H鈧� donates electrons, increasing basicity, whereas the chlorine in ClCH鈧侰H鈧侼H鈧� is an EWG that decreases basicity by pulling electron density away.
Amines Basicity
Amines are a fascinating class of compounds that exhibit basicity due to their nitrogen atoms. The nitrogen has a lone pair of electrons, making amines capable of accepting protons.
  • Primary amines like methylamine (CH鈧僋H鈧�) or ethylamine (CH鈧僀H鈧侼H鈧�) have one alkyl group attached, often resulting in higher basicity due to inductive effects that increase electron density.
  • Secondary amines, such as dimethylamine ((CH鈧�)鈧侼H), further enhance these effects with two alkyl groups, typically leading to even higher basicity than primary amines.
However, substituents play a pivotal role in this scenario. An electron-donating group will increase the basicity of an amine, while an electron-withdrawing group will decrease it. This understanding is essential for determining which amines are more basic in a given pair, as seen in textbook examples.

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Most popular questions from this chapter

Draw the products formed when \(p\)-methylaniline (\(p-\mathrm{CH}_3\mathrm{C}_6\mathrm{H}_4\mathrm{NH}_2\)) is treated with each reagent. a. HCI b. CH\(_3\)COCI c. (CH\(_3\)CO)\(_2\)O d. excess CH\(_3\)I e. (CH\(_3\))\(_2\)C\(=\)O f. CH\(_3\)COCI, AICl\(_3\) g. CH\(_3\)COOH h. NaNO\(_2\), HCI i. Step (b), then CH\(_3\)COCI, AICl\(_3\) j. CH\(_3\)CHO, NaBH\(_3\)CN

Draw the structure that corresponds to each name. a. cyclobutylamine b. \(N\)-isobutylcyclopentylamine c. tri-\(tert\)-butylamine d. \(N,N\)-diisopropylaniline e. \(N\)-methylpyrrole f. \(N\)-methylcyclopentylamine g. \(cis\)-2-aminocyclohexanol h. 3-methyl-2-hexanamine i. 2-\(sec\)-butylpiperidine j. (2S)-2-heptanamine

Draw all constitutional isomers of molecular formula C\(_4\)H\(_{11}\)N, and give an acceptable name for each amine.

Which amines cannot be prepared by reduction of an amide?

The p\(K_\mathrm{a}\) of the conjugate acid of guanidine is 13.6, making it one of the strongest neutral organic bases. Offer an explanation.
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