Chapter 4: Problem 97
The rate of esterification with acetic acid is highest with (a) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (d) \(\mathrm{CH}_{3} \mathrm{OH}\)
Short Answer
Expert verified
Answer: (d) Methanol
Step by step solution
01
Identify the alcohols
We are given four alcohols:
(a) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\) (tert-Butyl alcohol)
(b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH}\) (Isopropyl alcohol)
(c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (Ethanol)
(d) \(\mathrm{CH}_{3} \mathrm{OH}\) (Methanol)
02
Analyze the inductive effect and steric hindrance
Inductive effect: The presence of electron-donating or electron-withdrawing groups affects the reactivity of alcohols. Higher electron-donating groups make the oxygen atom of the hydroxyl group less electron rich, leading to decreased reactivity.
Steric hindrance: Larger alkyl groups near the hydroxyl group can hinder the approach of the acetic acid molecules, making it difficult for the reaction to occur.
03
Apply inductive effect and steric hindrance to the given alcohols
(a) tert-Butyl alcohol has three \(\mathrm{CH}_{3}\) groups leading to inductive electron donation. It also has a bulky tert-butyl group causing significant steric hindrance.
(b) Isopropyl alcohol has two \(\mathrm{CH}_{3}\) groups with inductive electron donation and moderate steric hindrance due to the isopropyl group.
(c) Ethanol has one \(\mathrm{CH}_{3}\) group with inductive electron donation and low steric hindrance due to the presence of only one ethyl group.
(d) Methanol has no inductive electron-donating alkyl groups and minimal steric hindrance.
04
Determine the order of reactivity
Considering both inductive effect and steric hindrance, the order of reactivity is as follows, from highest to lowest:
1. Methanol (the least inductive effect and minimum steric hindrance)
2. Ethanol (moderate inductive effect and low steric hindrance)
3. Isopropyl alcohol (higher inductive effect and moderate steric hindrance)
4. tert-Butyl alcohol (the highest inductive effect and significant steric hindrance)
05
Select the correct option
Since methanol (d) \(\mathrm{CH}_{3} \mathrm{OH}\) has the highest reactivity with acetic acid in esterification, the correct answer is (d).
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with Vaia!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Inductive Effect in Organic Chemistry
The inductive effect is a fundamental concept in organic chemistry, influencing how reactions occur.
It refers to the electron-donating or electron-withdrawing ability of substituents through sigma bonds in a molecule. This effect impacts the distribution of electron density within the molecule, affecting its reactivity.
The more electron-rich the oxygen, the more nucleophilic the alcohol, making it more reactive towards acids like acetic acid. In our exercise, methanol has the least electron-donating inductive effect due to the absence of alkyl groups, which leads to higher reactivity in esterification.
It refers to the electron-donating or electron-withdrawing ability of substituents through sigma bonds in a molecule. This effect impacts the distribution of electron density within the molecule, affecting its reactivity.
- Electron-withdrawing groups (EWGs) such as -NO2 or -CF3 pull electron density away from other parts of the molecule, increasing its positive character.
- Electron-donating groups (EDGs) like alkyl groups (-CH3 or -C2H5) push electron density towards the more electronegative atoms (like oxygen in alcohols) and decrease their positive character.
The more electron-rich the oxygen, the more nucleophilic the alcohol, making it more reactive towards acids like acetic acid. In our exercise, methanol has the least electron-donating inductive effect due to the absence of alkyl groups, which leads to higher reactivity in esterification.
Steric Hindrance in Organic Chemistry
Steric hindrance refers to the physical obstruction caused by the size of groups within a molecule, which can impede the progress of a chemical reaction.
The basic principle is simple: the bulkier the groups around a reactive site, the harder it is for reactants to come into close proximity and effectively react. It is a purely geometric effect, taking into account the three-dimensional structure of molecules.
The basic principle is simple: the bulkier the groups around a reactive site, the harder it is for reactants to come into close proximity and effectively react. It is a purely geometric effect, taking into account the three-dimensional structure of molecules.
- A larger alkyl group near the reactive hydroxyl group of an alcohol can prevent other molecules, like acetic acid, from getting close enough to react.
- This hindrance can significantly slow down or even prevent reactions such as esterification, which require close contact between reactants.
Alcohol Reactivity
Alcohol reactivity is a vital topic in organic chemistry, influenced by both inductive effects and steric hindrance, as previously discussed.
Let's delve into why reactivity trends in alcohols are crucial for many chemical reactions:
Let's delve into why reactivity trends in alcohols are crucial for many chemical reactions:
- Alcohols are a class of compounds with a hydroxyl group (-OH) attached to a carbon atom.
- The reactivity of an alcohol is markedly influenced by the electron density on the oxygen atom and the accessibility of the hydroxyl group to reagents.
- Alcohols can undergo a variety of reactions, with esterification being a common process whereby alcohols react with carboxylic acids to form esters.
Organic Chemistry IIT JEE
For students preparing for competitive exams like the IIT JEE, understanding the nuances of organic chemistry, such as esterification reactivity, is crucial.
These exams often include questions that assess a student's knowledge of functional groups, reaction mechanisms, and the effects of molecular structure on reactivity.
These exams often include questions that assess a student's knowledge of functional groups, reaction mechanisms, and the effects of molecular structure on reactivity.
- IIT JEE candidates must master concepts like the inductive effect and steric hindrance, as they directly apply to predicting reaction outcomes.
- Questions are designed to test the application of these principles in synthesizing compounds or analyzing reaction pathways.
- As seen in the exercise, the ability to determine the reactivity sequence of alcohols in esterification reactions can be pivotal for exam success.