NEET 2025 Organic Chemistry: Alcohols & Reagents

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Questions and Answers

Assertion: Two moles of Grignard reagent is consumed in the formation of tertiary alcohol from ester followed by hydrolysis. Reason: One mole of Grignard reagent converts ester into ketone and the second mole of Grignard reagent adds to ketone.

  • Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
  • Both Assertion and Reason are correct and Reason is the correct explanation for Assertion. (correct)
  • Assertion is correct but Reason is incorrect.
  • Both Assertion and Reason are incorrect.

Write the product of the following chemical reaction.

  • CH3CH2CH2MgBr + PhCHO ether H + --> Ph- CH-OH CH3 CH2 CH2 CH3 (correct)
  • S-PhMgBr + ether H + --> Ph OH
  • C2H5MgBr + Ph- C-CH3. ether H + --> Ph- C-CH3 OH
  • CH3MgBr + Ph- C-C2H5 ether H + --> Ph- C-C2H5 CH3 OH

Which of the following compound can produce chiral compound upon treatment with CH3MgCl and then acidification?

  • 3-hexanone Et C=O --> Et CH3 C-OH npr npr
  • Formaldehyde H- C=O 1. CH3MgCl 2. H+ --> H CH3 C-OH
  • Pentanone-2 CH3 C=O --> CH3 CH3 C-OH npr npr
  • 2-hexanone CH3 C=O --> CH3 CH3 C -OH npr npr (correct)

The reaction of Grignard reagent with formaldehyde followed by acidification gives:

<p>A primary alcohol (C)</p> Signup and view all the answers

3-methyl-3-hexanol cannot be prepared by

<p>C3H7MgI and 2-butanone followed by hydrolysis (B)</p> Signup and view all the answers

When CH3MgI is made to react with acetone and the addition product is hydrolysed, we get:

<p>tertiary alcohol (D)</p> Signup and view all the answers

Phenyl magnesium bromide reacts with methanol to give:

<p>a mixture of benzene and Mg(OMe)Br (D)</p> Signup and view all the answers

Ethyl acetate reacts with CH3MgBr to form

<p>tertiary alcohol (C)</p> Signup and view all the answers

Reaction of esters with Grignard reagents give rise to:

<p>ketones (B)</p> Signup and view all the answers

Which of the following compound does not react with methyl magnesium bromide to produce tertiary alcohol?

<p>Ethyl benzoate (C)</p> Signup and view all the answers

Et-O-C=O-Et 1. CH3MgBr 2. H3O+ (A), Product (A) is:

<p>CH3-C-CH3 OH CH3 (A)</p> Signup and view all the answers

In which of the following reaction 2º alcohol is obtained as a product?

<p>Both (A) and (B) (C)</p> Signup and view all the answers

All of the following compound react with ethyl magnesium bromide. Alcohols are formed from three of the compounds. Which one does not give as alcohol?

<p>Ph-O-C=O-H (D)</p> Signup and view all the answers

Acetone on reaction with methyl magnesium bromide followed by hydrolysis gives.

<p>Tertiary alcohol (B)</p> Signup and view all the answers

Which of the following are the starting materials for the Grignard's synthesis of tert. butyl alcohol?

<p>CH3MgI + CH3COCH3 (B)</p> Signup and view all the answers

Isobutyl alcohol can be obtained by the reaction between:

<p>(CH3)2CHMgBr and HCHO (D)</p> Signup and view all the answers

In the following sequence of reactins, CH3CH2OH -> P+12 -> (a) -> Mg -> (B) -> HCHO -> (C) -> H2O -> (D) ether the compound D is:

<p>n-propyl alcohol (A)</p> Signup and view all the answers

P -> PhMgBr -> H2O -> CH3-CH-Ph (d+l)
P can be:

<p>CH3CHO (D)</p> Signup and view all the answers

Formaldehyde forms an addition product with CH3MgI which on hydrolysis gives:

<p>ethyl alcohol (D)</p> Signup and view all the answers

CH3-CH2-C-CH3 (i) CH2MgBr (ii) H2O Product is:

<p>CH3-CH2-C-CH3 CH3 OH (C)</p> Signup and view all the answers

From which of the following tertiary butyl alcohol is obtained by the action of methyl magnesium iodide?

<p>CH3COCH3 (A)</p> Signup and view all the answers

H + CH3MgBr --> A --> H3O+ --> B

<p>3-methylbutan-2-ol (C)</p> Signup and view all the answers

Flashcards

Nucleophilic Addition Reaction (NAR)

A reaction where a nucleophile attacks a carbonyl group, forming a new carbon-nucleophile bond.

NAR in Grignard Reagent (GR)

A reaction where the Grignard reagent (R-Mg-X) acts as a nucleophile, attacking a carbonyl group and forming an alkoxide intermediate. Upon hydrolysis, this intermediate yields an alcohol.

Nucleophilic Addition followed by Elimination (SNAE)

A reaction where a nucleophile attacks an acid derivative (like esters, amides, acid chlorides), forming an intermediate. This intermediate undergoes elimination, leading to a new carbonyl compound and a leaving group.

Acid Derivatives

Acid derivatives are molecules that contain a carbonyl group directly attached to a leaving group.

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Steric Factor in NAR

The rate of a nucleophilic addition reaction is affected by the steric hindrance of the carbonyl group. Bulky groups near the carbonyl group hinder the attack, slowing down the reaction.

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Electronic Factor in NAR

The rate of nucleophilic addition is influenced by the electrophilicity of the carbonyl carbon atom. More electron-withdrawing groups around the carbonyl increase its electrophilicity, making it more susceptible to nucleophilic attack.

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Electronic Factor in SNAE

The rate of a nucleophilic addition followed by elimination (SNAE) reaction is affected by the electrophilicity of the carbonyl carbon atom. Electron-withdrawing groups (EWGs) enhance electrophilicity, increasing the reaction rate. Electron-donating groups (EDGs) decrease electrophilicity, slowing down the reaction.

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Steric Factor in SNAE

The rate of SNAE is also influenced by the steric hindrance of the leaving group. Bulky groups around the leaving group hinder its departure, slowing down the reaction.

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Reaction of GR with Cyclic Ethers

A Grignard reagent reacts with a cyclic ether to form an alkoxide intermediate. Subsequent acidification yields an alcohol.

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Reaction of GR with Carbonyl Compounds

A reaction where Grignard reagent, acting as a nucleophile, adds to a carbonyl compound (aldehyde or ketone) to form an alkoxide intermediate. This intermediate is then hydrolyzed to produce an alcohol.

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Tertiary Alcohol Formation from Ester with GR

A tertiary alcohol is produced by the reaction of a Grignard reagent with an ester followed by hydrolysis. Two moles of the Grignard reagent are required; one mole converts the ester into a ketone, and the second attacks the ketone.

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Chiral Compound

A chiral compound is a molecule that has a non-superimposable mirror image. It contains a chiral center, which is a carbon atom linked to four different groups.

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Reaction of Aldehyde with GR

The reaction of an aldehyde with a Grignard reagent, followed by hydrolysis, results in the formation of a primary alcohol.

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Reaction of Ketone with GR

The reaction of a ketone with a Grignard reagent, followed by hydrolysis, results in the formation of a secondary alcohol.

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Acid Base Reactions vs. NAR and SNAE

Acid-base reactions are faster than nucleophilic addition reactions (NAR) and nucleophilic addition followed by elimination (SNAE) reactions.

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Formaldehyde Reaction with GR

The reaction of formaldehyde (HCHO) with a Grignard reagent, followed by hydrolysis, results in the formation of a primary alcohol.

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Reaction of Ester with GR

When an ester reacts with a Grignard reagent, the product is a tertiary alcohol.

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Reaction of Acid Chloride with GR

The reaction of an acid chloride with a Grignard reagent, followed by hydrolysis, yields a ketone.

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Reaction of Acid Anhydride with GR

The reaction of an acid anhydride with a Grignard reagent, followed by hydrolysis, yields a ketone.

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Reaction of Amide with GR

The reaction of an amide with a Grignard reagent, followed by hydrolysis, yields a ketone.

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Reaction of Alcohol with GR

When an alcohol reacts with a Grignard reagent, the product is an alkane.

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Grignard Reagent Formation

A Grignard reagent is formed when an alkyl halide reacts with magnesium metal in dry ether.

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Moles of GR Required

The number of moles of Grignard reagent needed to react with a given molecule depends on the number of carbonyl groups and the nature of the molecule.

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GR Reactivity

Grignard reagents are highly reactive organometallic compounds. They can react with a variety of functional groups, such as carbonyl compounds, esters, and acid chlorides, to form new carbon-carbon bonds.

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Reactivity Order in GR Reactions

In a series of reactions involving a Grignard reagent and multiple carbonyl groups, the order of reactivity is: acid-base reactions, acid chlorides, acid anhydrides, aldehydes, ketones, esters, amides.

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Alcohol

An alcohol is a compound containing an -OH group attached to a saturated carbon atom.

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Ketone

A ketone is a compound containing a carbonyl group (C=O) bonded to two alkyl or aryl groups.

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Aldehyde

An aldehyde is a compound containing a carbonyl group (C=O) bonded to one alkyl group and one hydrogen atom.

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Ester

An ester is a compound containing a carbonyl group (C=O) bonded to an alkyl group and an alkoxy group (OR).

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Study Notes

Organic Chemistry Lecture Notes

  • Course: NEET 2025
  • Topic: Alcohols, Phenols and Ethers
  • Lecturer: Pankaj Sir (POPU MAMA)
  • Topics Covered:
    • Methods of Preparation of Alcohols (Part 3)
    • Grignard Reagent
    • Practice Problems

Methods of Preparation of Alcohols (Part 3) - Grignard Reagent

  • Grignard reagents (R-MgX) react with various compounds, including acid derivatives (e.g., aldehydes, ketones, esters).
  • The reaction proceeds in multiple steps:
    • Addition to Carbonyl Compounds: The Grignard reagent acts as a nucleophile, attacking the carbonyl carbon. This forms a new carbon-carbon bond.
    • Hydrolysis: The addition product is subsequently hydrolyzed (treated with water), leading to the formation of an alcohol.
    • Acid Derivatives: These are compounds that contain functional groups (e.g., carboxylic acid groups).
    • Nucleophilic Addition: Grignard reagents add to the carbonyl group of acid derivatives.
    • Elimination: The reaction proceeds through acid derivatives and elimination steps.
  • Steric factors and electronic factors influence the reaction rate.
  • Bulkier groups can hinder the approach of the nucleophile, thus decrease the reaction rate.

Mechanism of NAR (Nucleophilic Addition Reaction)

  • Nucleophilic addition reaction mechanisms in carbonyl compounds.
  • Nucleophilic attacks carbonyl carbon to form a tetrahedral intermediate.
  • The intermediate loses a leaving group to regenerate the carbonyl group.
  • Steps in the NAR mechanism: Addition, Proton transfer, and loss of the leaving group.

Reaction of Grignard Reagents with Cyclic Ethers

  • Limited reactivity: Only certain cyclic ethers (e.g., 3- and 4-membered rings) undergo reactions with Grignard reagents.
  • Stability and sterics play a role in determining reactivity

Reactions and Product Formation

  • Various reactions and their products (using different reagents).

Mechanism of SN2 Reaction in Acid Derivatives

  • SN2 reaction in acid derivatives is shown.

Reaction of Ester-Grignard Reagents

  • Esters react with Grignard reagents to produce tertiary alcohols.
  • The reaction involves nucleophilic attack on the carbonyl group by the Grignard reagent.
  • Hydrolysis step forms a tertiary alcohol as a final product.

Alcohol Production from Reactions

  • Various chemical reactions that yield tertiary alcohol(s).

Additional Information

  • Question on tertiary alcohol synthesis from carbonyl compounds.
  • The role of specific Grignard reagents (e.g., CH3MgBr) in producing various alcohols.
  • Determining the correct starting materials to form a specific tertiary alcohol using Grignard reactions.
  • Other Reactions for producing Tertiary Alcohols
  • Identifying the compound that does not form an alcohol when treated with ethyl magnesium bromide.

Answer Key

  • Correct answers to the questions are provided.

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