'L' in the above sequence of reaction is/are(where L≠M≠N)
'L' in the above sequence of reaction is/are(where L≠M≠N)
- Benzaldehyde
- Methyl benzoate
- Benzoyl chloride
- Benzonitrile
The Correct Option is A
Solution and Explanation
Given reaction sequence:
L → (i) PhMgBr → (ii) H3O+ → M → CrO3/H+ → N → Ph3P=CH2 → Ph2C=CH2
Step-by-step interpretation:
Step 1: L + PhMgBr → M (Grignard reaction)
This is a nucleophilic addition of Grignard reagent (PhMgBr) to a carbonyl compound. For the Grignard reagent to work, L must be a compound with a carbonyl group (like an aldehyde or ketone). If L = Benzaldehyde (Ph-CHO), the reaction proceeds as:
Ph-CHO + PhMgBr → Ph-CH(OH)-Ph (a secondary alcohol, M)
Step 2: M → N using CrO3/H+
This step is oxidation. The alcohol (Ph-CH(OH)-Ph) is oxidized to a ketone:
Ph-CH(OH)-Ph → Ph-CO-Ph (benzophenone, N)
Step 3: N → Final product using Ph3P=CH2 (Wittig reaction)
The ketone (benzophenone) reacts with Ph3P=CH2 to form an alkene:
Ph-CO-Ph + Ph3P=CH2 → Ph2C=CH2
Therefore, the correct identity of L is: Benzaldehyde
Correct option: (A): Benzaldehyde
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Concepts Used:
Alkynes
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon-carbon triple bond. Alkynes are an organic molecule that contains triple bonds between the carbon atoms. Its general formula is CnH2n-2. They are also known as acetylenes. In this article, we will deal with the structure of alkynes.
Isomerism in Alkynes:
Alkynes show three types of isomerism
- Chain isomerism - Due to the different arrangement of carbon atoms in the chain that is straight chain or branched.
- Position isomerism - Due to the difference in the location of the triple bond.
- Functional isomerism - Isomeric with alkadienes both being represented by the general formula CnH2n-1.
Properties of Alkynes:
Physical Properties:
- Non-polar, unsaturated hydrocarbons.
- Highly soluble in organic and non-polar solvents and slightly soluble in polar solvents.
- High boiling point, in comparison to other hydrocarbons.
- Release a high amount of energy due to the repulsion of electrons in a reaction.
- More acidic than alkanes and alkenes due to SP hybridization.
Chemical Properties:
- Hydrogenation - Alkynes undergoes two types of hydrogenation reactions. Complete hydrogenation (in presence of Pd-C/ H2) and partial hydrogenation (in presence of Linder’s catalyst/H2).
- Act as a strong nucleophile by converting into acetylide.
- React with BH3 and undergo hydroboration reactions to form aldehydes and ketones.
- Undergo halogenation reactions in the presence of different halogenating agents by different mechanisms and forms haloalkanes.