Test: Alcohols, Phenols & Ethers - NEET MCQ

• Ketones are organic compounds featuring a carbonyl group (C=O) bonded to two carbon atoms.
• During catalytic hydrogenation, the carbonyl group is reduced, adding hydrogen atoms.
• This process converts the ketone to an alcohol.
• The carbonyl carbon in a ketone is attached to two carbon groups, resulting in a secondary alcohol upon reduction.
• Therefore, the reduction of ketones yields secondary alcohols.
• Option A: secondary alcohols is the correct answer.

• CrO3 in anhydrous medium: This reagent can oxidize primary alcohols to aldehydes in controlled conditions without over-oxidizing to carboxylic acids.
• Heat in the presence of Cu at 573K: Copper can dehydrogenate primary alcohols, forming aldehydes at this temperature.
• Pyridinium chlorochromate (PCC): PCC is well-known for oxidizing primary alcohols to aldehydes without over-oxidizing them to carboxylic acids.

Thus, all these reagents can effectively oxidize primary alcohols to aldehydes, making the correct answer D: All of these.

• Cleavage of O–H Bond: Phenols have an O–H bond that can undergo cleavage, releasing a proton (H⁺).
• Proton Donation: Phenols can donate a proton to a stronger base, demonstrating their acidic behavior.
• Acidic Nature: Phenols are more acidic than alcohols due to the resonance stabilization of the phenoxide ion formed after deprotonation.
• Correct Answer: All statements (A, B, C) accurately describe phenols, making option D the comprehensive choice.

• The reactivity order for alcohols in reactions involving carbocation intermediates is based on carbocation stability.
• 3° alcohols form more stable carbocations due to alkyl group stabilization through hyperconjugation and inductive effects.
• 2° alcohols form less stable carbocations compared to 3° but more stable than 1°.
• 1° alcohols form the least stable carbocations, making them the least reactive.
• Therefore, the correct order is 3° >2° >1°, which corresponds to option D.

• Phenol can be distinguished from ethanol using Br₂/water and Neutral FeCl₃.
• Br₂/water: Phenol reacts with bromine water to give a white precipitate of 2,4,6-tribromophenol, while ethanol does not react.
• Neutral FeCl₃: Phenol forms a violet complex with neutral ferric chloride, whereas ethanol shows no color change.
• Therefore, options A and C are correct for distinguishing phenol from ethanol.

• Lithium aluminium hydride (LiAlH₄) is indeed a strong reducing agent capable of reducing carboxylic acids to primary alcohols.
• Despite its effectiveness, it is not frequently used for this purpose because:
  • Cost: LiAlH₄ is relatively expensive, making it less economical for large-scale or routine synthesis.
  • Handling: It requires careful handling as it reacts violently with water and moisture.
• Therefore, the correct answer is option A: it is an expensive reagent.

• The reaction provided is called Williamson's synthesis.
• Williamson's synthesis is a method for preparing ethers.
• It involves the reaction of an alkoxide ion (e.g., C₂H₅ONa) with an alkyl halide (e.g., C₂H₅I).
• The reaction results in the formation of an ether (e.g., C₂H₅OC₂H₅) and a salt (e.g., NaI).
• This synthesis is widely used in organic chemistry to create a variety of ethers efficiently.

Here, again carbon is not chiral in nature.
So, only one alcohol is chiral in nature

• When making ethers by using strong acids to dehydrate alcohols, the conditions of the reaction usually promote elimination rather than substitution.
• Secondary and tertiary alcohols, when exposed to strong acids, often undergo elimination because it is easier for them to form alkenes.
• The process creates a carbocation intermediate from these alcohols, which is stable. This stability encourages elimination reactions that produce alkenes instead of ethers.
• Because of the competition from elimination reactions, using this method with secondary or tertiary alcohols is not effective for making ethers.

• Alcohols have high boiling points primarily due to the presence of intermolecular hydrogen bonding.
• Hydrogen bonds occur between the hydrogen atom of the hydroxyl group (-OH) in one alcohol molecule and the oxygen atom of the hydroxyl group in another.
• This strong intermolecular force requires more energy to break, leading to higher boiling points.
• While van der Waals forces and carbon atom count can influence boiling points, hydrogen bonding is the dominant factor for alcohols.

• The Lucas test is used with alcohols to tell the difference between primary, secondary, and tertiary alcohols based on how they react with a special mixture known as Lucas reagent, which is made up of concentrated hydrochloric acid and zinc chloride.
• Tertiary alcohols react right away, creating a cloudy solution.
• Secondary alcohols take about 5 to 10 minutes to react, also forming a cloudy solution.
• Primary alcohols show very little to no reaction at room temperature.
• The test works because it leads to the creation of alkyl chloride, which does not mix well with water, making it easier to see the reactions.

When –CH₂OH group is replaced by –COOH group then only molecular wt will increase by 14units.

• Alkyl halides are converted into alcohols through a substitution reaction.
• In this process, the halogen atom in the alkyl halide is replaced by a hydroxyl group (-OH).
• A common method is the nucleophilic substitution reaction, where a nucleophile like hydroxide ion (OH^-) attacks the carbon atom bonded to the halogen.
• This reaction often occurs in an aqueous medium, facilitating the replacement of the halogen with the hydroxyl group, forming an alcohol.

The correct answer is Option A.
Phenol (C₆H₅OH) will react with sodium hydroxide solution in water , as phenols are more acidic than alcohols.

The correct answer is Option A.

Reimer Tiemann reaction which converts phenol to ortho- hydroxybenzaldehyde involves the formation of dichlorocarbene which acts as an electrophile and attacks on the ortho position of phenol.

Since the product of oxidation reacts with phenyl hydrazine, it is a carbonyl compound. Since it does not answer silver mirror test, it must be a ketone. Ketones are produced by the oxidation of secondary alcohols. So the compound X is isopropyl alcohol

• Reaction Type: The process of changing methyl bromide into ethane is called the Wurtz reaction, which is a type of coupling reaction.
• Reagent: The right chemical to use for this reaction is sodium (Na).
• Mechanism:
  • Sodium interacts with methyl bromide to create a methyl radical.
  • Two methyl radicals join together to produce ethane.
• Conditions: This reaction usually takes place in an ether solvent, which helps to stabilize the sodium and makes the reaction easier.
• Product: The outcome of the reaction is that two methyl groups combine to form ethane (C₂H₆).

• Correct Answer: Methanol (A)
• Reason:
• Methanol, also known as wood alcohol, is highly toxic.
• Even small quantities can cause severe poisoning.
• Metabolism of methanol in the body produces formaldehyde and formic acid, which are toxic.
• Symptoms include visual disturbances that may lead to blindness.
• Larger doses can lead to acidosis, nervous system damage, and death.
• Safety Note:
• Methanol is not safe for consumption and should be handled with caution.

• Picric acid, which is also called 2,4,6-trinitrophenol, is created by a process known as nitration of phenol.
• The process begins with phenol, which then undergoes multiple nitration steps.
• During nitration, nitro groups (noted as -NO₂) are added to the phenol, resulting in the formation of picric acid.
• The -OH group, known as the hydroxyl group, present in phenol makes the aromatic ring more reactive, allowing it to be more easily nitrated.
• Phenol is the most basic starting material for this production, confirming that option D is the right choice.

The correct answer is Option C.
Given molecule:

For IUPAC nomenclature following steps are followed:
1. Identify the functional group and their priority: -OH and -Cl are the side groups in the given molecule. OH has higher priority thus the name will have the suffix "ol".
2. Identify parent chain: The longest carbon chain that contains the functional group. Here its 6 C chain i.e hexyl
3. Assign locant number: lowest number to the main functional group and side chains i.e. 2-ol 
4. Identify side chains/groups: its chloro, and 5-chloro in the given molecule.

IUPAC name is: 5-chlorohexan-2-ol
 

• Phenol is not as acidic as O-nitrophenol.
• The nitro group is a type of group that pulls electrons away.
• This pulling of electrons reduces the electron density on the benzene ring and spreads out the negative charge of the phenoxide ion.
• Because of this, the acidity increases, making O-nitrophenol more acidic than phenol.
• In contrast, the methoxy group is a group that releases electrons.
• This release of electrons raises the electron density on the benzene ring and does not spread out the negative charge of the phenoxide ion.
• As a result, p-methoxyphenol is less acidic than phenol.
• Additionally, alcohols, such as 2-methylpropanol and 2,2-dimethylpentanol, are considered neutral.

• The hydrocarbon C₅H₁₀ does not react with chlorine in the dark, suggesting it is saturated (no double bonds), which excludes cyclopentene.
• It forms a single monochloro compound in bright sunlight, indicating it is a cycloalkane, as alkanes undergo substitution reactions with chlorine under UV light.
• Cyclopentane (option B) is C₅H₁₀ and fits this behavior, forming C₅H₉Cl in a substitution reaction.

• Basicity Concept: The strength of a base is based on how well it can give away a pair of electrons. Strong bases have a weak hold on protons, which makes them more likely to take in a proton.
• Alkoxide Ion (RO-): This is the conjugate base of an alcohol. Because oxygen is very electronegative, it easily shares its lone pair of electrons, making RO- a strong base.
• Comparison: Other options either contain less electronegative atoms or are more stable, which lowers their basicity.
• Conclusion: RO- is the strongest base because it has a lot of electron density and a strong desire to accept protons.