Alcohols, Phenols And Ethers MCQ Quiz - Objective Question with Answer for Alcohols, Phenols And Ethers - Download Free PDF

CONCEPT:

Cyclic Ethers and Isomerism

• Cyclic ethers are organic compounds that contain an oxygen atom within a ring structure.
• Isomers of cyclic ethers can include both structural isomers (different connectivity of atoms) and stereoisomers (same connectivity but different spatial arrangement).
• For a given molecular formula, isomer count depends on the number of possible ring sizes, substitution patterns, and stereoisomeric configurations.

EXPLANATION:

• Possible structures include:
  • Four-membered rings (oxetanes) with different substitution patterns.
  • Three-membered rings (epoxides) with different substitution patterns.
• Considering stereoisomerism:
  • Epoxides can have cis and trans stereoisomers due to the planar nature of the three-membered ring.
  • Oxetanes with different substitutions can also exhibit stereoisomerism.
• Upon counting all possible structural and stereoisomers:
  • Three-membered ring (epoxides): 6 isomers (including stereoisomers).
  • Four-membered ring (oxetanes): 4 isomers (including stereoisomers).
• Total number of isomers = 6 (epoxides) + 4 (oxetanes) = 10.

Therefore, the total number of possible isomers (both structural and stereoisomers) of cyclic ethers with the molecular formula C₄H₈O is 10.

CONCEPT:

Grignard Reaction with Esters and Carbonyls

• Grignard reagents (R–MgX) react with carbonyl compounds to form alcohols.
• With esters: Grignard reagents react in two steps:
  • First mole: Converts ester to a ketone intermediate.
  • Second mole: Reacts with ketone to form a tertiary alcohol.
• With ketones or aldehydes: Only one mole of Grignard is consumed per mole of carbonyl compound.

EXPLANATION:

• The given compound is a phenyl ester (ethyl ester of a carboxylic acid).
• Grignard reagent CH₃MgBr is added in excess.
• Reaction steps:
  1. 1st mole of CH₃MgBr attacks the ester, forming a ketone intermediate.
  2. 2nd mole attacks the ketone, forming a tertiary alcohol.
  3. 3rd mole attacks the aldehyde group formed (para to ester), forming a secondary alcohol.
• Total: 3 moles of Grignard reagent used.

Therefore, the value of x = 3 moles of CH₃MgBr are consumed in the reaction.

CONCEPT:

Solubility of Organic Compounds in Water

• The solubility of an organic compound in water is primarily influenced by the compound's ability to form hydrogen bonds with water molecules.
• Alcohols, amines, and alkanes have different capabilities for hydrogen bonding:
  • Alcohols (R-OH) have a hydroxyl group (-OH) that can form strong hydrogen bonds with water, making them highly soluble.
  • Amines (R-NH₂, R₂-NH, R₃-N) have an amino group (-NH₂) that can also form hydrogen bonds with water, but typically amines form weaker hydrogen bonds compared to alcohols.
  • Alkanes (R-H) are nonpolar hydrocarbons and cannot form hydrogen bonds with water, making them very poorly soluble.

EXPLANATION:

For compounds with comparable molar masses:

• Alcohols can form strong hydrogen bonds with water due to their -OH group, leading to high solubility.
• Amines can also form hydrogen bonds with water, but generally less effectively than alcohols, so their solubility is lower than that of alcohols.
• Alkanes, being nonpolar and unable to form hydrogen bonds, have the lowest solubility in water.

Therefore, the correct decreasing order of solubilities in water is Alcohol > Amine > Alkane

Concept:

• A tertiary allylic alcohol is an alcohol where the hydroxyl group (-OH) is attached to a carbon atom that is bonded to three other carbon atoms and is adjacent to a double bond (allylic position).
• 

Explanation:

•  Prop-2-en-1-ol: The -OH group is attached to the first carbon, which is a primary carbon (not tertiary).
•  But-3-en-2-ol: The -OH group is attached to the second carbon, which is a secondary carbon (not tertiary).
•  2-Methylprop-2-en-1-ol: The -OH group is attached to the first carbon, which is a primary carbon (not tertiary).
•  2-Methylbut-3-en-2-ol: The -OH group is attached to the second carbon, and this carbon is connected to three other carbon atoms (tertiary) and is adjacent to a double bond, making it a tertiary allylic alcohol.

Conclusion:

Therefore, 2-Methylbut-3-en-2-ol is the tertiary allylic alcohol among the given options.

Concept:

• The solvent plays a critical role in the bromination reaction of phenol, influencing the position and extent of bromination.

Explanation:

• Phenol reacts with bromine in the presence of different solvents to yield various products.
• For obtaining 2,4,6-tribromophenol, water is typically used as the solvent. This is because water helps in the rapid ionization of bromine (Br2) and enhances the reaction, leading to complete substitution of hydrogen atoms at ortho and para positions with bromine.
• 

Conclusion:

Therefore,  Water is the solvent used in the bromination of phenol to obtain 2,4,6-tribromophenol.

The correct answer is secondary alcohol.Key Points

• A hydroxy group (-OH) attached to a saturated carbon atom with two other carbon atoms attached to it is known as a secondary alcohol.
• There are two alkyl groups present; their structures can differ or be the same.
• Secondary alcohol examples include 2 – propanol and 2 – butanol.

Additional Information

• Primary alcohols have the hydroxy group attached to a carbon atom with only one other carbon atom attached to it.
• In the case of a tertiary alcohol, the hydroxy group is attached to a saturated carbon atom with three other carbon atoms attached to it.
• An aldehyde is a compound that contains a carbonyl group (-C=O) attached to at least one hydrogen atom.
  • This group is always located at the end of a carbon chain.

The correct answer is secondary alcohol.Key Points

• Butan-2-ol has a chemical formula of C₄H₁₀O and is a type of alcohol.
• It is a secondary alcohol because the hydroxyl (-OH) group is attached to a carbon atom that is bonded to two other carbon atoms.
• Butan-2-ol is commonly used as a solvent and is also used in the production of other chemicals such as butyl acetate.

Additional Information

• Tertiary alcohols have the hydroxyl group attached to a carbon atom that is bonded to three other carbon atoms, while primary alcohols have the hydroxyl group attached to a carbon atom that is bonded to only one other carbon atom.
  • Tertiary alcohols have a higher boiling point than primary and secondary alcohols because they have a more complex molecular structure.
• Ketones have a carbonyl group (C=O) in the middle of the carbon chain, which is not present in butan-2-ol.
  • Ketones are commonly used as solvents and are also used in the production of polymers, pharmaceuticals, and other chemicals.
• Primary alcohols can be oxidized to form aldehydes and then further oxidized to form carboxylic acids.
• Secondary alcohols can be oxidized to form ketones, but they cannot be further oxidized to form carboxylic acids.

Explanation:-

Acidic Strength:-

• Lewis acids are electron-pair acceptors while some acids are proton donors.
• HO^- is a conjugate base of water, where H₃O⁺ is the conjugate acid.
• Any molecule, atom or ion which stabilizes the conjugate base will always increase the acidity.
• The acidic character increases with the increase in formal charge in the molecule.
• Acidity is directly proportional to electronegativity.
• Resonance effect - delocalization of negative charge in a molecule increases acidity.
• Due to the increase in inductive effect acidic character increases.
• Due to higher s-character acidity increases. 

The correct answer is ether.Key Points

• Ether:-
  • It is a class of organic compounds that contains an oxygen atom between two alkyl groups.
  • The general formula for an ether is R-O-R', where .R and R' are alkyl groups
  • Ethers are commonly used as solvents in various industries, including pharmaceuticals, paints, and coatings.
  • Ethers are less reactive than alcohols, aldehydes, and ketones because the C-O bond is relatively stable.

Additional Information

• Alcohol:-
  • ​ A class of organic compounds that contains a hydroxyl (-OH) group attached to a carbon atom.
  • They are commonly used as solvents, disinfectants, and fuels.
• Aldehyde:-
  • ​ A class of organic compounds that contains a carbonyl group (-CHO) attached to a carbon atom at the end of the molecule.
  • They are commonly used in the production of plastics, resins, and dyes.
• Ketone:-
  • A class of organic compounds that contains a carbonyl group (-C=O) attached to a carbon atom in the middle of the molecule.
  • They are commonly used in the production of solvents, polymers, and pharmaceuticals.

Explanation:

• Alcohols react with sodium leading to the evolution of hydrogen.

e.g. 2Na + 2CH3CH2OH 🡪 2CH3CH2O–Na (Sodium ethoxide) + H2 (g)

• In the reaction of alcohols with sodium metal, bond cleavage of the O - H bond takes place.
• The ease of breakage of the O-H bond in alcohols is an indication of the acidity of alcohols.

We know that the ease of this bond breakage follows the order primary > secondary > tertiary.

So, the ease of reactivity of sodium follow the order

Additional InformationThe acidity of alcohols:

• Just as metals react with acids to liberate hydrogen, alcohols react with metals to liberate hydrogen acting as an acid.
• The conjugate base alkoxide ion formed after alcohol releases a proton is R -O -.
• The stability of the conjugate base depends on the +I of the alkyl group R attached because it is not resonance stabilized here.
• The strength of negative charge increases as we move on from primary to secondary to tertiary alcohols because of the number of alkyl groups increases.
• The increase in negative charge over the oxygen atom destabilizes the conjugate base.
• Thus, the acidity of alcohols follows the order Primary> Secondary > Tertiary.
• 

Concept:

Dehydration reaction of alcohols:

• Alcohols when heated at high temperatures in presence of conc acids, undergo dehydration.
• They lose a molecule of water and form alkenes.
• The reaction proceeds via a carbocationic intermediate.
• The ease of dehydration follows the order tertiary>secondary>primary.
• There is a formation of unexpected products because the rearrangement of carbocations takes place in the reaction.
• Carbocationic rearrangement takes place whenever there is a possibility of a more stable intermediate to be formed by rearrangement.
• More stable carbonation gives a more saturated alkene as the product.

Explanation:

• In the first step, the nucleophilic oxygen of the OH group of alcohol takes up a proton from the acid.
• In the next step elimination of water molecule takes place and gives the carbocationic intermediate. 
• In the third step Rearrangement of this intermediate takes place to give a more stable carbocation.
• Finally, elimination of proton occurs giving more substituted alkenes.
• The mechanism is:

Hence,  on dehydration is .

Methanol is an example of the Alcohol group.

• This liquid is acidic, flammable, colorless and has a distinctive fragrance close to that of ethanol (drinking alcohol).
• Methanol is a better proton donar than Water, so alcohols are weaker acids than water
• Methanol is slightly more acidic than water.
• The order of acidity in aqueous solution is as following:
• CH3OH > H2O > CH3CH2OH > (CH3)2 CHOH
• For an acid to be strong its conjugate base anion has to be very stable. Only then acid will disassociate faster to give hydronium ion.

Hence we can conclude that  CH3OH  is more acidic.

Concept:

The acidity of alcohols:

• Just as metals react with acids to liberate hydrogen, alcohols react with metals to liberate hydrogen acting as an acid.
• The conjugate base alkoxide ion formed after alcohol releases a proton is R -O ^-.
• The stability of the conjugate base depends on the +I of the alkyl group R attached because it is not resonance stabilized here.
• The strength of negative charge increases as we move on from primary to secondary to tertiary alcohols because of the number of alkyl groups increases.
• The increase in negative charge over the oxygen atom destabilizes the conjugate base.
• Thus, the acidity of alcohols follows the order Primary> Secondary > Tertiary.
• 

Explanation:

• In the reaction of alcohols with sodium metal, bond cleavage of the O - H bond takes place.
• The ease of breakage of the O-H bond in alcohols is an indication of the acidity of alcohols.

 We know that the ease of this bond breakage follows the order primary > secondary > tertiary.

So, the ease of reactivity of sodium follow the order 

Concept:

Nucleophilic substitution reactions-

Substitution reactions are the types of reactions where a nucleophile is the attacking reagent.

• There are three types of substitution reactions depending on the nature of the substrate.
  • Nucleophilic substitution at saturated carbon. 
  • Nucleophilic acyl substitution
  • Nucleophilic aromatic substitution.
• SN1 - Unimolecular nucleophilic substitution:
  • Depends upon the concentration of the substrate.
  • Is independent of the concentration of the nucleophile.
  • Follows first-order kinetics.
• SN2- bimolecular nucleophilic substitution.
  • the rate depends on the concentration of both the reactant and the substrate.
  • It follows second-order kinetics

Elimination reactions:

• Benzene and other aromatic compounds show characteristic electrophilic substitution reactions.
• In this reaction, a hydrogen atom of the aromatic ring is substituted by an electrophile.
• The substitution takes place through an addition-elimination mechanism.

Explanation:

Dow's Process: 

Dow’s process is a process by which phenol is prepared by reacting it with molten NaOH at very high-temperature conditions. The phenol formation mechanism by this method is called the benzyne mechanism since it involves the formation of the reactive intermediate Benzyne. 

Chlorobenzene is fused with NaOH at 623K and 300 atmospheric pressure giving sodium phenoxide (C6H5O-Na+).

Phenol is obtained by the acidification of sodium phenoxide so produced.

The given reaction is well known as Dows process, for the preparation of phenols.

As we can see that the OH-ion is the attacking reagent in the process, so it is a nucleophilic substitution reaction.

Correct Answer: 3)

Concept: 

• This is a type of Reduction Reaction. 
• The reduction is a chemical reaction that involves the gaining of electrons by one of the atoms involved in the reaction between two chemicals.
• Oxidation is the gain of oxygen and reduction in loss of oxygen.​

Explanation:

• When phenol is reacted with zinc dust it forms benzene with zinc oxide as a side product.
• It is because zinc dust is a strong reducing agent. 
• Zinc oxidized itself and become ZnO and reduces phenol to benzene.
• NaOH is just a base and H2SO4 is a strong oxidizing agent and acid.

​Additional Information

Phenol to C6H5COOH (Benzoic acid):

Phenol to C6H5CHO (Benzaldehyde)