Alcohols MCQ Quiz - Objective Question with Answer for Alcohols - Download Free PDF

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.

CONCEPT:

Reaction Sequence of Alcohols with Phosphorus Triiodide and Grignard Reagents

• The given sequence involves the conversion of ethanol (CH₃CH₂OH) to various intermediates through a series of reactions.
• In the first step, ethanol reacts with phosphorus triiodide (P + I₂) to form an alkyl iodide (ethyl iodide, A).
• The alkyl iodide then reacts with magnesium in ether to form a Grignard reagent (ethylmagnesium iodide, B).
• Grignard reagents react with formaldehyde (HCHO) to form primary alcohols with one additional carbon atom after hydrolysis.

CALCULATION:

• Step 1: Ethanol (CH₃CH₂OH) reacts with phosphorus triiodide (P + I₂) to form ethyl iodide (CH₃CH₂I), which is compound A.
• Step 2: Ethyl iodide (CH₃CH₂I) reacts with magnesium in ether to form ethylmagnesium iodide (CH₃CH₂MgI), which is compound B.
• Step 3: Ethylmagnesium iodide (CH₃CH₂MgI) reacts with formaldehyde (HCHO) to form a three-carbon compound after hydrolysis, resulting in n-propyl alcohol (CH₃CH₂CH₂OH), which is compound C.
• Step 4: Oxidation of n-propyl alcohol (C) would yield propanal (CH₃CH₂CHO), which is compound D.
• Reaction: 

CONCLUSION:

The correct option is: Option 4

CONCEPT:

Hydroboration-Oxidation and Oxymercuration-Demercuration

• Hydroboration-Oxidation:
  • The reaction follows anti-Markovnikov's rule, where the hydroxyl group (-OH) is added to the carbon with more hydrogen atoms.
  • This reaction forms a primary alcohol as the major product.
• Oxymercuration-Demercuration:
  • This reaction follows Markovnikov's rule, where the hydroxyl group (-OH) is added to the carbon with fewer hydrogen atoms.
  • This reaction forms a secondary alcohol as the major product.

EXPLANATION:

• In the hydroboration-oxidation reaction, water is added to the alkene in an anti-Markovnikov fashion, forming the primary alcohol.

Where the negative part of the reagent attached to that carbon where number of hydrogen atom are more and forms primary alcohol.

In the above reaction addition of water takes place according to Markonikov’s Rule where the negative part of the reagent attached to that carbon where number of hydrogen atom are less and forms secondary alcohol.

• In the oxymercuration-demercuration reaction, water is added following Markovnikov's rule, forming the secondary alcohol.

CONCLUSION:

The correct major products are given by Option 2, where A is a primary alcohol and B is a secondary alcohol.

CONCEPT:

Boiling Point Order Based on Molecular Interactions

• The boiling point of a compound depends on the type and strength of intermolecular forces present.
• Hydrogen bonding increases the boiling point significantly compared to compounds with only dipole-dipole interactions or Van der Waals forces.
• Among compounds with similar molecular weights, the order of boiling points typically follows: hydrogen bonding > dipole-dipole interactions > Van der Waals (dispersion) forces.

EXPLANATION:

• Compound A (Ether): It has no hydrogen bonding, only weak dipole-dipole interactions, leading to a relatively low boiling point.
• Compound B (Alkane): It only exhibits Van der Waals forces, resulting in the lowest boiling point among the compounds.
• Compound C (Ketone): It has dipole-dipole interactions, which provide moderate boiling points.
• Compound D (Alcohol): It has strong hydrogen bonding, resulting in the highest boiling point.

Compounds having same number of carbon atoms follow the boiling point order as: 

(Boiling point)Hydrogen bonding > (Boiling point)high polarity > (Boiling point)low polarity > (Boiling point)non polar 

Conclusion:-

The correct increasing order of boiling points is: (B) < (A) < (C) < (D).

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: -

Rectified spirit:

• Rectified spirit is the highly concentrated form of ethanol that contains 95% ethanol and 5% water by weight.
• Rectified spirit is highly concentrated ethanol that has been purified by means of repeated distillation in a process called rectification.
• Rectified spirit is a colourless, clear liquid with a pleasant alcoholic odour.

Denatured alcohol: 

• Denatured alcohol is also known as methylated spirits.
• Denatured alcohol is used as a solvent as well as a fuel source for alcohol burners and camping stoves.

Absolute alcohol:

• Absolute alcohol is defined as a liquid containing alcohol at least 99 percent pure alcohol by weight.
• Even a small amount of pure ethanol (also known as absolute alcohol) can be lethal.
• It is also used as a substitute fuel for gasoline in combustion engines.

Power alcohol:

• Power alcohol is made up of 80% petrol, 20% ethanol, and a small amount of benzene. It is used to generate electricity.

Diluted Alcohol: -

• The ethanol solution with other liquids mixed in it can be referred to as diluted alcohol regardless of concentration.

Thus, 95% ethanol is called Rectified spirit.

The correct answer is Rectified spirit, option 1.

Explanation:-

• More electron withdrawing group attached with alcohols or phenols, more will be the acidity

​Alkyl groups show +I effect and –NO₂ group show –M effect

Order of acids strength

C > B > D > E > A

CONCEPT:

Boiling Point Order Based on Molecular Interactions

• The boiling point of a compound depends on the type and strength of intermolecular forces present.
• Hydrogen bonding increases the boiling point significantly compared to compounds with only dipole-dipole interactions or Van der Waals forces.
• Among compounds with similar molecular weights, the order of boiling points typically follows: hydrogen bonding > dipole-dipole interactions > Van der Waals (dispersion) forces.

EXPLANATION:

• Compound A (Ether): It has no hydrogen bonding, only weak dipole-dipole interactions, leading to a relatively low boiling point.
• Compound B (Alkane): It only exhibits Van der Waals forces, resulting in the lowest boiling point among the compounds.
• Compound C (Ketone): It has dipole-dipole interactions, which provide moderate boiling points.
• Compound D (Alcohol): It has strong hydrogen bonding, resulting in the highest boiling point.

Compounds having same number of carbon atoms follow the boiling point order as: 

(Boiling point)Hydrogen bonding > (Boiling point)high polarity > (Boiling point)low polarity > (Boiling point)non polar 

Conclusion:-

The correct increasing order of boiling points is: (B) < (A) < (C) < (D).

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: -

Rectified spirit:

• Rectified spirit is the highly concentrated form of ethanol that contains 95% ethanol and 5% water by weight.
• Rectified spirit is highly concentrated ethanol that has been purified by means of repeated distillation in a process called rectification.
• Rectified spirit is a colourless, clear liquid with a pleasant alcoholic odour.

Denatured alcohol: 

• Denatured alcohol is also known as methylated spirits.
• Denatured alcohol is used as a solvent as well as a fuel source for alcohol burners and camping stoves.

Absolute alcohol:

• Absolute alcohol is defined as a liquid containing alcohol at least 99 percent pure alcohol by weight.
• Even a small amount of pure ethanol (also known as absolute alcohol) can be lethal.
• It is also used as a substitute fuel for gasoline in combustion engines.

Power alcohol:

• Power alcohol is made up of 80% petrol, 20% ethanol, and a small amount of benzene. It is used to generate electricity.

Diluted Alcohol: -

• The ethanol solution with other liquids mixed in it can be referred to as diluted alcohol regardless of concentration.

Thus, 95% ethanol is called Rectified spirit.

The correct answer is Rectified spirit, option 1.

Explanation:-

• More electron withdrawing group attached with alcohols or phenols, more will be the acidity

​Alkyl groups show +I effect and –NO₂ group show –M effect

Order of acids strength

C > B > D > E > A

Concept:

Conformers: a molecule can be rotated along a single bond in its 3D space. Due to this rotation, the position of an atom with respect to another atom changes which leads to a change in dihedral angle but no bond length and bond angle.

For ethane there are two types of conformer one is staggered and another is eclipsed.

Explanation:

When a Sawhorse projection structure is converted to the Newman projection formula there are four possibilities to draw a conformer –

1. Fully eclipsed – where the two biggest groups are syn to each other that is the bond angle between the group is 0o. It is always the least stable conformer due to steric strain.

2. Gauche conformer – when the two big groups are 60o apart from each other then the conformer is called a gauche conformed. It is more stable than eclipsed form

3. Partially eclipsed – where the big group is syn to compare a smaller group. It is more stable than fully eclipsed but less stable than gauche and anti conformer

4. Anti-conformer – here the two big groups are anti i.e. 180o to each other. Generally, this structure is the most stable  

So. it may be assumed that anti is also here most stable

But, the always fact is not sterically controlling that makes anti more stable there are also other facts like H-bonding and electrostatic interaction that make Gauche form more stable.

Here, in the Gauche form, there is present an H-bond that makes it as most stable conformer

So, the most stable conformer is the gauche form.

So, the Correct option is (4)