Alcohols, Phenols and Ethers

JEE Chemistry · 44 questions · Page 3 of 5 · Click an option or "Show Solution" to reveal answer

Q21

Given below are two statement : Statements I : Bromination of phenol in solvent with low polarity such as

\mathrm{CHCl}_3

\mathrm{CS}_2

requires Lewis acid catalyst. Statements II : The Lewis acid catalyst polarises the bromine to generate

\mathrm{Br}^{+}

. In the light of the above statements, choose the correct answer from the options given below :

A Statement I is true but Statement II is false

B Both Statement I and Statement II are true

C Statement I is false but Statement II is true

D Both Statement I and Statement II are false

Correct Answer

Option C

Solution

Presence of Lewis acid promotes the reaction due to ease in formation of electrophile.

Q22

The most suitable reagent for the conversion of R - CH2 - OH

\to

R - CHO is:

A CrO3

B PCC (Pyridinium Chlorochromate)

C KMnO4

D K2Cr2O7

Correct Answer

Option B

Solution

An excellent reagent for oxidation of

{1^ \circ }

alcohols to aldehydes is

PCC.

Q23

A solution of

\mathrm{Cr O_5}

in amyl alcohol has a __________ colour.

A Yellow

B Orange-Red

C Green

D Blue

Correct Answer

Option D

Solution

CrO

_5

is blue in colour in amyl alcohol.

Q24

Ortho–Nitrophenol is less soluble in water than p– and m– Nitrophenols because :

A o–Nitrophenol is more volatile in steam than those of m – and p–isomers

B o–Nitrophenol shows Intramolecular H–bonding

C o–Nitrophenol shows Intermolecular H–bonding

D Melting point of o–Nitrophenol is lower than those of m–and p–isomers.

Correct Answer

Option B

Solution

As in ortho-Nitrophenol H of -OH is already in Intra-moleculer H Bond and become stable so it will not perticipate in H bonding with H2O by breaking this H bonding.

That is why solublity of Ortho–Nitrophenol is less in water. para– and meta– Nitrophenols both shows inter-moleculer H bonding with H2O.

That is why both are more soluble in water.

Q25

An unknown alcohol is treated with the “Lucas reagent” to determine whether the alcohol is primary, secondary or tertiary. Which alcohol reacts fastest and by what mechanism:

A tertiary alcohol by SN1

B secondary alcohol by SN2

C tertiary alcohol by SN2

D secondary alcohol by SN1

Correct Answer

Option A

Solution

Tertiary alcohols reacts fastest with lucas reagnet as the rate of reaction is directly proportional to the stability of carbocation formed in the reaction.

Since most stable

{3^ \circ }

carbocation is formed in the reaction hence it will react fastest further tetriary alcohols appears to react by

{S_N}1

mechanism.

Q26

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Treatment of bromine water with propene yields 1-bromopropan-2-ol. Reason (R) : Attack of water on bromonium ion follows Markovnikov rule and results in 1-bromopropan-2-ol. In the light of the above statements, choose the most appropriate answer from the options given below :

A Both (A) and (R) are true but (R) is not the correct explanation of (A)

B (A) is false but (R) is true

C Both (A) and (R) are true and (R) is the correct explanation of (A)

D (A) is true but (R) is false

Correct Answer

Option C

Solution

Its IUPAC name 1-bromopropan-2-ol A and R are true and (R) is the correct explanation of (A).

Q27

Given below are two statements : Statement I : On heating with

\mathrm{KHSO}_{4}

, glycerol is dehydrated and acrolein is formed. Statement II : Acrolein has fruity odour and can be used to test glycerol's presence. Choose the correct option.

A Both Statement I and Statement II are correct.

B Both Statement I and Statement II are incorrect.

C Statement I is correct but Statement II is incorrect.

D Statement I is incorrect but Statement II is correct.

Correct Answer

Option C

Solution

Glycerol, on heating with KHSO4, undergoes dehydration to give unsaturated aldehyde called acrolein.

So, the statement I is correct.

Acrolein has a piercing unpleasant smell.

So, statement II is incorrect.

Q28

Incorrect method of preparation for alcohols from the following is:

A Hydroboration-oxidation of alkene.

B Reaction of Ketone with

\mathrm{RMgBr}

followed by hydrolysis.

C Ozonolysis of alkene.

D Reaction of alkyl halide with aqueous

\mathrm{NaOH}

Correct Answer

Option C

Solution

Reductive ozonolysis of alkenes will lead to formation of aldehyde or ketones, oxidative ozonolysis of alkenes will lead to formation of carboxylic acids or ketones.

So, alcohol is not formed by ozonolysis of alkenes.

Q29

Arrange the following compounds in increasing order of C–OH bond length : methanol, phenol, p-ethoxyphenol

A phenol < methanol < p-ethoxyphenol

B methanol < p-ethoxyphenol < phenol

C methanol < phenol < p-ethoxyphenol

D phenol < p-ethoxyphenol < methanol

Correct Answer

Option D

Solution

C-OH bond length in Among methanol, phenol and p-ethoxyphenol, C-OH bond length is least in phenol due to resonance and maximum in methanol due to lack of resonance whereas it will have some intermediate value in p-ethoxyphenol. phenol < p-ethoxyphenol < methanol

Q30

HBr reacts with CH2 = CH – OCH3 under anhydrous conditions at room temperature to give

A CH3CHO and CH3Br

B BrCH2CHO and CH3OH

C BrCH2 – CH2 – OCH3

D H3C – CHBr – OCH3

Correct Answer

Option D

Solution

Methyl vinyl ether under anhydrous condition at room temperature undergoes addition reaction .

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