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# Alcohols, Phenols and Ethers

#### Multiple Choice Questions

161.

Which among the following alcohols is most reactive with sodium wire?

• Ethanol

• 2-Propanol

• 2-Butanol

• 2-Methyl-2-butanol

A.

Ethanol

For the breaking of -O-H bond primary alcohol is most reactive.

162.

Lucas test is given by an alcohol within 5 minutes. 0.22 g of which liberates 56 mL of CH4 at STP on treating with CH3MgI. The structure of alcohol is

• CH3 - CHOH - CH3

• (CH3)2CH - CHOH - CH3

• CH- CH2 - CHOH - CH3

• (CH3)3C - CHOH - CH3

B.

(CH3)2CH - CHOH - CH3

Lucas test will be given by all the given alcohols within 5 minutes as all are secondary (2°) alcohols. Exact structure can be known by molecular mass or formula of alcohol which will be obtained as follows:

Let molecular mass of alcohol be M.

or,

M =  = 88

CnH2n + 1OH is the general formula of alcohols. The molecular mass 88 corresponds to the value of n = 5. Thus, 2° alcohol is (CH3)2CHCHOHCH3.

163.

The compound A on treatment with Na gives B, and with PCl5 gives C. B and C react together to give diethyl ether. A, B and C are in the order

• C2H5OH, C2H6, C2H5Cl

• C2H5OH, C2H5Cl, C2H5ONa

• C2H5OH, C2H5ONa, C2H5Cl

• C2H5Cl, C2H6, C2H5OH

C.

C2H5OH, C2H5ONa, C2H5Cl

164.

The correct order of reactivity of phenyl Magnesium bromide with the following compound is:

• (II)> (III)> (I)

• (I)> (III)> (II)

• (II)> (I)> (III)

• (I)> (II)> (III)

C.

(II)> (I)> (III)

Among aldehyde and a ketone, aldehydes are more electrophilic as in ketones. If charge on carbonyl carbon is decreased by +I effect of both alkyl groups.

Moreover in the tetrahedral intermediate aldehydes have less steric repulsion than ketone and aldehydes increases the--ve charge on oxygen less in comparison to ketmes.

Based on the above the order of reactivity is:

(II) > (I) > (III)

165.

In the reaction,

The electrophile involved is

• Dichloromethyl cation (C+HCl2)

• Formyl cation (C+HO)

• Dichlorocarbene (:CCl2)

• Dichloromethyl anion (C-HCl2)

C.

Dichlorocarbene (:CCl2)

Reimer-Tiemann reaction. The electrophile formed is :CCl2 (Dichlorocarbene) according to the following reaction

166.

(CH3)3COCH3 and CH3OC2H5 are treated with hydroiodic acid. The fragments obtained after reactions are respectively

• (CH3)3CI + CH3OH; CH3I + C2H5OH

• (CH3)3CI + CH3OH; CH3OH + C2H5I

• (CH3)3COH + CH3I; CH3OH + C2H5I

• CH3I + (CH3)3COH; CH3I + C2H5OH

A.

(CH3)3CI + CH3OH; CH3I + C2H5OH

The fragments obtained after reaction of (CH3)3COCH3 and CH3OC2H5 with hydroiodic acid are (CH3)3CI + CH3OH; CH3I + C2H5OH.

When mixed ethers are used, the formation of alkyl iodide depends on the nature of alkyl
groups. Methyl iodide is formed when one group is methyl and the other a primary or secondary alkyl group. This reaction follows SN2 mechanism and because of the steric effect of the larger group, I- attacks the smaller (Me) group.

CH3OC2H5 + HI $\to$ CH3I + C2H5OH

When the substrate is a methyl t-alkyl ether, the products are t-RI and MeOH. This reaction follows SN1 mechanism and formation of products is controlled by the stability of
carbocation.

+ HI   + CH3OH

167.

Assertion : Oxidation of 1-nitronaphthalene gives o-nitrophthalic acid whereas 1-amino naphthalene on oxidation gives phthalic acid.

Reason : An amino group attached to the benzene ring makes it resistant to oxidation whereas nitro group makes the benzene ring susceptible to oxidation.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

C.

If assertion is true but reason is false.

An amino group increases the electron density in the benzene ring to which it is attached thereby making it susceptible to oxidation while a nitro group decreases the electron density in the benzene ring to which it is attached thereby making it resistant to oxidation. Instead, the other benzene ring gets oxidised giving o- nitrophthalic acid as shown below:

168.

Decreasing order of reactivity in Williamson synthesis of the following :

I. Me3CCH2Br

II. CH3CH2CH2Br

III. CH2=CHCH2Cl

IV. CH3CH2CH2Cl

• III > II > IV > I

• I > II > IV > III

• II > III > IV > I

• I > III > II > IV

C.

II > III > IV > I

C-Br bond is weaker than C-Cl bond, therefore, alkyl bromide (II) reacts faster than alkyl chlorides, (III) and (IV). Since, CH2 = CH- is electron withdrawing therefore, CH2 has more +ve charge on III than on IV.

In other words, nucleophilic attack occurs faster on III than on IV. Further, since Williamson synthesis occurs by SN2 mechanism, therefore, due to steric hindrance alkyl bromide (I) is the least reactive.

Thus, the decreasing order of reactivity is II > III > IV > I.

169.

Assertion: Phenol forms 2, 4, 6-tribromophenol on treatment with Br2- water at 273 K.

Reason : Phenol is o, p- directing group.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false

• If both assertion and reason are false

B.

If both assertion and reason are true but reason is not the correct explanation of assertion.

Phenol forms 2, 4, 6 tribromophenol on treatment with Br2- water. In phenols, the polarisation of bromine takes place even in the absence of Lewis acid.

170.

Arrange X, Y and Z in order of increasing acidic strengths.

• X > Z > Y

• Z < X < Y

• X > Y > Z

• Z > X > Y

A.

X > Z > Y

Carboxylic acid is stronger acid than -$\stackrel{+}{\mathrm{N}}$H3, therefore, X is the strongest acid.Since -COOH has -I-effect which decreases with distance, therefore, -I-effect is more pronounced on Z than on Y. As a result, Z is more acidic than Y. Thus, overall order of increasing acidic strength is X > Z > Y.