Question Set C

CBSE 12th Standard Chemistry Alcohols , Phenols and Ethers HOT Questions Study Material - QB365

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Questions:

Generic 2

4 x 2 = 8

Draw the structure of p-methylbenzaldehyde molecule.

Name the reagents you will use to bring about the following conversions.
a. Ethane nitrile to ethanal
b. But-2-ene to ethanal

Anisole is less reactive than phenol towards electrophilic substitution reactions. Justify yours answer with proper reasoning.

Name a compound which is used as antiseptic as well as disinfectant.

Generic 5

4 x 5 = 20

An organic compound 'A' C₈H₆, on treatment with dilute H₂SO₄ containing mercuric sulphate gives Compound 'B',This compound 'B' can also be obtaincd from a reaction of benzene vith acetyl chloride in presence of anhy. AlCl₃, 'B' on treatment with I₂ ín aq KOH gives 'C' and a yellow compound 'D'.
Identify A,B,C and D, Cive the chemícal reactions involved.

(i) How are the following conversions carried out?
(a) Propene -7 Propan-2-ol
(b) Benzyl chloride -7 Benzyl alcohol
(c) Ethyl magnesium chloride -7 Prop an -1-ol
(d) Methyl magnesium bromide -7 2-methyl propan-2-ol.
(ii) Explain why propanol has higher boiling point than that of butane?

An organic compound (A) on treatment with CHCl₃ and KOH gives two compounds B and C.Both B and C give the same product (D) when distilled with zinc dust.Oxidation of D gives E having molecular formula C₇H₆O₂.The sodium salt of E on heating with soda-lime gives F which may also be obtained by distilling A with zinc dust.Identify A to F

Write down functional isomers of a carbonyl compound with molecular formula C₃H₆O. Which isomer will react faster with HCN and why? Explain the mechanism of the reaction also. Will the reaction lead to the completion with the conversion of whole reactant into product at reaction condition. If a strong acid is added to the reaction mixture what will be the effect on concentration of the product and why?

Multiple Choice Question

10 x 1 = 10

Salicylic acid reacts with Zinc dust on heating to give

(a)

Benzene

(b)

Benzoic acid

(c)

Phenol

(d)

None of these

10.

\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2} \stackrel{\text { Conc. } \mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow}\) is

(a)

(b)

(c)

(d)

11.

Dipole moment of diethyl ether is lower than that of

(a)

CH₃OH

(b)

C₆H₅OH

(c)

CH₃-I

(d)

CH₃CHO

12.

Trichloroacetaldehyde was subjected to Cannizaro's reaction by using NaOH. The mixture and another products contains sodium trichloroacetate and other compound. The other compound is

(a)

trichloromethanol

(b)

2,2,2-trichloropropanol

(c)

chloroform

(d)

2,2,2-trichloromethanol

13.

If the enolate ion combines with the carbonyl group of an ester, we get

(a)

aldol

(b)

\(\alpha ,\beta\) - unstaurated ester

(c)

\(\beta\) - ketoaldehyde

(d)

acid

14.

CH₃CHO and C₆H₅CH₂can be distinguished chemically by

(a)

Benedict's rect

(b)

Iodoform test

(c)

Tollens'reagent test

(d)

Fehling's solution test

15.

Haloform reaction does not take place with

(a)

acetone

(b)

2-chloropane

(c)

ethanol

(d)

methanol

16.

The correct order of basic strength is

(a)

H₂O<OH^-<CH₃O^-

(b)

CH₃OH<H₂O<CH₃O^-<OH^-

(c)

H₂O<CH₃OH<OH^-<CH₃O^-

(d)

OH^-H₂O<CH₃O^-<CH₃OH

17.

When propionic acid is treated with aqueous sodium bicarbonate, CO₂ is liberated. The 'C' of CO₂ comes from

(a)

methyl group

(b)

carboxylic acid group

(c)

methylene group

(d)

bicarbonate

18.

Chlorination of toluene in presence of light and heat followed by treatment with aqueous NaOH gives :

(a)

o-Cresol

(b)

p-Cresol

(c)

2, 4 - Dihydroxytoluene

(d)

Benzoic acid

Generic 3

5 x 3 = 15

19.

(i) How can diethyl ether be prepared from the following?
(a) Ethyl iodide (b) Ethyl alcohol
Write the chemical equation in each case.
(ii) Howis ethyl alcohol obtained from molasses?

20.

Explain the following with an example.
(i) Kolbes reaction.
(ii) Reimer-Tiemann reaction.
(iii) Williamson ether synthesis.
(iv) Unsymmetrical ether.

21.

(i) Give mechanism of preparation of ethoxy ethane from ethanol.
(ii) How is toluene obtained from phenol?

22.

Convert the following:
(a) Bromobenzene to 1-phenylethanol
(b) Benzaldehyde to 3-phenylpropan-1-ol
(c) Benzoic acid to m-Nitrobenzyl alcohol

23.

Write the reaction and conditions for the following conversions:
(i) Benzoyl chloride benzaldehyde
(ii) Acetaldehyde to crotonaldehyde

Assertion and reason

4 x 1 = 4

24.

Assertion (A) IUPAC name of the compound

Reason (R) In IUPAC nomenclature, ether is regarded as hydrocarbon derivative in which a hydrogen atom is replaced by -OR or -OAr group [where, R = alkyl group and Ar = aryl group].
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A).
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

25.

Assertion: Carboxylic acids have higher boiling points than alkanes.
Reason: Carboxylic acids a;e resonance hybrids.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

26.

Assertion: Hydrogen bonding in carboxylic acids is stronger than alcohols.
Reason: Highly branched carboxylic acids are more acidic than unbranched acids.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

27.

In the following questions. an Assertion (A) is followed by a corresponding Reason (R) Use the following keys to choose the appropriate answer.
Assertion (A) The boiling point of diethyl ether is much less than that of ethanol.
Reason (R) In ethanol, the molecules are associated by the formation of intermolecular hydrogen bonding whereas in diethyl, it is not possible.
Codes:
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A).
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

Case Study Questions

2 x 4 = 8

28.

The addition reaction of enol or enolate to the carbonyl functional group of aldehyde or ketone is known as aldol addition. The β-hydroxy aldehyde or β-hydroxy ketone so obtained undergo dehydration in the second step to produce a conjugated enone. The first part of the reaction is an addition reaction and the second part is an elimination reaction. The Carbonyl compound having α-hydrogen undergoes an aldol condensation reaction.

1.The condensation reaction is the reverse of which of the following reaction?
(a) Lock and key hypothesis
(b) Oxidation
(c) Hydrolysis
(d) Glycogen formation
2.Which of the following compounds would be the main product of an aldol condensation of acetaldehyde and acetone?

3.Which combination of carbonyl compounds gives phenyl vinyl ketone by an aldol condensation?

(a) Acetophenone and Formaldehyde
(b) Acetophenone and acetaldehyde
(c) Benzaldehyde and acetaldehyde
(d) Benzaldehyde and acetone
4.Which of the following will undergo aldol condensation?
(a) HCHO
(b) CH₃CH₂OH
(c) C₆H₅CHO
(d) CH₃CH₂CHO
5.Which of the following does not undergo aldol condensation?
(a) CH₃CHO
(b) CH₃CH

29.

Read the passage given below and answer the following questions:
Reimer- Tiemann reaction introduces an aldehyde group, on aromatic ring of phenol, ortho to the hydroxyl group. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.
The following questions are multiple choice questions. Choose the most appropriate answer:
(i) Reimer-Tiemann reaction is an example of

(a) nucleophilic substitution reaction	(b) electrophilic substitution reaction
(c) nucleophilic addition reaction	(d) electrophilic addition reaction

(ii) Which of the following reagents is used in the given reaction in steps I?

(a) aq. NaOH + CH₃CI

(b) aq. NaOH + CH₂Cl₂

(c) aq. NaOH + CHCl₃

(d) aq. NaOH + CCl₄

(iii) The structure of the intermediate [A] is

(iv) When phenol reacts with chloroform in presence of KOH, the product formed is

(a) salicylic acid

(b) salicylaldehyde

(c) both (a) and (b)

(d) none of these.

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Answers Key:

Generic 2

4 x 2 = 8

a. Tertiary butyl ketone does not give precipitate with sodium bisulphate whereas acetone does.
b. Dialkyl cadmium is considered superior to grignard reagent for the preparation of a ketone from an acid chloride.

Both -OH and -OCH³ groups have +Rveffect as shown below:

structures (II to IV) involve separation of +ve and -ve charges. Similarly, structures (VII-IX) involve separation of +ve and -ve charges. But structures (II to IV) can stabilize themselves by releasing a proton which is a very stable chemical species.

In contrast, structures (VII-IX) cannot stabilize themselves by releasing a methyl carbocation which is a very unstable chemical species. It is because of this extra stability of structures, II-IV through loss of a proton which is responsible for greater reactivity of phenol over anisole. For example, phenol reacts with Br2 water to give 2, 4, 6-tribromophenol but anisole does not react with Br2 water at all.

0.2% solution of phenol is used as antiseptic, 2% solution of phenol is used as disinfectant.

Generic 5

4 x 5 = 20

A, B, C and D respectively are

Complete reactions are as follows
C₈H₆ on reaction with dil. H₂SO₄, HgSO₄ gives

C₆H₅COCH₃ (B) can also be obtained from benzene with acetyl chloride in presence of anhyd. AlCl₃.
This reaction is known as Friedel-Crafts acetylation reaction.

The molecules of butane are held together by weak. van der Waals forces of attraction while those of propanol are held together by stronger intermolecular hydrogen bonding.
\(------\overset { \delta + }{ H } -\overset { \delta - }{ \underset { { | } }{ O } } ----\overset { \delta + }{ H } -\overset { \delta - }{ \underset { | }{ O } } ------\overset { \delta + }{ H } -\overset { \delta - }{ \underset { | }{ O } } -------\)
CH₂CH₂CH₃ CH₂CH₂CH₃ CH₂CH₂CH₃
Therefore, the b.p. of propanol is much higher than that of butane.

(i) Since compound (A) on treatment with CHCI3 and KOH (i.e., Reimer-Tiemann reaction), gives two products Band C, therefore, A must be phenol and Band C must be o-hydroxybenzaldehyde and P: hydroxybenzaldehyde respectively or vice-versa.
(ii) Since both Band C on distillation with Zn dust give the same compound (D), therefore, D must be benzaldehyde.
(iii) Since oxidation of D gives E with M.F. C7R602, therefore, E must be benzoic acid.
(iv) Since sodium salt of E, i.e.benzoic acid upon heating with soda-lime gives compound (F), therefore.
(F) must be benzene. Zn dust distillation of A would also give benzene (F).

Compound I will react faster with HCN because it is less stearically hindered and has more positive charge on carbonyl compounds.
Mechanism of the reaction:

The reaction will not lead to completion.It is reversible reaction, hence equilibrium established.
Addition of strong acid will will inhibit the reaction because dissociation of HCN will be reduced due to common ion effect and formation of CN^- is prevented.

Multiple Choice Question

10 x 1 = 10

(b)
Benzoic acid

10.

11.

(a)
CH₃OH

12.

(d)
2,2,2-trichloromethanol

13.

14.

(b)
Iodoform test

15.

(d)
methanol

16.

17.

(d)
bicarbonate

18.

(d)
Benzoic acid

Generic 3

5 x 3 = 15

19.

\(\begin{equation} \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{l}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}+\mathrm{HI} \end{equation}\)

20.

(i) Kolbes reaction.
It is a decarboxylative dimerisation of two carboxylic acids (or carboxylate ions) to form carbon carbon bond of alkane.

(ii) Reimer-Tiemann reaction.
It involves the ortho-formylation of phenols. Phenol is converted to salicylaldehyde.

(iii) Williamson ether synthesis.
Sodium alkoxide reacts with alkyl halide to form an ether.
\(\mathbf{C}_{2} \mathrm{H}_{5} \mathrm{ONa}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl} \rightarrow \mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5}+\mathrm{NaCl}\)
(iv) Unsymmetrical ether.
Two different alkyl groups are attached to O atom. The general formula is R−O−R′. An example is ethyl methyl ether
\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{O}-\mathrm{CH}_{3}\)

21.

22.

23.

Assertion and reason

4 x 1 = 4

24.

(d) (A) is incorrect statement but (R) is correct statement, Correct (A) The IUPAC name of the given compound is 1-(2-propoxy) propane.

25.

(b): Boiling points of carboxylic acids are higher due to th.eir tendency to associate and form dimers to a greater extent by hydrogen bonding.

26.

(c): Highly branched carboxylic acids are less acidic than unbranched acids. The +I effect of alkyl groups in branched acid increases the magnitude of negative charge. Thus, -COOH group is shielded from solvent molecules and cannot be stabilized by solvation as effectively as in unbranched carboxylic acids.

27.

(a) Both (A) and (R) are correct and (R) is the correct explanation of (A).

Case Study Questions

2 x 4 = 8

28.

1.(c) Hydrolysis
2.

3.(a) Acetophenone and Formaldehyde
4.(d) CH3CH2CHO
5.(d) C6H5CHO

29.

(i) (b): It is an electrophilic substitution reaction.
(ii) (c)

(iv) (b): It is known as Reimer-Tiemann reaction.