Short Answer Questions

Hydroxy Compounds and Ethers | Chemistry

Short Answer Questions

1. Identify the product (s) is / are formed when 1 – methoxy propane is heated with excess HI. Name the mechanism involved in the reaction

When 1-methoxy propane is heated with excess HI it forms methyl iodide and propyl iodide.

CH₃—O —CH₂—CH₂—CH₃ + 2 HI → CH₃I + CH₃CH₂CH₂I + H₂O

      1- methoxy propane                                    propyl iodide

Mechanism

It follows S_N² mechanism.

Ethers having primary alkyl group undergo S_N² reaction.

2. Draw the major product formed when 1-ethoxyprop-1-ene is heated with one equivalent of HI

1-ethoxyprop-l-ene is heated with one equivalent of HI gives ethyl iodide and prop-l-enol

CH₃CH₂ - O - CH = CH - CH₃ + HI  â†’   CH₃CH₂I      +    CH₃ - CH = CH - OH

        1-ethoxyprop−1-ene                     Ethyl iodide               Prop−1 en ol

3. Suggest a suitable reagent to prepare secondary alcohol with identical group using Grignard reagent.

Formate ester is used to prepare secondary alcohol with identical alkyl group

4. What is the major product obtained when two moles of ethyl magnesium bromide is treated with methyl benzoate followed by acid hydrolysis.

5. Predict the major product, when 2-methyl but -2-ene is converted into an alcohol in each of the following methods.

(i) Acid catalysed hydration (ii.) Hydroboration (iii.) Hydroxylation using bayers reagent

(i) Acid catalysed hydration

It follows Markownikoff's rule.

(ii) Hydroboration

It follows anti Markovnikov's rule

(iii) Hydroxylation using Bayers reagent

Bayer's reagent with alkene gives diol.

6. Arrange the following in the increasing order of their boiling point and give a reason for your ordering

(i) Butan – 2- ol, Butan -1-ol, 2 –methylpropan -2-ol

(ii) Propan -1-ol, propan -1,2,3-triol, propan -1,3 – diol, propan -2-ol

Answer:

(i) Butan - 2- ol, Butan -l-ol, 2 -methylpropan -2-ol

Hence the boiling point decreases with increase of branching

The van der Waals force decreases with decrease of surface area.

Therefore the order is 2 – methylpropan -2 – ol < Butan – 2- ol < Butan −1 - ol

(ii) Propan -l-ol, propan −1,2,3-triol, propan −1,3 - diol, propan -2-ol

The boiling point of the alcohol increases when the number of −OH group increases due to strong hydrogen bonding.

propan -2-ol < Propan -l-ol < propan −1,3 - diol < propan −1,2,3-triol

7. Can we use nucelophiles such as NH3,CH3O- for the Nucleophilic substitution of alcohols

No, we cannot use nucleophiles such as NH₃, for the nucleophilic substitution of alcohols because nucleophilic substitution reaction reacts two species a nucleophile (Lewis base) and a substrate in the leaving group.

8. Is it possible to oxidise t – butyl alcohol using acidified dichromate to form a carbonyl compound.

t - butyl alcohol do not undergo oxidation reaction under normal conditions, but at elevated temperatures, under strong oxidising agent cleavage of C -C bond takes place to give a mixture of carboxylic acid. Therefore it is not possible to get a carbonyl compounds from t-butyl alcohol.

9. What happens when 1-phenyl ethanol is treated with acidified KMnO4.

1-phenyl ethanol is treated with acidifed KMnO₄ gives acetophenone and then oxidized to give benzoic acid.

10. Write the mechanism of acid catalysed dehydration of ethanol to give ethene.

Mechanism

It follows E₂ mechanism 

11. How is phenol prepared from

i) chloro benzene ii) isopropyl benzene

i) chloro benzene

When chlorobenzene is hydrolysed with 6−8% NaOH at 300 bar and 633 K in a closed vessel, sodium phenoxide is formed which on treatment with dilute HCl gives phenol.

ii) isopropyl benzene

On passing air to a mixture of cumene and 5% aqueous sodium carbonate solution, cumene hydro peroxide is formed by oxidation. It is treated with dilute acid to get phenol and acetone.

12. Explain Kolbe’s reaction

• Phenol is first converted into sodium phenoxide which is more reactive than phenol

• It undergo electrophilic substitution reaction with CO₂ at 400K, 4-7 bar pressure gives sodium salicylate.

• Acid hydrolysis of sodium salicylate gives salicylic acid

13. Write the chemical equation for Williamson synthesis of 2-ethoxy – 2- methyl pentane starting from ethanol and 2 – methyl pentan -2-ol

14. Write the structure of the aldehyde, carboxylic acid and ester that yield 4- methylpent -2-en-1-ol.

15. What is metamerism? Give the structure and IUPAC name of metamers of 2-methyoxy propane

Metamerism:- It is a special type of isomerism in which molecules with same formula, same functional group, differing only in the nature of the alkyl group attached to oxygen

CH₃-O-CH₂-CH₂-CH₃

Methoxy propane

CH₃-CH₂-O-CH₂-CH₃

Ethoxy ethane

2-Methoxy propane

16. How are the following conversions effected

i) benzylchloride to benzylalcohol ii) benzyl alcohol to benzoic acid

Hydrolysis of benzyl chloride with aqueous NaOH gives benzyl alcohol

ii) benzylalcohol to benzoic acid

Benzyl alcohol is oxidised with acidified potassium dichromate or alkaline potassium permanganate, benzaldehyde is first formed which undergoes further oxidation to benzoic acid.

17. Complete the following reactions

Answer:

18. 0.44g of a monohydric alcohol when added to methyl magnesium iodide in ether liberates at STP 112 cm3 of methane with PCC the same alcohol form a carbonyl compound that answers silver mirror test. Identify the compound.

0.44g of a monohydric alcohol alcohol liberates 112 cm³ of methane

Mass of monohydric alcohol which gives 22400 cm³ of methane = (22400 × 0.44 ) / 112 = 88

C₅H₁₂O molecular formula has mass number 88 and it shows eight possible isomers.

But Neopentyl alcohol reacts with pcc to form neopentyl aldehyde which shows positive silver mirror test.

Therefore, compound is neopentyl alcohol.

19. Complete the following reactions

ii) C6H5 -CHCH(OH)CH(CH3 )2 ---ConH2 SO4 â†’

20. Phenol is distilled with Zn dust followed by friedel – crafts alkylation with propyl chloride to give a compound B, B on oxidation gives (c) Identify A,B and C.

Phenol is distilled with Zn dust gives benzene (A)

Benzene (A) undergoes Friedel - Craft's alkylation with propyl chloride gives cumene (B)

Cumene (B) on oxidation gives phenol and acetone

Answer:

A → Benzene; B → Cumene ; C → Phenol

21. 

Identify A,B,C,D and write the complete equation

22. What will be the product (X and A)for the following reaction

Acetylchloride 

23. How will you convert acetylene into n-butyl alcohol.

24. Predict the product A,B,X and Y in the following sequence of reaction

25. 3,3 – dimethylbutan -2-ol on treatment with conc. H2SO4 to give tetramethyl ethylene as a major product. Suggest a suitable mechanism

ALCOHOL

EVALUATE YOURSELF:

1. Classify the following alcohols as 1°, 2°, and 3° and give their IUPAC Names.

2. Suggest a suitable carbonyl compound for the preparation of pent-2-en-l-ol using LiAlH₄-.

3. Write all the possible isomers of an alcohol having the molecular formula C₅H₁₂O and give their IUPAC names.

4. 2-methylpropan-2-ene 

The reaction follows Markovnikov's rule

5. How will you prepare the following using Grignard reagent?

 i) t-butyl alcohol

 ii) allyl alcohol

i) t-butyl alcohol

6. Identify the products in the following reactions. Write their IUPAC names and mention the mechanism involved in the reactions.

Answer:

7. What is the major product obtained when 2,3 - dimethyl pentan-3 -ol is heated in the presence of H₂SO₄?

8. Which of the following set of reactants will give l-methoxy-4-nitrobenzene.

Equation (ii) only gives l-methoxy-4-nitrobenzene. The reaction is Williamson's synthesis. The Br atom attached to aromatic carbon atom is more strong and hence it will not cleaved easily and does not give l-methoxy-4-nitrobenzene.

9. What happens when m-cresol is treated with acidic solution of sodium dichromate?

10. When phenol is treated with propan-2-ol in the presence of HF, Friedel-Craft reaction takes place . Identify the products.

Alkylation takes place at ortho and para position

11. Give the IUPAC name for the following ethers and classify them as simple or mixed.

12. Which of the following reaction will give l-methoxy-4-nitrobenzene?

a) 4-nitro-l-bromobenzene + sodium methoxide.

b) 4-nitrosodium phenoxide+bromomethane

Reaction (b) only gives l-methoxy-4-nitrobenzene. The reaction is Williamson's synthesis. The Br atom attached to aromatic carbon atom is more strong and hence it will not cleaved easily and does not give the l-methoxy-4-nitrobenzene.

13. Arrange the following compounds in the increasing order of their acid strength.

propan-l-ol, 2,4,6-trinitrophenol,3-nitrophenol,3,5-dinitrophenol, phenol,4-methylphenol.

Aliphatic alcohols are less acidic than aromatic alcohol. Hence propan-l-ol is least acidic.

Electron releasing group decreases the acidity of phenol where as electron withdrawing group enhances the acidity of phenol. If electron withdrawing group like -NO₂ is attached to phenol, the compound is more acidic than phenol.

Hence the increasing order of their acid strength is given as

propan-l-ol < 4-methylphenol < phenol < 3-nitrophenol < 3,5-dinitrophenol < 2,4,6-trinitrophenol

14. 1 mole of HI is allowed to react with t-butyl methylether. Identify the product and write down the mechanism of the reaction.

  t-butyl methylether reacts with HI gives iodomethane and 2-methylpropan-2-ol

Mechanism

The reaction involves protonation of oxygen which is following by S_N¹ mechanism. The products are t-butyl alcohol and methyl idodide.