JEE Chemistry Alcohols Phenols and Ethers MCQs Set 14

Answer: (d) ROH

Explanation:
1. \( \ce{RMgBr + O2 -> ROOMgBr} \), which reacts with a second RMgBr to give \( \ce{2ROMgBr} \); hydrolysis gives ROH.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (c) Tertiary alcohol

Explanation:
1. The ketone formed first reacts again, giving a tertiary alcohol with two identical R groups.

Teacher's Note:
1. Grignard reagents add to carbonyl groups and are destroyed by water, alcohols and acids.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (c) \( \ce{(CH3)3S+ I-} \)

Explanation:
1. The trimethylsulphonium ion has an excellent leaving group (dimethyl sulphide), so hydroxide displaces it at the CH3 group most easily.

Teacher's Note:
1. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (b) Hydrogen peroxide

Explanation:
1. Auto-oxidation of the quinol to quinone produces \( \ce{H2O2} \) (industrial route).

Teacher's Note:
1. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (c) Ethyl alcohol

Explanation:
1. \( \ce{C2H5NH2 + HNO2 -> C2H5OH + N2 + H2O} \).

Teacher's Note:
1. Nitro groups at ortho and para positions increase the acidity of phenol, and ortho-nitrophenol is steam volatile.
2. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.

Answer: (b) Benzyl alcohol

Explanation:
1. \( \ce{C6H5CHO} \) is reduced to \( \ce{C6H5CH2OH} \).

Teacher's Note:
1. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (a) Reduction of CO in the presence of \( \ce{ZnO.Cr2O3} \)

Explanation:
1. \( \ce{CO + 2H2 ->[ZnO/Cr2O3, 300 atm] CH3OH} \).

Teacher's Note:
1. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.
2. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.

Answer: (a) (i) 2-Methylbutan-2-ol and (ii) propan-2-ol

Explanation:
1. Acid-catalysed hydration follows Markovnikov's rule through the more stable carbocation.

Teacher's Note:
1. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (c) An ether

Explanation:
1. Phenoxide reacts with RX to give an alkyl aryl ether.

Teacher's Note:
1. Ethers are cleaved by HI, form explosive peroxides in air, and act as Lewis bases forming etherates.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (b) Diethyl ether

Explanation:
1. Alkoxide with alkyl halide gives an ether.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction of an alkoxide with a primary alkyl halide; tertiary halides eliminate.
2. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.

Answer: (c) An ether

Explanation:
1. Williamson synthesis: SN2 displacement of halide by alkoxide.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction of an alkoxide with a primary alkyl halide; tertiary halides eliminate.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (b) Sodium ethoxide with ethyl bromide

Explanation:
1. \( \ce{C2H5ONa + C2H5Br -> C2H5OC2H5 + NaBr} \).

Teacher's Note:
1. Williamson synthesis is an SN2 reaction of an alkoxide with a primary alkyl halide; tertiary halides eliminate.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (b) Diethyl ether

Explanation:
1. \( \ce{2C2H5Br + Ag2O -> C2H5OC2H5 + 2AgBr} \).

Teacher's Note:
1. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (d) Grignard reagent

Explanation:
1. An alpha-halo ether reacts with RMgX to replace the halogen by R.

Teacher's Note:
1. Ethers are cleaved by HI, form explosive peroxides in air, and act as Lewis bases forming etherates.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (a) 2-Methylpropan-2-ol

Explanation:
1. The acyl halide gives acetone and then a tertiary alcohol with the second equivalent of CH3MgI.

Teacher's Note:
1. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (d) Benzyl alcohol

Explanation:
1. Side-chain chlorination gives benzyl chloride, hydrolysed to benzyl alcohol.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (c) 2-Propanol and acetal

Explanation:
1. CH3CHO + CH3MgBr gives propan-2-ol; ethanal also reacts with ethanol/dry HCl to give the acetal.

Teacher's Note:
1. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (a) Ethylene glycol

Explanation:
1. Ethylene chlorohydrin, \( \ce{ClCH2CH2OH} \), formed with HOCl, is hydrolysed to ethylene glycol.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (b) \( \ce{(CH3)3CONa + CH3Cl} \)

Explanation:
1. Williamson synthesis needs the bulky group on the alkoxide and the methyl on the halide (SN2); tert-butyl chloride would eliminate instead.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction of an alkoxide with a primary alkyl halide; tertiary halides eliminate.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (b) \( \ce{NaBH4} \)

Explanation:
1. NaBH4 reduces only the C=O group.
2. \( \ce{H2/Ni} \) would also saturate the C=C bond and dichromate would oxidise the aldehyde.

Teacher's Note:
1. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (d) \( \ce{C6H5CH2OH} \)

Explanation:
1. Aliphatic primary amines (including benzylamine) give the alcohol with nitrous acid.

Teacher's Note:
1. Nitro groups at ortho and para positions increase the acidity of phenol, and ortho-nitrophenol is steam volatile.
2. Grignard reagent with HCHO gives primary, with other aldehydes secondary, with ketones and esters tertiary alcohols.

Answer: (b) Secondary or tertiary alcohol

Explanation:
1. Markovnikov addition always puts OH on the more substituted carbon.

Teacher's Note:
1. Remember the industrial routes: hydration of ethene, fermentation of sugars, water gas to methanol, cumene process for phenol.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (a) Phenolate ions and methyl iodide

Explanation:
1. Williamson synthesis: \( \ce{C6H5O- + CH3I} \)
2. Aryl halides do not react with alkoxides.

Teacher's Note:
1. Williamson synthesis is an SN2 reaction of an alkoxide with a primary alkyl halide; tertiary halides eliminate.
2. Williamson synthesis is an SN2 reaction: keep the bulky group on the alkoxide and use a primary alkyl halide.

Answer: (c) Methane

Explanation:
1. The acidic O-H protonates the Grignard reagent: \( \ce{CH3OH + CH3MgX -> CH4 + CH3OMgX} \).

Teacher's Note:
1. Grignard reagents add to carbonyl groups and are destroyed by water, alcohols and acids.
2. Dehydration and substitution with HX both go through carbocations, so 3 degree > 2 degree > 1 degree.

Answer: (a) More

Explanation:
1. Alcohols form strong O-H...O hydrogen bonds; S-H...S bonding in thiols is much weaker.

Teacher's Note:
1. Hydrogen bonding raises boiling point and solubility, while intramolecular bonding (o-nitrophenol) lowers boiling point.
2. Hydrogen bonding explains most physical trends: boiling point, solubility and volatility of ethers, ortho-nitrophenol.

Answer: (c) Sodium hydroxide and iodine

Explanation:
1. Ethanol gives yellow iodoform with \( \ce{I2/NaOH} \); methanol does not.

Teacher's Note:
1. The iodoform test is positive for ethanol, CH3CH(OH)R and CH3CO-; methanol and primary alcohols other than ethanol do not respond.
2. Learn the identification tests: Lucas, iodoform, FeCl3, Victor Meyer, Liebermann, bromine water.

Answer: (a) A primary alcohol

Explanation:
1. Propan-1-ol is oxidised through propanal to propanoic acid, \( \ce{C3H6O2} \).

Teacher's Note:
1. Dehydration and substitution with HX both go through carbocations, so 3 degree > 2 degree > 1 degree.
2. Compare acidity through the stability of the conjugate base: electron-withdrawing groups strengthen the acid, electron-donating groups weaken it.

Answer: (d) \( \ce{CH3CH(OH)CH2CH2CH3} \)

Explanation:
1. Pentan-2-ol is oxidised to pentan-2-one, which is cleaved at the CO-CH2 bond to give acetic and propanoic acids.

Teacher's Note:
1. Compare acidity through the stability of the conjugate base: electron-withdrawing groups strengthen the acid, electron-donating groups weaken it.
2. Hydrogen bonding explains most physical trends: boiling point, solubility and volatility of ethers, ortho-nitrophenol.