Title ALCOHOLS, PHENOLS & ETHERS.pdf ✅

 Digital www.allendigital.in [ 55 ] Alcohols and Phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group. Classification of Alcohols and Phenols Alcohols and Phenols may be classified as mono, di, tri or polyhydric depending on whether they contain one, two, three or more hydroxyl groups respectively in their structures. C2H5OH Ethanol (Monohydric) H2C—OH Ethane-1,2-diol (Dihydric) H2C—OH H2C—OH HC—OH H2C—OH OH OH Propane-1,2,3-triol (Trihydric) Benzene-1,3-diol (Dihydric) Monohydric alcohols can be further classified according to the hybridisation of the carbon atom to which the hydroxyl group is attached. (A) Compounds containing sp3 C–OH bond : (a) Primary, secondary and tertiary alcohols In these three types of alcohols, the –OH group is attached to primary, secondary and tertiary carbon atom, respectively. CH3—CH2—OH Primary (1°) alcohol OH Secondary (2°) alcohol H3C—CH—CH3 OH CH3 H3C—C—OH CH3 Secondary (2°) alcohol Tertiary (3°) alcohol (b) Allylic alcohols These are the compounds in which the – OH group is bonded to a sp3 hybridised carbon atom next to carbon-carbon double bond. H2C=CH—CH2—OH OH (c) Benzylic alcohols These are the compounds in which the –OH group is bonded to an sp3 hybridised carbon atom next to an aromatic ring. CH2—OH C—OH R' R 03 Alcohols, Phenols and Ethers
NEET : Chemistry [ 56 ] www.allendigital.in  Digital (B) Compounds containing sp2 C–OH bond : Vinylic alcohols These are the compounds in which the –OH group is bonded to sp2 hybridised carbon atom of a carbon-carbon double bond. H2C=CH—OH OH 1. Which of the following is an allylic alcohol? (1) CH2=CHCH2OCH3 (2) HOCH=CHCH2CH3 (3) CH3CH=CHCH2OH (4) CH2=CHCH2CH2OH 2. Identify which of the following compound is 2° alcohol ? (1) OH (2) OH (3) OH (4) OH 3. Identify 2° alcohol among the following alcohols : (1) HO (2) OH (3) OH (4) OH 4. Cyclohexanol is a (1) Primary alcohol (2) Secondary alcohol (3) Tertiary alcohol (4) Phenol Methods of Preparation of Alcohols (1) From alkenes : (a) By acidic hydration R—CH=CH2 +H2O R—CH—CH2 H OH H (b) By hydroboration oxidation R—CH=CH2 R—CH—CH2 (i) BH3/THF H OH (ii) H2O2/OH (c) By oxymercuration demercuration R—CH=CH2 R—CH—CH2 (i) Hg(OAc)2, H2O OH H (ii) NaBH4 / OH BEGINNER’S BOX-1
Alcohols, Phenols and Ethers  Digital www.allendigital.in [ 57 ] (2) By reaction of Grignard reagent with aldehydes and ketones : (3) By reduction using LiAlH4, NaBH4 and H2/metal catalyst : LiAlH4 / Lithium Aluminium Hydride (LAH): It reduces all functional groups containing polar  bonds. LAH reacts explosively with water and alcohols liberating hydrogen gas. Ether is commonly used as solvent for LAH reductions. NaBH4 / Sodium Borohydride: It reduces only 4 functional groups R—C—H/R O Aldehyde / Ketone R—C—X O Acid halide R—CH=NH Imine Sodium borohydride can be used in water as well as alcohol solvents H2 / metal catalyst It reduces all polar as well as non-polar  bond containing functional groups except carboxylic acid. (1) R—C—R' NaBH4 O R—CH—R' OH (2) R—C—H H2 O R—CH2—OH Pd (3) R—C—OH (i) LiAlH4 O R—CH2—OH (ii) H2O (4) R—C—OR' O LiAlH4 R—CH2—OH + R'—OH H2 Pd H—C—H CH3 (ii) H / H2O CH3—MgBr + H—C—H O OH 1° Alcohol H3C—C—H CH3 (ii) H / H2O CH3—MgBr + CH3—C—H O OH 2° Alcohol H3C—C—CH3 CH3 (ii) H / H2O CH3—MgBr + H3C—C—CH3 O OH 3° Alcohol
NEET : Chemistry [ 58 ] www.allendigital.in  Digital Methods of Preparation of Phenols 1. From haloarenes : (i) 623 K, 300 atm Cl + NaOH (ii) H OH (Dow's Process) ONa Sodium phenoxide (ii) H 2. From benzene sulphonic acid : Oleum OH (ii) H SO3H (i) NaOH (350°C) 3. From cumene (Industrial preparation of phenol) : O2 OH (ii) H / H2O CH H3C CH3 H3C—C—O—O—H CH3 H3C—C—CH3 O + Cumene Acetone hydroperoxide Cumene (Isopropyl benzene) Phenol 4. From diazonium salts : NaNO2 + NH2 OH H2O Aniline HCl (0-5)oC N2Cl Benene diazonium chloride Warm + N2 + HCl 1. When acetone reacts with Grignard reagent followed by hydrolysis, it gives : (1) 1°–alcohol (2) 2°–alcohol (3) 3°–alcohol (4) Methyl alcohol 2. For the reduction of aldehydes and ketones into alcohol the reagent which can be used is/are : (1) H2 in presence of Ni, Pt or Pd (2) NaBH4 (3) LiAlH4 (4) All of these 3. Which of the following compound when reacts with CH3Mg Br formation of 3° alcohol take place? (1) H—C—H O (2) CH3—C—H O (3) CH3—C—CH3 O (4) –C–H O BEGINNER’S BOX-2