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ALCOHOLS, ETHERS AND PHENOLS, , , , , , 1. INTRODUCTION, , The compounds in which hydroxy! group (-OH) is attached to a, saturated carbon atom are called as Alcohols. The compounds in, which a hydroxyl group is attached to an unsaturated carbon, atom of a double bond are called as Enols, The saturated carbon, may be that of an alkyl, alkenyl, alkynyl, cycloalkyl or benzyl, group. However, if a hydroxyl group is attached to a benzene ring,, the compounds are called as Phenols., , The alcohols are further classified as : Monohydric (containing, one —OH group), Dihydric (containing two -OH groups) and, Trihydric (containing three -OH groups)., , , , Alcohols find usage in industry as well as day to day life. For, example, ordinary spirit used for polishing wooden furniture is, chiefly ethanol. Sugar, cotton, paper are all made up of compounds, containing -OH groups. Phenols are used in several important, polymers such as Bakelite and in several drugs such as Aspirin., , , , Ethers are commonly used as solvents and anaesthetics., , pa SS) era le) |, , , , , , CH,—OH Methanol, R—CH;—OH 1° Alcohol Primary, i, R—CH—OH 2° Alcohol Secondary, 3° Alcohol Tertiary, R—O—R Symmetrical Ether, R—O—R' Unsymmetrical Ether, , , , , , , , 3. STRUCTURES OF FUNCTIONAL GROUPS, , In alcohols, the oxygen of the -OH group is attached to carbon, by a sigma (6) bond formed by the overlap of a = hybridised, , , , ;, orbital of carbon with a sp’ hybridised orbital of oxygen. The, following figure depicts structural aspects of methanol, phenol, , and methoxymethane., , , , 142 pm 96 pm, , , , Bond angle is slightly, , , , HL less due to LP-LP repulsion., Lx 1ox9° H, H’ \, H, Methanol, , , , , , , , , , , , , , , , , , H, Lone pair of oxygen, is delocalised on ring, due to which C—O, 136 pm bond length is less,, Phenol, 141 pm ., Bond angle in methoxymethane, is more than tetrahedral angle, H H due to repulsive interaction, Nc nee co between the two bulky (R), aa TX groups. The C—O bond length, H H is same as inalc: ., H H is same as in alcohols., Methoxymethane, 4. PHYSICAL PROPERTIES, [4.1 Boiling Point >, , The boiling points of alcohols and phenols increase with increase, in the number of carbon atoms (increase in van der Waals forces)., In alcohols, the boiling point decreases with inc! in branching, (decrease in Van der Waals forces due to decrease in surface area)., , , , , , , , The -OH group in alcohols and phenols contains a hydrogen,, bonded to an electronegative oxygen atom, Therefore, iti able, of forming intermolecular hydrogen bond, strength of which is, even greater than amine., , , , , , , , H—O, “H—O, H-O, , , , , , , It is due to the presence of strong intermolecular hydrogen, bonding that alcohols and phenols have higher boiling points, corresponding to other classes of compounds, namely,, hydrocarbons, ethers and haloalkanes/haloarenes, amines of, , , , comparable molecular ma:, Their boiling points are lower than carboxylic acid which have, even more strong H-bond. For isomeric alcohols boiling points, decreases with increase in branching due to decrease in van der, Waals forces with decrease in size. The order of boiling point is, 1° alcohol > 2° alcohol > 3° alcohol.

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(d) Addition to an Acid Halide or an Ester - 3° Alcohol, , , , , , , , eT H oO, ll NaBH, ,, Ci ——+ ‘CH,OH, Oo 0, CH—C—Cl or CH,—C—OCH, Benzaldehyde Benzyl Alcohol, Ane aioites a 2. Reduction of a ketone gives a secondary alcohol, C»- Example - 13, (2 MgBr, Cyclohexylmagnesium Bromide O H, NaBH., 2), i ‘OH, OH Cyclohexanone Cyclohexanol, CH,—C 3. Reduction of an acid or ester gives a primary alcohol, enna e, O oO, 1, 1-Dicyclohexylethanol CH,—(CH,),—C—OH or CH,;—(CH;).—C—OCH,, Decanoie Acid Methyl! Decanoate, (e) Addition to Ethylene Oxide - 1° Alcohol (with two carbon ” as, atoms added) @H,9, Example - 11 CH,—(CH,),—CH,—OH, Decan-1-ol, MgBr//O. CH,CH,OH Reactions of LiAIH, and NaBH,, , (1) CH—CH,, , a ac ei Fe, Qn Presse] stracture NT LiAlH,, , Cyclohexy! Magnesium Bromide 2-Cyclohexylethanol 0, , 5.4 Carbonyl Compounds >, , ll, Aldehyde |R—C—H |{R—CH,—OH]|R—CH,—OH, , , , , , , , f pe ", 54-1 Catalytic Hydrogenation Ketone |R—C—R' |R—CH—R' | R—CH—R', 9 OH, ll Raney Ni , kere Ne” — =, —C— +H, > ~—cH— ene - x No Reaction | No Reaction, , , , This method is usually not as selective or as effective as the ri, use of hydride reagents. ll, Acid Anion|R—C—O> | No Reaction R—CH,—OH, , $.4.2 Reduction with Metal Hydrides > anion in base, ° R—CH,OH, , 1. Reduction of an aldehyde gives a primary alcohol Ester \| No Reaction +, R—C—OR' R'OH