Alcohols, Phenols and Ethers, Study notes of Chemistry

Download Alcohols, Phenols and Ethers and more Study notes Chemistry in PDF only on Docsity! After studying this Unit, you will be able to • name alcohols, phenols and ethers according to the IUPAC system of nomenclature; • discuss the reactions involved in the preparation of alcohols from alkenes, aldehydes, ketones and carboxylic acids; • discuss the reactions involved in the preparation of phenols from haloarenes, benzene sulphonic acids, diazonium salts and cumene; • discuss the reactions for preparation of ethers from (i) alcohols and (ii) alkyl halides and sodium alkoxides/aryloxides; • correlate physical properties of alcohols, phenols and ethers with their structures; • discuss chemical reactions of the three classes of compounds on the basis of their functional groups. Objectives Alcohols, phenols and ethers are the basic compounds for the formation of detergents, antiseptics and fragrances, respectively. 11 Unit Alcohols, Phenols and Ethers l l l You have learnt that substitution of one or more hydrogen atom(s) from a hydrocarbon by another atom or a group of atoms result in the formation of an entirely new compound having altogether different properties and applications. Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group. These classes of compounds find wide applications in industry as well as in day-to-day life. For instance, have you ever noticed that ordinary spirit used for polishing wooden furniture is chiefly a compound containing hydroxyl group, ethanol. The sugar we eat, the cotton used for fabrics, the paper we use for writing, are all made up of compounds containing –OH groups. Just think of life without paper; no note-books, books, news- papers, currency notes, cheques, certificates, etc. The magazines carrying beautiful photographs and interesting stories would disappear from our life. It would have been really a different world. An alcohol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s), of an aliphatic system (CH3OH) while a phenol contains –OH group(s) directly attached to carbon atom(s) of an aromatic system (C6H5OH). The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R–O/Ar–O) yields another class of compounds known as ‘ethers’, for example, CH3OCH3 (dimethyl ether). You may also visualise ethers as compounds formed by 2022-23 324Chemistry substituting the hydrogen atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group. In this unit, we shall discuss the chemistry of three classes of compounds, namely — alcohols, phenols and ethers. Monohydric alcohols may be further classified according to the hybridisation of the carbon atom to which the hydroxyl group is attached. (i) Compounds containing 3C OH− sp bond: In this class of alcohols, the –OH group is attached to an sp 3 hybridised carbon atom of an alkyl group. They are further classified as follows: Primary, secondary and tertiary alcohols: In these three types of alcohols, the –OH group is attached to primary, secondary and tertiary carbon atom, respectively as depicted below: Allylic alcohols: In these alcohols, the —OH group is attached to a sp 3 hybridised carbon adjacent to the carbon-carbon double bond, that is to an allylic carbon. For example Benzylic alcohols: In these alcohols, the —OH group is attached to a sp 3 —hybridised carbon atom next to an aromatic ring. For example. The classification of compounds makes their study systematic and hence simpler. Therefore, let us first learn how are alcohols, phenols and ethers classified? Alcohols and phenols may be classified as mono–, di–, tri- or polyhydric compounds depending on whether they contain one, two, three or many hydroxyl groups respectively in their structures as given below: 11.1 Classification 11.1.1 Alcohols— Mono, Di, Tri or Polyhydric alcohols Monohydric Dihydric Trihydric 2022-23 327 Alcohols, Phenols and Ethers Common name Phenol o-Cresol m-Cresol p-Cresol IUPAC name Phenol 2-Methylphenol 3-Methylphenol 4-Methylphenol Dihydroxy derivatives of benzene are known as 1, 2-, 1, 3- and 1, 4-benzenediol. OH CH3 OH CH3 OH CH3 OH OH OH OH OH OH OH Common name Catechol Benzene- diol1,2- Resorcinol Benzene- diol1,3- Hydroquinone or quinol Benzene- diol1,4-IUPAC name (c) Ethers: Common names of ethers are derived from the names of alkyl/ aryl groups written as separate words in alphabetical order and adding the word ‘ether’ at the end. For example, CH3OC2H5 is ethylmethyl ether. Table 11.2: Common and IUPAC Names of Some Ethers Compound Common name IUPAC name CH3OCH3 Dimethyl ether Methoxymethane C2H5OC2H5 Diethyl ether Ethoxyethane CH3OCH2CH2CH3 Methyl n-propyl ether 1-Methoxypropane C6H5OCH3 Methyl phenyl ether Methoxybenzene (Anisole) (Anisole) C6H5OCH2CH3 Ethyl phenyl ether Ethoxybenzene (Phenetole) C6H5O(CH2)6 – CH3 Heptyl phenyl ether 1-Phenoxyheptane CH3 CH O 3 CH CH3 Methyl isopropyl ether 2-Methoxypropane Phenyl isopentyl ether 3- Methylbutoxybenzene CH3– O – CH2 – CH2 – OCH3 — 1,2-Dimethoxyethane — 2-Ethoxy- -1,1-dimethylcyclohexane 2022-23 328Chemistry If both the alkyl groups are the same, the prefix ‘di’ is added before the alkyl group. For example, C2H5OC2H5 is diethyl ether. According to IUPAC system of nomenclature, ethers are regarded as hydrocarbon derivatives in which a hydrogen atom is replaced by an –OR or –OAr group, where R and Ar represent alkyl and aryl groups, respectively. The larger (R) group is chosen as the parent hydrocarbon. The names of a few ethers are given as examples in Table 11.2. (i) 4-Chloro-2,3-dimethylpentan-1-ol (ii) 2-Ethoxypropane (iii) 2,6-Dimethylphenol (iv) 1-Ethoxy-2-nitrocyclohexane NO2 OC H2 5 Example 11.1 Solution OH CH3 H3C (i) (iii) (ii) CH3 CH O CH2CH3 CH3 (ii)CH3 CH CH OH2 Cl CH CH CH3 CH3 (i) (iv) 11.3 Name the following compounds according to IUPAC system. Intext Question (i) (ii) (iii) (iv) (v) In alcohols, the oxygen of the –OH group is attached to carbon by a sigma (σ ) bond formed by the overlap of a sp 3 hybridised orbital of carbon with a sp 3 hybridised orbital of oxygen. Fig. 11.1 depicts structural aspects of methanol, phenol and methoxymethane. 1 1 .3 Structures of Functional Groups Fig. 11.1: Structures of methanol, phenol and methoxymethane Give IUPAC names of the following compounds: 2022-23 329 Alcohols, Phenols and Ethers The bond angle in alcohols is slightly less than the tetrahedral angle (109°-28′). It is due to the repulsion between the unshared electron pairs of oxygen. In phenols, the –OH group is attached to sp 2 hybridised carbon of an aromatic ring. The carbon– oxygen bond length (136 pm) in phenol is slightly less than that in methanol. This is due to (i) partial double bond character on account of the conjugation of unshared electron pair of oxygen with the aromatic ring (Section 11.4.4) and (ii) sp 2 hybridised state of carbon to which oxygen is attached. In ethers, the four electron pairs, i.e., the two bond pairs and two lone pairs of electrons on oxygen are arranged approximately in a tetrahedral arrangement. The bond angle is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky (–R) groups. The C–O bond length (141 pm) is almost the same as in alcohols. 11.4.1 Preparation of Alcohols Alcohols are prepared by the following methods: 1. From alkenes (i) By acid catalysed hydration: Alkenes react with water in the presence of acid as catalyst to form alcohols. In case of unsymmetrical alkenes, the addition reaction takes place in accordance with Markovnikov’s rule (Unit 13, Class XI). Mechanism The mechanism of the reaction involves the following three steps: Step 1: Protonation of alkene to form carbocation by electrophilic attack of H3O + . H2O + H + → H3O + Step 2: Nucleophilic attack of water on carbocation. Step 3: Deprotonation to form an alcohol. 1 1 .4 Alcohols and Phenols 2022-23 332Chemistry 1. From haloarenes Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced (Unit 10, Class XII). 2. From benzenesulphonic acid Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol. 3. From diazonium salts A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO2 + HCl) at 273-278 K. Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids (Unit 13, Class XII). H O OHNH2 NaNO2 +HCl Aniline N Cl2 2 N + HCl 2 + Benzene diazonium chloride Warm + – 4. From cumene Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide. It is converted to phenol and acetone by treating it with dilute acid. Acetone, a by-product of this reaction, is also obtained in large quantities by this method. Most of the worldwide production of phenol is from cumene. 2022-23 333 Alcohols, Phenols and Ethers Alcohols and phenols consist of two parts, an alkyl/aryl group and a hydroxyl group. The properties of alcohols and phenols are chiefly due to the hydroxyl group. The nature of alkyl and aryl groups simply modify these properties. Boiling Points 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 points decrease with increase of branching in carbon chain (because of decrease in van der Waals forces with decrease in surface area). The –OH group in alcohols and phenols is involved in intermolecular hydrogen bonding as shown below: It is interesting to note that boiling points of alcohols and phenols are higher in comparison to other classes of compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of comparable molecular masses. For example, ethanol and propane have comparable molecular masses but their boiling points differ widely. The boiling point of methoxymethane is intermediate of the two boiling points. 11.4.3 Physical Properties 11.4 Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanal ? 11.5 Write structures of the products of the following reactions: Intext Questions (ii) (iii) (i) 2022-23 334Chemistry The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding in them which is lacking in ethers and hydrocarbons. Solubility Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecules as shown. The solubility decreases with increase in size of alkyl/aryl (hydro- phobic) groups. Several of the lower molecular mass alcohols are miscible with water in all proportions. Arrange the following sets of compounds in order of their increasing boiling points: (a) Pentan-1-ol, butan-1-ol, butan-2-ol, ethanol, propan-1-ol, methanol. (b) Pentan-1-ol, n-butane, pentanal, ethoxyethane. (a) Methanol, ethanol, propan-1-ol, butan-2-ol, butan-1-ol, pentan-1-ol. (b) n-Butane, ethoxyethane, pentanal and pentan-1-ol. Example 11.3 Solution Alcohols are versatile compounds. They react both as nucleophiles and electrophiles. The bond between O–H is broken when alcohols react as nucleophiles. 11.4.4 Chemical Reactions Alcohols as nucleophiles (i) (ii) The bond between C–O is broken when they react as electrophiles. Protonated alcohols react in this manner. Protonated alcohols as electrophiles Based on the cleavage of O–H and C–O bonds, the reactions of alcohols and phenols may be divided into two groups: 2022-23 337 Alcohols, Phenols and Ethers phenoxide ion more stable and favours the ionisation of phenol. Although there is also charge delocalisation in phenol, its resonance structures have charge separation due to which the phenol molecule is less stable than phenoxide ion. o-Nitrophenol o–O2N–C6H4–OH 7.2 m-Nitrophenol m–O2N–C6H4–OH 8.3 p-Nitrophenol p-O2N–C6H4–OH 7.1 Phenol C6H5–OH 10.0 o-Cresol o-CH3–C6H4–OH 10.2 m-Cresol m-CH3C6H4–OH 10.1 p-Cresol p-CH3–C6H4–OH 10.2 Ethanol C2H5OH 15.9 Table 11.3: pKa Values of some Phenols and Ethanol Compound Formula pKa From the above data, you will note that phenol is million times more acidic than ethanol. Arrange the following compounds in increasing order of their acid strength: Propan-1-ol, 2,4,6-trinitrophenol, 3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol. Propan-1-ol, 4-methylphenol, phenol, 3-nitrophenol, 3,5-dinitrophenol, 2,4, 6-trinitrophenol. Example 11.4 Solution 2. Esterification Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters. In substituted phenols, the presence of electron withdrawing groups such as nitro group, enhances the acidic strength of phenol. This effect is more pronounced when such a group is present at ortho and para positions. It is due to the effective delocalisation of negative charge in phenoxide ion when substituent is at ortho or para position. On the other hand, electron releasing groups, such as alkyl groups, in general, do not favour the formation of phenoxide ion resulting in decrease in acid strength. Cresols, for example, are less acidic than phenol. The greater the pKa value, the weaker the acid. 2022-23 338Chemistry Pyridine R/Ar +R’ lOH COC R/ArOCOR + HCl’ The reaction with carboxylic acid and acid anhydride is carried out in the presence of a small amount of concentrated sulphuric acid. The reaction is reversible, and therefore, water is removed as soon as it is formed. The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to neutralise HCl which is formed during the reaction. It shifts the equilibrium to the right hand side. The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin. (b) Reactions involving cleavage of carbon – oxygen (C–O) bond in alcohols The reactions involving cleavage of C–O bond take place only in alcohols. Phenols show this type of reaction only with zinc. 1. Reaction with hydrogen halides: Alcohols react with hydrogen halides to form alkyl halides (Refer Unit 10, Class XII). ROH + HX → R–X + H2O The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another (Lucas test). Alcohols are soluble in Lucas reagent (conc. HCl and ZnCl2) while their halides are immiscible and produce turbidity in solution. In case of tertiary alcohols, turbidity is produced immediately as they form the halides easily. Primary alcohols do not produce turbidity at room temperature. 2. Reaction with phosphorus trihalides: Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide (Refer Unit 10, Class XII). 3. Dehydration: Alcohols undergo dehydration (removal of a molecule of water) to form alkenes on treating with a protic acid e.g., concentrated H2SO4 or H3PO4, or catalysts such as anhydrous zinc chloride or alumina (Unit 13, Class XI). Ethanol undergoes dehydration by heating it with concentrated H2SO4 at 443 K. Aspirin possesses analgesic, anti- inflammatory and antipyretic properties. 2022-23 339 Alcohols, Phenols and Ethers Secondary and tertiary alcohols are dehydrated under milder conditions. For example Thus, the relative ease of dehydration of alcohols follows the following order: Tertiary Secondary Primary>> The mechanism of dehydration of ethanol involves the following steps: Mechanism Step 1: Formation of protonated alcohol. Step 2: Formation of carbocation: It is the slowest step and hence, the rate determining step of the reaction. Step 3: Formation of ethene by elimination of a proton. The acid used in step 1 is released in step 3. To drive the equilibrium to the right, ethene is removed as it is formed. 4. Oxidation: Oxidation of alcohols involves the formation of a carbon- oxygen double bond with cleavage of an O-H and C-H bonds. Such a cleavage and formation of bonds occur in oxidation reactions. These are also known as dehydrogenation reactions as these involve loss of dihydrogen from an alcohol molecule. Depending on the oxidising agent used, a primary alcohol is oxidised to an aldehyde which in turn is oxidised to a carboxylic acid. Tertiary carbocations are more stable and therefore are easier to form than secondary and primary carbocations; tertiary alcohols are the easiest to dehydrate. 2022-23 342Chemistry (ii) Halogenation: On treating phenol with bromine, different reaction products are formed under different experimental conditions. (a) When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2 and at low temperature, monobromophenols are formed. The usual halogenation of benzene takes place in the presence of a Lewis acid, such as FeBr3 (Unit 10, Class XII), which polarises the halogen molecule. In case of phenol, the polarisation of bromine molecule takes place even in the absence of Lewis acid. It is due to the highly activating effect of –OH group attached to the benzene ring. (b) When phenol is treated with bromine water, 2,4,6-tribromophenol is formed as white precipitate. Write the structures of the major products expected from the following reactions: (a) Mononitration of 3-methylphenol (b) Dinitration of 3-methylphenol (c) Mononitration of phenyl methanoate. The combined influence of –OH and –CH3 groups determine the position of the incoming group. Example 11.5 Solution 2. Kolbe’s reaction Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product. 2022-23 343 Alcohols, Phenols and Ethers 3. Reimer-Tiemann reaction On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of alkali to produce salicylaldehyde. 4. Reaction of phenol with zinc dust Phenol is converted to benzene on heating with zinc dust. 5. Oxidation Oxidation of phenol with chromic acid produces a conjugated diketone known as benzoquinone. In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing quinones. 11.6 Give structures of the products you would expect when each of the following alcohol reacts with (a) HCl –ZnCl2 (b) HBr and (c) SOCl2. (i) Butan-1-ol (ii) 2-Methylbutan-2-ol 11.7 Predict the major product of acid catalysed dehydration of (i) 1-methylcyclohexanol and (ii) butan-1-ol 11.8 Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions. 11.9 Write the equations involved in the following reactions: (i) Reimer - Tiemann reaction (ii) Kolbe’s reaction Intext Questions 2022-23 344Chemistry Methanol and ethanol are among the two commercially important alcohols. 1. Methanol Methanol, CH3OH, also known as ‘wood spirit’, was produced by destructive distillation of wood. Today, most of the methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of ZnO – Cr2O3 catalyst. Methanol is a colourless liquid and boils at 337 K. It is highly poisonous in nature. Ingestion of even small quantities of methanol can cause blindness and large quantities causes even death. Methanol is used as a solvent in paints, varnishes and chiefly for making formaldehyde. 2. Ethanol Ethanol, C2H5OH, is obtained commercially by fermentation, the oldest method is from sugars. The sugar in molasses, sugarcane or fruits such as grapes is converted to glucose and fructose, (both of which have the formula C6H12O6), in the presence of an enzyme, invertase. Glucose and fructose undergo fermentation in the presence of another enzyme, zymase, which is found in yeast. In wine making, grapes are the source of sugars and yeast. As grapes ripen, the quantity of sugar increases and yeast grows on the outer skin. When grapes are crushed, sugar and the enzyme come in contact and fermentation starts. Fermentation takes place in anaerobic conditions i.e. in absence of air. Carbon dioxide is released during fermentation. The action of zymase is inhibited once the percentage of alcohol formed exceeds 14 percent. If air gets into fermentation mixture, the oxygen of air oxidises ethanol to ethanoic acid which in turn destroys the taste of alcoholic drinks. Ethanol is a colourless liquid with boiling point 351 K. It is used as a solvent in paint industry and in the preparation of a number of carbon compounds. The commercial alcohol is made unfit for drinking by mixing in it some copper sulphate (to give it a colour) and pyridine (a foul smelling liquid). It is known as denaturation of alcohol. Nowadays, large quantities of ethanol are obtained by hydration of ethene (Section 11.4). 1 1 .5 Some Commercially Important Alcohols Ingestion of ethanol acts on the central nervous system. In moderate amounts, it affects judgment and lowers inhibitions. Higher concentrations cause nausea and loss of consciousness. Even at higher concentrations, it interferes with spontaneous respiration and can be fatal. 2022-23 347 Alcohols, Phenols and Ethers The C-O bonds in ethers are polar and thus, ethers have a net dipole moment. The weak polarity of ethers do not appreciably affect their boiling points which are comparable to those of the alkanes of comparable molecular masses but are much lower than the boiling points of alcohols as shown in the following cases: Formula CH3(CH2)3CH3 C2H5-O-C2H5 CH3(CH2)3-OH n-Pentane Ethoxyethane Butan-1-ol b.p./K 309.1 307.6 390 The large difference in boiling points of alcohols and ethers is due to the presence of hydrogen bonding in alcohols. The miscibility of ethers with water resembles those of alcohols of the same molecular mass. Both ethoxyethane and butan-1-ol are miscible to almost the same extent i.e., 7.5 and 9 g per 100 mL water, respectively while pentane is essentially immiscible with water. Can you explain this observation ? This is due to the fact that just like alcohols, oxygen of ether can also form hydrogen bonds with water molecule as shown: 1. Cleavage of C–O bond in ethers Ethers are the least reactive of the functional groups. The cleavage of C-O bond in ethers takes place under drastic conditions with excess of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules. Alkyl aryl ethers are cleaved at the alkyl-oxygen bond due to the more stable aryl-oxygen bond. The reaction yields phenol and alkyl halide. Ethers with two different alkyl groups are also cleaved in the same manner. The order of reactivity of hydrogen halides is as follows: HI > HBr > HCl. The cleavage of ethers takes place with concentrated HI or HBr at high temperature. 11.6.2 Physical Properties 11.6.3 Chemical Reactions 2022-23 348Chemistry The reaction of an ether with concentrated HI starts with protonation of ether molecule. Step 1: The reaction takes place with HBr or HI because these reagents are sufficiently acidic. Step 2: Iodide is a good nucleophile. It attacks the least substituted carbon of the oxonium ion formed in step 1 and displaces an alcohol molecule by SN2 mechanism. Thus, in the cleavage of mixed ethers with two different alkyl groups, the alcohol and alkyl iodide formed, depend on the nature of alkyl groups. When primary or secondary alkyl groups are present, it is the lower alkyl group that forms alkyl iodide (SN2 reaction). When HI is in excess and the reaction is carried out at high temperature, ethanol reacts with another molecule of HI and is converted to ethyl iodide. Step 3: Mechanism However, when one of the alkyl group is a tertiary group, the halide formed is a tertiary halide. CH C CH +HI CH OH +CH C I3 3 3 3 CH3 CH3 CH3 CH3 O It is because in step 2 of the reaction, the departure of leaving group (HO–CH3) creates a more stable carbocation [(CH3)3C + ], and the reaction follows SN1 mechanism. In case of anisole, methylphenyl oxonium ion, is formed by protonation of ether. The bond between O–CH3 is weaker than the bond between O–C6H5 because the carbon of phenyl group is sp 2 hybridised and there is a partial double bond character. CH3 C CH3 CH3 O H + CH3 slow CH3 C CH3 CH3 + + CH OH3 fast CH3 C CH3 CH3 CH3 C CH3 CH3 + + I – I 2022-23 349 Alcohols, Phenols and Ethers Therefore the attack by I – ion breaks O–CH3 bond to form CH3I. Phenols do not react further to give halides because the sp 2 hybridised carbon of phenol cannot undergo nucleophilic substitution reaction needed for conversion to the halide. Give the major products that are formed by heating each of the following ethers with HI. Example 11.7 Solution (iii) (i) (ii) (iii) (i) (ii) 2. Electrophilic substitution The alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards electrophilic substitution in the same way as in phenol. (i) Halogenation: Phenylalkyl ethers undergo usual halogenation in the benzene ring, e.g., anisole undergoes bromination with bromine in ethanoic acid even in the absence of iron (III) bromide catalyst. It is due to the activation of benzene ring by the methoxy group. Para isomer is obtained in 90% yield. 2022-23 352Chemistry Exercises 11.1 Write IUPAC names of the following compounds: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) C 6 H 5 –O–C 2 H 5 (xi) C 6 H 5 –O–C 7 H 15 (n–) (xii) 11.2 Write structures of the compounds whose IUPAC names are as follows: (i) 2-Methylbutan-2-ol (ii) 1-Phenylpropan-2-ol (iii) 3,5-Dimethylhexane –1, 3, 5-triol (iv) 2,3 – Diethylphenol (v) 1 – Ethoxypropane (vi) 2-Ethoxy-3-methylpentane (vii) Cyclohexylmethanol (viii) 3-Cyclohexylpentan-3-ol (ix) Cyclopent-3-en-1-ol (x) 4-Chloro-3-ethylbutan-1-ol. 11.3 (i) Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their IUPAC names. (ii) Classify the isomers of alcohols in question 11.3 (i) as primary, secondary and tertiary alcohols. 11.4 Explain why propanol has higher boiling point than that of the hydrocarbon, butane? 11.5 Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact. 11.6 What is meant by hydroboration-oxidation reaction? Illustrate it with an example. 11.7 Give the structures and IUPAC names of monohydric phenols of molecular formula, C7H8O. 11.8 While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason. 11.9 Give the equations of reactions for the preparation of phenol from cumene. 11.10 Write chemical reaction for the preparation of phenol from chlorobenzene. 11.11 Write the mechanism of hydration of ethene to yield ethanol. 11.12 You are given benzene, conc. H2SO4 and NaOH. Write the equations for the preparation of phenol using these reagents. 2022-23 353 Alcohols, Phenols and Ethers 11.13 Show how will you synthesise: (i) 1-phenylethanol from a suitable alkene. (ii) cyclohexylmethanol using an alkyl halide by an SN2 reaction. (iii) pentan-1-ol using a suitable alkyl halide? 11.14 Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol. 11.15 Explain why is ortho nitrophenol more acidic than ortho methoxyphenol ? 11.16 Explain how does the –OH group attached to a carbon of benzene ring activate it towards electrophilic substitution? 11.17 Give equations of the following reactions: (i) Oxidation of propan-1-ol with alkaline KMnO4 solution. (ii) Bromine in CS2 with phenol. (iii) Dilute HNO3 with phenol. (iv) Treating phenol wih chloroform in presence of aqueous NaOH. 11.18 Explain the following with an example. (i) Kolbe’s reaction. (ii) Reimer-Tiemann reaction. (iii) Williamson ether synthesis. (iv) Unsymmetrical ether. 11.19 Write the mechanism of acid dehydration of ethanol to yield ethene. 11.20 How are the following conversions carried out? (i) Propene → Propan-2-ol. (ii) Benzyl chloride → Benzyl alcohol. (iii) Ethyl magnesium chloride → Propan-1-ol. (iv) Methyl magnesium bromide → 2-Methylpropan-2-ol. 11.21 Name the reagents used in the following reactions: (i) Oxidation of a primary alcohol to carboxylic acid. (ii) Oxidation of a primary alcohol to aldehyde. (iii) Bromination of phenol to 2,4,6-tribromophenol. (iv) Benzyl alcohol to benzoic acid. (v) Dehydration of propan-2-ol to propene. (vi) Butan-2-one to butan-2-ol. 11.22 Give reason for the higher boiling point of ethanol in comparison to methoxymethane. 2022-23 354Chemistry 11.23 Give IUPAC names of the following ethers: 11.24 Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: (i) 1-Propoxypropane (ii) Ethoxybenzene (iii) 2-Methoxy-2-methylpropane (iv) 1-Methoxyethane 11.25 Illustrate with examples the limitations of Williamson synthesis for the preparation of certain types of ethers. 11.26 How is 1-propoxypropane synthesised from propan-1-ol? Write mechanism of this reaction. 11.27 Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason. 11.28 Write the equation of the reaction of hydrogen iodide with: (i) 1-propoxypropane (ii) methoxybenzene and (iii) benzyl ethyl ether. 11.29 Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and (ii) it directs the incoming substituents to ortho and para positions in benzene ring. 11.30 Write the mechanism of the reaction of HI with methoxymethane. 11.31 Write equations of the following reactions: (i) Friedel-Crafts reaction – alkylation of anisole. (ii) Nitration of anisole. (iii) Bromination of anisole in ethanoic acid medium. (iv) Friedel-Craft’s acetylation of anisole. 11.32 Show how would you synthesise the following alcohols from appropriate alkenes? CH3 OH OH OH OH (i) (ii) (iii) (iv) 11.33 When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place: Give a mechanism for this reaction. (Hint : The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom. 2022-23