Physical properties of aldehydes And Ketones

Transcription

1 Unit-12. Aldehydes, Ketones & Carboxylic Acids Topic Aldehydes & Ketones The functional unit >C=O, present in the organic compounds, is called carbonyl group. Although Class XII Chemistry a large variety of organic compounds containing a carbonyl group is possible, we shall limit our study to those compounds in which an acyl group (R C=O) is bonded to hydrogen, carbon, oxygen, halogens and nitrogen. These compounds are known as carbonyl compounds and are grouped into families of aldehydes, ketones, carboxylic acids and their derivatives. The functional derivatives of carboxylic acids are further subdivided into families of esters, acyl (or acid) halides, acid anhydrides and amides. Physical properties of aldehydes And Ketones Except formaldehyde (a gas) the other lower members of aldehydes and ketones are volatile liquids and the higher members are waxy solids. Ketones have pleasant odour. They have boiling points higher than hydrocarbons (polar nature of carbonyl group) and lower than alcohols (absence of OH group). Solubility of carbonyl compounds decreases with the increase in their molecular masses. Because with the increase in the length of carbon chain the capacity of the carbonyl group to form hydrogen bonds with water decreases. Methanal is a gas at room temperature. Ethanal is a volatile liquid. Other aldehydes and ketones are liquid or solid at room temperature. The boiling points of aldehydes and ketones are higher than hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipoledipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding. This is clear by comparing the boiling points of the following compounds: n-pentane Ethoxyethane Butanal Butan-2-one Butan-1-ol b.p.(k) Mol. mass The lower members of aldehydes and ketones such as methanal, ethanal and propanone are miscible with water in all proportions, because they form hydrogen bond with water. However, the solubility of aldehydes and ketones decreases rapidly on increasing the length of alkyl chain. All aldehydes and ketones are fairly soluble in organic solvents like benzene, ether, methanol, chloroform, etc. The lower aldehydes have sharp pungent odours. As the size of the molecule increases, the odour becomes less pungent and more fragrant. In fact, many naturally occurring aldehydes and ketones are used in the blending of perfumes and flavouring agents.

2 Some Commercially Important Aldehydes and Ketones Uses of Aldehydes : (a) 40% aqueous solution of formaldehyde is known as formalin and is used as a preservative for biological specimens and in leather tanning. (b) A condensation product with ammonia, known as urotropine is used in medicine for urinary infection. (c) In the process of Vat dyeing to decolourise vat dyes by reduction. (d) In the manufacture of polymeric resin called Bakelite (a condensation polymer with phenol). (i) Methanal (Formaldehyde, HCHO): It is manufactured by air oxidation or dehydrogenation of methanol in the presence of heated metallic copper or silver catalyst or by oxidation of methane with air in the presence of various metallic oxide catalysts. Methanal is a colourless, pungent smelling gas, bp 252 K and readily forms a trimer (metaformaldehyde or trioxane) and a polymer (paraformaldehyde). Metaformaldehyde and paraformaldehyde give formaldehyde on heating. Methanal is extremely soluble in water and is available as its 40% aqueous solution called formalin. Formalin is a disinfectant and a preservative for biological samples. Methanal finds use in the manufacture of bakelite, resins and other polymers. (ii) Ethanal (Acetaldehyde, CH 3 CHO): It is manufactured by passing a mixture of ethene and oxygen under pressure into an aqueous solution of palladium chloride and cupric chloride catalysts (Wacker s process). Wacker s process has almost replaced the earlier method involving hydration of ethyne. Ethanal is a colourless, pungent smelling, water miscible, volatile liquid, bp 294 K. It forms a trimer (paraldehyde and a tetramer (metaldehyde). Paraldehyde is a pleasant smelling liquid bp 401K. It is used as a hypnotic. Metaldehyde is a white solid mp 519 K. Both paraldehyde and metaldehyde generate ethanal on distillation with dilute H 2 SO 4. Acetaldehyde is used in the manufacture of organic compounds such as chloroform, acetic acid, ethanol, lactic acid, acetic acid, ethyl acetate, vinyl acetate, etc. For silvering of mirror. (iii) Benzaldehyde (C 6 H 5 CHO): It is obtained commercially by side chain chlorination of toluene followed by hydrolysis. Benzaldehyde is a colourless liquid, bp 452 K which smells like bitter almonds. It is used in perfumery, flavouring agent and dye industry. In the preparation of cinnamaldehyde, cinnamic acid and mandelic acid. Benzoin prepared from benzaldehyde is used as tincture benzoin in medicine for throat infection. With phenols and aromatic tertiary amines, it forms triphenyl methane dyes. (iv) Propanone (Acetone, CH 3 COCH 3 ): It is produced industrially from propan-2-ol either by oxidation with air in the presence of silver or by dehydrogenation over Cu or ZnO catalyst. It is also prepared from propene by Wacker s process (see ethanal). It is also obtained as a byproduct in the manufacture of phenol from cumene. Acetone is a colourless, pleasant smelling, water miscible liquid, bp 329 K. It is used as a solvent for paints, lacquers, cellulose acetate, etc. It is also used in organic synthesis.

3 Topic CARBOXYLIC ACIDS Carbon compounds containing a carboxyl functional group, -COOH, are called carboxylic acids. The carboxyl group consists of a carbonyl group attached to a hydroxyl group, hence its name carboxyl. Carboxylic acids may be aliphatic (RCOOH) or aromatic (ArCOOH) depending on the group, alkyl or aryl, attached to the carboxyl group. Carboxylic acids occupy a central place amongst compounds containing a carbonyl group. A great number of carboxylic acids are found in nature. Some higher members of aliphatic carboxylic acids (C 12 - C 18 ) occur in natural fats as esters of glycerol. Therefore, these are known as fatty acids. Carboxylic acids are not only important as such, but they also serve as starting materials for preparing several other important compounds such as esters, acid chlorides and amides. Physical Properties Aliphatic carboxylic acids upto nine carbon atoms are colourless liquids at room temperature with unpleasant odours. The higher acids are wax like solids and are practically odourless due to their low volatility. Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding. The hydrogen bonds are not broken completely even in the vapour phase. In fact, most carboxylic acids exist as dimer in the vapour phase or in the aprotic solvents. Simple aliphatic carboxylic acids having upto four carbon atoms are miscible in water due to the formation of hydrogen bonds with water. The solubility decreases with increasing number of carbon atoms. Higher carboxylic acids are practically insoluble in water due to the increased hydrophobic interaction of hydrocarbon part. Benzoic acid, the simplest aromatic carboxylic acid is nearly insoluble in cold water. Carboxylic acids are also soluble in less polar organic solvents like benzene, ether, alcohol, chloroform, etc. Some Commercially Important Carboxylic acids (i) Methanoic acid (Formic acid, HCOOH): It occurs in a variety of biting and stinging plants and insects. It is manufactured by the reaction of carbon monoxide with sodium hydroxide under pressure at 473 K. The resultant sodium methanoate is acidified and distilled to give the acid. Methanoic acid is a colourless, pungent smelling liquid with bp K. Due to the presence of aldehyde-like hydrogen, it is a powerful reducing agent. It reduces Tollens reagent and Fehling solution. It is used in rubber, textile, dyeing, leather and electroplating industries. (ii) Ethanoic acid(ii) Ethanoic acid (Acetic acid, CH 3 COOH): It is the main constituent of vinegar and is obtained by fermentation of molasses in the presence of air. Industrially, however, it is obtained in pure form by oxidation of ethanal with air in the presence of cobalt acetate catalyst or by carbonylation of methanol in the presence of rhodium catalyst. Ethanoic acid is a colourless liquid with pungent odour, bp 391 K.

4 It freezes at unusually high temperature (mp 289 K) forming ice like crystals. For this reason, water free ethanoic acid, obtained by melting of the crystals is called glacial acetic acid. It is used in the manufacture of rayon, and in plastic, rubber and silk industries. It is also used as a solvent. Vinegar is used in food industry. Some More Points to remember Benzoic acid and 1,2-and 1,4- benzenedicarboxylic acids are obtained by oxidation of toluene and 1,2- and 1,4- dimethylbenzenes, respectively, in air in the presence of various catalysts. These are colourless solids. Esters of benzoic acid are used in perfumery. Sodium benzoate is used as a food preservative. 1,2-Benzenedicarboxylic acid (phthalic acid) is used in the manufacture of plasticizers and resins. Methanoic acid is used in rubber, textile, dyeing, leather and electroplating industries. Ehanoic acid is used as solvent and as vinegar in food industry. Hexanedioic acid is used in the manufacture of nylon-6, 6. Higher fatty acids are used for the manufacture of soaps and detergents. 1,4-Benzenedicarboxylic acid (terephthalic acid) is a basic raw material for polyester. Being polar in nature, the acid derivatives have higher boiling points than hydrocarbons of comparable molecular masses. Acid chlorides, anhydrides and esters have nearly the same boiling points as the aldehydes and ketones of comparable molecular masses. Their boiling points are however, lower than that of the carboxylic acids of similar molecular masses, apparently due to the absence of hydrogen bonding in acid derivatives. Primary amides have quite high melting points and boiling points because they form strong intermolecular hydrogen bonds, as shown below. Esters and amides of low molecular masses are fairly soluble in water due to formation of hydrogen bonds with water. The solubility in water decreases with increasing molecular mass and becomes negligible for compounds containing more than six carbon atoms. All the acid derivatives are soluble in usual organic solvents. Volatile esters have pleasant fruity smell. Acyl halides and anhydrides have sharp irritating odours and are lachrymatory (tear producing). Aldehydes, ketones and carboxylic acids are widespread in plants and animal kingdom. They play an important role in biochemical processes of life. They add fragrance and flavour to nature, for example, vanillin (from vanilla beans), salicylaldehyde (from meadow sweet) and cinnamaldehyde (from cinnamon) have very pleasant fragrances. Acid halides and anhydrides do not occur in nature due to their high reactivity. In contrast, other carbonyl compounds are widespread in plants and animals. They play important roles in biochemical processes to sustain life. They add fragrance and flavour to the Nature and constitute several pharmaceuticals. Some members of these families are manufactured in large quantities for use as solvents, For producing materials like adhesives, paints, resins, perfumes, plastics, fabrics, etc. From synthesis viewpoint, they are the most important compounds.

5 Unit-12. Aldehydes, Ketones & Carboxylic Acids Topic Aldehydes & Ketones Work Sheet ( WS 12. 1) Name -. Class/ sec.. Roll No.. Class XII Chemistry A. Fill in the blanks: 1. The carbonyl carbon atom is hybridised and forms sigma (σ)bonds. 2. The carbon-oxygen double bond is polarised due to electronegativity of oxygen relative to carbon. 3. Aldehydes and ketones are generally prepared by of primary and secondary alcohols, respectively. 4. Ozonolysis of followed by reaction with zinc dust and water gives aldehydes. 5. Addition of water to in the presence of H2SO4 and HgSO4 gives acetaldehyde. 6. Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called reduction. 7. are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde. 8. Nitriles are selectively reduced by diisobutylaluminium hydride, (DIBAL-H) to imines followed by hydrolysis to. 9. Strong oxidising agents oxidise toluene and its derivatives to. 10. Chromyl chloride oxidizes methyl group of toluene to a chromium complex, which on hydrolysis gives corresponding. 11. Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in anhydride. The benzylidene diacetate can be hydrolysed to corresponding with aqueous acid. 12. Side chain chlorination of toluene gives benzal chloride, which on gives benzaldehyde. 13. Treatment of acyl chlorides with dialkylcadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives. 14. Treating a with Grignard reagent followed by hydrolysis yields a ketone. 15. The boiling points of aldehydes and ketones are than hydrocarbons and ethers of comparable molecular masses. 16. Aldehydes are generally reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. 17. Electronically, aldehydes are reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl effectively than in former. 18. The carbon atom of the carbonyl group of benzaldehyde is electrophilic than carbon atom of the carbonyl group present in propanal. 19. Aldehydes and ketones react with hydrogen cyanide (HCN) to yield. 20. Aldehydes and ketones are reduced to and alcohols respectively by sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4) as well as by catalytic hydrogenation

6 Class XII Chemistry Unit-12. Aldehydes, Ketones & Carboxylic Acids Topic Aldehydes & Ketones Class Assignment ( CA 12. 1) : NCERT Solved examples 12.1 to Example 12.1 Give names of the reagents to bring about the following transformations: (i) Hexan-1-ol to hexanal ; (ii) Cyclohexanol to Cyclohexanone ; (iii) p-fluorotoluene to p-fluorobenzaldehyde (iv) Ethanenitrile to ethanal ; (v) Allyl alcohol to propanal ; (vi) But-2-ene to ethanal Example 12.2 Arrange the following compounds in the increasing order of their boiling points: CH 3CH 2CH 2CHO, CH 3CH 2CH 2CH 2OH, H 5C 2-O-C 2H 5, CH 3CH 2CH 2CH 2CH 3 Example 12.3 Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal? Explain your answer. Example 12.4 An organic compound (A) with molecular formula C8H8O forms an orange-red precipitate with 2,4- DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide. It neither reduces Tollens or Fehlings reagent, nor does it decolourise bromine water or Baeyer s reagent. On drastic oxidation with chromic acid, it gives a carboxylic acid (B) having molecular formula C7H6O2. Identify the compounds (A) and (B) and explain the reactions involved. + Intext Questions 12.1 to Write the structures of the following compounds. (i) α-methoxypropionaldehyde ; (ii) 3-Hydroxybutanal ; (iii) 2-Hydroxycyclopentane carbaldehyde ; (iv) 4-Oxopentanal ; (v) Di-sec. butyl ketone ; (vi) 4-Fluoroacetophenone 12.3 Arrange the following compounds in increasing order of their boiling points. CH3CHO, CH3CH2OH, CH3OCH3, CH3CH2CH Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions. (i) Ethanal, Propanal, Propanone, Butanone. (ii) Benzaldehyde, p-tolualdehyde, p-nitrobenzaldehyde, Acetophenone. [Hint: Consider steric effect and electronic effect.]

7 Unit-12. Aldehydes, Ketones & Carboxylic Home Assignment ( HA 12.1) : Topic Aldehydes & Ketones Class XII Chemistry NCERT EXERCISE Question number 12.1, 12.8 to & What is meant by the following terms? Give an example of the reaction in each case. (i) Cyanohydrin ; (ii) Acetal ; (iii) Semicarbazone ; (iv) Aldol ; (v) Hemiacetal ; (vi) Oxime ; (vii) Ketal ; (vii) Imine ; (ix) 2,4-DNP-derivative ; (x) Schiff s base How will you convert ethanal into the following compounds? (i) Butane-1,3-diol ; (ii) But-2-enal ; (iii) But-2-enoic acid Write structural formulas and names of four possible aldol condensation products from propanal and butanal. In each case, indicate which aldehyde acts as nucleophile and which as electrophile An organic compound with the molecular formula C9H10O forms 2,4-DNP derivative, reduces Tollens reagent and undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,2-benzenedicarboxylic acid. Identify the compound An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-1-ene. Write equations for the reactions involved Arrange the following compounds in increasing order of their property as indicated: (i) Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN) (ii) CH3CH2CH(Br)COOH, CH3CH(Br)CH2COOH, (CH3)2CHCOOH, CH3CH2CH2COOH (acid strength) (iii) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength) Give simple chemical tests to distinguish between the following pairs of compounds. (i) Propanal and Propanone ; (ii) Acetophenone and Benzophenone ; (iii) Phenol and Benzoic acid ; (iv) Benzoic acid and Ethyl benzoate ; (v) Pentan-2-one and Pentan-3-one ; (vi) Benzaldehyde and Acetophenone ; (vii) Ethanal and Propanal Give plausible explanation for each of the following: (i) Cyclohexanone forms cyanohydrin in good yield but 2,2,6-trimethylcyclohexanone does not. (ii) There are two NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones. (iii) During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed. Home Assignment ( HA 12.2) : NCERT EXERCISE Question number 12.15, & How will you bring about the following conversions in not more than two steps? (i) Propanone to Propene ; (ii) Benzoic acid to Benzaldehyde ; (iii) Ethanol to 3-Hydroxybutanal ; (iv) Benzene to m-nitroacetophenone ; (v) Benzaldehyde to Benzophenone ; (vi) Bromobenzene to 1-Phenylethanol ; (vii) Benzaldehyde to 3-Phenylpropan-1-ol; (viii) Benazaldehyde to α-hydroxyphenylacetic acid (ix) Benzoic acid to m- Nitrobenzyl alcohol Describe the following: (i) Acetylation ; (ii) Cannizzaro reaction ; (iii) Cross aldol condensation ; (iv) Decarboxylation Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why?

8 HOTS Ch 12 - Aldehydes, Ketones & Carboxylic Acids Special Assignment-12 Date: 1. Compound A C 4 H 8 Cl 2 is hydrolysed to a compound B C 4 H 8 O which form an oxime with NH 2 OH and give negative Tollens test. What are the structures of A and B. Write balanced chemical equations for the reactions involved. (Hint: A is a gemdihallide and B is a ketone) 2. Give reasons for the following: i) Iodoform is obtained when methyl ketones react with hypoiodite but not with iodide. (Hint: Hypoiodite ion being stronger base than iodide ion, can easily remove acidic hydrogen atom.) ii) Hydrazones of aldehydes and ketones are not prepared in highly acidic medium. (Hint: In strong acidic medium N of reagent gets protonated to get an electrophile which cannot react.) 3. Benzaldehyde gives positive test with Tollens reagent but not with Fehling s solution. State the reason. ( Hint :+R effect increases electron density on carbonyl group and C-H become strong. [Ag(NH 3 ) 2 ] + is a stronger oxidizing agent than Cu 2+ + tartarate + base). 4. Compound X, containing Chlorine on treatment with strong ammonia gives a solid Y which is free from Chlorine. Y on analysis gives C=49.31%, H=9.59% and N=19.18% and reacts with Br 2 and caustic soda to give a basic compound Z. Z reacts with HNO 2 to give ethanol. Suggest structures for X, Y and Z. 5. A compound X (C 2 H 4 O) on oxidation gives Y (C 2 H 4 O 2 ). X undergoes haloform reaction. On treatment with HCN, X forms a product Z which on hydrolysis gives 2-Hydroxy propanoic acid. a) Write down the structures of X and Y. b) Name the product when X reacts with dil. NaOH. c) Write down the equations for the reactions involved. (Hint: - X is an aldehyde since it has general formula C n H 2n O and has only two carbon atoms.) 6. An alkene (A), with molecular formula C 7 H 14 ; on ozonolysis yields an aldehyde. The aldehyde is easily oxidized to an acid (B). When B is treated with Bromine in presence of Phosphorous it yields a compound (C) which on hydrolysis gives a hydroxy acid (D). This acid can also be obtained from acetone by the reaction with hydrogen cyanide followed by hydrolysis. Identify A, B, C and D and write the chemical equations for the reactions involved. 7. Five isomeric para-di- substituted aromatic compounds, A to E with molecular formula C 8 H 8 O 2 were given for identification. Based on the following observations give the structures of the compounds: Both A and B form silver mirror with Tollens reagent, also B gives a positive test with FeCl 3. C gives positive Iodoform test. D is readily extracted in aqueous NaHCO 3 solution. E on acid hydrolysis gives 1,4-dihydroxy benzene. ( Hint: A and B contain CHO groups since they ve shown positive Tollens test. B has phenolic group as it reacts with FeCl 3 solution. C should have CH 3 CO- group. D should have COOH group. E should be p-hydroxy phenyl vinyl ether).

9 Class XII Chemistry Unit-12. Aldehydes, Ketones & Carboxylic Acids Topic Carboxylic acids Work Sheet ( WS 12. 2) Name -. Class/ sec.. Roll No.. B. Fill in the blanks: 1. Carboxylic acids are considerably acidic than alcohols and most of simple phenols. 2. Carboxylic acids are to primary alcohols with LiAlH4, or better with diborane in ether solution. 3. acid is used in rubber, textile, dyeing, leather and electroplating industries. 4. acid is used as solvent and as vinegar in food industry. 5. acid is used in the manufacture of nylon-6, of benzoic acid are used in perfumery. 7. Sodium benzoate is used as a food. 8. Higher fatty acids are used for the manufacture of and. 9. Aromatic carboxylic acids undergo electrophilic substitution reactions in which the carboxyl group acts as a and meta-directing group. 10. Aromatic carboxylic acids however, do not undergo reaction because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group. 11. Carboxylic acids having an -hydrogen are halogenated at the -position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give -halocarboxylic acids. The reaction is known as reaction. 12. Carboxylic acids lose carbon dioxide to form when their sodium salts are heated with sodalime (NaOH and CaO in the ratio of 3 : 1). The reaction is known as decarboxylation. 13. Diborane does not easily functional groups such as ester, nitro, halo, etc. 14. Sodium borohydride does not reduce the group. 15. Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature give. 16. Carboxylic acids on heating with mineral acids such as H2SO4 or with P2O5 give corresponding. 17. The presence of electron group on the phenyl of aromatic carboxylic acid increases their acidity while electron groups decrease their acidity. 18. Electron withdrawing groups the acidity of carboxylic acids by stabilising the conjugate base through delocalisation of the negative charge by inductive and/or resonance effects. Conversely, electron donating groups the acidity by destabilising the conjugate base. 19. The carboxylate ion is more stabilised than phenoxide ion, so carboxylic acids are acidic than phenols. 20. hydrolysis of esters gives directly carboxylic acids while hydrolysis gives carboxylates, which on acidification give corresponding carboxylic acids.

10 Class XII Chemistry Unit-12. Aldehydes, Ketones & Carboxylic Acids Topic Carboxylic acids Class Assignment ( CA 12. 2) : NCERT Solved examples Intext Questions 12.6 & NCERT EXERCISE Question number NCERT Solved examples Example 12.5 Write chemical reactions to affect the following transformations: (i) Butan-1-ol to butanoic acid ; (ii) Benzyl alcohol to phenylethanoic acid ; (iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid ; (v) Cyclohexene to hexane-1,6-dioic acid ; + Intext Questions 12.6 & Give the IUPAC names of the following compounds: (i) Ph CH2CH2COOH ; (ii) (CH3)2C=CHCOOH (iv) 4-Methylacetophenone to benzene-1,4-dicarboxylic acid; (vi) Butanal to butanoic acid Show how each of the following compounds can be converted to benzoic acid. (i) Ethylbenzene ; (ii) Acetophenone ; (iii) Bromobenzene ; (iv) Phenylethene (Styrene) 12.8 Which acid of each pair shown here would you expect to be stronger? (i) CH3CO2H or CH2FCO2H ; (ii) CH2FCO2H or CH2ClCO2H ; (iii) CH2 FCH2CH2CO2H or CH3CHFCH2CO2H NCERT EXERCISE Question number