Aldehydes Ketones and Carboxylic Acids Class 12 Important Questions & Answers

Ans. (a) Diacetone alcohol, (b) Crotonaldehy de. (a) $\quad 4$ - Hy droxy - 4 -methylpentan-2-one (b) $\quad$ But- 2 -en- 1 -al.

Ans. Tollen’s reagent or Fehling’s solution.

Ans. Chromyl chloride in $\mathrm{CS}_{2}\left(\mathrm{CrO}_{2} \mathrm{Cl}_{2} / \mathrm{CS}_{2}\right)$ or chromic trioxide in acetic anhydride $\left[\mathrm{CrO}_{3} /\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}\right]$ followed by acid or alkaline hydrolysis.

Ans. Aldehydes and ketones containing $\alpha$ -hydrogens.

Ans. Aromatic and aliphatic aldehydes which do not contain $\alpha$ hydrogens

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Ans. 2-Methylpentan-3-one

Ans. +1 oxidation state

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Ans. (a) Due to deactivation of the benzene ring by electronwithdrawing effect of the $-C O O H$ group. $(b)$ $A I C l_{3}$ gets bonded to the $-C O O H$ group.

Ans. Due to resonance between lone pairs of electrons on the -atom of the group and the carboxyl carbon is less electrophilic than carbonyl carbon in aldedhydes and ketones. Therefore, nucleophilic addition of to the group of carboxylic acids does not occur and hence carboxylic acids do not form oximes.

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Ans. In the carbonyl group $(>C=O),$ the $\pi$ -electron pair is loosely held and can be readily shifted to the oxygen atom. It is not the case with the alcoholic $(O-H)$ group. Therefore, carbonyl compounds are more polar and have higher dipole moment values $(2.3-2.8 D)$ than the alcohols $(1.6-1.8 D)$

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Ans. 2, 3-dimethylbut-2-ene will form acetone by reductive ozonolysis

Ans. Formaldehyde does not have an $\alpha$ -hydrogen. It therefore, takes part in cannizzaro's reaction when heated with strong $N a O H$ to form a methyl alcohol and sodium formate mixture. Acetaldehyde fails to react since it has $\alpha$ -hydrogens present.

Ans. Benzoic acid is formed.

Ans. The $K_{a}$ value of benzoic acid $\left(6.3 \times 10^{-5}\right)$ is more than that of acetic acid $\left(1.75 \times 10^{-5}\right) .$ Actually, $C_{6} H_{5}$ group with $-I$ effect in facilitates the release of $H^{+}$ from benzoic acid while $\mathrm{CH}_{3}$ group with $+I$ effect tends to retard it.

Ans. Acetic acid $\left(p K_{a}=4.8\right)$ is stronger than peracetic acid $\left(p K_{a}=8.2\right) .$ It is because after losing $H^{+}$ ion acetic acid molecule gets stabilised by resonance while the peracetate ion does not.

Ans. Due to the presence of lone pairs of electrons on the oxygen atom of the OH group, the carboxylic acids are stabilized by resonance. As a result, the double bond character of the bond in carboxylic acids is greatly reduced as compared to that in aldehydes and ketones. In other words, the carbonyl group in carboxylic acids is not a true carbonyl group as in aldehydes and ketones and hence does not give some of the characteristic reactions of the carbonyl group. For example, unlike aldehydes and ketones, carboxylic acids do not form oximes, hydrazones, semicarbazones etc.

Ans. (a) By Kolbe's reaction. Sodium salt of phenol reacts with $\mathrm{CO}_{2}$ under high pressure of $4-7$ atm, at about $400 \mathrm{K}$ to form salicylic acid.

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Ans. The $>\mathrm{C}=\mathrm{C}<$ undergoes electrophilic addition reactions while $>\mathrm{C}=\mathrm{O}$ shows nucleophilic addition reactions. This difference in behaviour is due to the different shapes of their $\pi$ -electron clouds. The electron cloud of bond due to similar electronegativities of the two carbon atoms is almost symmetrical and surrounds both the carbon atoms equally. Consequently, if a reagent is to attack one of the carbon atoms of the bond, it has to pass through the electron cloud. since the -electron cloud consists of loosely held electrons, therefore, it can readily allow electrophiles to react. As a result, the typical reactions of are electrophilc addition reactions. In contrast, the electron cloud of the $\succ \mathrm{C}=0$ is unsymmetrical i.e., shifts towards oxygen due to greater electronegativity of O than C. As a result, the C-atom of the bond acquires a partial charge and hence is readily attacked by nucleophiles. Thus, the typical reactions of are nucleophilic addition reactions.

Ans. In alkaline medium, $C u^{2+}$ ions get precipitated as $C u(O H)_{2}$ To keep ions in solution in alkaline medium, Rochelle salt is added. The insoluble first formed goes into solution due to the formation of a soluble complex between ions and tartrate ion as shown below:

Ans. Alkaline $K M n O_{4},$ acidified $K_{2} C r_{2} O_{7}$ or $H N O_{3}$ cannot be used since all of these will cleave the molecule at the site of double bond giving a mixture of ketone/acids. The most suitable reagent for this oxidation is $\mathrm{NaOI} \quad\left(I_{2} / N a O H\right)$ since methyl ketones on treatment with NaOI undergo iodoform reaction to give iodoform along with the salt of a carboxylic acid having one carbon atom less than the starting methyl ketone.

Ans. since halogens are more electronegative than carbon and also possess lone pairs of electrons, therefore, they exert both $-I$ and $+R$ -effects. Now in $F,$ the lone pairs of electrons are present in $2 p$ -orbitals but in $C l,$ they are present in $3 p-$ orbitals. since $2 p$ -orbitals of $F$ and $C$ are of almost equal size, therefore, the $+R$ -effect is more pronounced in $p-$ fluorobenzoic acid than in -chlorobenzoic acid Thus, in $p$ -fluorobenzoic acid, $+R$ -effect outweighs the $-I-$ effect but is p-chlorobenzoic acid, it is the I-effect which outweighs the $+$ R-effect. Consequently acid is a weaker acid than p-chlorobenzoic acid.

Ans. If the Grignard reagent or the ketone contains branching at the $\alpha$ -carbon, sometimes the usual addition reaction does not occur due to steric hindrance. Instead reduction occur in which a hydride ion is transferred from the Grignard reagent to the ketone via a six-membered cyclic transition state in a manner similar to M.P.V. reduction. For example, when isopropylmagnesium bromide is added to di-isopropyl ketone, the expected $3^{\circ}$ alcohol (i.e., tri-isopropylcarbinol) is not formed; instead the secondary alcohol, di-isopropylcarbinol is obtained by reduction of the keto group.

Ans. Alkanes are non-polar in nature and the attractive forces are weak vander Waal’s forces. In alcohols, intermolecular hydrogen bonding is present in the molecules. In the carbonyl compounds, only dipolar forces exist in the molecules. It is, therefore, quite obvious that the attractive forces in carbonyl compounds are more than in alkanes and less in comparison to alcohols. This justifies the trend in boiling point values in the members of these families.

Ans. Halogen acids (HX) react with alkenes to form haloalkanes but they fail to react with the carbonyl compounds. In fact, the attack does take place but the product is unstable and decomposes to form carbonyl compound along with halogen acid. Thus, the reaction is reversible.

Ans. Propionaldehyde is more reactive than benzaldehyde towards nucleophilic addition. Actually, in benzaldehyde the aldehydic group has (mesomeric) effect. As a result, the electron density on the carbonyl carbon atom tends to increase and the nucleophile attack is more difficult as compared to propanal where alkyl group is attached to the aldehydic group.

Ans. In chloral hydrate, the presence of three $C l$ atoms with $-I$ effect increases the magnitude of the positive charge on the carbonyl carbon atom. As a result, even a weak nucleophile like $H_{2} O$ attacks to form a hydrate. Moreover, there is weak intermolecular hydrogen bonding in the chloral hydrate which tends to increase its stability.

Ans. Aldol condensation involves the nucleophile attack of carbanion generated by one molecule of a particular carbonyl compound on the other molecule. For this, the carbonyl compound must have atleast one $\alpha$ -hydrogen present. since formaldehyde $(H C H O)$ has no such hydrogen present, it fails to take part in aldol condensation alongwith another carbonyl compound with atleast one -hydrogen atom e.g., formaldehyde and acetaldehyde.

Ans. The addition of ammonia derivative $\left(N H_{2}-G\right)$ to aldehydes and ketones is done in weakly acidic medium (pH about 3.5). In case the medium is strongly acidic (pH close to 1 ), then the ammonia derivative will be also protonated and will not be able to act as a nucleophile.

Ans. The addition of $N a H S O_{3}$ on benzophenone $\left[\left(C_{6} H_{5}\right)_{2} C=O\right]$ involves the nucleophile attack of bisulphite $\left(H S O_{3}^{-}\right)$ ion. The phenyl groups act as hindrance to the attacking nucleophile. Therefore, benzophenone does not react with $\mathrm{NaHSO}_{3}$.

Ans. Aldehydes are more easily hydrated than ketones. Further, the presence of electron withdrawing groups increases the ease of hydration of a carbonyl compound. In the light of this, the correct order is : (a) $\mathrm{HCHO}>\mathrm{CH}_{2} \mathrm{ClCHO}>\mathrm{CH}_{3} \mathrm{CHO}>\mathrm{CH}_{2} \mathrm{ClCOCH}_{3}>\mathrm{CH}_{3} \mathrm{COCH}_{3}$

Ans. Phenylacetylene

Ans. The carbonyl group in carboxylic acid is not a free group as in aldehydes and ketones. It is involved in resonance. Therefore, carboxylic acids fail to give the characteristic reactions of the carbonyl groups as given by aldehydes and ketones.

Ans. $\mathrm{HCOOH}$ has an aldehydic (CHO) group in addition to carboxyl group $(\mathrm{COOH}) .$ Therefore, it is expected to behave as reducing agent also and reduces Tollens to form a shining mirror.

Ans. In the trimethylbenzoic acid there are three electron releasing $\mathrm{CH}_{3}$ groups present. They tend to increase the electron density on the oxygen atom of $O-H$ bond in carboxylic acid. As a result, the acidic strength is reduced considerably and it is not so easy to esterify $2,4,6$ -trimethyl benzoic acid.

Ans. The hydroxyl $(O H)$ group has both $-I$ effect and $+R$ effect. Whereas the former helps in the release of $H^{+}$ from the carboxylic group, the latter tends to oppose the same because of resonance. At the para position, the $+\mathrm{R}$ effect dominates the effect. Therefore, p-hydroxy benzoic acid is a weaker acid than benzoic acid. But in case of m-hydroxybenzoic acid, the $+\mathrm{R}$ effect does not operate to the same extent as in para isomer. Thus, the acidic weakening effect is smaller and meta hydroxy benzoic acid is a stronger acid than benzoic acid.

Ans. In sodium formate, the contributing structures for the anion are equivalent while these are not the same in formic acid. Thus, carbon-oxygen bond length in formate ion is the same for both the bonds while these are different in formic acid.

Ans. In phenate ion, the negative charge available is dispersed only one electrongative oxygen atom while there are two oxygen atoms in benzoate ion to disperse the negative charge. This means that benzoate ion is more stable than phenate ion and this makes benzoic acid stronger acid than phenol although the contributing structures for phenate ion (five) are more than for benzoate ion (two).

Ans. In order that an alkyl group attached to benzene ring may be oxidised to carboxyl group, the presence of atleast one $\alpha$ -hydrogen is necessary. For example, toluene is oxidised to benzoic acid. But tertiary butyl benzene has no -hydrogen atom. It is therefore, not oxidised to benzoic acid.

Ans. In acetate ion, the negative charge gets dispersed due to the electron withdrawing nature of carbonyl group. On the other hand, in ethoxide ion, the $C_{2} H_{5}$ group with $+I$ effect tends to increase the electron density on the ion and destabilise it.

Ans. (a) $\mathrm{HCOOH}$ (b) $\mathrm{CH}_{3} \mathrm{COOH}$ (c) HCOOH (d) $\mathrm{CH}_{2}(\mathrm{Cl}) \mathrm{COOH}$

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Ans. The acetylation is carried by acetyl carbocation $\left(\mathrm{CH}_{3} \mathrm{CO}^{+}\right)$ The cation is formed by acetyl chloride and not by acetic acid. Therefore, acetyl chloride is a better acetylating agent than acetic acids.

Ans. (i) Transesterification : This reaction involves the nucleophilic acyl substitution of the alkoxy group of an ester with the alkoxy group of an alcohol in the presence of an acid or alkali $R C O O R^{\prime}+R^{\prime \prime} O H \longrightarrow R C O O R^{\prime \prime}+R^{\prime} O H$ (ii) Hofmann bromamide reaction: This reaction involves the conversion of an amide into primary amine with one carbon atom less than the parent amide, by reaction with bromine and alkali

Ans. (c) $\quad \mathrm{NH}_{2}$ attached to $\mathrm{NH}$ is more nucleophile than $\mathrm{NH}_{2}$ attached to $\mathrm{C}=$ O group, therefore, reaction occurs through $\mathrm{NH}_{2}$ attached to NH to give the corresponding semicarbozone, i.e.,

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Ans. In the resonating structure of phenoxide ion the negative charge is dispersed on only one oxygen atom whereas in the carboxylate ion the charge gets dispersed on two oxygen atoms. Thus, the dispersal of charge is more in the case of carboxylate ion and hence the resonance stabilisation is more. This is why the carboxylic acids are more stronger than phenol (s).

Ans. (i) The reactivities of aldehydes is more than that of ketones due to the following reasons: (a) Inductive effect: The ease with which a nucleophile attacks the carbonyl group depends upon the electron deficiency i.e., the magnitude of the positive charge on carbonyl carbon. since an alkyl group has electron donating inductive effect ( $+$ I effect), therefore greater the number of alkyl groups attached to carbonyl carbon greater is the electron density on the carbonyl carbon and hence lower is its reactivity. Aldehydes are more polar than ketones. In ketone we have two alkyl groups whereas in aldehydes only one alkyl group is attached to carbonyl carbon. Since there is lesser number of alkyl groups in case of aldehydes so they undergo nucleophillic addition more readily than ketones. (b) Steric effect : The presence of more alkyl groups in case of ketones hinders the attack of nucleophile on the carbonyl group and so the ketones are less reactive than aldehydes. (ii) Aromatic acids contain benzene ring and their molecular masses are much higher than aliphatic acids of acetic acid group. Aromatic, acids also involve stronger inter molecular attractions, thus they are solids.

Ans. $2-(2-$ bromophenyl) ethanal. It can also be named as $2-(\text { o-bromophenyl })$ ethanal. (b) 5 -chloro-3-ethyl-2-pentanone. (c) $3,5$ -dimethyl phenyl ethanoate

Ans. (a) The acidic nature of a carboxylic acid is due to its ability to release the $H^{+}$ (proton). Any factor that stabilise the carboxylate ion would facilitate the release of proton and thus increase the acid strength. The electron withdrawing group (attached to $-\mathrm{COOH}$ gp) increases the acid strength. Due to electron withdrawing effect $(-I \text { effect })$ of chlorine atom, the negative charge of carboxylate ion formed gets dispersed. As such this ion gets stabilised and is, therefore, more easily formed. The acetate ion obtained from acetic acid gets detabilised due to electron releasing effect of methyl group and is not formed easily. Consequently dissociation of $\mathrm{CH}_{3} \mathrm{COOH}$ takes place to lesser extent. (b) Formation of ammonia derivatives (oximes, hydrazone, semi-carbazone etc.) proceeds via the attack of carbonyl carbon with proton to form the conjugate acid. Therefore, presence of an acid is a must for preparing these derivatives $(p H<7)$ However, in strongly acid medium, the proton attacks the unshared pair of electrons on nitrogen to form the species $R N^{+} H_{3}$ which cannot attack the carbonyl carbon. $\stackrel{+}{H}+: N H_{2} R \longrightarrow N H_{3} R$ In basic medium, there is no protonation of carbonyl group and hence no reaction. $>C=O \frac{\text { basic medium }}{\text { medium }} \rightarrow$ No protonation Therefore, preparation of ammonia derivatives requires slightly acidic medium $(p H=3.5)$ and its careful control is essential.

Ans. (a) $N H_{3}$ reacts with formaldehyde to form hexamethylene tetramine (also called urotropine).

Ans. (a) Esters react with ammonia to form amides. The reaction is called ammonolysis of esters.

Ans. since electronegativity of $L i(\mathrm{E} . \mathrm{N} .=1.0)$ is lower than that of $M g(\mathrm{E.N.}=1.2),$ therefore, organolithium compounds are more nucleophilite than Grignard reagents. As a result, organolithium compounds not only add to the more reactive $\mathrm{CO}_{2}$ but also to the less reactive resonance stabilized lithium salt of carboxylic acid thus formed to yield ketones. Grignard reagents, on the other hand, being less nucleophilic add only to the more reactive $\mathrm{CO}_{2}$ but not to the less reactive resonance stabilized magnesium salt of the carboxylic acid from which carbxylic acid can be generated by hydrolysis with mineral acids.

Ans. Cannizzaro reaction is a disproportionation reaction in which one molecule of an aldehyde is reduced while the other is oxidised. Here a conc. solution of $N a O H$ is used which is not a reducing agent.

Ans. (i) $\quad \mathrm{CH}_{3} \mathrm{CHO}$ and $\mathrm{CH}_{3} \mathrm{COCH}_{3}$ can be distinguished by : LiAIH$_{4}$ and Schiff's reagent. (ii) $\mathrm{CH}_{3} \mathrm{CHO}$ and $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHO}$ can be distinguished by $\mathrm{I}_{2} / \mathrm{NaOH}$ and Schiff's reagent (Benzaldehy de restores pink colour to Schiff's reagent very slowly). (iii) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COCH}_{3}$ and $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COC}_{6} \mathrm{H}_{5}$ can be distinguished by $\mathrm{NaHSO}_{3}$ and $\mathrm{I}_{2} / \mathrm{NaOH}$

Ans. The data suggests that the given compound [A] is an aliphatic ketone butanone $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{3}\right) .$ The reactions involved are listed.

Ans. (a) According to available data [C] is a $\beta$ -keto acid which upon decarboxylation gives pentane- 3 -one. The structure of is : $[\mathrm{C}]$ (b) The compound $[\mathrm{C}]$ along with ethanol has been obtained from compound [B] upon acid hydrolysis. since $[\mathrm{B}]$ is a $\beta$ ketoester, its structure may be given as follows: (c) since $[\mathrm{B}]$ has been formed by the condensation of two moles of $[\mathrm{A}]$ in the presence of sodium ethoxide, the ester $[\mathrm{A}]$ is ethyl propanoate and it participates in Claisen Condensation as follows:

Ans. (a) When propanal is added to tollen's reagent (an ammoniacal solution of silver nitrate), silver oxide is reduced to metallic silver which deposits as a mirre (b) When ethyl acetate is treated with aqueous $N a O H$ Sodium ethanoate and ethanol is formed ethanol on treatment with $I_{2}$ and $N a O H$ forms yellow ppt of iodoform. When methyl acetate is treated with aqueous NaOH sodium ethanoate and Methanol is formed. Methanol does not respond to iodoform reaction (c) When benzoic acid is warmed with ethyl alcohol and a little concentrated $\mathrm{H}_{2} \mathrm{SO}_{4},$ a fragrant odour of ethyl benzoate is obtained. Benzaldehyde does not respond to this test.

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Ans. Dehydration of C gives but-1-ene i.e., a product with four carbon atoms, therefore the other product B is also with four carbon atoms and has a terminal COOH group. Accordingly, A is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$ (butyl butanoate) $\mathrm{B}$ is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}$ and $\mathrm{C}$ is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$

Ans. (a) The reactivity of aldehydes and ketones toward nudeophillic addition depends upon (i) $+$ I effect (ii) steric hinderance. Hence the order is Di-tert-butyl ketone $<$ methyl-tert-butyl ketone < Acetone $<$ Acetaldehy de. (b) The acidic strength depends upon (i) nature of $+$ I effect (ii) nature of atom/group attached (iii) position of substituent on the chain. Hence, $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCOOH}<\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}$ $<\mathrm{CH}_{3} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{2} \mathrm{COOH}<\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{COOH}$ (c) $\quad 4$ -Methoxy benzoic acid $<$ Benzoic acid $<4$ Nitrobenzoic acid $<3,4$ -Dinitrobenzoic acid

Ans. (a) The carbonyl group in cyclohexanone is highly polarised and nuleophilic addition of $H^{\delta+}-C N^{\delta-}$ at carboxyl group $\left(>C^{\delta+}=O^{\delta-}\right)$ takes place easily. centre of nucleophilic attack by $C N^{-}$ The presence of three methyl group (which are electron repelling) reduces the polarity of $>C=O$ group on one hand and offer a steric hindrance to nucleophilic attack of $C N^{-}$ at group. Therefore, trimethyl cyclohexanone does not give good yield i.e., it gives very poor yield. (b) The study of semicarbazide (NH3 derivative of urea, reveal that two $\mathrm{N}-\mathrm{H}$ bonds of $\mathrm{NH}_{2}$ group away from group in semicarbazide are comparatively weaker than two $\mathrm{N}-\mathrm{H}$ bond of the other $-N H_{2}$ group closer to $>C=O$ group. Thus it produces $H^{+}$ easily for protonation of group of aldehyde or ketone. The nature of reaction, esterification of carboxylic acid, is reversible as ester formed react with water and produces reactants and thus an equilibrium is set up between reactants and products. The removal of ester or water shifts the equilibrium to right according to Le-Chatelier's principle and more ester is formed.

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Ans. (a) (i) Benzoyl chloride is subjected to Rosenmund reduction.

Ans. (i) Chloroacetic acid is a stronger acid than acetic acid and has higher value of dissociation constant $K a$ than that of acetic acid. We know that $p K a=-\log K a,$ it means that chloroacetic acid having higher value $K a$ will have lower value of $p K a .$ Chloroacetic acid is stronger than acetic acid because $C l$ group is electron withdrawing and chloroacetate ion is more stabilised than acetate ion (as methyl group is electron releasing). (ii) Carboxyl group (-COOH) is electron withdrawing i.e. deactivating the benzene ring and thus electron density becomes very less at ortho and para position in comparison to meta position. Electrophiles (+vely charged species) find it easier to attack at meta position as there is higher electron density thus $-C O O H$ group is meta directing. As there is positive charge on ortho and para position, electron density is higher at meta position and hence electrophilic substitution takes place at meta position. (Similarly nitro group is meta directing) (iii) Carboxylic group (-COOH) in acids is highly polar and carboxylic acid, generally, exists as dimers containing two hydrogen bonds each as shown below. These hydrogen bonds in carboxylic acids are stronger than those in alcohols. It is due to following two factors (a) The $O-H$ bond of the carboxylic acids are more strongly polarised due to adjacent electron attracting $>C=$ O groups. (b) The oxygen atom of the group $C=O$ in carboxylic acid is more negative as compared to the oxygen atom of the alcohol. Thus carboxylic acids posses higher boiling points than corresponding alcohols of similar molecular masses.

Ans. (i) Acetone can be prepared by oxidation or catalytic dehydrogenation of isopropyl alcohol.

Ans. (a) Ethanal to lactic acid

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Ans. (A) forms $2,4$ -DNP derivative. Therefore, it is an aldehyde or a ketone. since it does not reduce Tollen's or Fehling reagent, (A) must be a ketone. (A) responds to iodoform test. Therefore, it should be a methyl ketone. The molecular formula of (A) indicates high degree of unsaturation, yet it does not decolourise bromine water or Baeyer's reagent. This indicates the presence of unsaturation due to an aromatic ring. Compound (B), being an oxidation product of a ketone should be a carboxylic acid. The molecular formula of (B) indicates that it should be benzoic acid and compound (A) should, therefore, be a monosubstituted aromatic methyl ketone. The molecular formula of $(\mathrm{A})$ indicates that it should be phenyl methyl ketone (acetophenone). Reactions are as follows:

Ans. (a) Cyanohydrin is a compound which contains both OH and CN group. For example, Lactic acid can be obtained by hydrolysis of cyanohydrin. (b) The product of carbonyl compounds with semicarbazide is known as semicarbazone. (c) Hemiacetal is a compound which contains an ether as well as alcohol functional group. For example, methoxyethanol is a hemiacetal. (d) Ketal is a cyclic compound obtained by reaction of acetone with ethylene glycol. (e) $2,4$ -DNP derivative: see properties of aldehydes/ ketones in section 12.7 of text. (f) Acetal : Acetal are the product of aldehyde and monohydric alcohol (g) Aldol is a condensation product of acetaldehyde in the presence of dil. $N a O H$ (h) Oxime : Aldehyde and Ketones react with hydroxylamine to form oximes. (i) Schiff's base : Schiff's reagent is an aqueous solution of magenta or pink coloured rosaniline hydrochloride which has been decolourised by passing $\mathrm{SO}_{2}$ when aldehyde are treated with decolourised solution of schiff's reagent, its pink or magenta colour is restored. This reaction is used as a test for aldehyde because ketones do not restore the pink colour of schiff reagent.