ALDEHYDES, KETONES AND CARBOXYLIC ACIDS. Points to Remember

Size: px

Start display at page:

Download "ALDEHYDES, KETONES AND CARBOXYLIC ACIDS. Points to Remember"

Mercy Carson
5 years ago
Views:

193 UNIT 12 ALDEHYDES, KETNES AND CARBXYLIC ACIDS Points to Remember 1. Aldehydes, ketones, carboxylic acids and their derivatives are commonly called as carbonyl compounds. 2.

1 193 UNIT 12 ALDEHYDES, KETNES AND CARBXYLIC ACIDS Points to Remember 1. Aldehydes, ketones, carboxylic acids and their derivatives are commonly called as carbonyl compounds. 2. In Rosemund s reduction, poisoning of Pd with BaS 4 prevent reduction of R CH to R H. 3. In the reaction of toluene with Cr 3, acetic anhydride is used to protect benzaldehyde by forming benzylidenediacetate to avoid its oxidation to benzoic acid. 4. rder of reactivity of aldehydes and ketones towards nucleophilic addition is : (i) HCH > CH > CH. HCH > RCH > R C R. ArCH > Ar CR > Ar C Ar. 5. Benzaldehyde does not reduce Fehling s reagent. 6. Aldehydes and ketones with atleast one H atom get condensed in presence of a base. This is known as Aldol condensation. 7. Aldol condensation involves carbanion as intermediate. 8. Aldehydes with no H atoms under Cannizzaro s reaction. 9. Ketones react with dihydric alcohols to form cyclic ketals. 10. Monocarboxylic acids having (C 12 C 18 ) carbon atoms, are called fatty acids. 11. Boiling points of carboxylic acids is greater than corresponding alcohols. 12. Presence of EWGs enhances the acidic character of carboxylic acids. 13. group is m-directing in electrophilic substitution reactions. 14. Compounds containing CH group are named as carbaldehydes if CH groups are three or more. 15. Isomerism : Chain, position and functional.

2 2 Chemistry-XII 16. Structure of CH group sp 2 hybridised. 17. General Methods of Preparation : (i) Controlled oxidation of 1º alcohols : PCC/Cr3 R H RCH (Collin s reagent) Dehydration of 1º alcohols : R H Cu/573 K RCH + H 2 From Rosemund reaction/reduction : (iv) Hydration of alkynes : Pd/BaS4 RCCl + H 2 RCH + HCl CH CH CH CH H CHCH (v) Reductive ozonolysis of alkenes : 1% HgS4 Tautomerism 40% H2S4 (i) 3 R H = CH R 2RCH + H 2 2 (vi) From salts of fatty acids : (RC) 2 Ca + (HC) 2 Ca Zn/H2 (vii) Stephen s reduction of nitrile compounds : D Dist. 2RCH + 2CaC 3 SnCl 2 /HCl H3 R C N [R CH = NH HCl].HCl RCH + NH 4 Cl (viii) Hydrolysis of germinal halides : (ix) From Grignard s reagent : RCH + NH 3 + Mg (H)X

3 General Methods of Preparation of Ketones only (i) Dehydrogenation of 2º alcohols : Aldehydes, Ketones And Carboxylic Acids 3 R C (iv) From Grignard's reagents : R'MgX + R C N R C = + NH 3 + Mg (H) X R' (iv) From acid chlorides : RCCl + R 2 Cd 2R C R' + CdCl 2 Physical Properties : Reactivity : HCH is a gas at normal temperature. Formalin is 40% as solution of HCH. Due to polarity they have high values of boiling point. Solubility in water is only for lower members. (i) + I effect of alkyl groups decreases the +ve charge on carbonyl carbon. Steric hindrance : Bulky group hinder approach of nucleophile. -hydrogen atom is acidic due to resonance. 18. Vinegar is 8 to 10% solution of hydrogen atoms in carboxylic acid are acidic in nature and can be easily replaced by halogen atoms in HVZ reaction.

4 4 Chemistry-XII 21. Relative acid strength of R > HH > RH > HC CH > NH 3. It is because a strong acid has weak conjugate base. 22. Some dicarboxylic acids bearing general formula HC ( ) n where n 0, 1, 2,...etc. HC xalic acid 1, 2 ethanedioic acid HC Malonic acid 1, 3 propanedioic acid HC ( ) 2 Succinic acid HC ( ) 3 Glutonic acid 1, 4 butanedioic acid 1, 5 pentamdioic acid HC ( ) 4 Adipic acid 1, 6 hexanedioic acid 23. Melting points : Higher : Even carbon atoms than next lower or higher homologues containing even number of carbon atoms due to symmetry and closer packing of molecules in the crystal lattice. VERY SHRT ANSWER TYPE QUESTINS (1 Mark) Q. 1. Arrange the following compounds in increasing order of their acid strengths : ( ) 2 CH, CH(Br), CH(Br) Ans. ( ) 2 CH < CH(Br) < CH(Br) Q. 2. Draw the structure of the compound whose IUPAC name is 4-chloropentan- 2-one. Cl Ans. CH C Q. 3. Which type of aldehyde can go Cannizzaro reaction? Ans. Aromatic and aliphatic aldehydes which do not contain -hydrogen. Q. 4. Name the aldehyde which does not give Fehling s solution test. Ans. Benzaldehyde. Q. 5. Arrange the following in order of their increasing reactivity towards HCN : CH, C, HCH, C 2 C Ans. C 2 C < C < CH < HCH

5 Aldehydes, Ketones And Carboxylic Acids 5 Q. 6. Mention industrial product obtained from HCH. Ans. Bakelite Q. 7. Arrange the following compounds in increasing order of their boiling point : CH, H,, Ans. < < CH < H Q. 8. How is acetone obtained from ethanol? Q. 9. Why do aldehydes and ketones have lower boiling point than alcohols? Ans. Due to presence of associated molecules with H-bonding in alcohols. Q. 10.Write reaction between acetyl chloride and dimethyl cadmium. Q. 11. What happens when CH is treated with K 2 Cr 2 7 in presence of H 2 S 4? K2Cr27 H2S4 Ans. CH + [] Q. 12. Write the IUPAC name of Ans. 3, 7-Dimethylocta-2, 6 dien-1-al Q. 13.Give balanced equation and name of products when is treated with PCl 5? Ans. + PCl 5 CCl + PCl 3 + HCl Q. 14.Write the name of ester which gives the flavor of pineapple. Ans. Ethyl butanoate. Q. 15.What product is obtained when ethyl benzene is oxidized with alkaline KMn 4? Ans. Benzoic acid (C 6 ) is obtained.

6 6 Chemistry-XII Q. 16. What is RDX? Ans. RDX is Research and Development Explosive which is prepared by the nitration of hexamethylene under controlled conditions. Q. 17.Write IUPAC names of the following compound : HC CH = CH - Ans. But-2-ene-1, 4-dioic acid Q. 18. Write the IUPAC name of Ans. Methyl-2-methylbenzoate. Q. 19.Why does benzoic acid not undergo Friedel-Craft reaction? Ans. group in C 6 is an E. W. G. which deactivates the benzene ring. Hence electrophilic substitution becomes difficult. SHRT ANSWER-I TYPE QUESTINS (2 Marks) Q. 1. How will you convert : (i) C 2 H 2 C 6 CNH 2 C 6 Ans. (i) C 6 CNH 2 + HN 2 C 6 + N 2 + H 2 Q. 2. Complete the following : (i)

7 Aldehydes, Ketones And Carboxylic Acids 7 Ans. (i) Q. 3. An organic compound X has molecular formula C 5 H 10. It does not reduce Fehling s solution but forms a bisulphate compound. It also gives positive Iodoform test. What are possible structures of X? Explain your reasoning relating structure. Ans. Ketone give +ve test with Iodoform. It is methyl-ketone. C and C CH are possible structures of the compound. Q. 4. Give the chemical test to distinguish between : Ans. (i) (i) CH and C CH and C 6 CH CH gives Tollen s reagent test. CH + 2AgN 3 + 2NH 4 H + 2Ag + 2NH 4 N 3 + 2H 2 CH gives brick red ppt. Silver mirror CH + 2CuS 4 + 4NaH + Cu 2 + Na 2 S 4 + 2H 2 Brick red ppt. Q. 5. Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal? Explain your answer. Ans. Carbon atom of carbonyl is C 6 CH is less reactive than that of propanal. C 6 CH less polar due to resonance.

8 8 Chemistry-XII Q. 6. Which acid of each pair shown here would you expect to be stronger? (i) C 2 H or FC 2 H FC 2 H or ClC 2 H F C 2 H or CHF C 2 H (iv) Ans. (i) F F or F CH (iv) Q. 7. Carboxylic acids do not give reactions of aldehydes and ketones why? Ans. It is due to resonance keep changing. Q. 8. Write IUPAC name of the following : (i) Ans. (i) 3, 5 Dimethylphenylethanoate 5 bromo 3-chloro-2-iodobenzoic acid Q. 9. Account for the following : Position of > C = group (i) xidation of toluene to C 6 CH with Cr 3 is carried out in presence of acetic anhydride. Melting point of an acid with even number is higher than those of its neighbours with odd number of carbon atoms. Ans. (i) It is used to prevent oxidation to benzoic acid. Acids with even number of carbon atoms fit into crystal lattice. Q. 10.Distinguish between : (i) C 2 H and CH C 6 C and C 6 CH

9 Aldehydes, Ketones And Carboxylic Acids 9 Ans. (i) C 2 H evolves H 2 gas with Na, CH not. Acetophenone will give yellow ppt. of iodoform while C 6 CH will not. Q. 11. Complete the following reactions by identifying A, B and C : Pd/BaS (i) A + Hydrogen (g) 4 ( ) 2 CH CH C C + NaI B + C Ans. (i) A is B is CHI 3 and C is Q. 12. Benzaldehyde gives a positive test with Tollen s reagent but not with Fehling s and Benedict solutions. Why? Ans. It is due to stronger oxidizing nature of Tollen s reagent as compared to Fehling and Benedict s solution and cannot oxidise benzaldehyde to benzoic acid. In general, all these three can oxidise aliphatic acids. Q. 13.Aldehydes usually do not form stable hydrates but chloral normally exists as chloral hydrate. Give reason. Ans. In case of aldehyde reaction is reversible. In case of CCl 3 CH, Cl atoms increases +ve charge on carbonyl carbon. Therefore, weak nucleophiles like water readily added to the carbonyl group. Q. 14. Give possible explanation for the following : (i) Cyclohexanone forms cyanohydrins in good yield but 2, 2, 6 trimethylcyclohexanone does not. There are two NH 2 groups in semicarbazide. However, only one is involved in formation of semi carbozone.

10 10 Chemistry-XII Ans. (i) Due to steric hindrance for CN at C = and not of 3-methyl groups at -position but in case of nly one NH 2 group attached to C = is involved in resonance. As result electron density on theis NH 2 group decreases and hence does not act as nucleophile. Q. 15. Aldehydes are easily oxidisable yet propanal can conveniently be prepared by the oxidation of propanol by acidic K 2 Cr 2 7. Ans. Aldehydes having boiling points less than 373 K can be removed by distillation therefore propanal 323 can easily be prepared from propanol-1 by distillation from the alcohol acid dichromate solution. SHRT ANSWER-II TYPE QUESTINS (3 Marks) Q. 1. Illustrate the following name reactions : (i) Clemmensen s Reduction Beckmann Rearrangement Benzoin Condensation Ans. (i) Both aldehydes and ketones are reduced to hydrocarbons. CH + 4[H] Zn-Hg/HCl + H 2

11 Aldehydes, Ketones And Carboxylic Acids 11 Formation of ketoximes on treatment with an acid (H 2 S 4 ) or reagents like PCl 5, SCl 2 etc. Q. 2. Predict the organic products of the following reactions : (i) (iv) (v) (vi) Ans. (i) C 6 CK C 6 CN = N NHCNH 2

12 12 Chemistry-XII (iv) C 6 CCl/AlCl 3 (v) (vi) Q. 3. Write chemical reaction to affect the following transformations : (i) Butan-1-ol Butanoic acid Benzyl alcohol to pheynylethanoic acid 3-Nitrobromobenzene to 3-nitrobenzoic acid (iv) 4-methylacetophenone to Terephthalic acid (v) Cyclohexene Hexane-1, 6 dioic acid (vi) Butanal Butanoic acid Cr3 H2S4 Ans. (i) H Jones reagent C 6 H HBr KCN C 6 Br C 6 H 2 CN (iv) C 6 + H3

13 Aldehydes, Ketones And Carboxylic Acids 13 (v) Amm. AgN Tollen's reagent 3 (vi) CH Q. 4. Draw the structure of the following derivatives : (i) 2, 4-dinitrophenylhydrazone of C 6 CH Cyclopropanone oxime Acetaldehydedimethylacetal (iv) Semicarbazone to cyclobutanone (v) Ethylene ketal of hexan-3-one (vi) Methylhemiacetal of formaldehyde Ans. (i) (iv) (v) (vi)

14 14 Chemistry-XII Q. 5. Draw the structure of a carbonyl group and indicate : (i) hybridized state of carbon the and bonds the electrophilic and nucleophilic centres Ans. (i) hybridized state of C is sp 2 Q. 6. Complete the following as missing starting material, reagent or products : (i) Ans. (i) B 2 H 6 /THF, PCC (Hydroboration) Q. 7. How can the following converted : (i) Ethanol Acetone Benzene Acetophenone Benzoic acid Benzaldehyde

15 Aldehydes, Ketones And Carboxylic Acids 15 PCl5 Pd/BaS4 C 6 C 6 CCl + H 2 C 6 CH + HCl Q. 8. Give reasons for the following : (i) Carboxylic acids do not give characteristic reactions of carbonyl group. Treatment of C 6 CH with HCN gives a mixture of two isomers which cannot be separated even by fractional distillation. Sodium bisulphate is used for purification of ketones and aldehydes. Ans. (i) group is changing. Because of resonance, the position of > C = Due to two optical isomers fractional distillation is not possible. Due to formation of additional compound with NaHC 3 whereas impurities do not. Q. 9. Write tests to distinguish between : (i) CH and C 6 CH C 6 H and Pentanal and Pentan-2-one

16 16 Chemistry-XII Ans. (i) CH gives brick red ppt. with Fehling, C 6 CH not. Phenol does not give brisk effervescence but gives this test with NaHC 3. Pentanal forms silver mirror but pentan-2-one does not. Q. 10.Convert : (i) Benzaldehyde to acetophenone Malonic acid to acetic acid Acetaldehyde to 2-butanol Ans. (i) Q. 11. Write the structures of organic compound A to F in the following sequence of reactions : Ans. A = C 6 H 6 B = C 6 N 2 C =

17 Aldehydes, Ketones And Carboxylic Acids 17 D = E = F = Q. 12. Complete the following : (i) CNH 2 + HN 2 CNH 2 + NaH + Br 2 Ans. (i) + N 2 + H 2 NH 2 + Na 2 C 3 + NaBr + H 2 LNG ANSWER TYPE QUESTINS (5 Marks) Q. 1. Which of the following compounds would undergo Aldol condensation, which the Cannizzaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction : (i) Methanal 2-Methylpentanal Benzaldehyde (v) Cyclohexanone (iv) Benzophenone (vi) 1-Phenylpropanone (vii) Phenylacetaldehyde (viii) Butan-1-ol (ix) 2, 2 Dimethylbutanal Ans. (i), and (ix) will give Cannizzaro reaction due to absence of -hydrogen., (v), (vi) and (vii) will give aldol condensation due to presence of -hydrogen. (iv) and (viii) will neither undergo Cannizzaro s reaction nor Aldol condensation because benzophenone does not give -hydrogen and butanol is alcohol, not aldehyde which cannot undergo aldol condensation.

18 18 Chemistry-XII Q. 2. An organic compound A (C 3 H 6 ) is resistant to oxidation but forms compound B (C 3 H 8 ). n reduction B reacts with HBr to form the compound C. C with Mg forms Grignard s reagent D which reacts with A to form a product which on hydrolysis gives E. Identify A to E. Ans. A must be ketone. Dry ether Dry ether Q. 3. Give structure of the following compounds : (i) 2-methoxypropionaldehyde 3-hydroxy butanal 2-hydroxy cyclopentanecarbaldehyde (iv) 4-oxopentanal (v) Di-seebutyl ketone Ans. (i)

19 Aldehydes, Ketones And Carboxylic Acids 19 (iv) (v) Q. 4. (i) How will you prepare (a) acetic anhydride and (b) acetyl chloride from? Write the equation involved in each case. Why is the boiling point of acid anhydride higher than the acid from which it is obtained? Ans. (i) (a) (b) Acid anhydride bigger size than corresponding acids and stronger van der Waal s forces of attraction than their corresponding acids. Q. 5. Complete the following reactions and write main products : (i) CNH 2 + HN 2 (i) C 2 /H MgBr + + H2/H CCl + H 2 (steam) (iv) + NH 3 (v) + C 2 H conc. H2S 4 (vi) HCH + NH 3 (vii) CH LiAlH (viii) CH 4 3 CH (ix) CR + NaI Ans. (i) (x) C 6 CH + NH 2 NH 2 (iv) CNH 2 (v) CC 2 (vi) ( ) 6 N 4 (Urotropine)

20 20 Chemistry-XII (vii) H (viii) (ix) CHI 3 (x) Q. 6. Give reasons for the following : (i) C 6 is weaker than formic acid. H and differentiated by Tollen s reagent. R do not give characteristic reaction with > C =. (iv) Carboxylic acids are stronger acids than phenols. (v) Acid amides are weakly basic in nature. Ans. (i) Due to disabilities of carboxylate anion due to conjugation. H acid is a stronger acid than. > C = group is sterically hindered in carboxylic acid. (iv) Dispersal of ve charge on carboxylate ions than phenate ion. (v) Acid amides are basic due to lone pair of electrons on nitrogen atom.

Chemistry Questions ans Answers BASED ON HIGH ORDER THINKING SKILL (HOTS) UNIT- 12 ALDEHYDES, KETONES AND CARBXYLIC ACID

Chemistry Questions ans Answers BASED N IG RDER TINKING SKILL (TS) UNIT- 12 ALDEYDES, KETNES AND CARBXYLIC ACID 1 MARK QUESTINS Q. 1. Name the reaction and the reagent used for the conversion of acid chlorides