1. Write the structures of the following compounds. (i) α-methoxypropionaldehyde. (ii) 3-Hydroxybutanal. (iii) 2-Hydroxycyclopentane carbaldehyde

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1 1. Write the structures of the following compounds. (i) α-methoxypropionaldehyde (ii) 3-Hydroxybutanal (iii) 2-Hydroxycyclopentane carbaldehyde (iv) 4-Oxopentanal. (i) (ii) (iii) (iv) 2. Write the structures of products of the following reactions i. (C 6 H 5 CH 2 ) 2 Cd + 2 CH 3 COCl ii. 1

2 i. ii. 3. Arrange the following compounds in increasing order of their boiling points. CH 3 CHO, CH 3 CH 2 OH, CH 3 OCH 3, CH 3 CH 2 CH 3. CH 3 CH 2 CH 3 < CH 3 OCH 3 < CH 3 CHO < CH 3 CH 2 OH. 4. 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. i. Butanone < Propanone < Propanal < Ethanal ii. Acetophenone < p-tolualdehyde < Benzaldehyde < p-nitrobenzaldehyde. 5. Predict the products of the following reactions: i. ii.. 2

3 i. ii. 6. Give the IUPAC names of the following compounds (i) Ph CH 2 CH 2 COOH (ii) (CH 3 ) 2 C=CHCOOH. (i) 3 Phenyl propanoic acid (ii) 3 - Methyl but-2-enoic acid. 7. Show how each of the following compounds can be converted to benzoic acid. (i) Ethylbenzene (ii) Acetophenone. i. ii. 8. Which acid of each pair shown here would you expect to be stronger? (i) CH 3 CO 2 H or CH 2 FCO 2 H (ii) CH 2 FCO 2 H or CH 2 ClCO 2 H 3

4 (iii) CH 2 FCH 2 CH 2 CO 2 H or CH 3 CHFCH 2 CO 2 H. i. CH 2 FCO 2 H ii. CH 2 FCO 2 H iii. CH 3 CHFCH 2 CO 2 H. 9. What is meant by the following terms? Give an example of the reaction in each case. (i) Cyanohydrin (ii) Acetal (iii) Aldol (iv) Hemiacetal (v) Schiff s base. (vi)semicarbazone (vii)oxime (viii) 2,4-DNP derivative (ix) ketal. (x) imines (i) Cyanohydrin Aldehydes and ketones react with hydrogen cyanide, HCN to form the addition products called cyanohydrins. (ii) Acetal It is dialkoxy compound formed by the reaction of aldehyde and two moles of alcohols, e.g., 4

5 (iii) Aldol The compounds having alchoholic group and aldehyde or ketone group are called aldols. E.g., (iv) Hemiacetal It is formed by the reaction of aldehyde with one mole of alcohol. It contains both alcohol and alkoxy group e.g., (v) Schiff s base They are the class of compounds having general formula C 6 H 5 -N=CR 2, where R is alkyl or aryl group or hydrogen atoms. It is formed by reaction of primary aromatic amine with aldehyde or ketones. It turns aldehyde pink. (vi) Semicarbazones are derivatives of aldehydes and ketones that are formed by their action with semicarbozide in acid medium (vii) Oximes are the products of the reaction of aldehydes and ketones with hydroxylamine (viii) 2, 4-DNP derivatives are the products of reaction of aldehydes and ketones with 2,4- dimetrophenyl hydrazine (ix) Ketal is formed when a ketone reacts with ethylene glycol in the presence of dry hydrogen chloride 5

6 (x) Imines are produced when aldehydes and ketones react with ammonia derivatives. These have a?ch = N?group. 10. Name the following compounds according to IUPAC system of nomenclature: (i) CH 3 CH(CH 3 )CH 2 CH 2 CHO (ii) CH 3 CH 2 COCH(C 2 H 5 )CH 2 CH 2 Cl (iii) CH 3 CH=CHCHO (iv) CH 3 COCH 2 COCH 3 (v) CH 3 CH(CH 3 )CH 2 C(CH 3 ) 2 COCH 3 (vi) (CH 3 ) 3 CCH 2 COOH (vii) OHCC 6 H 4 CHO-p. (i) 4- methyl pentanal (ii) 6 Chloro 4- ethyl hexane 3 one (iii) 2 Butenal (iv) pentane 2,4 dione (v) 3,3,5 - Trimethyl - 2 hexanone vi) 3,3- Dimethyl butanoic acid (vii) 1,4- Benzene dial. 11. Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.

7 (i) CH 3 CO(CH 2 ) 4 CH 3 (ii) CH 3 CH 2 CHBrCH 2 CH(CH 3 )CHO (iii) CH 3 (CH 2 ) 5 CHO (iv) Ph-CH=CH-CHO. (v) (vi) Ph CO Ph (i) Hepatan-2-one (ii) 4-Bromo-2-methyl hexanal (iii) Heptanal (iv) 3-phenyl propenal. (Cinnamaldehyde) (v) Cyclopentane carbaldehyde (vi)(benzophenone) 12. Draw structures of the following derivatives. (i) The 2,4-dinitrophenylhydrazone of benzaldehyde (ii) Cyclopropanone oxime (iii) Acetaldehydedimethylacetal. (iv) the semicarbazone of cyclobutanone (v) the ethylene ketal of hexan-3-one (vi) the methyl hemiacetal of formaldehyde 7

8 i. ii. iii.. (iv) (v) (vi) 13. Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents. (i) Tollens reagent (ii) Zinc amalgam and dilute hydrochloric acid. (iii) Ph Mg Br and then (iv) semicarbazide and weak acid 8

9 (v) Excess ethanol and acid (i) (ii). (iii) (iv) (v) 14. Which of the following compounds would undergo aldol condensation, which the cannizaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction. (a) Methanal (b) 2 Methyl pentanal (c) Benzaldehyde (d) Benzo phenone 9

10 (e) Cyclohexanone (f) 3-Phenyl propanal (g) Phenyl acetaldehyde (h) Butan -1-ol (i) 2-2-dimethyl butanal. The criteria for Aldol condensation is the one containing - hydrogen atom. These compounds will undergo condensation with the elimination of water molecule to form αβ unsaturated aldehyde or ketone. Cannizaro reaction is the one in which compounds which do not contain hydrogen atom undergo dispropotionation to form an acid and an alcohol. Therefore, based on the above criteria, compounds (b), (e), (f) (g) undergo Aldol condensation (a) (c) (i) cannizaro reaction (d) and (h) neither. a, c, i undergo Cannizzaro reaction b, e, f, g undergo Aldol condensation d, h neither 15. 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. Propanal and Butanal give two self aldol condensation products as well as two cross aldol condensation products i. Self aldol condensation products of propanal and Butanal 10

11 ii. Cross aldol condensation products c) Between propanol and Butanal. 16. An organic compound with the molecular formula C 9 H 10 O forms 2,4-DNP derivative, reduces Tollens reagent and undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,3-benzenedicarboxylic acid. Identify the compound. As the compound does not contain a hydrogen atom it must be a derivative of Benzaldehyde. It reduces the Tollens reagent forming Silver mirror. 11

12 17. An organic compound (A) Mol.F C 8 H 16 O 2 was hydrolsed with dilute sulphuric acid and produced (B) and an alcohol (C) oxidation of (C) with chromic acid gives (B). Write the possible structures of (A) and give their IUPAC names. 18. Arrange the following compounds in increasing order of their property as indicated: (a) Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN) (b) CH 3 CH 2 CH (Br)COOH, CH 3 CH(Br)CH 2 COOH, (CH 3 ) 2 CHCOOH, CH 3 CH 2 CH 2 COOH (acid strength) (c) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength). (a) Ditert butyl ketone < Methyl ter butyl ketone < Actone < Acetaldhyde (b) (c ) 4 Methoxy benzoic < Benzoic acid < 4 Nitro benzoic acid < 3,4 dinitro benzoic acid. 19. Give simple chemical tests to distinguish between the following pairs of compounds. (a) Propanal and Propanone (b) Phenol and Benzoic acid (c) Benzamide and p Amino benzoic acid (d) Ethanal and propanal (e) Methyl acetate and Ethyl acetate (f) Benzoic acid and Ethyl benzoate 12

13 (g) Propanal and Diethyl ether. (h) pentan-2one and pentan-3 one (i) benzaldehyde and acetophenone (a) Propanal Propanone It gives positive Iodoform test It gives negative Iodoform test Give yellow precipitate of iodoform. No reaction (b) Phenol Phenol does not give effervescence with NaHCO 3. Benzoic acid Benzoic acid gives brisk effervescence with NaHCO 3 solution C 6 H 5 COOH + NaHCO 3 C 6 H 5 COONa + CO 2 + H 2 O (c) Benzamide It does not give effervescence with NaHCO 3. P - Amino benzoic acid Brisk effervescence is produced. (d) Positive Iodoform test Ethanal Propan Negative Iodoform test Yellow precipitate of iodoform 13

14 CH 3 - CHO + 4I 2 + 6NaOH CHI 3 + CH 3 COONa + 5 NaI + 3H 2 O (e) Methyl Acetate Ethyl Acetate CH 3 OH gives negative Iodoform test C 2 H 5 OH gives positive Iodoform test. (f) Benzoic acid C 6 H 5 COOC 2 H 5 Benzoic acid gives a brisk effervescence with NaHCO 3 C 6 H 5 - COOC 2 H 5 + NaH CO 3 No reactio C 6 H 5 COOH + NaHCO 3 C 6 H 5 COONa + CO 2 +H 2 O (g) Negative Iodoform test Propanal Diethyl ether Positive Tollen's reagent test and Fehlings solution test CH 3 - CH 2 - CHO + 2[Ag(NH 3 ) 2 ] H - CH 3 COO - + 2Ag + 4NH 3 + 2H 2 O Diethyl ether does not give a positive Fehlings and Tollen's test CH 3 - CH 2 - CHO + 2Cu OH - R COO - + Cu 2 O + 3H 2 O Reddish brown (h) Pentan-2-one It has the CH 3 CO group and also gives positive iodoform test Pentan-3-one No reaction with I 2 and NaOH (i) Benzaldehyde With Tollen s reagent gives silver mirror Acetophenone No reaction with tollen s reagent 14

15 20. Describe the following: (i) Acetylation (ii) Cannizzaro Reaction (iii) Cross Aldol Condensation (iv) Decarboxylation. (i) Acetylation Acylation/ Acetylation is a reaction in which -CH 3 CO (actyl or acyl group) is introduced into an organic molecule by the replacement of H-atom of Benzene or from OH or NH 2 group. Acetylation it is the reaction of Acid Chlorides and acid anhydrides with alcohols or phenols. (ii) Cannizzaro Reaction Aldehydes which do not contain an a - hydrogen atom, when treated with concentrated alkali solution undergo disproportionation i.e. self oxidation reduction. As a result, one molecule of aldehyde is reduced to the corresponding alcohol at the cost of the other which is oxidized to the corresponding carboxylic acid. (iii) Cross Aldol Condensation If the aldol condensation takes place between two Aldehyds or ketones or between an Aldehyde and ketone e.g. Cross Aldol condensation is possible between one aldehyde/ketone, having no a - H atom and other having a -H atom. 15

16 (iv) Decarboxylation:- It is the removal of CO 2 from an acid molecule. Sodium salts of carboxylic acids when distilled with soda lime (NaOH + CaO) undergo decarboxylation to yield alkanes Predict the organic products of the following reactions. a. b. c. d. e. f. g. 16

17 h. (i) 17

18 22. 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 NH 2 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. (i) 18

19 In cyclohexnone the C atom of the carbonyl group possesses +ve charge necessary for nucleophilic attack whereas in the other compound the methyl groups on the carbon atom induces +I effect considerably reducing the +ve charge, the nucleophilic attack is not facilitated.also the three methyl groups cause steric hindrance. (ii) In semi carbazide H2N NH-CO- NH2 the hydrogen atom close to the carbonyl group is involved in resonance with the CO group and so does not get involved in the reaction (iii) This is due to the reversible nature of the reaction. If water is removed as soon as it is formed according to Le Chatelier s principle the reaction proceeds in the forward direction and more product is formed. Otherwise the reverse reaction will take place. 23. An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollens reagent but forms an addition compound with sodium hydrogensulphite and give positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acid. Write the possible structure of the compound. Element Percentage At. Mass Reactive no of mass Simplest ratio C /12 = /1.16 = 5 H /1 = /1.16 = 10 O /16 = /11.6 = 1 Empirical formula = C 5 H 10 O Empirical formula mass = 5 x x = = 86 Molecular mass = 86 N = Molecular formula mass/empirical formular mass= 86/86 = 1 Molecular formula = C 5 H 10 O The compound does not give Tollen s test.so it is not an aldehyde.it gives addition compound with sodium hydrogen sulphite. So it is a ketone. Gives positive iodoform test. So it is a methyl ketone.it gives ethanoic and propanoic acids on strong oxidation. 19

20 Structure of the compound = CH 3 CO CH 2 CH 2 CH Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why? In carboxylate anion,the negative charge on the oxygen atom is delocalized.but in phenoxide the negative charge on the oxygen is not delocalized. The resonance structures of phenoxide ion,though more in number, are due to the delocalization of electrons of benzene ring and not due to the phenoxide ion.. And is, therefore, a stronger in behaviour. 20

21 (e) 21

ALDEHYDES, KETONES AND CARBOXYLIC ACIDS

Unit - 12 ALDEHYDES, KETONES AND CARBOXYLIC ACIDS 1. Indicate the electrophilic and nucleophilic centres in acetaldehyde. 2. Write the IUPAC names of the following organic compounds : 122 XII Chemistry