Solution: (v) Hemiacetals are a type of α−alkoxyalcohols. A hemiacetal's overall structure. Aldehyde interacts with one molecule of monohydrated alcohol in the presence of dry HCl gas. (vi) Oxime:...
Question 12.1: What is meant by the following terms? Give an example of the reaction in each case. (iii) Semicarbazone (iv) Aldol
Solution: (iii) Semicabarbazone: Semicarbazone is made up of aldehydes and ketones, and it is generated when a ketone or aldehyde reacts with semicarbazide. The reaction type is condensation....
Question 12.1: What is meant by the following terms? Give an example of the reaction in each case. (ii) Acetal
Acetal refers to gemdialkoxy alkanes with two groups of alkoxy at the terminal carbon atom. The alkyl group is...
15.1 What is meant by the following terms? Give an example of the reaction in each case. (i) Cyanohydrin
Cyanohydrins are organic compounds having the formula RR'C(OH)CN, where R and R ‘ are alkyl or aryl groups. Aldehydes and ketones react with hydrogen cyanide in the presence of excess sodium cyanide...
Question 12.19: 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.
Solution: The number of carbon, hydrogen, and oxygen atoms in an organic compound can thus be expressed as: Therefore, the empirical formula of the compound is C5H10O. Now, the empirical formula...
Question 12.20: Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why?
Solution: The phenoxide ion has the following resonance structures: The resonance structures of the phenoxide ion show that less electronegative carbon atoms carry a negative charge in II, III, and...
Question 12.18: Give a plausible explanation for: (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.
Solution: In the presence of an acid, an ester along with water is generated reversibly from a carboxylic acid and an alcohol. Because the reaction is reversible, if either water or ester is not...
Question 12.18: Give a plausible explanation for: (ii) There are two −NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.
Solution: Only one of the two −NH2 groups, which is connected directly to the carbonyl-carbon atom, undergoes resonance in semicarbazide. As a result, the electron density on the −NH2 group in the...
Question 12.18: Give a plausible explanation for: (i) Cyclohexanone forms cyanohydrin in good yield but 2, 2, 6 trimethylcyclohexanone does not.
Solution: (i) According to the equation below, cyclohexanones produce cyanohydrins. There will be no steric hindrance in this situation, allowing the nucleophile CN– to attack with ease. However,...
Question 12.25: Complete each synthesis by giving missing starting material, reagent or products
Solutions:
Question 12.24: Complete each synthesis by giving missing starting material, reagent or products
Solutions:
Question 12.23: Complete each synthesis by giving missing starting material, reagent or products
Solutions:
Question 12.22: Complete each synthesis by giving missing starting material, reagent or products.
Solutions:
Question 12.21: Complete each synthesis by giving missing starting material, reagent or products.
Solutions:
Question 12.20: Complete the synthesis by giving missing starting material, reagent or products.
Solution:
Question 12.19: Describe decarboxylation.
Decarboxylation is the process by which carboxylic acids lose carbon dioxide and create hydrocarbons when their sodium salts are heated with soda-lime. Decarboxylation occurs when alkali metal salts...
Question 12.18: Describe Cross aldol condensation.
Cross-aldol condensation occurs when two different aldehydes, two different ketones, or an aldehyde and a ketone react together. If both reactants contain α-hydrogens, four compounds are produced as...
Question 12.17: Describe Cannizzaro reaction.
The self-disproportionation (oxidation-reduction) reaction of aldehydes with no alpha hydrogens, when treated with concentrated alkalis, is known as the Cannizzaro reaction. In this reaction, one...
Question 12.16: Describe Acetylation.
Acetylation is the process of adding an acetyl function group to a chemical molecule. When this process is carried out, bases such as pyridine, dimethylaniline, and others are present. In this...
Question 12.15.5: How will you bring about the following conversions in not more than two steps? (ix) Benzoic acid to m- Nitrobenzyl alcohol
Question 12.15.4: How will you bring about the following conversions in not more than two steps? (vii) Benzaldehyde to 3-Phenylpropan-1-ol (viii) Benazaldehyde to α-Hydroxyphenylacetic acid
Question 12.15.3: How will you bring about the following conversions in not more than two steps? (v) Benzaldehyde to Benzophenone (vi) Bromobenzene to 1-Phenylethanol
Question 12.15.2: How will you bring about the following conversions in not more than two steps? (iii) Ethanol to 3-Hydroxybutanal (iv) Benzene to m-Nitroacetophenone
Question 12.15.1: How will you bring about the following conversions in not more than two steps? (i) Propanone to Propene (ii) Benzoic acid to Benzaldehyde
Question 12.14: How will you prepare the following compounds from benzene? You may use any inorganic reagent and any organic reagent having not more than one carbon atom. (v) p-Nitrobenzaldehyde
Question 12.14: How will you prepare the following compounds from benzene? You may use any inorganic reagent and any organic reagent having not more than one carbon atom. (iii) p-Nitrobenzoic acid (iv) Phenylacetic acid
Question 12.14: How will you prepare the following compounds from benzene? You may use any inorganic reagent and any organic reagent having not more than one carbon atom. (i) Methyl benzoate (ii) m-Nitrobenzoic acid
Solution:
Question 12.13: 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
Solution: (i) Propanal and propanone can be distinguished by the following tests. (a) Tollen’s test Because propanal is an aldehyde, it reduces Tollen's reagent. However, because propanone is a...
Question 12.12: 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)
Solution: (i) The attacking species when HCN reacts with a compound, is a nucleophile, CN–. The reactivity of HCN decreases when the negative charge on the compound increases. The +I effect and...
Question 12.11: 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.
Solution: According to the question, A is an organic compound having molecular formula C8H16O2. This gives a carboxylic acid (B) and an alcohol (C) on hydrolysis with dilute sulphuric acid. Thus,...
Question 12.10: 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.
Solution: According to the question, the compound has molecular formula C9H10O and forms 2, 4-DNP derivative while also reducing Tollen’s reagent. Therefore, the given compound must be an aldehyde....
Question 12.9: Write structural formulae 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
Solution: (i) One molecule of propanal acts as a nucleophile and the other molecule acts as an electrophile. (ii) One molecule of butanal acts as a nucleophile and the other as an...
Question 12.8: How will you convert ethanal into Butane-1, 3-diol?
Solution: Ethanal on reaction with dilute alkali produces 3-hydroxybutanal and then on further reduction with NaBH4 gives butane-1, 3-diol.
Question 12.7: 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 (ii) 2-Methylpentanal (iii) Benzaldehyde (iv) Benzophenone (v) Cyclohexanone (vi) 1-Phenylpropanone (vii) Phenylacetaldehyde (viii) Butan-1-ol (ix) 2, 2-Dimethylbutanal
Solution: The compounds (ii) 2−methylpentanal, (v) cyclohexanone, (vi) 1-phenylpropanone, and (vii) phenylacetaldehyde contain one or more α-hydrogen atoms. Therefore, these undergo aldol...
Question 12.6: Predict the products formed when cyclohexanecarbaldehyde reacts with the following reagents: (i) PhMgBr and then H3O+ (ii)Tollens’ reagent (iii) Semicarbazide and weak acid (iv)Excess ethanol and acid (v) Zinc amalgam and dilute hydrochloric acid
Solution:
Question 12.5: 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...
Question 12.4: Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.
(i) CH3CO(CH2)4CH3 (ii) CH3CH2CHBrCH2CH(CH3)CHO (iii) CH3(CH2)5CHO (iv)Ph-CH=CH-CHO (v) (vi) PhCOPh Solution: (i) CH3CO(CH2)4CH3 IUPAC name: Heptan-2-one Common name: Methyl pentyl ketone (ii)...
Question 12.3: Draw the structures of the following compounds.
(i) 3-Methylbutanal (ii) p-Nitropropiophenone (iii) p-Methylbenzaldehyde (iv)4-Methylpent-3-en-2-one (v) 4-Chloropentan-2-one (vi) 3-Bromo-4-phenylpentanoic acid (vii)...