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“Aldehydes, Ketones, and Carboxylic Acids” chapter of Chemistry Class 12 teach about the physical and chemical properties of ketones, carboxylic acids, and aldehydes; their uses, mechanism of nucleophilic addition, methods of preparation, acidic nature, nature of carbonyl group, etc.
Give names of the reagents to bring about the following conversions :
Arrange the following compounds in the increasing order of their boiling points :
Would you expect benzaldehyde to be less or more reactive in nucleophilic addition reactions than propanal ? Explain.
The carbon atom of the carbonyl group of benzaldehyde is less electrophilic than carbon atom of the carbonyl group in the propanal. This is because the polarity of the carbonyl group is decreased in benzaldehyde due to resonance. Therefore, benzaldehyde is less reactive than propanal.
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 Tollen's reagent or Fehling solution, 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 compound (A) and (B) and explain the reactions involved.
Write chemical reactions to affect the following transformations:
Write the structures of the following compounds :
Write the structures of products of the following reactions :
Arrange the following compounds in the increasing order of their boiling points :
CH3CHO, CH3CH2OH, CH3OCH3, CH3CH2CH3
Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions:
(i) As we move from ethanal to propanal, to propanone to butanone, the +I inductive effect of alkyl group increases. As a result, the +ve charge on the carbon atom of the carbonyl group progressively decreases and hence attack by nucleophile becomes slower and slower.
Predict the products of the following reactions :
Give the IUPAC names of the following compounds :
(i) PhCH2CH2COOH (ii) (CH3)2C==CHCOOH
Show how each of the following compounds could be converted to benzoic acid :
(i) Ethylbenzene (ii) Acetophenone (iii) Bromobenzene (iv) Phenylethene (Styrene)
Which acid of each pair shown here would you expect to be stronger ?
What is meant by the following terms ? Give an example in each case.
The compounds containing hydroxyl and cyano groups on the same carbon atom are called cyanohydrins. These are also called gem-hydroxynitriles. These are obtained by the addition of HCN to a carbonyl group in weakly basic medium :
Name the following compounds according to IUPAC system of nomenclature:
Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.
Draw structures of the following derivatives :
Predict the product formed when cyclohexanecarbaldehyde reacts with following reagents :
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.
(ii) 2-Methylpentanal (v) 1-cyclohexanone, (vi) 1-Phenylpropanone and (vii) phenylacetaldehyde contain one or more a-hydrogen atoms and therefore, undergo aldol condensation.
How will you convert ethanal into the following compounds ?
Write structural formulas and names of the four possible aldol condensation products from propanal and butanal. In each case, indicate which aldehyde served 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.
The given compound forms 2,4-DNP derivative. Therefore, it is an aldehyde or ketone. Since it reduces Tollen’s reagent, it must be an aldehyde. The compound undergoes Cannizzaro’s reaction, so it does not contain a-hydrogen. On vigorous oxidation, it gives 1,2-benzendicarboxylic acid, it means that it must be containing alkyl group at 2-position with respect to CHO group on the benzene ring.
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.
(a) Since the given compound on hydrolysis with dil. H2SO4 gives carboxylic acid (B) and an alcohol (C), it must be an ester.
(b) Since the oxidation of alcohol (C) gives the acid B, therefore, both the carboxylic acid B and alcohol C must contain same number of C atoms.
(c) Since ester (A) contains 8 carbon atoms, therefore, both carboxylic acid (B) and the alcohol (C) must contain 4 C atoms each.
(d) Alcohol (C) on dehydration gives but-1-ene and therefore, C must be a straight chain alcohol i.e., butan-1-ol.
(e) (B) is obtained by the oxidation of (C) and therefore, B must be butanoic acid.
This also suggests that the ester (A) must be butyl butanoate. The relevant reactions are:
Arrange the following compounds in increasing order of their property as indicated :
(i) The reactivity towards HCN addition decreases as + I effect of alkyl group (or groups) increases and /or the steric hindrance to the nucleophilic attack by CN– at the carbonyl carbon increases.br> Thus, the increasing order of reactivity is :
Give simple chemical tests to distinguish between the following pairs of compounds :
(i) Propanal and propanone
(a) Propanal gives silver mirror with Tollen’s reagent.
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.
Describe the following:
(i) Acetylation
The replacement of an active hydrogen of alcohols, phenols or amines with acetyl group to form corresponding esters or amides is called acetylation. It is carried out by using acid chlorides or anhydrides in the presence of a base such as pyridine, dimethyl aniline, etc. For example,
Complete each synthesis by giving missing starting material, reagent or products
Give plausible explanation for each of the following:
(i) Cyclohexanone forms cyanohydrin in good yield.
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 hydrogen sulphite and give positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acid. Write the possible structure of the compound.
Step 1: To determine the molecular formula of the compound
%C = 69.77, % H = 11.63
%O = 100 – (69.77 + 11.63) = 18.60
Simple atomic ratio
Although phenoxide ion has more number of resonating structure than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why?
The phenoxide ion has more number of resonating structures but carboxylic acid is more stronger acid than phenol. This is because the electron charge in the carboxylate ion is more dispersed in comparison to phenate ion since there are two electronegative oxygen atoms in carboxylate ion as compared to only one oxygen atom in phenate ion.
In other words, carboxylate ion is relatively more stable as compared to phenate ion. Thus, the release of H+ ion from carboxylic acid is comparatively easier and therefore, it behaves as stronger acid than phenol.
