NCERT Solutions For Class 12 Chemistry Chapter 12 Aldehydes Ketones and Carboxylic Acids: Free PDF

A 12.1 (i) The compound contains ether group and an aldehydic functional group with the longest chain having 3 carbon atoms. α means the position of the carbon atom attached to attached to the carbon atom of the functional group, in this case, it is an aldehyde functional group.

• (ii) The compound contains an alcoholic group and an aldehydic functional group with the longest chain having 4 carbon The numbering of the chain starts from a carbon atom of aldehyde group.
• (iii) The compound contains alcoholic group and an aldehydic functional group with the longest chain having 5 carbon atoms which are cyclic in The numbering of the chain starts from a carbon atom of aldehyde group attached to the cyclopentane ring.
• (iv) The compound contains ketone group and an aldehydic functional group with the longest chain having 5 carbon The numbering of the chain starts from a carbon atom of aldehyde group.
• (v) The compound contains ketone functional group with the longest chain having 8(butyl is used because there is two similar butyl group attached to the carbonyl carbon of ketone group) carbon
• (vi) The compound contains a fluorine atom and a ketone functional group with the longest chain which is a derivative of a phenyl group and an acetyl substituent.

A 12.2 dia

• CH₃ CHO, CH₃ CH₂OH, CH₃OCH₃ , CH₃ CH₂ CH₃

A 12.3 The molecular masses of the given compounds are in the range of 44-66 g/mol. The second molecule, CH₃CH₂OH contains OH alcoholic group due to which it undergoes extensive H bonding with each other, leading to the association of the molecules. Therefore it has a highest boiling point. In the molecule CH₃CHO , there is strong intermolecular dipole-dipole attraction due to presence of - CHO aldehydic group( as H will have partial positive charge and oxygen will have partial negative charge, so there will attraction between molecules),which is weak in case of CH₃OCH₃ as both CH₃ groups have +I effect which results in decrease in electron affinity for the oxygen attached to it( with no partially positive H atom). And in CH₃CH₂CH₃ there are only weak van der Waals forces of attraction. So the compounds in increasing order of their boiling point are:

CH₃CH₂CH₃< CH₃OCH₃< CH₃CHO< CH₃CH₂OH.

A 12.4 (i) Ethanal, Propanal, Propanone, Butanone

The +I effect increases in the order as:

Ethanal

Therefore the electron density of the carbonyl carbon increases as the +I effect due to the alkyl group increases. As a result, the chances of attack by a nucleophile (which are rich in electron and carries a negative charge, not necessary usually have a lone pair of an electron) decreases because the carbonyl carbon has electron density on it. Hence the increasing order of the reactivity of given compounds in nucleophilic addition reaction is:

Ethanal > Propanal> Propanone > Butanone.

(ii) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone:

The +I effect is more in ketone than in aldehyde because in ketone there are 2 alkyl groups contributing in the +I effect whereas in aldehydes there is only one alkyl group. Hence, acetophenone(being ketone group attached to it) is the least reactive in nucleophilic addition reactions.

Among aldehydes, the +I effect is the highest in p-tolualdehyde because of the presence of the electron- donating –CH₃ group(which increase the electron density on the carbonyl carbon via resonance through the benzene ring) and the lowest in p-nitrobenzaldehyde because of the presence of the electron- withdrawing –NO₂ group(which decreases the electron density on the carbonyl carbon via resonance through the benzene ring). Hence, the increasing order of the reactivity of the given compounds is:

Acetophenone<p-tolualdehyde p-Nitrobenzaldehyde

A 12.5 Cyclopentanone reacts with hydroxylamine to give cyclopentanone oxime. As you can see the cyclopentanone has ketone functional group with oxygen attached to carbonyl carbon and the hydroxylamine has two H atoms attached to N. And hence in the product this O and two H atoms are removed and form a water molecule.

Remember if any aldehyde or ketone bearing compound reacts with primary or secondary amine then for finding the product formed simply remove the oxygen atom from the aldehyde or ketone functional group and two H atoms attached to N in amines and add a double bond between C and N.

 

 

A 12.6 (i) Ph CH₂ CH₂ COOH The compound contains carboxylic acid as the functional group and Ph means a phenyl group. The longest chain contains 3 carbon atom with phenyl group of carbon 3 so the IUPAC name of the compound is 3-phenylpropanoic

• (ii) (CH₃ ) ₂ C=CHCOOH

The longest chain contains 4 carbon atom with a methyl group as a substituent and a carboxylic acid as a functional group. The no. Of the chain starts from the carbon atom of the –COOH group with double bond on carbon 2 so the IUPAC name of the compound is 3-Methylbut-2-enoic acid.

• (iii) The longest chain has 5 carbon atom(all are saturated) which are cyclic with the carboxylic group attached and a methyl group as a substituent. The no. Of the chain starts from the carbon atom of the – COOH group so the IUPAC name of the compound is 2-Methylcyclopentane carboxylic acid.
• (iv) The longest chain is derivative of benzene with the carboxylic group attached and 3 nitro groups. The number of the chain starts from the carbon atom of the –COOH group so the IUPAC name of the compound is 2,4,6-Trinitrobenzoic acid.

A 12.7 (i) Ethylbenzene

In the presence of nascent oxygen i.e. [O] along with KMnO₄/ KOH(it is a very strong oxidizing agent which oxidizes the whole alkyl group to carboxylic salt) followed by hydrolysis leads to the formation of benzoic acid. Carbon dioxide and water are formed as byproducts.

(ii) Acetophenone

The oxidation with alcoholic KMNO₄ followed by hydrolysis leads to the formation of benzoic acid. The reaction is given below:

(iii) Bromobenzene is first reacted with magnesium in presence of dry ether to give an intermediate which on reaction with solid carbon dioxide followed by hydrolysis leads to the formation of benzoic acid.

(iv) Phenylethene (Styrene)

Here the oxidation of styrene with alcoholic KMNO₄ is followed by hydrolysis leads to the formation of benzoic acid.

(i) CH₃CO₂H or CH₂FCO₂H (ii) CH₂FCO₂H or CH₂ClCO₂H

(iii) CH₂ FCH₂ CH₂ CO₂H or CH₃ CHFCH₂ CO₂H

A 12.8 (i) The +I effect of –CH₃ group increases the electron density on the O-H bond. Therefore, the release of proton becomes difficult. On the other hand, the -I effect of F decreases the electron density on the O-H bond. Therefore, the proton can be released easily. Hence, CH₂FCO₂H is a stronger acid than CH₃CO₂H.

• (ii) F has stronger -I effect than Cl(as fluorine is more electronegative than chlorine). Therefore, CH₂FCO₂H can release proton more easily than CH₂ClCO₂H. Hence, CH₂FCO₂H is a stronger acid than CH₂ClCO₂H.
• (iii) Inductive effect decreases with increase in distance (the more will be the distance of the inductive group from the carboxylic group less will be its effect of polarisability). Hence, the -I effect of F in CH₃CHFCH₂CO₂H is more than it is in CH₂FCH₂CH₂CO₂H . Hence, CH₃CHFCH₂CO₂H is a stronger acid than CH₂FCH₂CH₂CO₂H .
• (iv) Due to the -I effect of F (being electronegative), it is easier to release proton in the case of compound (A). However, in the case of compound (B), the release of the proton is difficult due to the +I effect of –CH₃ e. methyl group. Hence, (A) is a stronger acid than (B).

A 12.1 (i) Cyanohydrin:

Cyanohydrins are those organic compounds having the formula RR“²C(OH)CN, wherever R and R“² can be alkyl or aryl groups.

Aldehydes and ketones react with compound (KCN) within the presence of excess cyanide (NaCN) as a catalyst to field organic compound.

• (ii) Acetal:

Acetals are gem - dialkoxy alkanes within which 2 alkoxy teams groups attached to the terminal atom. One bond is connected to associate degree alkyl whereas the opposite is connected to the hydrogen atom.

When aldehydes are treated with 2 equivalents of a monohydric alcohol within the presence of dry HCl gas, hemiacetals are produced which are further reacted with one more molecule to alcohol to yield acetal as shown below:

• (iii) Semicarbarbazone:

Semicarbazones are the derivatives of organic compounds produced by the condensation reaction between a ketone or aldehyde and semicarbazide.

Semicarbazones square measure helpful for identification and characterization of aldehydes and ketones.

• (iv) Aldol:

An aldol is a β-hydroxy organic compound. It's produced by the by the condensation reaction of 2 molecules of an equivalent or one molecule every of 2 totally different aldehydes or ketones within the presence of a base.

The reaction is shown as below:

• (v) Hemiacetals are α-alkoxyalcohols.

Aldehyde reacts with one molecule of a monohydric alcohol in the presence of dry HCl gas to from aloxy alcohol, known as hemiacetal.

The following reaction shows the formation of hemiacetal:

• (vi) Oxime:

Oximes are a category of organic compounds having the final formula RR“²CNOH, where R is an associate organic aspect chain associated R“² is either H or an organic aspect chain. If R“² is H, then it's called aldoxime associated if R“² is an organic aspect chain, it's called ketoxime.

On treatment with hydroxylamine in a very decrepit acidic medium, aldehydes or ketones kind oximes.

• (vii) Ketal:

Ketals area gem – dialkoxyalkanes in which two which 2 alkoxy teams are attached inside the chain. The opposite 2 bonds of the atom are unit connected to 2 alkyl groups.

The general structure of ketal is shown as below:

Ketones react with glycol within the presence of dry HCl gas to grant a cyclic product referred to as glycol ketals.

(vii) Imine:

An organic compound which contains a carbon–nitrogen double bond. The structure of imine is shown as below:

Imines are produced when aldehydes and ketones react with ammonia Gas.

• (ix) 2, 4 - DNP - derivative:

2, 4 - DNP - derivative is a substituted hydrazine,

The molecular formula for 2,4-DNP–derivative is C₆H₃(NO₂)₂NHNH₂.

The other name is Dinitrophenylhydrazine is the chemical compound. Dinitrophenylhydrazine is a red to orange solid. An aldehydes or ketones react with 2, 4 - dinitrophenylhydrazine to form yellow, orange, or red coloured derivatives named as 2,4 dinitrogenphenylhydrazones. These are also known as 2,4-DNP derivative.

• (x) Schiff's base:

Aldehydes and ketones on react with primary amines in the presence of trace of an acid yields a Schiff's base.

(i) CH₃CH(CH₃ )CH₂CH₂CHO                                          (ii) CH₃CH₂COCH(C₂H₅ )CH₂CH₂Cl

(iii) CH₃CH=CHCHO                                                         (iv) CH₃COCH₂COCH₃

(v) CH₃CH(CH₃ )CH₂C(CH₃ )₂COCH₃                            (vi) (CH₃ )₃CCH₂COOH

(vii) OHCC₆H₄CHO-p

A 12.2 

A 12.3 

• CH₃CO(CH₂ )₄CH₃
• CH₃CH₂CHBrCH₂CH(CH₃ )CHO
• CH₃ (CH₂ )₅CHO
• Ph-CH=CH-CHO

A 12.4 

A 12.5 

A 12.6 

A 12.7

• Aldehydes and ketones having at least one α-hydrogen undergo aldol The compounds

(ii) 2-methylpentanal (v)cyclohexanone

• 1-phenylpropanone
• phenylacetaldehyde

contain one or more α-hydrogen atoms. Therefore, these undergo aldol condensation.

• Aldehydes having no α-hydrogen atoms undergo Cannizzaro The compounds

(i) Methanal (iii)Benzaldehyde

• 2, 2-dimethylbutanal

do not have any α-hydrogen. Therefore, these undergo cannizzaro reactions.

• Compound (iv) Benzophenone is a ketone having no α-hydrogen atom and compound (viii) Butan-1-ol is an alcohol. Hence, these compounds do not undergo either aldol condensation or cannizzaro

Structures of the expected products of aldol condensation and Cannizzaro reaction- Aldol condensation-

(ii) 2-methylpentanal-

• cyclohexanone-
• 1-phenylpropanone-
• phenylacetaldehyde –

Cannizzaro reaction-

(i) Methanal-

(iii) Benzaldehyde –

(ix) 2, 2-dimethylbutanal –