What is meant by the following terms? Give an example of the reaction in each case.
\((i)\)\(Cyanohydrin\)
\((ii)Acetal \)
\((iii)Semicarbazone \)
\((iv)Aldol \)
\((v)Hemiacetal \)
\((vi)Oxime \)
\((vii)Ketal \)
\((vii)Imine \)
\((ix)\)\(2,4-DNP-derivative \)
\((x)Schiff's base\)
What is meant by the following terms? Give an example of the reaction in each case.
\((i)\)\(Cyanohydrin\)
\((ii)Acetal \)
\((iii)Semicarbazone \)
\((iv)Aldol \)
\((v)Hemiacetal \)
\((vi)Oxime \)
\((vii)Ketal \)
\((vii)Imine \)
\((ix)\)\(2,4-DNP-derivative \)
\((x)Schiff's base\)
Solution and Explanation
(i) Cyanohydrin:
Cyanohydrins are organic compounds having the formula\( RR“²C(OH)CN,\) where R and \(R“²\) can be alkyl or aryl groups.
Aldehydes and ketones react with hydrogen cyanide (HCN) in the presence of excess sodium cyanide (NaCN) as a catalyst to field cyanohydrin. These reactions are known as cyanohydrin reactions.
Cyanohydrins are useful synthetic intermediates.
(ii) Acetal:
Acetals are gem - dialkoxy alkanes in which two alkoxy groups are present on the terminal carbon atom. One bond is connected to an alkyl group while the other is connected to a hydrogen atom.
When aldehydes are treated with two equivalents of a monohydric alcohol in the presence of dry HCl gas, hemiacetals are produced that further react with one more molecule of alcohol to yield acetal.
(iii) Semicarbarbazone:
Semicarbazones are derivatives of aldehydes and ketones produced by the condensation reaction between a ketone or aldehyde and semicarbazide.
Semicarbazones are useful for identification and characterization of aldehydes and ketones.
(iv) Aldol: A β-hydroxy aldehyde or ketone is known as an aldol. It is produced by the condensation reaction of two molecules of the same or one molecule each of two different aldehydes or ketones in the presence of a base. 
(v) Hemiacetal:
Hemiacetals are α - alkoxyalcohols
General structure of a hemiacetal Aldehyde reacts with one molecule of a monohydric alcohol in the presence of dry HCl gas.
(vi) Oxime:
Oximes are a class of organic compounds having the general formula \(RR“²CNOH\), where R is an organic side chain and \(R“² \) is either hydrogen or an organic side chain. If R“² is H, then it is known as aldoxime and if R“² is an organic side chain, it is known as ketoxime.
On treatment with hydroxylamine in a weakly acidic medium, aldehydes or ketones form oximes.
(vii) Ketal:
Ketals are gem - dialkoxyalkanes in which two alkoxy groups are present on the same carbon atom within the chain. The other two bonds of the carbon atom are connected to two alkyl groups.
Ketones react with ethylene glycol in the presence of dry HCl gas to give a cyclic product known as ethylene glycol ketals.
(viii) Imine:
Imines are chemical compounds containing a carbon nitrogen double bond.
Imines are produced when aldehydes and ketones react with ammonia and its derivatives.
(ix) 2, 4 - DNP - derivative:
2, 4 - dinitrophenylhydragones are 2, 4 - DNP - derivatives, which are produced when aldehydes or ketones react with 2, 4 - dinitrophenylhydrazine in a weakly acidic medium
To identify and characterize aldehydes and ketones, 2, 4 - DNP derivatives are used.
(x) Schiff's base:
Schiff's base (or azomethine) is a chemical compound containing a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group-but not hydrogen. They have the general formula \(R1R2C = NR3\). Hence, it is an imine.
It is named after a scientist, Hugo Schiff. 
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(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
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Top CBSE CLASS XII Aldehydes, Ketones and Carboxylic Acids Questions
Name the following compounds according to IUPAC system of nomenclature:
\((i) CH_3CH(CH_3)CH_2CH_2CHO \)
\((ii) CH_3CH_2COCH(C_2H_5)CH_2CH_2Cl \)
\((iii) CH_3CH=CHCHO \)
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\((iv) Ph-CH=CH-CHO\)
\((v)\)
\((vi) PhCOPh\)Draw structures of the following derivatives.
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(ii)Cyclopropanone oxime
(iii)Acetaldehydedimethylacetal
(iv)The semicarbazone of cyclobutanone
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(vi)The methyl hemiacetal of formaldehydePredict the products formed when cyclohexanecarbaldehyde reacts with 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 acidWhich 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.
\((i) Methanal \)
\((ii) 2-Methylpentanal \)
\((iii) Benzaldehyde \)
\((iv) Benzophenone \)
\((v) Cyclohexanone \)
\((vi) 1-Phenylpropanone \)
\((vii) Phenylacetaldehyde \)
\((viii) Butan-1-ol \)
\((ix) 2, 2-Dimethylbutanal\)
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