Question -
Answer -
(i) Cyanohydrin (ii) Acetal
(iii) Semicarbazone (iv) Aldol
(v) Hemiacetal (vi) Oxime
(vii) Ketal (vii) Imine
(ix) 2,4-DNP-derivative (x) Schiff’sbase
Answer
(i) Cyanohydrin:
Cyanohydrins are organic compounds having the formulaRR′C(OH)CN, where R and R′ can be alkyl or aryl groups.
Aldehydes and ketones react with hydrogen cyanide (HCN) inthe presence of excess sodium cyanide (NaCN) as a catalyst to fieldcyanohydrin. These reactions are known as cyanohydrin reactions.
Cyanohydrins are useful synthetic intermediates.
(ii) Acetal:
Acetals are gem−dialkoxy alkanes in which two alkoxygroups are present on the terminal carbon atom. One bond is connected to analkyl group while the other is connected to a hydrogen atom.
When aldehydes are treated with two equivalents of amonohydric alcohol in the presence of dry HCl gas, hemiacetals are producedthat further react with one more molecule of alcohol to yield acetal.
(iii) Semicarbarbazone:
Semicarbazones are derivatives of aldehydes and ketonesproduced by the condensation reaction between a ketone or aldehyde andsemicarbazide.
Semicarbazones are useful for identification andcharacterization of aldehydes and ketones.
(iv) Aldol:
A β-hydroxy aldehyde or ketoneis known as an aldol. It is produced by the condensation reaction of twomolecules of the same or one molecule each of two different aldehydes orketones 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 alcoholin the presence of dry HCl gas.
(vi) Oxime:
Oximes are a class of organic compounds having the generalformula RR′CNOH, where R is an organic side chain and R′ is either hydrogen oran organic side chain. If R′ is H, then it is known as aldoxime and if R′ is anorganic 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 groupsare present on the same carbon atom within the chain. The other two bonds ofthe carbon atom are connected to two alkyl groups.
Ketones react with ethylene glycol in the presence of dryHCl gas to give a cyclic product known as ethylene glycol ketals.
(viii) Imine:
Imines are chemical compounds containing a carbon nitrogendouble bond.
Imines are produced when aldehydes and ketones react withammonia 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 chemicalcompound containing a carbon-nitrogen double bond with the nitrogen atomconnected to an aryl or alkyl group-but not hydrogen. They have the generalformula R1R2C = NR3. Hence, it is an imine.
It is named after a scientist, Hugo Schiff.
Aldehydes and ketones on treatment with primary aliphaticor aromatic amines in the presence of trace of an acid yields a Schiff’s base.
