question_answer 9)

What is meant by the following terms? Give an example ofthe reaction in each case. (i) Cyanohydrin                                 (ii) Acetal (iii) Semicarbazone                          (iv) Aldol (v) Hemiacetal                  (vi) Oxime (vii) Ketal                                             (viii) lmine (ix) 2,4-DNP derivative                  (x) Schiffs base   (i) Product of addition reaction of carbonyl group with HCN. (ii) Reaction of aldehyde with monohydric alcohol. (iii) Reaction of carbonyl compound with semicarbazide, (iv) Carbonyl compounds with a-H atom react with dil, NaOH (catalyst) (v) Addition of monohydric alcohol with aldehyde. (vi) Reaction of carbonyl compound with hydroxylamine. (vii) Reaction of ketone with ethylene glycol. (viii) Reaction of carbonyl compound with ammonia derivatives. (ix) 2,4-DNP derivative of carbonyl compound. (x) Reaction of carbonyl compound with primary amines.  

Answer:

(i) Cyanohydrin Addition products formed by the reactionof aldehydes and ketones with hydrogen cyanide(HCN) areknown as cyanohydrins.   For example   (ii) Acetal When an aldehyde reacts with two equivalents of amonohydric alcohol in the presence of dry  gas, gem-dialkoxycompounds are formed; which are known as acetals. In acetal, twoalkoxy groups are present on the terminal C-atom. For example:     (iii) Semicarbazone The compounds formed on the reaction ofaldehydes   /ketones   with   semicarbazide   are   calledsemicarbazones. For example: (iv) Aldol When an aldehyde (or ketone) having at least onea-hydrogen atom undergo a reaction in the presence of dilutealkali as catalyst to form aldol or p-hydroxyaldehydes (or ketals incase of ketones), the reaction is called aldol condensation. For example: (v) Hemiacetal When an aldehyde reacts with one molecule of amonohydric alcohol in presence of dry  gas, gem-alkoxyalcohols are formed. These are known as hemiacetals. For example:   (vi) Oxime When an aldehyde or ketone reacts with hydroxyiamine inweak acidic medium, the product obtained is known as oxime.   (vii) Ketal The compound formed by heating a ketone with ethyleneglycol in the presence of dry HCl gas is known as ketal(gem-dialkoxy alkane). For example:     (viii) Imine Compounds formed by the reaction of aldehydes andketones with ammonia derivatives are called imines. These compounds contain  group. General reaction is:   Z = Alkyl, aryl, OH,  etc. (ix) 2,4-DNP derivative 2,4-dinitrophenyl hydrazine reacts withaldehyde or ketone to produce 2,4-din'i.trophenvi hyarazones (i.e.,2,4-DNP derivative). The reaction takes place in weak acidicmedium.     Uses 2,4-DNP derivatives are used for the identification ofaldehydes and ketones. (x) Schifi's base When an aldehyde or ketone reacts with primary aliphatic or aromatic amines, the formed compound is called Schiff base or azomethine.