InterviewSolution
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InterviewSolution
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(a) An organic compound (A) having molecular formula C_(4) H_(8) O gives orange red precipitate with 2, 4-DNP reagent. It does not reduce Tollens' reagent but gives yellow precipitate of iodoform on heating with NaOH and I_2. Compound (A) on reduction with NaBH_4 gives compound (B) which undergoes dehydration reaction on heating with cone. H_(2) SO_(4)to form compound (C). Compound (C) on ozonolysis gives two molecules of ethanal. Identify (A), (B) and (C) and write their structures. Write the reactions of compound (A) with (i) NaOH//I_2 and (ii) NaBH_4. (b) Give reasons : (i) Oxidation of propanal is easier than propanone. (ii) alpha-hydrogen of aldehydes and ketones is acidic in nature. Or (a) Draw structures of the following derivatives : (i) Cyanohydrin of cyclobutanone (ii) Hemiacetal of ethanal (b) Write the major product(s) in the following : (i) CH_(3) - CH=CH- CH_(2) - CN underset((ii) H_(3) O^(+)) overset((i)"DIBAL"-H)(to) (ii) CH_(3) - CH_(2) - OH overset(CrO_(2)) (to) (c) How can you distinguish between propanal and propanone ? |
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Answer» Solution :(A) `= underset("Butan-2-one")(CH_(3) COCH_(2) CH_(3))` (B) `=CH_(3) - overset(overset(OH)|)(C)underset("Butan-2-ol")(H-CH_(2)) -CH_(3)` ( C) `=CH_(3) - underset("But-2-ene")(CH=CH)- CH_(3)` (D) `=underset("Ethanal")(CH_(3) CHO)` Ketones react with 2, 4-DNP REAGENT to form orange red precipitate. Ketones do not reduce Tollen.s rc,]gent. Methyl ketones (containing `CH_(3) CO-`group) give iodoform test. Hence the above structure of (A).`CH_(3) - overset(overset(O)||)C-CH_(2) - CH_(3) underset("NaOI")overset(NaOH//l_(2) )(to) underset("Iodoform")(CHI_(3)) +underset("Sodium propionate")(CH_(3) CH_(2) COONa)` `CH_(3) -overset(overset(O)||)C-CH_(2) underset(2[H]) overset(NaBH_(4) ) to CH_(3) -overset(overset(O)||) (C) underset("Butan-2-ol")(H- CH_(2) )- CH_(3)` (b) (i) Oxidation of propanal is easier than propanone Propanol is easily oxidised to PROPANOIC acid on treatment with common oxidising agents like nitric acid, POTASSIUM permanganate or potassium dichromate. Oxidation of propanone involves breaking of carbon-carbon bond and therefore requires drastic conditions. (ii) `alpha-` hydrogen of ALDEHYDES and ketones is acidic in nature  The species obtained after the removal of H+ is stabilised by resonance. OR (a) (i) Cyanohydrin of cyclobutanone  (ii) HEMIACETAL of ethanal  (b) (i) `CH_(3) - underset("Pent-3-enal") (CH = CH )- CH_(2) - CHO` (ii) `underset("Ethanal")(CH_(3) CHO)` (c) Distinguish between propanal and propanone. Tollens. Reagent Test: Propanal on treatment with ammoniacal silver nitrate gives a bright silver mirror. This test is not given by propanone. Fehling.s Solution Test: Propanal on heating with Fehling solution gives a reddish brown precipitate. Propanone does not give this test. |
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