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An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollens' reagent but forms an addition compound with sodium hydrogensulphite and gives positive iodoform test. On vigorous oxidation, it gives ethanoic and propanoic acid. Write the possible structure of the compound |
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Answer» Solution :Step 1. To find out the molecular formula of the compound. Percentage of carbon = 69.77 Percentage of hydrogen = 11.63 Percentage of oxygen = 100 - (69.77 + 11.63) = 18.6 (By difference) Calculate atomic ratio as under: `C: H : O = (69.77)/12 : (11.63)/1 : (18.6)/16 = 5.88 : 11.63 : 1.16 = 5 : 10 :1` The empirical formula of the GIVEN compound is `C_(5)H_(10)O` `therefore` Empirical formula mass `= 5 xx 12 + 10 xx 1 + 1 xx 16 = 60 + 10 + 16= 86` Molecular mass=86 (given) Molecular formula = `C_(5)H_(10)O xx 86/86 = C_(5)H_(10)O` Thus, molecular formula of the given compound `=C_(5)H_(10)O` Step 2. To determine the structure of the compound. (i) As the given compound forms sodium hydrogen sulphite addition product, it is an aldehyde or ketone., (II) As the compound does not reduce Tollens. reagent, it is not an aldehyde and hence it MUST be a ketone. (ii) As the compound gives positive iodoform test, the given compound is a methyl ketone. (iv) As the given compound on vigorous oxidation gives a mixture of ethanoic acid and propanoic acid, the methyl ketone is pentan-2-one, i.e., `underset("Pepton-2-one"[C_(5)H_(10)O])(CH_(3)-overset(O)overset(||)C - CH-(2)CH_(2)CH_(5))` The reactions can be explained with the above structure.  `underset("Pentan -2- one")(CH_(3)-overset(O)overset(||)C-CH_(2)CH_(2)CH_(3))+3I_(2)+4NaOH overset("Iodoform")underset("reaction")rarr underset("Iodoform")(CHI_(3))+underset("Sodium Butanoate")(CH_(3)CH_(2)CH_(2)COONa)+3NaI+3H_(2)O` `underset("Pentan-2- one")(CH_(3)-overset(O)overset(||)C-CH_(2))CH_(2)CH_(3)overset(K_(2)Cr_(2)O_(7))underset (H_(2)SO_(4))rarr underset("Ethanoic acid")(CH_(3)COOH)+underset("Propanoic acid")(CH_(3)CH_(2)COOH)` |
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