(a) Give chemical tests to distinguish between compounds in the following pairs of substances ,
(i) Ethanal and Propanal
(ii) Benzoic acid and Ethyl benzoate
(b) 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 Tollen 's reagent but forms an addition compound with sodium hydrogen sulphite and gives positive iodoform test. On vigorous oxidation, it gives ethanoic and propanoic acids . Derive the structure of the compound.

Explanation

i. The molecular formula of the compound:
Percentage of `C=69.77%` , `%H=11.63%`
`:.` Percentage of `O = 100-(67.77+11.63)=18.6%`
`C:H:O=(69.77)/(12):(11.63)/(1)=(18.6)/(6)`
`=5.88:11.63:1.16=5:10:1`
The E.F. of the given compound is `C_(5)H_(10)O`.
E.F. mass `=5xx12+10xx1+1xx16=86`
Molecular mass `=86` (given)
`M.F. = C_(5)H_(10)Oxx(86)/(86)=C_(5)H_(10)`
Thus, molecular formula of the given compound `=C_(5)H_(10)O`
ii. Negative Tollens test suggests that `(CHO)` group is absent.
iii. Positive Iodoform test and formation of `NaHSO_(3)` adduct compounds suggest `(MeCO-)` group in the compound.
iv. On oxidation, the compound gives `(MeCOOH)` and `(C_(2)H_(5)COOH)` which suggests that the compound is penta-2-one.