Q. An unknown compound of carbon, hydrogen and oxygen contains $69.77\%\, C$ and $11.63\%\, H$ and has a molecular weight of $86$. It does not reduces Fehling's solution but forms a bisulphate addition compound and gives a positive iodoform test. What is the possible structure(s) of unknown compound?
IIT JEEIIT JEE 1987Some Basic Concepts of Chemistry
Solution:
From the given elemental composition, empirical formula can be derived as :
Element
C
H
O
Weight %
69.77
11.63
18.60
Mole %
5.81
11.63
$1.1625$ (obtained by dividing from $M$)
Simple ratio
5
10
1
Hence, empirical formula is $C_5H_{10}O$ and empirical formula
weight is $86$.
Since, empirical formula weight and molecular weight both are
$(86)$, empirical formula is the molecular formula also.
Also, the compound does not reduce Fehling's solution, therefore it is not an aldehyde, but it forms bisulphite, it must be a ketone.
Also, it gives positive iodofonn test, it must be a methyl ketone.
$C_3H_7 - \overset{\underset{||}{O}}{C} - CH_3$
Based on the above information, the compound may be one of the following :
| Element | C | H | O |
|---|---|---|---|
| Weight % | 69.77 | 11.63 | 18.60 |
| Mole % | 5.81 | 11.63 | $1.1625$ (obtained by dividing from $M$) |
| Simple ratio | 5 | 10 | 1 |