17 mg of a hydrocarbon (M.F. ) takes up 8.40 mL of the gas measured at 0°C and 760 mm of Hg. Ozonolysis of the same hydrocarbon yields
The number of double bond/s present in the hydrocarbon is _________.
The number of double bond/s present in the hydrocarbon is _________.
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Answer: 03
Solution
Moles of hydrocarbon = 17/136 = 0.125 mmol. Volume of H₂ at STP = 8.40 mL, so moles of H₂ = 8.40/22400 = 0.375 mmol. Moles of H₂ per mole of hydrocarbon = 0.375/0.125 = 3. So the compound absorbs 3 moles of H₂, indicating 3 degrees of unsaturation from double bonds (since C₁₀H₁₆ has degree of unsaturation = (2×10+2−16)/2 = 3, all from double bonds, no rings or triple bonds). This is confirmed by ozonolysis giving three carbonyl fragments (acetone, formaldehyde, and succinaldehyde), which accounts for exactly 3 C=C bonds being cleaved. Therefore, the number of double bonds is 3.
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