Question

Which alkane, having a molecular weight of 86, will form only two monobromo alkanes? If the alkane is $C_n{H}_m$, find n?

• A. 4
• B. 5
• C. 6
• D. 7

Answer 1

Answer: (C)

6

The molecular formula of the alkane is $C_n{H}_{2n+2}$
It's molecular weight is $12n+2n+2=14n+2=86$.
$14n=84$
$n=6$
Hence, the molecular formula of alkane is $C_6{H}_{14}$. Since, it gives only two monobromination products, the compound must be 2,3-dimethylbutane.