Chemistry Labs

Problem 5

Only one product was obtained by the reaction of bromine with an unknown hydrocarbon. Its density was 5.207 times as great as that of the air. Determine the structural formula of the unknown hydrocarbon. Relative atomic masses: Ar(H)=1A_r(\text{H}) = 1; Ar(C)=12A_r(\text{C}) = 12; Ar(Br)=80A_r(\text{Br}) = 80.
Step 3 of 3: Identify the isomer
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Intuition

A single substitution product signals maximal symmetry: every H must be equivalent.

C(CHX3)X4+BrX2→C(CHX3)X3CHX2Br+HBr\ce{C(CH3)4 + Br2 -> C(CH3)3CH2Br + HBr}
Analysis

Pentane and isopentane have non-equivalent hydrogens and give several monobromides. Only 2,2-dimethylpropane (neopentane), C(CHX3)X4\ce{C(CH3)4}, has all twelve H equivalent — one product only. The unknown hydrocarbon is neopentane.