Propane has six primary hydrogen atoms and two secondary hydrogen atoms…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Propane has six primary hydrogen atoms and two secondary hydrogen atoms. In the light, one secondary hydrogen is times as reactive as one primary hydrogen towards chlorine, and times as reactive towards bromine.
Find the percentage of 2-halopropane in the monohalogen product for chlorine and for bromine.
Need a reminder? The key ideaShow
Halogenation of an alkane is a free-radical chain. The share of a product is the number of hydrogen atoms of that kind times their relative rate, divided by the total. Chlorine: for primary, secondary and tertiary. Bromine: . Complete combustion of an alkane gives and .
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Chlorine. Primary: . Secondary: . Share of 2-chloropropane: .
Step 2. Bromine. Primary: . Secondary: . Share of 2-bromopropane: .
Answer: with chlorine and with bromine. Bromine is far more selective.
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