3. Based on these retention times, what does the GC results tell you. The number

Question

3. Based on these retention times, what does the GC results tell you.

The number of peaks tells you the number of substances in your sample, e.g., 1 peak means 1 substance (pure sample) and 2 peaks means 2 substances in your sample

Compare the retention time of the reference samples (2-methyl-1-butene and 2-methyl-2-butanol) to the retention time of your samples.
If the retention time of your sample matches (to within 0.01 minutes) the retention time of the reference, you can conclude your sample contains that substance.
If the retention time of your sample does not match the retention time of any of the references, then that peak is an unknown substance. In general, the higher the boiling point of a substance, the longer the retention time. Compare the b.p. of the two possible alkene products to determine which alkene was produced in your experiment.

2-Methyl-1-butene boils at 31.2°C, and 2-methyl-2-butene boils at 38.6°C

(Here are the reference retention times and below that are our what we got).

So since we got 2 peaks and they dont match .01 minutes. I think we look to the boiling point like it says. So since 2 methyl 2 butene has a higher boiling point is that what we got? Its confusing because it says higher boiling point longer retention time but our longest retention time has an area of 9.9 so wouldn't that mean there's less of it in our sample and whatever is 90.1 is what we actually got since there's more of that?

Explanation / Answer

The boiling point of your unkown sample is not given. Hence, it cannot be compared with the boiling points of 2-Methyl-1-butene and 2-methyl-2-butene. Since the difference between the retention time of the sample and 2-Methyl-1-butene or 2-methyl-2-butene is more than 0.01, the sample cannot be 2-Methyl-1-butene boils or 2-methyl-2-butene. It is an unknown substance.

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