Volatile hydrocarbon (7)
I believe the answer is:
benzene
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">volatile hydrocarbon</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for benzene that I've seen before include "Chemical" , "Liquid hydrocarbon" , "Substance found in oil" , "Solvent" , "Hydrocarbon with ring-shaped molecule" .)