What is the displayed formula for methylpropene? I am currently studying organic chemistry at school and I came across a question in my textbook which asked me to find the full displayed formula of methylpropene. I knew that there would be three carbons because of the 'prop' and that there would be a one-carbon side chain on the first carbon. However, in my chemistry textbook the one-carbon side chain is on the second carbon (the middle one). I don't know whether this is correct or not. Could someone please explain to me what the correct answer is?
"Propene" is what defines the main chain of three atoms so that the maximum number of carbon atoms in any other chain cannot exceed this number. Hence your proposition that


  there would be a one-carbon side chain on the first carbon


is wrong as in this case there would be a 4-membered chain of either 1-butene or 2‐butene:



In order to comply with the methylpropene name, one can only attach methyl group to the second carbon, and not to the terminal one:



To sum it up, your textbook is correct.