In my Organic Chemistry II class, we were asked to blog on our muddiest or most unclear point thus far in the semester. One thing that has been discussed so far that I do not understand, is the mass spectrum of cyclic alkanes. It was explained to me in class that, when talking about methylcyclopentane, the fragment with a m/z=56 is more stable and therefore more concentrated than the m/z=69 fragment. I do not understand what makes this a more stable or more favorable fragmentation. After looking into this subject, I was not able to find anything that explained it more clearly. The most informative source that I found on this subject further confused me because, from how I read it, it goes against what I was taught in lecture. The source talks about the fragmentation of cyclic alkanes, methylcyclohexane specifically, and says "Note that the loss of the methyl side chain is perhaps the most important fragmentation event, and the M - 15 ion of m/z 83 gives the most intense signal in the spectrum." To my followers, if you can clarify my issue or provide information that you think might be of help, it would be greatly appreciated. OK, no really, someone help!
-The High School Chemist
