After studying Chapter 13 Mass Spectrometry and Infrared Spectroscopy, my muddiest point is section 13.2 Alkyl Halides and the M + 2 Peak on pg. 467. I don’t understand the ratio concepts. For example, 35Cl and 37Cl occur at a 3:1 ratio. The text states that if it is a 3:1 ratio, there will be a Cl in the atom. How are we supposed to determine the ratio or is it generally given information? Also, it states that the bromine is a 1:1 ratio. Why is it different from the Cl, which is 3:1? Also, understanding the M + 2 Peak is very confusing. I understand that it is the mass of the compound + 2, but what is the significance? After further reading of the text, the M + 2 peak is used for alkyl halides that have a mass slightly higher than their mass on the periodic table. With further reading, I learned that with an M + 2 peak, there will be two peaks towards the end of a graph showing the presence of the alkyl halide. Based on the text, chlorine and bromine have two isotopes and carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, fluorine, and iodine only have one major isotope. After reviewing the sample problem for determining molecular ions in a mass spectrum of a particular compound, I feel like I understand the concept better.
I was confused about that as well! So I sat down with the book and really tried to figure it out. You can determine whether or not the ratio is 3:1 by comparing the peaks. If there is a peak at 35 and it is three times higher than the peak at 37, then you know the molecule contains Chlorine—it has to; Chlorine is the only element appearing on the spectrum that has two isotopes, one peaking at 35 and the other at 37. The reason that the peak for the 35Cl is three times higher than that of 37Cl is because 35Cl appears three times more often in nature as 37Cl. I thought that was neat.
ReplyDeleteI liked your blog! It’s nice seeing that someone else has the same difficulties as I do : )
To be honest, I wasn't particularly confused about this topic until I read your post. I feel like you might be thinking a little too in depth on this particular subject, however at the same time any extra information you can gain would help in the overall class as well as the overall class because im sure you aren't the only one lost in this subject or not completely sure. The blog was great and all of the information was stated well in a way that showed great writing skills!!! one thing that you could add just for the benfit of people not in your class would be which particular lecture book you were using as well as the pages in case someone were to creep and follow the pages and graphs that you read in a fight ot better understand the topic. Keep up the good work!
ReplyDeleteAs with most of the topic we'll learn about this year, it will take a few times reading it to fully comprehend the difficult issues. I looks like your question has already been answered about how to determine the 3:1 and 1:1 ratio peaks but I'll try to help as well. Since they are just ratios and not exact number, you can compare the height of two peaks and if peak a is three times, roughly, the height of peak b, then a Cl atom in the compound.
ReplyDeleteIf only all atoms had a ratio correlation IR would be easier to determine. Good question and way to go on finding most of the answer. I'd recommend citing where you found the information for your answer, as in the page number for this instance.