Monday, January 24, 2011
Organic Muddiest Point
In chapter 13, my muddiest point is basically not being able to read and understand M+1 and the base peak in a mass spectrometry. I understand that the mass spectrometry is used for determining the molecular weight of a compound and identifying components of a compound. So as I explored the internet and I found the website: http://www.cbu.edu/~ddawson/212/Handouts/Mass%20Spectrometry%20Handout.pdf. This website was a handout and it helped me so much. The handout basically stated that, if the particle of interest is not positively charged, it can not be seen. This handout gave an example of the mass spectrum of toluene. In a mass spectrometry, a molecule is vaporized and ionized, usually by a bombardment with a beam of high-energy electrons; toluene has a molecular weight of 92. Also the M+1 peak is one mass unit greater than the mass ion peak, which is 93. Finally the base peak, which is the peak with the relative intensity of 100%, is caused by the most stable cation. For toluene, the base peak is 91; the base peak is caused by the most stable cation and is also the tallest peak in the spectrum. Lastly, the handout went on to explain how to read a mass spectrum, which said to see if the M+ peak is even or odd. If it is even the molecule contains an even number of nitrogens (0 being even), like in toluene above which is 92. If the M+ peak is odd, the molecule contains an odd number of nitrogens. It also shows a comparison between the M+ and M+2 peaks. Overall, this website/handout was a great source and a lot of help because it just simply broke it down a lot better then the book did.
I’m glad the handout really helped you to understand how to read the spectrum! There are, however, a few things I, personally, think the book explains better than the website. The website just states that the M+1 peak is one unit greater than the mass ion peak. That’s true, however, it personally does me no good unless I know why, which Smith explains on p.465. The reason that the M+1 peak is one unit higher is because the element in question has second isotope whose atomic mass is one amu higher than the other, due to an extra neutron. It helped me to know that carbon, hydrogen, nitrogen, oxygen, phosphorus, fluorine, iodine, and sulfur are the elements that would have an M+1 peak. The same rule applies for M+2 peaks, except these two elements, chlorine and bromine, have two isotopes instead of one. I found this information on p.467 of Smith.
ReplyDeleteThe only thing I would add to your blog, is to state that the odd/even number of nitrogen atoms causing the odd/even molecular ion, is referred to as the Nitrogen Rule.
This was a great post. While Tiger11 does state some good points, I agree that the website you found adds some good input to some of the knowledge already gained in lecture. Your post was easy to follow leaving me little room to lose focus on what your muddiest point was and how you found a source to add light to the darkness. In my opinion there would be almost nothing you could add to this post. owever, if you were really inclined to go all out, I might add more on how the book did not clarify as well as the website, just a tad.
ReplyDeleteI agree with Tigers11 on the fact that the explanation on the Nitrogen rule on this website could have been stated much clearer. But the site does contain a couple helpful definition of terms we have learned about in Ch. 13. Both the base peak and M/Z definitions help to reinforce those topics. Thanks for adding this link. Although it simplified some of the issues, once past the basics this handout does not add much.
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