The one topic from Ch. 13 of Smith that I have been confused about, is how to read peaks and intensities on the IR spectrum. At first, they all just looked like a lot of spikes and dips on a graph. One of the most helpful tools I found to determine what molecule a peak may represent, is the four regions of the IR spectrum. In the first region, the wavenumbers range between 4000 and 2500. Bonds in this region typically involve lighter atoms and hydrogen bonding. An molecule peaking in this region is probably a hydrocarbon. Molecules containing triple bonds are usually found in the 2500-2000 range. These include C-C and C-N triple bonds. The third region contains molecules with double bonds. The fourth region is also referred to as the fingerprint region and includes frequencies from 1500-400. In other words, the molecules found in the fingerprint region have relatively long wavelengths and are lower in energy.
The intensity of a peak is, in part, determined by that molecule's hybridization. Molecules having a hybridization of sp3 has a much greater intensity than that of a molecule who's hybridization is sp. This means that molecules with lower sp hybridizations contain stronger bonds, which, in turn, lower the intensity of the peak.
Applying this information to the IR spectrum, can help one to determine the types of atoms in a molecule and how they are bonded together. This, in turn, will help to determine the over-all shape of the molecule so it may be identified.
Once you learn to read the spectrum, the deciphering of molecules is not only much easier, but kind of neat!
Very good blog entry! I was also having some difficulty understanding peaks and intensities on the IR spectrum as well. After I read your blog I feel like I fully grasp the concept now. You did a very good job at explaining your topic. Your blog was very easy to read and understand. The only think I can suggest is maybe add some links so the people reading it can get more information or see were your information came from. Keep up the good work! :)
ReplyDeleteBethany, this is a very nice blog entry on a tricky topic within the subject of Organic Chemistry. Reading IR spectrums is a very confusing and tricky task that involves fully understanding and applying the concept. After reading over the IR spectrum I understood a small portion of the concept, however after reading your blog I feel a lot more confident about these concepts. Thank you for specifying where each molecule belongs and where the differnt wavenumbers and regions are located on the spectrum. I really enjoyed reading the blog entry and can not wait to read the ones in the future. Thank you
ReplyDeleteChapter 13 of Smith is an extremely good reference for reading Infrared Spectroscopy. I think everyone was confused when the class initially started this subject. Although, I must say after carefully reading through the Chapter I felt more confident about IR spectroscopy. There is a section in the Chapter that specifies each bond to the specific wavelength, i.e. a carbon-carbon double bond can be found at approximately 1650 cm-1. I wrote these values down in my notebook for quick reference and would advise others to do so as well. They have came in very handy during the discussion of IR. It seems you have a solid grasp on the concept, and I would be glad to help you if you have any questions.
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