Exam 1 study guide
Exam 1 study guide Chem 372
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Popular in Chemistry
This 4 page Study Guide was uploaded by Rachel Taylor on Thursday January 28, 2016. The Study Guide belongs to Chem 372 at Eastern Michigan University taught by Dr. Friebe in Winter 2016. Since its upload, it has received 57 views. For similar materials see Organic Chemistry in Chemistry at Eastern Michigan University.
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Date Created: 01/28/16
Organic Chemistry 2 Study guide Exam 1: NMR, IR, and Mass Spectroscopy Directions: The questions listed below cover the most important concepts of MS, IR, and NMR spectroscopy. Make sure that you attempt to find the answer in your book or online before looking at the answer key at the bottom. Also, to get the most out of this, make sure you can do more than just regurgitate the answer, but can explain the reasoning behind it. Ultimately you will need to combine the information from all three spectrums to come to the correct structural formula of a molecule, so make sure to practice reading the spectrums in the back of your book. 1. Why do we use Mass spectrometry? 2. What do the peaks represent? How are they formed? 3. What is the M peak? What is the M+1 peak? 4. What would the ratios of the M peak and the M+2 peak represent? 5. What is the X-axis on a Mass Spectrum? How does it relate to the peaks? 6. What is the Y-axis on a Mass Spectrum? Why is the Base Peak the tallest peak? 7. What is high resolution mass spectrometry? Why do we use it? 8. Why do we use the IR Spectrum? 9. Where is the fingerprint region? 10. What is IR Spectrometry measuring? 11. Why do we use NMR spectroscopy? 12. What does NMR spectroscopy measure? 13. What does peak intensity represent on an NMR spectrum? 13 14. In C NMR spectrometry, why can’t we use carbon 12 (the most common isotope)? 15. What is the peak at 0 ppm? 16. What are enantiotopic protons? Diastereotopic protons? 17. What does it mean for a proton to be shielded? Does shielding shift a proton upfield or downfield? 18. When does deshielding occur? 19. How many sigma bonds away can a proton be from another proton for spin-spin splitting to occur? Answers: 1. We use mass spectrometry to determine the molecular formula of a molecule 2. They represent molecule fragments. They are formed by blasting the molecule with high energy electrons so they form carbocations and radicals and break apart. 3. The M peak represents the molecular ion. The M+1 peak represents the carbon-13 molecular ion. 4. It represents common isotopes and their relative abundance. When it is in a 1:3 ratio, Chlorine is present. If it is in a 1:1 ratio, bromine is present. 5. The X-axis is the molecular ion. It is equal to the molecular weight because electron mass is negligible. 6. The Y-axis is the relative abundance of the molecular ions. The base peak is the tallest because it is the most abundant ion (most likely because it is the most stable molecular ion). 7. High resolution Mass Spectrometry measures exact masses to up to the fourth decimal so they can determine the molecule from others with similar masses. 8. To determine the functional groups. 9. Between 1500 and 400 cm . -1 10. The bending and flexing of bonds. 11. We use NMR spectroscopy to find the structure of a molecule. 12. NMR Spectroscopy measures the magnetic field around atoms. The magnetic field is created by nuclear flips. 13. Peak intensity measures the relative abundance of the absorbing molecule. 14. Only atoms with odd mass numbers show up on the NMR spectrum. 15. The TMS reference. It is a highly shielded molecule with a Si surrounded by 4 CH gro3ps. 16. Enantiotopic protons are two equivalent protons that are on the same carbon that has two different groups on it. Diastereotopic protons are two non-equivalent protons that are attached to the same carbon that is bonded to a molecule with a stereogenic center. 17. A proton is shielded when it has a higher electron density around it shifting it upfield. 18. Deshielding occurs when electronegative atoms, double bonds, or benzene rings pull the electron density away from the proton shifting it downfield.
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