lecture 7 sp 09 preview

lecture 7 sp 09 preview - Lecture 7 Chemistry 310N...

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Unformatted text preview: Lecture 7 Chemistry 310N Chemistry 310N Organic Chemistry II for Prehealth Professionals Unique number: 53185 Tu,Th 12:30-2:00 pm, Welch 2.224 Professor: Jonathan Sessler, Ph.D. sessler@mail.utexas.edu Notes: 13 C NMR spectroscopy, although in the book, will not be on Exam I Exam 1 will cover chapters 12 and 13 in detail and chapter 14 in cursory fashion. It is Thursday in class! Dr. Sesslers office hours in Wel. 3.422 2:00-3:30 pm today. Aromatic Systems Sometimes easy but often complex because of multiple splittings The rule of next door neighbors being the only ones that lead to splitting breaks down. Look for symmetry; count number of hydrogen atoms, and keep an eye out for classic, so-called AB splitting pattern that arises from two adjacent ( ortho ) protons in different chemical and magnetic environments. Interpreting NMR Spectra Spectral Problem; molecular formula C 7 H 14 O. Taken From Book. Come to Office Hours if You Need Help Figuring This One Out !! 13 C-NMR Spectroscopy Each nonequivalent 13 C gives a different signal A 13 C signal is split by the 1 H bonded to it according to the ( n + 1) rule. Coupling constants of 100-250 Hz are common, which means that there is often significant overlap between signals, and splitting patterns can be very difficult to determine. The most common mode of operation of a 13 C-NMR spectrometer is a proton-decoupled mode. 13 C-NMR Spectroscopy In a proton-decoupled mode, a sample is irradiated with two different radiofrequencies, one to excite all 13 C nuclei. a second broad spectrum of frequencies to cause all protons in the molecule to undergo rapid transitions between their nuclear spin states. On the time scale of a 13 C-NMR spectrum, each proton is in an average or effectively constant nuclear spin state, with the result that 1 H- 13 C spin-spin interactions are not observed; they are decoupled. 13 C-NMR Spectroscopy Proton-decoupled 13 C-NMR spectrum of 1-bromobutane. Chemical Shift - 13 C-NMR 13 C-NMR chemical shifts of representative groups. Chemical Shift - 13 C-NMR R C H 3 R C H 2 R R 3 C H R 2 C =CR 2 R C CR R 3 C OR R C H 2 Cl R C H 2 Br R C H 2 I R 3 C OH R C R C NR 2 O R C H, R C R O O RC C OH O R C OR O 0-40 110-160 165 - 180 160 - 180 165 - 185 180 - 215 40-80 40-80 35-80 25-65 65-85 100-150 20-60 15-55 10-40 Type of Carbon Chemical Shift ( 29 (29 Nuclear Magnetic Nuclear Magnetic Resonance Resonance End Chapter 13 End Chapter 13 Chapter 14 Mass Spectrometry Mass Spectrometry (MS) An analytical technique for measuring the mass-to- charge ratio ( m/z ) of ions in the gas phase....
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lecture 7 sp 09 preview - Lecture 7 Chemistry 310N...

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