Lecture 4 - CH 310 N T Th 2-3:30 LECTURE 4 Textbook...

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1 CH 310 N T Th 2-3:30 LECTURE 4 Textbook Assignment: Chapter 12 cont’d Homework (for credit): POW 2 posted- Material from Last Lecture: Spectroscopy Intro Today’s Topics: NMR-theory Notice & Announcements: EXAM 1 (Posted to BB-”Course Documents”) Kyle Williams Mon: 3-4 WEL 5.330 Lisa Alexander Mon: 10-11 Cubicle “B” Dan Propheter Tues: 8-9 Cubicle “B” Matt Sanderson Tues: 12-1 Cubicle “A” Organic Lecture Series 2 Molecular Spectroscopy Molecular Spectroscopy • Nuclear magnetic resonance (NMR) Nuclear magnetic resonance (NMR) spectroscopy spectroscopy : a spectroscopic technique that gives us information about the number and types of atoms in a molecule, for example, about the number and types of – hydrogen atoms using 1 H-NMR spectroscopy – carbon atoms using 13 C-NMR spectroscopy – phosphorus atoms using 31 P-NMR spectroscopy Organic Lecture Series 3 Nuclear Spin States • An electron has a spin quantum number of 1/2 with allowed values of +1/2 and -1/2 – this spinning charge creates an associated magnetic field – in effect, an electron behaves as if it is a tiny bar magnet and has what is called a magnetic moment • The same effect holds for certain atomic nuclei – any atomic nucleus that has an odd mass number, an odd atomic number, or both also has a spin and a resulting nuclear magnetic moment – the allowed nuclear spin states are determined by the spin quantum number, I , of the nucleus
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2 Organic Lecture Series 4 Nuclear Spin States – a nucleus with spin quantum number I has 2 I + 1 + 1 spin states; if I = 1/2, there are two allowed spin states – Table 13.1 gives the spin quantum numbers and allowed nuclear spin states for selected isotopes of elements common to organic compounds 1 H 2 H 12 C 13 C 14 N 16 O 31 P 32 S Element Nuclear spin quantum number ( I ) Number of spin states 1/2 1 0 0 0 1/2 1 2312 31 1/2 21 Organic Lecture Series 5 Nuclear Spins in B 0 – within a collection of 1 H and 13 C atoms, nuclear spins are completely random in orientation – when placed in a strong external magnetic field of strength B 0 , however, interaction between nuclear spins and the applied magnetic field is quantized, with the result that only certain orientations of nuclear magnetic moments are allowed Organic Lecture Series 6 –for 1 H and 13 C, only two orientations are allowed E = h ν ν is called the resonance frequency or the Larmor frequency.
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3 Organic Lecture Series 7 Nuclear Spins in B 0 • In an applied field strength of 7.05T, which
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Lecture 4 - CH 310 N T Th 2-3:30 LECTURE 4 Textbook...

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