318-3 - CH 318 N LECTURE 3 Textbook Assignment: Chapter 13...

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1 CH 318 N LECTURE 3 Textbook Assignment: Chapter 13 begin NMR Homework (for credit): POW 2 posted Material from Last Lecture: IR spectroscopy Today’s Topics: IR: interpretation -finish Notice & Announcements: No Class on Thursday 1/29 Podcast will be posted to WEB Organic Lecture Series 2 IR of Molecules with C=O Groups C=O C-H OH RCOH O RCH O RCR' O C= O Strong 1700-1725 Stretching Carboxylic acids Aldehydes Vibration Carbonyl Group Frequency (cm -1 ) Intensity Stretching 1630-1820 Stretching 2720 Weak Stretching 2500-3300 Strong (broad) Ketones Stretching Strong
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2 Organic Lecture Series 3 C= O sp 3 CO 2 NH C N RC N RCOCR OO RCOR' O RCN H 2 O Stretching 900-1300 Strong Strong 1735-1800 Carboxylic esters Stretching 1000-1100 Strong Stretching 1200-1250 Strong Acid anhydrides Stretching 1740-1760 and 1800-1850 Strong Strong 1630-1680 Amides Stretching 3200, 3400 Medium (1° amides have two N-H stretches) (2° amides have one N-H stretch) Nitriles Stretching 2200-2250 IR of Molecules with C=O Groups Organic Lecture Series 4 Aldehydes and Ketones • IR spectrum of menthone (Fig 12.12)
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3 Organic Lecture Series 5 Carboxylic acids • IR spectrum of pentanoic acid (Fig 12.13) Organic Lecture Series 6 Amide • IR of N-methylpropanamide (Fig 12.14)
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4 Organic Lecture Series 7 Ester • IR of Ethyl butanoate (Fig 12.15) Organic Lecture Series 8 Strategies for IR Interpretation Inspect the spectrum from left to right. 9 If there is a strong, but broad band 3500 cm -1 then, OH is present. One or two weak peaks in this area are indicative of amines (N—H stretch). 9 Examine the 3000 cm -1 C—H aliphatic stretches are to the right and C—H from alkenes & aromatics are to the left. 9 Aldehyde C—H stretch will be ~ 2720 cm -1 9 Check the area from 1820 to 1630 cm -1 . Strong peaks in this area indicate C=O and this is often the strongest peak in the spectrum. 9 The area from 1250 to 1000 cm -1 are the C—O stretches of ethers, esters, acids.
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5 Organic Lecture Series 9 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 10 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
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This note was uploaded on 04/20/2009 for the course CH 318N taught by Professor Willson during the Spring '08 term at University of Texas at Austin.

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318-3 - CH 318 N LECTURE 3 Textbook Assignment: Chapter 13...

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