week 3 - 2 - anno

week 3 - 2 - anno - Chemistry S-20ab Chemistry E-2a:...

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Unformatted text preview: Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Introduction to Spectroscopy Reading: Sections 12.1 and 12.2 2 158 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Factors That Determine IR Stretching Frequencies • First, we should ask: why is it that the frequency of vibration is the same as the frequency of the IR light that is absorbed? • Now, let’s explore the two main factors that determine the frequencies of IR absorption: 1. the mass of the atoms 2. the strength of the bond • Explain the following comparisons of C=O stretching frequencies: O Me O N Me O Me O O Me O O Me 1735 cm–1 vs 1650 cm–1 1735 cm–1 vs 1720 cm–1 Reading: Section 12.2 3 159 Chemistry S-20ab Week 3 Identifying Functional Groups Using IR Spectroscopy Reading: Sections 12.3 and 12.4 160 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Identifying Functional Groups Using IR Spectroscopy • Identify the functional groups in each of the following IR spectra: Reading: Section 12.4 and Appendix II 5 161 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Nuclear Magnetic Resonance Spectroscopy Reading: Sections 13.1 and 13.2 6 162 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 The NMR Spectrum: Chemical Shifts Reading: Section 13.3 7 163 Chemistry S-20ab Chemistry E-2a: Lecture 7 Week 32 November 13, 2008 Chemical and Stereochemical Equivalence • The following molecule has many hydrogen atoms. Let’s take a look at various pairs of hydrogen atoms and ask: are they the same or not the same? The best way to do so is to perform a substitution test. If the two compounds are entirely different, the groups are constitutionally inequivalent. If the two compounds are diastereomers, the groups are diastereotopic. If the two compounds are enantiomers, the groups are enantiotopic. If the two compounds are identical, the groups are homotopic. Let’s look at some examples: Br Br Br Reading: Section 10.8 14 136 Chemistry S-20ab Chemistry E-2a: Lecture 7 Week 32 November 13, 2008 Br Br Br Br Reading: Section 10.8 15 137 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Chemical Shifts and Integrals Reading: Section 13.3 8 164 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Spin-Spin Splitting Reading: Section 13.4 9 165 Chemistry S-20ab Chemistry E-2a: Lecture 9 Week 3 December 11, 2008 Spin-Spin Splitting: Counting Neighbors Reading: Section 13.4 10 166 ...
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This note was uploaded on 07/21/2010 for the course CHEM S20ab taught by Professor Mccarty during the Summer '10 term at Harvard.

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