Chemistry 30A3 Fall 2011 Labs Dr. Troendle 34

Chemistry 30A3 Fall 2011 Labs Dr. Troendle 34 - NMR...

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Chemical Biology 3OA3, September 2009 Page 34 NMR analysis: Your TA will collect one or more samples of the diol 2 and you will obtain the NMR spectra of these samples in deuterated chloroform (CDCl 3 ). You will first use these spectra to confirm the identity and purity of the diol. Typical spectra are also provided in this manual in Appendix 2, but you should also interpret your own results. IR and NMR data for 1 , 2 , 3 ,and 4 are given below: O O OH O H O OH H OH H H OH 1 2 3 4 δ 2.4 (3H, s) 1680 cm -1 1710 cm -1 1710 cm -1 1680 cm -1 δ 7.7-7.9 (m, 2H) δ 7.3-7.5 (m, 3H) δ 2.0 (3H, s) δ ca. 4.0 (1H, s) δ 4.9 (1H, s) δ 7.2 (s, 5H) δ 7.6-8.0 (m, 2H) δ 7.2-7.6 (m, 3H) δ 5.0 (1H, q) δ ca. 3.6 (1H, s) δ 1.4 (3H, d) δ 1.1 (3H, d) δ 3.9-4.1 (m, 1H) δ ca. 3.2 (2H, s) δ 4.7 (1H, d) δ 7.3 (s, 5H) Analysis of the coupling constants in the diol can be used to determine which diastereomer is formed. NMR spectroscopy in an achiral environment cannot distinguish pairs of enantiomers, e.g. (1 R ,2 R ) and its enantiomer (1 S ,2 S ), but a pair of diastereomers such as (1 R ,2 R ) and (1 R ,2 S ) give different spectra.
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