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Lecture 5c

Lecture 5c. NMR Spectroscopy of Epoxides. Introduction. 1 H-NMR spectroscopy is used to determine the structure of the epoxide based on characteristic splitting patterns in the aromatic range and the epoxide range

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Lecture 5c

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  1. Lecture 5c NMR Spectroscopy of Epoxides

  2. Introduction • 1H-NMR spectroscopy is used to determine the structure of the epoxide based on characteristic splitting patterns in the aromatic range and the epoxide range • When analyzing the spectrum, it will become much more difficult if the submitted sample is a mixture of many compounds i.e., epoxide, aldehyde, water (d=1.56 ppm), ethyl acetate (d=1.26 ppm, 2.05 ppm and 4.12 ppm), hexane (d=0.88 ppm, 1.26 ppm), etc. (see SKR, p. 260) • The proton spectrum will exhibit a singlet at d=7.26 ppm due to the presence of CDCl3 if the concentration of the epoxide is very low • The carbon spectrum will show a “triplet” at d=77 ppm due to the presence of CDCl3

  3. 4-Methylstyrene oxide • 1H-NMR spectrum (integration in blue) 4 CH3 3 H1, dd H2, dd H3, dd 1 1 1

  4. 4-Methylstyrene oxide • 13C{1H}-NMR spectrum • Seven signals total • Epoxide carbons at ~ 50-60 ppm • Four signals in the aromatic range • The size of the peakfor CDCl3depends on the concentration of the sample CDCl3

  5. 4-Methylbenzacetaldehyde • 1H-NMR spectrum (J3(CH2-CHO)= 2.56 Hz) CHO, “s” CH3 1 3 CH2, “s” 2 4

  6. 4-Methylbenzacetaldehyde • 13C{1H}-NMR spectrum • Aldehyde: ~200 ppm • Methylene: 45-50 ppm • Methyl group: ~30 ppm CH3 CHO CH2 CDCl3

  7. 4-Methylacetophenone • 1H-NMR spectrum • Two doublets in the aromatic range, one of then significantly shifted downfield due to the adjacent carbonyl function • Two singlets in the d= 2-2.5 ppm rangedue to the two methylgroups 3 3 2 2

  8. 4-Methylacetophenone • 13C{1H}-NMR spectrum • Carbonyl: ~195 ppm (small) • Methyl groups: 20-30 ppm CH3 CDCl3 CO

  9. What is that? • Interpret the following 1H-NMR spectrum

  10. How about that one? • Interpret the following 13C{1H}-NMR spectrum

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