NMR Spectroscopy of Epoxides Lecture 5c NMR Spectroscopy of Epoxides

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. 284) 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

4-Methylstyrene oxide 1H-NMR spectrum (integration in blue) 4 3 1 1 1 H1-H2 H1-H3 H2-H3 J3 3.31 Hz 3.30 Hz 5.68 Hz 4 CH3 3 1 1 1 H1, dd H2, dd H3, dd

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 peak for CDCl3 depends on the concentration of the sample CDCl3

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

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

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 range due to the two methyl groups 3 3 2 2

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

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

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