1. NMR Spectroscopy of Epoxides
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. 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

3. 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. 4-Methylstyrene oxide 13C{1H}-NMR spectrum Seven signals total
Epoxide carbons at ~ ppm
Four signals in the aromatic range
The size of the peak for CDCl3 depends 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: ppm
Methyl group: ~30 ppm
CHO
CH2
CH3
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= ppm range due to the two methyl groups 3 3 2 2

8. 4-Methylacetophenone 13C{1H}-NMR spectrum Carbonyl: ~195 ppm (small)
Methyl groups: 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