NMR Spectroscopy in Epoxides Analysis
Lecture 5c
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
•
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 (
=1.56 ppm),
ethyl acetate (
=1.26 ppm, 2.05 ppm and 4.12 ppm),
hexane (
=0.88 ppm, 1.26 ppm), etc. (see SKR, p. 284)
•
The proton spectrum will exhibit a singlet at
=7.26 ppm
due to the presence of CDCl
3
if the concentration of the
epoxide is very low
•
The carbon spectrum will show a “triplet” at
=77 ppm
due to the presence of CDCl
3
4-Methylstyrene oxide
•
1
H-NMR Spectrum (integration in
blue
)
H
1
, dd
H
2
, dd
H
3
, dd
4
1
1
1
3
CH
3
4-Methylstyrene oxide
•
13
C{1
H}-NMR Spectrum
•
Seven signals total
•
Epoxide carbons at
~ 50-60 ppm
•
Four signals in the
aromatic range
•
The size of the peak
for CDCl
3
depends on
the concentration of
the sample
CDCl
3
•
1
H-NMR Spectrum (J
3(CH
2
-CHO)
= 2.56
Hz
)
4-Methylbenzacetaldehyde
CH
2
, “s”
CHO, “s”
4
1
2
3
CH
3
4-Methylbenzacetaldehyde
•
13
C{1
H}-NMR Spectrum
•
Aldehyde: ~200 ppm
•
Methylene: 45-50 ppm
•
Methyl group: ~30 ppm
CHO
CH
2
CDCl
3
CH
3
4-Methylacetophenone
•
1
H-NMR Spectrum
•
Two doublets in the
aromatic range, one
of then significantly
shifted downfield due
to the adjacent
carbonyl function
•
Two singlets in the
2-2.5 ppm range
due to the two methyl
groups
2
2
3
3
4-Methylacetophenone
•
13
C{1
H}-NMR Spectrum
•
Carbonyl: ~195 ppm (small)
•
Methyl groups: 20-30 ppm
CO
CDCl
3
CH
3
What is that?
•
Interpret the following
1
H-NMR Spectrum
How about that one?
•
Interpret the following
13
C{1
H}-NMR Spectrum
spectrum
NMR spectroscopy plays a crucial role in determining the structure of epoxides by analyzing characteristic splitting patterns in the spectrum. The differentiation of epoxides from other compounds in a mixture can be challenging, highlighting the importance of understanding the unique signals and patterns associated with epoxide compounds. Detailed spectra and integration values aid in the interpretation and identification of epoxides amidst varying chemical environments.
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Presentation Transcript
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 ( =1.56 ppm), ethyl acetate ( =1.26 ppm, 2.05 ppm and 4.12 ppm), hexane ( =0.88 ppm, 1.26 ppm), etc. (see SKR, p. 284) The proton spectrum will exhibit a singlet at =7.26 ppm due to the presence of CDCl3if the concentration of the epoxide is very low The carbon spectrum will show a triplet at =77 ppm due to the presence of CDCl3
4-Methylstyrene oxide 1H-NMR Spectrum (integration in blue) H1-H2 H1-H3 H2-H3 11.5 4 5.5 CH3 11.0 J3 3.31 Hz 3.30 Hz 5.68 Hz 10.5 5.0 10.0 9.5 4.5 9.0 8.5 4.0 8.0 3 7.5 3.5 7.0 6.5 3.0 6.0 5.5 2.5 5.0 4.5 H1, dd 1 1 1 4.0 H2, dd H3, dd 2.0 3.5 3.0 1.5 2.5 2.0 1.0 1.5 1.0 0.5 0.5 0.0 0.0 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 3.5 3.0 2.5
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 O 1 120 H 3a H 2b 115 9 3 2 110 H 2a 8 4 105 129.60 125.78 100 7 5 95 6 H310 C 90 85 80 75 70 65 60 55 51.46 52.67 21.49 50 45 40 35 CDCl3 30 25 20 138.29 15 77.08 77.28 10 5 0 140 130 120 110 100 90 80 70 60 50 40 30 20 10
4-Methylbenzacetaldehyde 1H-NMR Spectrum (J3(CH2-CHO)= 2.56 Hz) CHO, s 1 CH3 11 3 10 CH2, s 9 8 2 7 4 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1
4-Methylbenzacetaldehyde 13C{1H}-NMR Spectrum Aldehyde: ~200 ppm Methylene: 45-50 ppm Methyl group: ~30 ppm 120 O 9 H 7a H 7b 115 6 7 8 110 (5;3) (2;6) 105 5 1 H 8a 100 95 4 2 90 H310 C 3 85 80 75 70 65 CH3 CHO CH2 60 55 (8) (7) (10) 50 45 40 35 30 25 CDCl3 20 (4) (1) (Sol.) (Sol.) (Sol.) 15 10 5 0 200 150 100 50
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 = 2-2.5 ppm range due to the two methyl groups 11.5 3 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3 3.5 2 2 3.0 2.5 2.0 1.5 1.0 0.5 0.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
4-Methylacetophenone 13C{1H}-NMR Spectrum Carbonyl: ~195 ppm (small) Methyl groups: 20-30 ppm 120 115 110 128.31 128.92 105 100 95 90 85 80 75 70 65 CH3 60 21.41 55 26.52 50 45 40 35 CDCl3 30 25 197.41CO 76.28 77.08 77.88 20 143.46 15 10 5 0 200 150 100 50
What is that? Interpret the following 1H-NMR Spectrum 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 10 9 8 7 6 5 4 3 2 1 0
How about that one? Interpret the following 13C{1H}-NMR Spectrum spectrum 110 125.78 128.31 129.14 129.60 120 115 105 31.62 22.70 14.12 100 95 90 85 80 75 70 65 76.28 77.08 77.88 60 52.67 51.46 55 199.91 60.50 50 45 40 35 30 25 20 136.60 197.41 171.38 143.46 15 10 5 0 200 150 100 50 0
