2. (a) Provide the type (R, R-T, R-X) for the protons in each of two methyl groups. (b) Estimate the approximate range of chemical shift for each set of protons (0 -1.5 ppm, 1.6 – 2.9 ppm, and 3.0 – 4.5 ppm). You may use the chart provided on the previous slide.

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2. (a) Provide the type (R, R-T, R-X) for the protons in each of two methyl groups.
(b) Estimate the approximate range of chemical shift for each set of protons (0 -1.5
ppm, 1.6 – 2.9 ppm, and 3.0 – 4.5 ppm). You may use the chart provided on the
previous slide.
(0 -1.5 ppm)
(R)
(R-T)
(1.6 – 2.9 ppm)
(R-X)
(3.0 – 4.5 ppm)
Transcribed Image Text:2. (a) Provide the type (R, R-T, R-X) for the protons in each of two methyl groups. (b) Estimate the approximate range of chemical shift for each set of protons (0 -1.5 ppm, 1.6 – 2.9 ppm, and 3.0 – 4.5 ppm). You may use the chart provided on the previous slide. (0 -1.5 ppm) (R) (R-T) (1.6 – 2.9 ppm) (R-X) (3.0 – 4.5 ppm)
Neighboring Effect on Proton Chemical Shifts
1H Chemical Shifts
X=0,CI,Br
X=N,S
H
X H
X H
Alkanes
H
R
10
-CHO
8
aromatic
6.
vinylic
ppm
7
4
R-X
3
2
1
R-л
R
Base Shift
Increment
Base shift CH2: 1.2
a Cl:
Base shift CH:
1.5
-OC(=0)R 3.0
-OR
CHз 0.9
OH
a Ph:
a OH:
2.3
1.4
2.4
CH2 1.2
2.3
-Br
2.2
Ph
Calculated:
3.6
-CI
-Aryl
-C(=0)R
-C=C
CH
1.5
2.4
Calculated:
5.3
Observed:
3.65
1.4
with some small
Observed:
4.8
1.0
variations
1.0
With the same neighboring effect, methine > methylene > methyl
1.
- R-T (-C=C, -C=0, -Ph, etc.) < R-X (-OR, halogen, etc.)
The effects are additive
• The B-effect of EWG also contributes
Transcribed Image Text:Neighboring Effect on Proton Chemical Shifts 1H Chemical Shifts X=0,CI,Br X=N,S H X H X H Alkanes H R 10 -CHO 8 aromatic 6. vinylic ppm 7 4 R-X 3 2 1 R-л R Base Shift Increment Base shift CH2: 1.2 a Cl: Base shift CH: 1.5 -OC(=0)R 3.0 -OR CHз 0.9 OH a Ph: a OH: 2.3 1.4 2.4 CH2 1.2 2.3 -Br 2.2 Ph Calculated: 3.6 -CI -Aryl -C(=0)R -C=C CH 1.5 2.4 Calculated: 5.3 Observed: 3.65 1.4 with some small Observed: 4.8 1.0 variations 1.0 With the same neighboring effect, methine > methylene > methyl 1. - R-T (-C=C, -C=0, -Ph, etc.) < R-X (-OR, halogen, etc.) The effects are additive • The B-effect of EWG also contributes
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