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Propose chemical structures consistent with the following
Chapter 18, Problem 21P(choose chapter or problem)
Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a) explain why the peaks around \(\delta 1.65\) and \(\delta 3.75\) are not clean multiplets, but show complex splitting. In spectrum (b) explain why some of the protons are likely to be missed.
FIGURE 13-37
Proton NMR spectrum of ethyl carbamate, showing a broad \(\mathrm{N}-\mathrm{H}\) absorption.
Equation Transcription:
Text Transcription:
1.65 delta
3.75 delta
C_{4}H_{10}O_2
CHCl_3
4.2 delta
4.1 delta
4.0 delta
3.8 delta
3.7 delta
1.7 delta
1.6 delta
1.2 delta
1.1 delta
delta (ppm)
C_{2}H_{7}NO
CHCl_3
3.7 delta
3.6 delta
2.9 delta
2.8 delta
delta (ppm)
N-H
Questions & Answers
QUESTION:
Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a) explain why the peaks around \(\delta 1.65\) and \(\delta 3.75\) are not clean multiplets, but show complex splitting. In spectrum (b) explain why some of the protons are likely to be missed.
FIGURE 13-37
Proton NMR spectrum of ethyl carbamate, showing a broad \(\mathrm{N}-\mathrm{H}\) absorption.
Equation Transcription:
Text Transcription:
1.65 delta
3.75 delta
C_{4}H_{10}O_2
CHCl_3
4.2 delta
4.1 delta
4.0 delta
3.8 delta
3.7 delta
1.7 delta
1.6 delta
1.2 delta
1.1 delta
delta (ppm)
C_{2}H_{7}NO
CHCl_3
3.7 delta
3.6 delta
2.9 delta
2.8 delta
delta (ppm)
N-H
ANSWER:
Solution:
Step 1
(a)
The given molecular formula C4H10O2 is a saturated compound. The oxygen atom present in the molecule must be an alcohol or ether functional group. The doublet at 1.2 indicates 3H atoms thus it must be a methyl group (CH3) near to CH. The peaks at
1.65 represents two H appear as an uneven quartet and indicates a CH2 between two non-equivalent protons and formed overlapping of peaks. The remaining 5 H -atoms appear in four groups of 1H, 1H,1H and 2H between
3.7 and 4.2. The 2H multiplet at
3.78 is a CH2 group. The 1H multiplet at
4.0 is a CH between many neighbours. The broad singlet peak at
4.12 indicates the two OH peaks.
Or
Two possible structures:-
or
(Correct)