1H-NMR Spectroscopy The 1H-NMR spectroscopy allows the identification of hydrogen atoms in organic m — Organic Chemistry Chemistry Question
NMR Spectroscopy
1H-NMR Spectroscopy
The 1H-NMR spectroscopy allows the identification of hydrogen atoms in organic molecules. From the position of the signals (chemical shift) and the splitting of the signals, the type and connectivity of the hydrogen atoms can be recognized. Some characteristic hydrogen atom resonances are given below.
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1H-NMR Resonance ranges of typical functional groups in ppm relative to TMS
13C-NMR Spectroscopy
The 13C-NMR is analogous to 1H-NMR and allows the identification of carbon atoms in organic molecules. The 13C-NMR spectrum of a given compound shows as many signals (singlets) as the number of the different carbon atoms. The relative intensities of all kinds of carbon (primary, secondary, tertiary, and quaternary) signals will be assumed to be equal. Some characteristic carbon resonances are given below.
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13C-NMR Resonance ranges of typical functional groups in ppm relative to TMS
Description of six isomeric (constitutional) compounds (A, B, C, D, E and F) having the formula C5H10O2 is as follows:
* None of the compounds is branched.
* There is no O-H absorbance in the IR spectra of the isomers.
* In each compound, one oxygen atom is sp2- and the other is sp3-hybridized.
Determine the structures of all isomers by using the information given above and analyzing the 1H- and 13C-NMR spectra given below.
Abbreviations: s = singlet, d = doublet, t = triplet, q = quartet, qui = quintet, h = hextet.
Compound A
01234 PPM
2 (t) 2 (h)
3 (t)
3* (s)
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1H-NMR spectrum of A
*) The numbers on the signals give the number of the resonating protons
020406080100120140160180 PPM
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13C-NMR spectrum of A
Compound B
012345 PPM
2 (q) 2 (q)
3 (t) 3 (t)
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1H-NMR spectrum of B
020406080100120140160180 PPM
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13C-NMR spectrum of B
Compound C
020406080100120140160180200220 PPM
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13C-NMR spectrum of C
Compound D
012345 PPM
2 (t)
3 (s)
2 (h)
3 (t)
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1H-NMR spectrum of D
020406080100120140160180 PPM
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13C-NMR spectrum of D
Compound E
012345 PPM
2 (s)
2 (q)
3 (s)
3 (t)
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1H-NMR spectrum of E
020406080100120140160180200220 PPM
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13C-NMR spectrum of E
Compound F
0246810 PPM
1 (t)
2 (d)
2 (t)
2 (h)
3 (t)
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1H-NMR spectrum of F
020406080100120140160180200220 PPM
Two signals overlap
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13C-NMR spectrum of F
Model Answer
A: CH3-CH2-CH2-C(=O-O-CH3 (methyl butyrate / methyl butanoate)
B: CH3-CH2-O-C(=O-CH2-CH3 (ethyl propionate / ethyl propanoate)
C: CH3-O-CH2-C(=O-CH2-CH3 (1-methoxybutan-2-one)
D: CH3-C(=O-O-CH2-CH2-CH3 (propyl acetate)
E: CH3-C(=O-CH2-O-CH2-CH3 (1-ethoxypropan-2-one)
F: H-C(=O-CH2-O-CH2-CH2-CH3 (2-propoxyacetaldehyde)