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Advanced Organic Chemistry: Carbon-13 NMR spectrum of butanal

The Carbon-13 NMR spectrum of butanal

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing C-13 NMR spectra of butanal

C-13 nmr spectrum of butanal analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of butyraldehyde C13 13-C nmr doc brown's advanced organic chemistry revision notes 

TMS is the acronym for tetramethylsilane, formula Si(CH3)4, whose 13C atoms are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in 13C NMR spectroscopy and all other 13C shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - butanal here.

butanal (butyraldehyde), C4H8O,  aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

Interpreting the C-13 NMR spectrum of butanal

As you can see from the diagram above there are only 4 chemical shift lines in the C-13 NMR spectrum of butanal indicating 4 different chemical environments of the carbon atoms.

CH3CH2CH2CHO 

Note the 4 colours indicating the 4 different chemical environment of the carbon atoms in butanal.

The 13C chemical shifts for butanal (a) to (d) on the diagram above.

(a) 13C NMR chemical shift of 13.7 ppm for the methyl CH3 group carbon atom.

(b) 13C NMR chemical shift of 15.7 ppm for the left CH2 group carbon atom.

(c) 13C NMR chemical shift of 45.8 ppm for the right CH2 carbon atom.

(d) 13C NMR chemical shift of 202.8 ppm for the carbon CHO atom of the aldehyde group.

Note the decreasing effect on the chemical shift as the carbon atom is further from the highly electronegative oxygen atom of butanal.

The carbon-13 NMR spectra a provides direct evidence of 4 different carbon atom environments in the butanal molecule from 4 different chemical shifts (ppm).


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Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of butanal. Deducing the number of different chemical environments of the carbon atoms in the butanal molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of butanal. Revision notes on the carbon-13 NMR spectrum of butanal. Matching and deducing the structure of the butanal molecule from its 13C NMR spectrum.


Links associated with butanal

The chemistry of ALDEHYDES and KETONES revision notes INDEX

The infrared spectrum of Butanal

The mass spectrum of Butanal

The H-1 NMR spectrum of Butanal

C-13 NMR spectroscopy index

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