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Advanced Organic Chemistry: Carbon-13 NMR spectrum of cyclohexene

Interpreting the Carbon-13 13C NMR spectrum of cyclohexene

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 cyclohexene

13C nmr spectrum of cyclohexene C6H10 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of cyclohexene C13 carbon-13 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 resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - cyclohexene here.

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Interpreting the C-13 NMR spectrum of cyclohexene

As you can see from the diagram above there are 3 different chemical shift lines in the C-13 NMR spectrum of cyclohexene indicating 3 different chemical environments of the 10 carbon atoms of cyclohexene.

13C chemical shifts δ (a) to (c) on the C-13 NMR spectrum diagram for cyclohexene.

(a)  structure : 13C NMR chemical shift δ of 22.8 ppm

The 13C NMR resonance for the 2 x equivalent C atoms furthest from the C=C bond.

(b)  structure : 13C NMR chemical shift δ of 25.3 ppm

The 13C NMR resonance for the 2 x equivalent C atoms nearest to the C=C bond.

(c)  structure : 13C NMR chemical shift δ of 127.3 ppm

The  13C NMR resonance for the 2 x equivalent C atoms of the actual C=C bond itself.

The presence of the pi electron cloud produces the largest chemical shift for the C=C bond carbons compared to the other two.

The carbon-13 NMR spectra provides direct evidence of 3 different carbon atom environments for the 10 carbon atoms in the cyclohexene molecule, deduced from the presence of 3 different 13C NMR chemical shifts (ppm).


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Links associated with cyclohexene

The infrared spectrum of cyclohexene

The mass spectrum of cyclohexene

The H-1 NMR spectrum of cyclohexene

The chemistry of ALKENES revision notes INDEX

C-13 NMR spectroscopy index

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