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Advanced Organic Chemistry: Carbon-13 NMR spectrum of 2-methylpropene

Interpreting 13C NMR spectrum: 2-methylpropene (2-methylprop-1-ene)

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 2-methylpropene

13C nmr spectrum of 2-methylpropene C4H8 (CH3)2C=CH2 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of 2-methylprop-1-ene 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 - 2-methylpropene here.

2-methylpropene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b , skeletal formula of methylpropene 2-methylpropene advanced organic chemistry

Interpreting the C-13 NMR spectrum of 2-methylpropene

As you can see from the diagram above there are 3 different chemical shift lines in the C-13 NMR spectrum of 2-methylpropene indicating 3 different chemical environments of the 4 carbon atoms of 2-methylpropene.

(CH3)2C=CH2

(Note the 3 different colours indicating the 3 different chemical environments of the 4 carbon atoms in 2-methylpropene).

13C chemical shifts δ (a) to (c) on the C-13 NMR spectrum diagram for 2-methylpropene.

(a)  (CH3)2C=CH2 : 13C NMR chemical shift δ of 24 ppm for the methyl group carbon atoms.

The two methyl group carbon atoms are equivalent to each other, giving the same 13C NMR chemical shift.

(b)  (CH3)2C=CH2 : 13C NMR chemical shift δ of 142 ppm for the 'left' C=C carbon atom.

(c)  (CH3)2C=CH2 : 13C NMR chemical shift δ of 112 ppm for the 'right' =CH2 carbon atom of the CC double bond..

The carbon-13 NMR spectra provides direct evidence of 3 different carbon atom environments for the 4 carbon atoms in the 2-methylpropene molecule, deduced from the presence of 3 different 13C NMR chemical shifts (ppm).


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Links associated with 2-methylpropene

The chemistry of ALKENES revision notes INDEX

The infrared spectrum of 2-methylpropene (2-methylprop-1-ene)

The mass spectrum of 2-methylpropene (2-methylprop-1-ene)

The H-1 NMR spectrum of 2-methylpropene (2-methylprop-1-ene)

C-13 NMR spectroscopy index

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