The Carbon-13 NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene)

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 3-methylbut-1-ene (3-methyl-1-butene)

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 - 3-methylbut-1-ene (3-methyl-1-butene) here.

Interpreting the C-13 NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene)

As you can see from the diagram above there are 4 different chemical shift lines in the C-13 NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene) indicating 4 different chemical environments of the carbon atoms.

H₂C=CHCH(CH₃)₂

(Note the 4 colours indicating the 4 different chemical environments of the carbon atoms in 3-methylbut-1-ene (3-methyl-1-butene).

Chemical shifts (a) to (d) on the C-13 NMR spectrum diagram for 3-methylbut-1-ene.

The carbon-13 NMR spectra a provides direct evidence of 4 different carbon atom environments in the 3-methylbut-1-ene (3-methyl-1-butene) molecule from 4 different chemical shifts (ppm).