The Carbon-13 NMR spectrum of Pent-1-ene (1-pentene)

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 pent-1-ene 1-pentene

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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 - pent-1-ene here.

Pent-1-ene, , , (1-pentene)

Interpreting the C-13 NMR spectrum of pent-1-ene (1-pentene)

As you can see from the diagram above there are only 5 chemical shift lines in the C-13 NMR spectrum of pent-1-ene indicating 5 different chemical environments of carbon atoms.

CH₃CH₂CH₂CH=CH₂

(note the 5 different colours indicating the different chemical environment of the carbon atoms)

There are 5 carbon atoms in the molecule, all in a different chemical environment, so you observe 5 different chemical shifts.