C ARBON -13 NMR SPECTROSCOPY Analyse carbon-13 NMR spectra to make predictions about the different types of carbon atoms present. Predict the chemical shifts of carbons in a given molecule.

DEFINITIONS Chemical shift Retention time R f value Nucleon Adsorption Phase

C ARBON -13 NMR S PECTROSCOPY What is the relative atomic mass of carbon? How much of naturally occurring carbon is carbon -13? 1.1% Why might carbon-13 be used for NMR spectroscopy? It has an odd number of nucleons, resulting in a residual magnetic spin Carbon – 13 NMR spectroscopy allows the identification of carbon atoms in an organic molecule

T YPICAL CARBON – 13 SHIFTS Chemical shifts indicate the chemical environment of the carbon atoms present More electronegative atoms or groups cause a significant chemical shift The range of chemical shifts values is between 0 – 230ppm so carbon atoms will typically have a separate signal (unless they are in an identical environment)

I NTERPRETING CARBON – 13 NMR SPECTRA From a carbon-13 spectrum, the most important information is: The number of different carbon environments (from the number of peaks) The types of carbon environment (from the chemical shift) NB the size of the peak tells us nothing about the number of carbon atoms responsible!

W ORKED EXAMPLE Carbon-13 NMR spectra of propan-1-ol and propan-2-ol 1. How many carbon environments for each compound? Propan-1-ol = 3 peaks: 3 C atoms in 3 environments Propan-2-ol = 2 peaks: 3 C atoms in 2 environments

W ORKED EXAMPLE 1. What are the environments of each carbon atom? (Use the chemical shift values) Propan-1-ol 1 peak at δ = 64ppm for C-O 1 peak at δ = 15 ppm for C-C 1 peak at δ = 27 ppm for C-C Propan-2-ol 1 peak at δ = 64 ppm for C-O 1 peak at δ = 28 ppm for C-C

Q UESTIONS Complete questions 1 and 2 on page 87 Complete question 3 on page 105