Worksheet: Carbon NMR Spectra
In this worksheet, we will practice interpreting ¹³C NMR spectra, using the positions and relative intensities of peaks to determine molecular structure.
How does the range of chemical shifts in carbon-13 NMR differ from that in proton NMR?
- ACarbon-13 and proton NMR signals span similar ranges of chemical shifts, but the positions of carbon-13 signals are more sensitive to the effects of solvation and hydrogen bonding.
- BCarbon-13 and proton NMR signals span similar ranges of chemical shifts, but changes in chemical shift are harder to detect in carbon-13 NMR due to the lower signal intensity.
- CCarbon-13 NMR signals span a much narrower range of chemical shifts and are less sensitive to the chemical environment.
- DCarbon-13 NMR signals span a much wider range of chemical shifts and are more sensitive to the chemical environment.
- ECarbon-13 NMR signals span a much wider range of chemical shifts, but changes in chemical shift are harder to detect due to the lower signal intensity.
Carbon NMR is harder to do than proton NMR because:
- AThe mechanism of interaction of the isotopes of carbon (number 13) with a magnetic field is dependent on how many hydrogens are attached to it.
- BIt has a higher atomic mass which makes it slower to move and relax on the NMR time scale.
- CThe gyromagnetic ratio (NMR sensitivity factor) is over 100 times less for carbon-13 than for hydrogen-1.
- DThe actual atoms of carbon observed (the isotope we can detect) is of lower relative abundance than for hydrogen.