NMR spectroscopy [O2] PAPER 2

Question 1

Draw tetramethylsilane (TMS).

Answer 1

Question 2

State why TMS is used in 1H NMR spectroscopy.

Answer 2

• as a standard (has a peak at 0ppm)
• is inert
• gives one signal
• peak is upfield from others (as low electronegativity of Si shifts the signal right)
• low boiling point (so volatile and easy to remove)

Question 3

State why CCl4 or CDCl3 (deuterated solvents) are used in 1H NMR spectroscopy.

Answer 3

• as solvents
• is inert
• both have no H atoms tied to either molecule (so give no signals in the spectrum)
• CCl4 is non-polar (so good solvent for non-polar organic molecules)
• CDCl3 is a polar covalent molecule (so good solvent for polar organic compounds)

Question 4

n+1 rule for 1H NMR spectroscopy?

Answer 4

splitting pattern according to the number of Hs on adjacent carbons

• singlet = no H on adjacent carbon
• doublet = 1 H on adiacent carbon
• triplet = 2 H on adjacent carbon
• quartet = 3 H on adjacent carbon

Question 5

what does chemical shift depend on?

Answer 5

molecular environment (so, the bond, the surrounding groups, etc)

Question 6

what is integration spectra in 1H NMR spectroscopy?

Answer 6

indicates the relative numbers of H atoms in different environments

Question 7

13C NMR analyses…

Answer 7

different carbon environments