3.3.15 - NMR spectroscopy

Question 1

How to determine number of carbon environments?

Answer 1

Look at the number of carbons, the number of environments is all carbons which are bonded to different things.

Question 2

Why is tetramethylsilane used in C-13 spectroscopy? (5)

Answer 2

• Used as reference
• Only one peak
• Inert
• Low electronegativity of Si shifts peak to the right
• Easy to remove from the sample

Question 3

What does Carbon-13 spectroscopy tell us?

Answer 3

Tells us how many different carbon environments there are

Question 4

How does C-13 Spectroscopy work?

Answer 4

• X-axis = chemical shift
• The closer a carbon is to an electronegative element (i.e Cl), the higher the shift to the left

Question 5

How do you check for carbon environments in cyclic compounds?

Answer 5

Use lines of symmetry

Question 6

What is the difference between an ether and an ester?

Answer 6

Ether = R-O-R bond
Ester = C=O as well as C-O (same carbon)

Question 7

Why is CCL4 used in 1H spectroscopy? (2)

Answer 7

• Used as a solvent for non-polar compounds
• Contains 0 hydrogens

Question 8

Why is CDCL3 used in 1H spectroscopy?

Answer 8

• Polar solvent for polar molecules

Question 9

What does the integration ratio tell us?

Answer 9

Ratios of hydrogen in each carbon environment

Question 10

What does the number of peaks tell us?

Answer 10

N+1 of hydrogens on adjacent carbon