Chapter 32 - Structure determination

Question 1

What does no. of signals, position of the signals and height of signals indicate in 13C NMR?

Answer 1

• No. of signals - No. of c environments
• Position of signals - Chemical environment of C’s
• Heights of peaks are not relevant

Question 2

What does no. of signals, position of the signals and height of signals indicate in 1H NMR?

Answer 2

• No. of signals - Chemical environment of H’s
• Position of signals - Chemical environment of H’s
• Height of peaks - Relative to the number of H’s causing the signal

Question 3

What is the zero value in 1H NMR?

Answer 3

All 1H NMR is comparative to the reference compound tetramethylsilane (TMS)

Question 4

Why is tetramethylsilane used as the reference compound for 1H NMR?

Answer 4

• Non-toxic
• Inert
• Produces a single peak
• Low boiling point (easily removed from sample afterwards)

Question 5

Describe solvents used in 1H NMR

Answer 5

• Must not contain any hydrogens as these would also produce peaks

E.g:
* Tetrachloromethane
* Deuterated solvent (H’s replaced with an isotope of hydrogen, Deuterium)

Question 6

What does the number of peaks in a splitting pattern mean for 1H NMR?

Answer 6

Number of chemically different adjacent H’s + 1

Question 7

Describe the 1H NMR splitting pattern for O-H bonds

Answer 7

• OH hydrogens do not have a splitting pattern
• Always seen as a singlet

Question 8

Describe what the area under the signal signifies in 1H NMR

Answer 8

• Proportional to the number of hydrogen atoms present
• You could also measure this using an integration trace