NMR Spectroscopy

Question 1

What does NMR Spectroscopy do?

Answer 1

Detects nuclei in a magnetic field

Question 2

What property do H1 and C13 atoms have?

Answer 2

A property called nuclear spin - they act like tiny magnets

Question 3

What does the amount of energy needed to ‘flip’ the spin of H1 and C13 depend on?

Answer 3

Their chemical environment

Question 4

What happens when H1 and C13 atoms are placed in a strong magnetic field?

Answer 4

These tiny magnets can absorb energy and ‘flip’ their spin - known as resonance

Question 5

What is chemical shift?

Answer 5

Describes the energy needed for resonance

Question 6

What is chemical energy measured in?

Answer 6

Parts per million, relative to TMS

Question 7

What does the amount of peaks in a C13 NMR spectra depend on?

Answer 7

Depends on how many unique C environments there are

Question 8

What does chemical shift depend on?

Answer 8

Electron density around a nucleus

Question 9

What will shift peaks more downfield?

Answer 9

More electronegative groups (higher chemical shift values)

Question 10

What is TMS?

Answer 10

(CH3)4Si

Question 11

What is TMS used as?

Answer 11

An internal standard - enables comparison of absorbances in NMR spectra

Question 12

Why is TMS used as an internal standard?

Answer 12

• Produces a single peak (as all atoms are in the same environment)
• Non-reactive
• Low chemical shift (does not interfere with peaks)
• Low boiling temperature so easily removed
• Gives a strong signal so small amount needed

Question 13

What does integration of H1 NMR show?

Answer 13

The ratio of protons in each unique environment

Question 14

What causes peaks to split in H1 NMR?

Answer 14

Hydrogens bonded to adjacent, non-equivalent carbon atoms

Question 15

What determines how many times the peak is split in H1 NMR spectra?

Answer 15

The number of hydrogens on adjacent carbon atoms

Question 16

What rule does the splitting in H1 NMR spectra follow?

Answer 16

n+1

Question 17

What solvents are used for H-NMR?

Answer 17

Deuterated solvents - or CCl4
(to avoid interfering signals)