Spectoscopy

Question 1

What does a mass spectrometer do?

Answer 1

Detects the mass to charge ratio (m/z) of the molecular ion which gives the molecular mass of a compound.

Question 2

How do you find the molecular mass from a mass spectrum?

Answer 2

M+ has to be located, the clear peak at the highest m/z value on right hand side.

Question 3

(M+1)

Answer 3

Small peak after M+. It exists because 1.1% of carbon is present as the carbon-13 isotope. Would have one extra

Question 4

What is fragmentation?

Answer 4

When molecular ions break down into fragments -> molecules with the same molecular mass will have different fragmentation patterns if they have different structures.

Question 5

What does the simplest fragmentation break a molecular ion into?

Answer 5

A positively charged ion and a radical.

Question 6

What are some common fragment ions?

Answer 6

CH3+ - 15
C2H5+ - 29
C3H7+ - 43
C4H9+ - 57

Question 7

Infrared spectroscopy

Answer 7

Use of absorption peaks from an infrared spectrum to identify bonds and functional groups present in a molecule.

Question 8

What do covalent bonds do around a central point?

Answer 8

Covalent bonds vibrate around a central point - increases with temp.

Question 9

What can bonds absorb?

Answer 9

Bonds can absorb IR radiation which makes them bend and stretch more

Question 10

Vibration - Stretch

Answer 10

Rhythmic movement, distance from atomic centre increases or decreases.

Question 11

Vibration - Bend

Answer 11

Results in change of bond angle