Synthetic routes, Mass spectrum and IR

Question 1

What happens when a molecule absorbs infrared radiation?

Answer 1

It makes the covalent bond vibrate more in a stretching or bonding motion where it can then absorb energy

Question 2

What factors affect the amount of vibration of a bond?

Answer 2

• Bond strength
• Bond length
• Mass of each atom in a bond

Question 3

How does infrared spectroscopy work?

Answer 3

The IR radiation is passed through a sample where the different type of bonds absorb the radiation in different amounts. These varying amounts of absorbance are measured and recorded.

Question 4

What are the 2 peaks that must be present to identify a substance as carboxylic acid?

Answer 4

• Very broad peak O-H groups
• Sharp peaks C=O

Question 5

What happens inside a mass spectrometer?

Answer 5

• Organic compounds is vaporised and passed through the spectrometer where a high voltage is passed
• This causes electrons to be removed from the atoms (they are ionised) leaving +1 charged ions
• Energy causes vibrations and the bonds weaken and fragment

Question 6

Is fragmentation predictable?

Answer 6

No, because it can happen anywhere in the molecule

Question 7

What is the m/z value of CH3+?

Answer 7

15

Question 8

What is the m/z value of OH from an alcohol?

Answer 8

17

Question 9

What is the m/z value of C2H5+

Answer 9

29

Question 10

What is the m/z value of C3H7+

Answer 10

43

Question 11

What are 2 advantages of using mass spectrometry?

Answer 11

• Cheap
• Small quantities of sample required

Question 12

What is the main disadvantage of using mass spectrometry?

Answer 12

The sample is completely destroyed

Question 13

How do you convert an alkene to an alkane?

Answer 13

H2 and a Ni catalyst

Question 14

How do you convert an alkene to a haloalkane?

Answer 14

Hydrogen halide

Question 15

How do you convert an alkane to a haloalkane?

Answer 15

Halogen/UV

Question 16

How do you convert an alcohol to a haloalkane?

Answer 16

Sodium halide and H2SO4

Question 17

How do you convert an alcohol to an alkene?

Answer 17

Dehydration, conc H2S04

Question 18

How do you convert a haloalkane to an alcohol?

Answer 18

NaOH (aq) and reflux

Question 19

How do you convert an alkene to an alcohol?

Answer 19

H3PO4 and steam (H2O)

Question 20

What is the process of purifying organic products?

Answer 20

1. Pour liquids into separating funnel and allow them to separate
2. Add water to aq later and add a flask under and collect the bottom layer
3. Collect the final layer

Question 21

When purifying an organic product what are the 2 layers and how can you make a distinction between them?

Answer 21

There is an aq layer and an organic layer, adding water will make the aq layer bigger

Question 22

How do you purify a impure product that may contain acid?

Answer 22

Add aq sodium carbonate and shake and open tap slowly to release gas

Question 23

In a mass spectrometer how is a molecular ion represented?

Answer 23

• M+
• The peak with the highest m/z ratio

Question 24

How might you dry an organic product?

Answer 24

1. Add organic layer to a flask
2. Add a drying agent (anhydrous sodium sulfate)
3. Place a stopper to avoid evaporation
4. Decant liquid into a round bottomed flask

Question 25

Give an everyday use for infrared spectroscopy

Answer 25

Breathalysers