Unit 9

Question 1

Where in the spectrum is the energy needed to make bonds vibrate

Answer 1

infrared

Question 2

What ways can bonds vibrate?

Answer 2

symmetric, asymmetric and bend

Question 3

Are vibration levels quantised?

Answer 3

yes, incoming radiation must match the energy difference between energy levels

Question 4

what does an infrared spectrometer do?

Answer 4

it measures which energy is absorbed and how much

Question 5

how will the pen move when there is more absorbance?

Answer 5

it will move down. Each peak is caused by a bond and energy used to make it vibrate

Question 6

What is a group frequency?

Answer 6

its a range of frequencies eg the 1/wavelength number which correlate to functional groups

Question 7

Alcohol group frequency? (o-H) (c-o)

Answer 7

3300 and 1050

Question 8

Carbonyl group frequency? (c=o)

Answer 8

1720-1750

Question 9

Ester group frequency? (c-o)

Answer 9

1070-1150

Question 10

Acids group frequency? (o-h)

Answer 10

2500-3000

Question 11

Nitriles group frequency? (triple bond c-n)

Answer 11

2000-2500

Question 12

Where will a strong bond be on a IR spectra and why?

Answer 12

It will be at a high wavenumber as this is proportional to frequency. A strong bond will need more energy to make it vibrate and more energy means a higher frequency.

Question 13

Where will a weak bond be on an IR spectra?

Answer 13

It will have a low wavenumber as it doesn’t need a high frequency to vibrate the bond

Question 14

Protons have spins and are like magnets, their magnetic field will try to line up if in a magnetic field. T or F

Answer 14

T

Question 15

Can you cause protons to be in different spin states?

Answer 15

Yes by giving them radio wave energy and an applied magnetic field

Question 16

What has more energy a proton aligned against the field or with it?

Answer 16

against the field

Question 17

What does NMR detect?

Answer 17

Change in spin

Question 18

What does a peak in NMR represent?

Answer 18

Different hydrogen environments. The different conditions mean they need different energies to move them

Question 19

What does the height of a NMR peak tell us?

Answer 19

How many hydrogens are in that environment, the ratio between peaks tells you not the actual height.

Question 20

Why should you ignore an NMR peak if its at 0?

Answer 20

Because that is the standard for comparison called TMS

Question 21

What does splitting tell you on a NMR spectrum ?

Answer 21

It tells you the number of other hydrogens next to the one you’re looking at. It follows the n+1 rule

Question 22

What is an equivalent hydrogen atom in NMR

Answer 22

A hydrogen attached to the same carbon wont have any affect. Also, if a hydrogen on another atom is in exactly the same environment it is also equivalent

Question 23

How can you work out the split ratio?

Answer 23

you can use pascals triangle. Just do 
1
1 + 1 
1+2+1   make sure you add ones at edge
1 + 3+ 3+ 1
1+4+6+4+1
1+5+10+10+5+1
can keep going

Question 24

How do you work out pascals triangle and what can you use it for ?

Answer 24

Can use it to work out the split ratio in NMR 
1
1 + 1 
1+2+1   make sure you add ones at edge
1 + 3+ 3+ 1
1+4+6+4+1
1+5+10+10+5+1
can keep going

Question 25

What does a strong signal at 3000 and 1720 on IR indicate?

Answer 25

A carboxylic acid

Question 26

What is wavenumber?

Answer 26

its 1/wavelength

Question 27

what does infrared spectroscopy measure?

Answer 27

The absorption of IR

Question 28

What is IR absorbed for in molecules?

Answer 28

used to increase vibrations of the bonds in molecules but the incoming energy must match the difference between vibrational energy levels

Question 29

In NMR what is radio wave energy used for?

Answer 29

change the spin state of protons to a higher spin state