NMR

Question 1

What is NMR?

Answer 1

An analytical technique that allows the structure of a molecule to be determined by analysing the energy of each bond environment.

Question 2

What produces the different NMR peaks?

Answer 2

Different bond environments absorb different amounts of energy.

Question 3

What is the standard molecule the bond environments are measured against?

Answer 3

TMS

Question 4

How to draw TMS?

Answer 4

Si bonded to 4 CH3

Question 5

Why is TMS a standard molecule? (2)

Answer 5

• It only gives one signal.
• it has a low boiling point so it can be removed from the sample easily.

Question 6

What happens to carbon environments that are near to an oxygen?

Answer 6

The values are shifted to the right. Because oxygen is very electronegative and changes the bond environment and how it absorbs energy.

Question 7

What must the samples being analysed in Proton NMR be done?

Answer 7

They must be dissolved in a non hydrogen-containing solvent.

Question 8

What is a common non hydrogen-containing solvent that can be used?

Answer 8

CCl4 or CDCl3.
CCl4 - non-polar organic molecules.
CDCl3 - polar organic molecules.

Question 9

Why is a non hydrogen containing solvent needed?

Answer 9

So they don’t give peaks in the proton NMR spectrum.

Question 10

What do the heights of the peaks in proton NMR show?

Answer 10

Relative intensity of each value. This shows the number of hydrogens.

Question 11

What do the peaks in proton NMR show?

Answer 11

Where each environment is positioned within the molecule.

Question 12

What are peaks split into?

Answer 12

Small clusters with smaller peaks indicating how many hydrogens are on the adjacent carbon atom.

Question 13

What is the rule for the splitting pattern?

Answer 13

n+1

Question 14

What is n in n+1?

Answer 14

The number of hydrogen atoms on the adjacent carbon.

Question 15

What is it called if there are no hydrogens on the adjacent carbon?

Answer 15

Singlet

Question 16

What is it called if there is 1 hydrogen on the adjacent carbon?

Answer 16

Doublet

Question 17

What is it called if there are 2 hydrogens on the adjacent carbon?

Answer 17

Triplet

Question 18

What is it called if there are 3 hydrogens on the adjacent carbon?

Answer 18

Quartet

Question 19

What does a triplet-quartet splitting pattern show?

Answer 19

A CH2-CH3 fragment

Question 20

What is the chemical shift?

Answer 20

How much the field has shifted away from the field for TMS.

Question 21

What is S+?

Answer 21

A measure of parts per million (ppm) - it is a relative scale of how far the frequency of the proton signal has shifted away from that for TMS.

Question 22

What is the ratio for a doublet?

Answer 22

1:1

Question 23

What is the ratio for a triplet?

Answer 23

1:2:1

Question 24

What is the ratio for a quartet?

Answer 24

1:3:3:1

Question 25

What does a singlet of a relative intensity tell you?

Answer 25

There are 3 CH3 groups bonded to one C.