3.15 NMR Flashcards Preview

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Flashcards in 3.15 NMR Deck (19):
1

What does NMR give information about?

NMR gives information about the position of :
C13 atoms
H1 atoms

2

What are Nuclear Environments and why do they have different chemical shift data?

The nucleus is shielded by different electrons
Magnetic fields affect each nucleus differently
Nuclei will absorb energy at different frequencies

3

What is chemical shift?

NMR measures differences in energy absorbtion
This is called chemical shift ∂
Measured in ppm (parts per million)

4

What is TMS?

TMS is TetraMethylSilane
Standard to which chemical shift is relative
Has 12 H in identical environments
4 C in identical environments
∂=0

5

Why do we use TMS?

It has a far right trace so we can label ∂=0
Inert, non toxic, volatile- so easily removed from our product we're testing
12H and 4C in identical environments so has a strong trace.

6

How to read a C13 NMR spectra?

Number of peaks= C environments
Use table to interpret.
Remember that symmetry will only show once.

7

How to read a H1 NMR spectra?

Number of peaks= H environments
Area under peak= relative number of H
Splitting pattern/ multiplets= number of H on adjacent carbon (This occurs similar to Pascals Triangle)

Exceptions: OH is always a singlet

8

What solvent do we use in H1 NMR?

We cant use protonated solvents so we use Deuterated Solvents
These solutions contain H2
This doesnt react with the magnetic field
No spectra produced

9

Cheat Tips for Reading H NMR

Look at Spliiting First!
Then Chemical Shift Data
Then read the whole question- is there any more clues?

10

H NMR:
2 Triplets with 3 H

R-CH2-CH2-R

11

H NMR:
1 Triple w 3H
1 Quartet 2 H

R-CH2-CH3

12

H NMR:
1 Singlet 3 H

CH3-CR3

13

H NMR:
1 Singlet 6 H

R- C(CH3)2. -R

14

H NMR:
1 SInglet 9 H

C(CH3)3- R

15

What is the N+1 Rule?

Shows us the splitting of the peaks.
3 Splits= Triplet = 2 Adjacent H

16

What does the Integration trace tell us?

The ratio of Hs

17

Why may we have more C than peaks in C NMR?

If there is symmetry in the molecule, some peaks wont show twice.

18

What is the formula for TMS?

Si (CH3) 4

19

Why do we use deuterated solvents?

The solvent cannot have an H1 environments as it would interfere with the trace so we use CDCl3 which has 1 H2 environment. H2= Deuterium