3.15 NMR Flashcards

1
Q

What does NMR give information about?

A

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

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2
Q

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

A

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

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3
Q

What is chemical shift?

A

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

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4
Q

What is TMS?

A
TMS is TetraMethylSilane
Standard to which chemical shift is relative
Has 12 H in identical environments
4 C in identical environments 
∂=0
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5
Q

Why do we use TMS?

A

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.

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6
Q

How to read a C13 NMR spectra?

A

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

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7
Q

How to read a H1 NMR spectra?

A

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

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8
Q

What solvent do we use in H1 NMR?

A

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

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9
Q

Cheat Tips for Reading H NMR

A

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

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10
Q

H NMR:

2 Triplets with 3 H

A

R-CH2-CH2-R

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11
Q

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

A

R-CH2-CH3

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12
Q

H NMR:

1 Singlet 3 H

A

CH3-CR3

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13
Q

H NMR:

1 Singlet 6 H

A

R- C(CH3)2. -R

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14
Q

H NMR:

1 SInglet 9 H

A

C(CH3)3- R

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15
Q

What is the N+1 Rule?

A

Shows us the splitting of the peaks.

3 Splits= Triplet = 2 Adjacent H

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16
Q

What does the Integration trace tell us?

A

The ratio of Hs

17
Q

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

A

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

18
Q

What is the formula for TMS?

A

Si (CH3) 4

19
Q

Why do we use deuterated solvents?

A

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