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A2 Chemistry Unit 2 > NMR > Flashcards

Flashcards in NMR Deck (21)
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1

What do the peaks show in NMR

Different external magnetic fields
Needed to bring to resonance
At a particular radio frequency

2

What compound produces a peak at 0

Tetramethylsilane

3

Draw TMS

See notes

4

Why is TMS used

⭕️ inert
⭕️ 12 H chemically equivalent - strong peak and single peak
⭕️ Peak to extreme right - outside normal range for most compounds

5

What unit is chemical shift measured in

Parts per million
Ppm

6

If something is to the left of TMS what term is used to describe it

Downfield
Further left = more downfield

7

How does an -OH affect chemical shift

- Electronegative O draws e towards it
- electron density around H decreases
- reduction in shielding
- the further away a H is ➡️ shielded to greater extent ➡️ need higher applied field to bring to resonance ➡️ further downfield

8

How big will a poorly shielded H’s chemical shift be

Large

9

How big will a highly shielded H’s chemical shift be

Small

10

What do different peaks represent in low resolution NMR

Different environments for H atoms

11

What does the ratio of areas under the peaks give an indication of

Ratio of number of H atoms in each environment

12

What does the integrator trace give a measure of

The relative area under peak

13

What is the definition of low resolution NMR

Spectrum which does not show the spin spin splitting pattern

14

What is the definition of high resolution NMR

Spectrum which does show the spin-spin splitting pattern

15

What is the definition of a doublet

Signal which appears as a pair of lines of equal intensity

16

What is the definition of a triplet

Signal which appears as three lines in the approximate intensity ratio 1:2:1

17

What is the definition of a quartet

A signal which appears as four lines in the approximate intensity 1:3:3:1

18

Describe the n+1 rule

The number of sub peaks is one more than the number of H attached to the next door carbon(s)

19

What are equivalent hydrogen atoms

H atoms attached to the same C atom
No splitting
Produce one peak

20

What happens when a H becomes deshielded

H bonded to O or N
Becomes more positive

21

What conditions can cause chemical shift to vary

Temperature
Solvent
Concentration