quick review a2 high resolution nor spectroscopy
DESCRIPTION
A level chemistry AQA A2 Proton NMR- quick review for classTRANSCRIPT
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A2 Chemistry
Quick Guide High Resolution 1H Nuclear Magnetic
Resonance Spectroscopy
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High Resolution 1H Nuclear Magnetic Resonance Spectroscopy
10 0
EnergyAbsn.
TMS
3 different environments of 1H nuclei, thus 3 nmr signals
Reminder: CH3-CH2-CO-CH3
CH3 CH2 CH3
At high resolution nmr, signals are seen to be split.
10 0
Absn. TMS
Are there >1 1H nuclei environment in CH3COCH3
and what will the integration number be for the signal(s)?
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The “n+1” RuleThe signal produced by a H group
which has “n” H atoms on itsneighbouring atom is split
into “n +1” signals.
The relative heights of the peaks give the relative number of hydrogen atoms for that particular H environment.• If there is 1 peak, no integration number is
recorded• If peaks have identical numbers of hydrogen
atoms then their integration ratios will be 1:1:1:1 etc
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LOW RESOLUTION nmr
HIGH RESOLUTION nmr
Caused by
how many H neighbours?
Singlet 0
Doublet 1
Triplet 2
Quartet 3
Described as a
1:1
1:2:1
1:3:3:1
SUMMARY OF SPLITTING PATTERNS
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Example:
10
CH3-CO-O-CH2-CH3
CH3CH2 CH3
(a) (b) (c)
What is this?
RCO-CH 2.1-2.6 Int. 3 singlet
RCO-O-CH 3.7-4.1 Int. 2 quartet
R-CH3 0.7-1.2 Int. 3 triplet
2 3 3 TMS
0
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Example:
10
CH3-CO-O-CH3
CH2 CH3
(a) (b)What is this?
RCO-CH 2.1-2.6 Int. 3 singlet
RCO-O-CH 3.7-4.1 Int. 3 singlet
2 3 TMS
0
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Patterns to look for :
(a) 2 doublets
W―CH―CH―Z
X Y│ │
(b) 2 triplets W―CH2―CH2―Z
(c) Triplet and quartet
W―CH2―CH3
(d) Triplet and doublet
(e) Doublet and quartet
W―CH―CH2
X Y│ │
W―CH―CH3
X│
W , X , Y and Z = atom with NO H bonded to it
QuartetTriplet
TripletDoublet
QuartetDoublet
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SPLITTING BY NEIGHBOURING OH and NH GROUPS-usually NONE
10 0
Absn. TMS
RCH3 0.7-1.2 Int. 3 triplet
R-O-CH 3.1-3.9 Int. 2 quartet
R-OH 0.5-5.0 Int. 1 singlet*
Example: CH3-CH2-OH(a) (b) (c)
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Two 1H nmr spectra shown below were obtained from compounds X and Y, both containing just one functional group and having the molecular formula, C3H6O2.
Deduce the structures of X and Y.
Possible structures?
(a) CH3CH2COOH
(b) CH3COOCH3
(c) HCOOCH2CH3
X Y
3 signals, Integration: 3:2:1Triplet, quartet, singletδ 0.7-1.2, 2.1-2.6, 10.0-12.0
2 signals, Integration: 1:1 to each otherBoth singletsδ 2.1-2.6 and 3.7-4.1
3 signals, Integration 1:2:3Singlet, quartet, tripletδ 9.0-10.0, 3.7-4.1, 0.7-1.2
= Y
= X