A2 Chemistry

Quick Guide High Resolution 1H Nuclear Magnetic

Resonance Spectroscopy

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)?

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

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

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

Example:

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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

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

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)

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