interpreting 1 h nmr spectra n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Interpreting 1 H nmr spectra PowerPoint Presentation
Download Presentation
Interpreting 1 H nmr spectra

Loading in 2 Seconds...

play fullscreen
1 / 39

Interpreting 1 H nmr spectra - PowerPoint PPT Presentation


  • 197 Views
  • Uploaded on

Interpreting 1 H nmr spectra. L.O.: Intrepet 1 H nmr spectra using the n+1 rule. H. - C - X. - C - H. CHEMICAL SHIFT. Low d. ‘shielding’. Bonding to electronegative atoms (O, N). High d. ‘deshielding’. Approximate chemical shifts The actual values depend on the environment.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Interpreting 1 H nmr spectra' - liberty-preston


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
interpreting 1 h nmr spectra

Interpreting 1H nmr spectra

L.O.:

Intrepet 1H nmr spectra using the n+1 rule

slide2

H

- C - X

- C - H

CHEMICAL SHIFT

Low d

‘shielding’

Bonding to electronegative atoms (O, N)

High d

‘deshielding’

Approximate

chemical shifts

The actual values depend on the environment

ROH

-CHO

-COOH

-C=CH-

TMS

13 12 11 10 9 8 7 6 5 4 3 2 1 0 d

‘deshielding’

slide3

LOWRESOLUTION

  • low resolution NMR gives 1 peak for each environmentally different group of protons
  • Strengths of the absorption are proportional to number of equivalent 1H atoms. It is measured by the are under each peak. Integration.

LOW RESOLUTION SPECTRUM OF 1-BROMOPROPANE

slide5

The simplified NMR spectrum of EtOH shows three single peaks.

A detailed, high-resolution spectrum of EtOH shows that some peaks are split into a number of subsidiary peaks. This splitting is caused by spin-spin coupling between protons on neighbouring atoms.

slide7

The ‘n +1’ rule

The n.m.r. absorption of a proton which has n equivalent neighbouring protons will be split into n + 1 peaks.

slide9

MULTIPLICITY (Spin-spin splitting)

O adjacent H’s

There is no effect

1 adjacent H

can be aligned either with a or against b the field

there are only two equally probable possibilities

the signal is split into 2 peaks of equal intensity

slide10

MULTIPLICITY (Spin-spin splitting)

O adjacent H’s

There is no effect

1 adjacent H

can be aligned either with a or against b the field

there are only two equally probable possibilities

the signal is split into 2 peaks of equal intensity

2 adjacent H’s

more possible combinations

get 3 peaks in the ratio 1 : 2 : 1

slide11

MULTIPLICITY (Spin-spin splitting)

O adjacent H’s

There is no effect

1 adjacent H

can be aligned either with a or against b the field

there are only two equally probable possibilities

the signal is split into 2 peaks of equal intensity

2 adjacent H’s

more possible combinations

get 3 peaks in the ratio 1 : 2 : 1

3 adjacent H’s

even more possible combinations

get 4 peaks in the ratio 1 : 3 : 3 : 1

slide12

MULTIPLICITY (Spin-spin splitting)

Number of peaks = number of chemically different H’s on adjacent atoms + 1

1 neighbouring H 2 peaks “doublet” 1:1

2 neighbouring H’s 3 peaks “triplet” 1:2:1

3 neighbouring H’s 4 peaks “quartet” 1:3:3:1

4 neighbouring H’s 5 peaks “quintet” 1:4:6:4:1

Signals for the H in an O-H bond are unaffected by hydrogens on adjacent atoms - get a singlet

slide13

INTEGRATION

  • the area under a signal is proportional to the number of hydrogen atoms present
  • an integration device scans the area under the peaks
  • lines on the spectrum show the relative abundance of each hydrogen type
  • By measuring the distances between the integration lines one can
  • work out the simple ratio between the various types of hydrogen.
  • before integration after integration

NOTICE THAT THE O-H SIGNAL IS ONLY A SINGLET

slide14

INTEGRATION

Measure the distance between the top and bottom lines.

Compare the heights from each signal and make them into a simple ratio.

  • HOW TO WORK OUT THE SIMPLE RATIOS
  • Measure how much each integration line rises as it goes of a set of signals
  • Compare the relative values and work out the simple ratio between them
  • In the above spectrum the rises are in the ratio... 1:2:3

IMPORTANT: It doesn’t provide the actual number of H’s in each environment, just the ratio

slide15

1

2

3

4

NMR SPECTROSCOPY

When is a hydrogen chemically different?

TWO SIGNALS

Quartet and triplet :- ratio of peak areas = 3 : 2

Carbons 1 & 4 are the similar and so are carbons 2 & 3 so there are only two different chemical environments.

The signal for H’s on carbon 2 is a quartet - you ignore the two neighbours on carbon 3 because they are chemically identical.

BUTANE

slide16

1

2

3

4

NMR SPECTROSCOPY

When is a hydrogen chemically different?

TWO SIGNALS

Quartet and triplet :- ratio of peak areas = 3 : 2

Carbons 1 & 4 are the similar and so are carbons 2 & 3 so there are only two different chemical environments.

The signal for H’s on carbon 2 is a quartet - you ignore the two neighbours on carbon 3 because they are chemically identical.

TWO SIGNALS

both singlets :- ratio of peak areas = 2 : 1

Hydrogens on OH groups only give singlets. The signal for H’s on each carbon are not split, because

- H’s on the neighbouring carbon are chemically

identical... and

- H’s on adjacent OH groups do not couple.

BUTANE

ETHANE-1,2-DIOL

slide17

NMR SPECTROSCOPY - SUMMARY

An nmr spectrum provides several types of information :-

number of signal groups tells youthe number of different proton environments

chemical shift the general environment of the protons

peak area (integration) the number of protons in each environment

multiplicity how many protons are on adjacent atoms

In many cases this information is sufficient to deduce the structure of an organic molecule but other forms of spectroscopy are used in conjunction with nmr.

slide18

NMR spectra of –OH and –NH protons

  • They are usually broad
  • The is usually no splitting pattern.
slide19

D2O Shake

CH3CH2OH + D2O → CH3CH2OD + HOD

slide21

1H NMR TASK 4

For each of the following compounds,

draw the molecule, predict the number of signals, predict the relative intensity of each signal and predict the approximate chemical shift (of each signal

a)propanoic acid

b)propanal

c)2-chloropropane

d)2-methylbutane

e)methylpropene

f)methyl propanoate

interpreting 1 h nmr spectra1

Interpreting 1H nmr spectra

L.O.:

Intrepet 1H nmr spectra using the n+1 rule

slide26

WHAT IS IT!

C2H5Br

3

2

slide27

WHAT IS IT!

C2H3Br3

2

1

slide28

WHAT IS IT!

C2H4Br2

3

1

slide29

WHAT IS IT!

C2H4O2

1

3

1

slide30

WHAT IS IT!

C4H8O2

3

3

2

slide32

WHAT IS IT!

C3H6O

3

2

1

slide33

WHAT IS IT!

C4H8O

3

3

2