what is nmr? nmr is a technique used to probe the structure of molecules. paired with other...
TRANSCRIPT
![Page 1: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/1.jpg)
What is NMR?
NMR is a technique used to probe the structure of molecules.
Paired with other techniques such as MS and elemental analysis it can be used to successfully predict the structure of organic molecules.
01234PPM 0102030405060
PPM
H1 NMR of Ethanol C13 NMR of Ethanol
![Page 2: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/2.jpg)
How it works?
Atoms behave a little bit like magnets
![Page 3: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/3.jpg)
Atoms have a property called spin angular momentum (I).
This can assume values of 0,, 1, , 2,
It is determined by the number of unpaired protons and neutrons in the nucleus of an atom.
Protons and nucleons (nucleons) have a spin number of
![Page 4: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/4.jpg)
I Nuclide
0 12C, 16O1H, 13C, 15N, 19F, 29Si, 31P
1 2H, 14N11B, 23Na, 35Cl, 37Cl
17O, 27Al
3 10B
![Page 5: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/5.jpg)
Nuclei with spin can either:-Line up with the magnetic fieldor oppose the magnetic field
Nuclei which oppose the field have a higher energy than those aligned. This gap in energy, ∆E, can be measured.
Nuclei in a low energy state can be promoted to a higher energy state if energy, equal to ∆E is provided. This is called excitation. This will soon drop back to the lower energy state, called relaxation. This process is called resonance.
![Page 6: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/6.jpg)
What affects the magnetic field?
The strength of the field felt by each nucleus in a molecule is affected by two factors:-a) The strength of the fieldb) Shielding generated by a weak magnetic field generated by
the electrons surrounding the nucleus.
![Page 7: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/7.jpg)
024681012PPM
EnergyShielding
OH
O
HO
H H
H H
The amount of shielding and
absorbed energy is called a chemical
shift, δ
![Page 8: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/8.jpg)
020406080100120140160180PPM
OH
O
HO
EnergyShielding
![Page 9: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/9.jpg)
The δ Scale
024681012PPM
Measured against a standard, TMS.
Why TMS?• It is chemically unreactive• It has 12 equivalent protons and one carbon environment which give one sharp
and easily measured peak on both 13C and 1H spectra.• It’s nuclei are heavily shielded so there are rarely peaks below it• It is volatile and easily removed from a sample after
![Page 10: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/10.jpg)
Solvents
NMR is usually carried out in solution.Most solvents are organic and therefore contain both carbon and hydrogen which would give peaks.Deuterated solvents are used instead. Deuterium produces no 1H NMR signal.It’s 13C is easily recognised and removed by computer software.
CCl
Cl
Cl
2H
![Page 11: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/11.jpg)
Carbon-13 NMR
13C nuclei can be excited using a magnetic field of the energy corresponding to its energy gap.
The size of the energy gap differs depending on the electron density around each nuclei.
![Page 12: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/12.jpg)
Carbon-13 NMR
• The number of peaks in the NMR spectra is equal to the number of carbons in chemically different environments.
![Page 13: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/13.jpg)
Step 1: Predict the number of environments
HO O
OH
(E)-but-2-ene
![Page 14: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/14.jpg)
Step 1: Predict the number of environments
HO O
OH
(E)-but-2-ene
3
2
![Page 15: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/15.jpg)
Predict the number of carbon environments in each of these examples
butane2-chlorobutane
Cl
benzene
OH
phenol
![Page 16: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/16.jpg)
Predict the number of carbon environments in each of these examples
butane2-chlorobutane
Cl
benzene
OH
phenol
4
4
1
2
![Page 17: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/17.jpg)
Step 2: Predict Each Carbon’s Chemical Shift
e.g. HO O
OHCarbon Functional Group δ / ppm
1
2
3
1
23
![Page 18: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/18.jpg)
Step 2: Predict Each Carbon’s Chemical Shift
e.g. HO O
OHCarbon Functional Group δ / ppm
1 C-O 60ppm
2 C-C 30ppm
3 C=O (carboxylic acid) 180ppm
1
23
![Page 19: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/19.jpg)
Did we get it right?
020406080100120140160180PPM
HO O
OH
1
23
![Page 20: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/20.jpg)
Predict the chemical shift for each carbon in
O
but-3-en-2-one
Carbon Functional Group δ / ppm
1
2
3
4
1
23
4
![Page 21: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/21.jpg)
Predict the chemical shift for each carbon in
O
but-3-en-2-one
Carbon Functional Group δ / ppm
1 C-C 40ppm
2 C=O (ketone) 200ppm
3 C=C 130ppm
4 C=C 120ppm
1
23
4
![Page 22: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/22.jpg)
Did you get it right?
020406080100120140160180200PPM
![Page 23: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/23.jpg)
Final NoteOH
benzene
phenol1 aromatic environment
4 aromatic environments
![Page 24: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/24.jpg)
Proton NMR
• The number of peaks in the NMR spectra is equal to the number of hydrogens in chemically different environments.
![Page 25: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/25.jpg)
Step 1: Predict the number of different environments and therefore the number of peaks
O O
O
H H
H
H
H
H 3-hydroxypropanoic acid
CC
CCH
HH
H
H
H
HH
(2E)-but-2-ene
![Page 26: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/26.jpg)
Step 1: Predict the number of different environments and therefore the number of peaks
O O
O
H H
H
H
H
H 3-hydroxypropanoic acid
024681012PPM
CC
CCH
HH
H
H
H
HH
(2E)-but-2-ene
0123456PPM
4
2
![Page 27: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/27.jpg)
Predict the number of proton environments in each of these examples
H
HH
H
H
H
H
H
HH
OH
HH
H
H
H
HH
H
H
H
H
H
H
H
H
OH
CH3
H
H
![Page 28: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/28.jpg)
Predict the number of proton environments in each of these examples
H
HH
H
H
H
H
H
HH
OH
HH
H
H
H
HH
H
H
H
H
H
H
H
H
OH
CH3
H
H
2
1
4
4
![Page 29: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/29.jpg)
Step 2: Predict Each Protons’ Chemical Shift
e.g.Proton Relative Area Functional
Groupδ / ppm
1
2
3
4
O O
O
H H
H
H
H
H
1
2
3
4
3
2
![Page 30: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/30.jpg)
Step 2: Predict Each Protons’ Chemical Shift
e.g.Proton Relative Area Functional
Groupδ / ppm
1 1 O-H 1-12
2 2 O-CH 3-4.5
3 2 O=CCH 2-3
4 1 COOH 11-12
O O
O
H H
H
H
H
H
1
2
3
4
3
2
![Page 31: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/31.jpg)
Did we get it right?
024681012PPM
![Page 32: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/32.jpg)
Predict the chemical shift for each proton inProton Relative Area Functional
Groupδ / ppm
1
2
H
HH
H
H
H
H
H
HH
![Page 33: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/33.jpg)
Predict the chemical shift for each proton inProton Relative Area Functional
Groupδ / ppm
1 6 R-CH 1-22
2 4 R-CH 1-2
H
HH
H
H
H
H
H
HH
![Page 34: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/34.jpg)
Did you get it right?
0123PPM
![Page 35: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/35.jpg)
Spin-spin coupling
On high resolution proton NMR you may see little clusters rather than a single peak. These ‘clusters’ can help you identify the number of protons in the environment next to it.
![Page 36: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/36.jpg)
The N+1 RuleN N+1 Multiplicity
0 0+1 = 1 Singlet
1 1+1 = 2 Doublet
2 2+1 = 3 Triplet
3 3+1 = 4 Quartet
The relative intensities of the lines can be determined by Pascal’s triangle.i.e. a doublet has a relative intensity of 1:1 a triplet has an intensity of 1:2:1 a quartet has an intensity of 1:3:3:1
The gap between the peaks also stays the same and is determined by the adjacent proton environment, this is called the coupling constant.
![Page 37: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/37.jpg)
The N+1 rule
We can use the N+1 rule to identify how many protons are in the environment next to it.Example.
O
0123PPM
![Page 38: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/38.jpg)
The N+1 rule
We can use the N+1 rule to identify how many protons are in the environment next to it.Example.
O
0123PPM
Look at this CH2 group, it has a CH3 group next to it, with 3 protons.
3+1 = 4,Therefore we expect to see 4 mini peaks next
to it, or a quartet.
![Page 39: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/39.jpg)
The N+1 rule
We can use the N+1 rule to identify how many protons are in the environment next to it.Example.
O
0123PPM
Look at this CH3 group. It has no protons next to it.
0+1 = 1, therefore we expect to see one peak, or a singlet.
![Page 40: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/40.jpg)
The N+1 rule
We can use the N+1 rule to identify how many protons are in the environment next to it.Example.
O
0123PPM
Look at this CH3 group. It has a CH2 group next
to it. The CH2 group contains 2 protons.
2+1 = 3Therefore we expect to see 3 miniature peaks,
or a triplet.
![Page 41: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/41.jpg)
The N+1 Rule, 2nd Example
O
HH
HH
0246810PPM
This aldehyde proton has a CH3 group next to it.
3 + 1 = 4, Therefore we see a quartet
group.
![Page 42: What is NMR? NMR is a technique used to probe the structure of molecules. Paired with other techniques such as MS and elemental analysis it can be used](https://reader030.vdocuments.us/reader030/viewer/2022032313/56649e695503460f94b6670c/html5/thumbnails/42.jpg)
The N+1 Rule, 2nd Example
O
HH
HH
0246810PPM
This CH3 group has a group next to it with one proton.
1 + 1 = 2, therefore we see a doublet.