ib chemistry on nuclear magnetic resonance (nmr) spectroscopy and spin spin coupling

Electromagnetic Radiation and Spectroscopy

Radiowaves

Nuclear spin

Nuclear Magnetic Resonance Spectroscopy

• Organic structure determination • MRI and body scanning

Infra Red

Molecular vibration

Infra Red Spectroscopy

UV or visible

Transition of outer most valence electrons

• Organic structure determination • Functional gp determination • Measuring bond strength • Measuring degree unsaturation in fat • Measuring level of alcohol in breath

Electromagnetic Radiation

UV Spectroscopy Atomic Absorption Spectroscopy

• Quantification of metal ions • Detection of metal in various samples

Electromagnetic Radiation Interact with Matter (Atoms, Molecules) = Spectroscopy

Main features of HNMR Spectra 1. Number of different absorption peaks – Number of different proton/chemical environment

2. Area under the peaks - Number of hydrogen in a particular proton/chemical environment (Integration trace) - Ratio of number of hydrogen in each environment

3. Chemical shift - Chemical environment where the proton is in - Spinning electrons create own magnetic field, creating a shielding effect - Proton which are shielded appear upfield. (Lower frequency for resonance to occur) - Proton which are deshielded appear downfield away. (Higher frequency for resonance to occur)

- Measured in ppm (δ) 4. Splitting pattern - Due to spin-spin coupling - The number of peak split is equal to number of hydrogen on neighbouring carbon +1 (n+1) peak

Nuclear Magnetic Resonance Spectroscopy (NMR)

Splitting Pattern NMR spectrum of CH3CH2Br

http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Atomic_Theory/Electrons_in_Atoms/Electron_Spin

Singlet – Neighbouring Carbon with No H Doublet – Neighbouring Carbon with 1 H Triplet – Neighbouring Carbon with 2H Quartet – Neighbouring Carbon with 3H

• Equivalent H in same chemical environment have no splitting effect on each other • Equivalent H do not split each other • All Equivalent H in the same chemical environment will produce a same peak /signal. • Spin spin coupling – occurs when protons have different chemical shift • Splitting not observed for protons that are chemically equivalent/same chemical shift


(n + 1 rule) • Equivalent H in same chemical environment do not split each other. • If a proton H has n equivalent protons on neighboring carbons, then the signal for H will be split into n + 1 peaks. • H nuclei split neighbouring H in CH3 into 2 peaks, called a doublet.

1H nuclei split the CH3 methyl gp into doublet • H can align with EMF or against EMF. • CH3 will experience 2 different EMF • One lower, one higher EMF • Split into doublet

EMF couple with magnetic field by H • Overall magnetic field experience CH3 lower • H from CH3 will absorb at lower radiofreq (upfield)

EMF

EMF couple with magnetic field by H • Overall magnetic field experience by CH3 higher • H from CH3 will absorb at higher radiofreq (downfield)

EMF

• CH3 spilt to doublet by 1 adj H • CH3 experience two slightly different magnetic field due to neighbouring H

MF MF

Split with relative intensity of 1 : 1

Downfield Upfield


(n + 1 rule) • If a proton H has n equivalent protons on neighboring carbons, then the signal for H will be split into n + 1 peaks. • 2H nuclei split neighbouring H in CH3 into 3 peaks, called triplet.

2H nuclei split the CH3 methyl into triplet • H can align with EMF or against EMF. • CH3 will experience 3 different EMF • One lower, one higher , one no net change • Split into triplet (ratio 1 : 2 : 1 )

EMF couple with magnetic field by H • Both align against EMF (Net lower EMF) •Overall magnetic field experience CH3 lower • H from CH3, absorb at lower radiofreq (upfield)

EMF

EMF couple with magnetic field by H • Both H align with EMF (Net greater EMF) • Overall magnetic field experience by CH3 higher • H from CH3, absorb at higher radiofreq (downfield)

EMF

EMF MF MF

MF

MF

EMF couple with magnetic field by H • One align with and one against EMF • MF by H cancel each other • Overall magnetic field experience CH3 the same

Split with relative intensity of 1 : 2 : 1 • CH3 spilt to triplet by 2 adj H • CH3 experience three different magnetic field due to 2 adjacent H

Downfield Upfield


(n + 1 rule) • If a proton H has n equivalent protons on neighboring carbons, then the signal for H will be split into n + 1 peaks. • 3 H nuclei split neighbouring H in CH2 into 4 peaks, called a quartet.

3H nuclei split the CH2 methylene into quartet • H can align with EMF or against EMF. • CH2 will experience 4 different EMF • Split into quartet (ratio 1 : 3 : 3 : 1 )

EMF couple with MF by H • Three H align against EMF (Net lower EMF) •Overall magnetic field experience CH2 lower • H from CH2, absorb at lower radiofreq (upfield)

EMF

EMF couple with MF by H • Three H align with EMF (Net greater EMF) • Overall magnetic field experience by CH2 higher • H from CH2, absorb at higher radiofreq (downfield)

EMF EMF

MF MF

EMF couple with MF by H • Two align with and one against EMF (higher) • Two align against and one with EMF (lower) • Two different MF experience by CH2 in 3 : 3 ratio

Split with relative intensity of 1 : 3 : 3 : 1 • CH2 spilt to quartet by 3 adjacent H • CH2 experience four different magnetic field due to 3 adjacent H

Upfield Downfield


Singlet peak • H nuclei attach to electronegative atom , O - NO splitting – Singlet • H nuclei attach to neighbouring C without any H - NO splitting – Singlet • Equivalent H nuclei do not split each other but will split neighbouring H • CH3CH2OH, quartet, triplet and singlet split

• CH3 spilt to triplet by 2 adj H • CH3 experience three different magnetic field due to 2 adj H

• CH2 spilt to quartet by 3 adj H • CH2 experience four different magnetic field due to 3 adj H

• No signal splitting from coupling between hydroxyl proton and methylene proton of CH2 – despite 2 adjacent H • Protons attached to OH, undergo rapid chemical exchange, transfer rapidly from each other /loss of H • Spin coupling due to H (OH) on methylene proton CH2 is negligible /not seen. • NO triplet split on OH due to 2 adjacent H from CH2 – Only singlet

H H

| | HO- C- C- H

| | H H

CH3

• chemical shift ≈ 1

• integration = 3 H

• split into 3

CH2

• chemical shift ≈ 3.8


• split into 4

OH

• chemical shift ≈ 4.8


• No split (Singlet)

3 2 1

Triplet split Quartet split

Singlet split

Equivalent Hydrogen in same chemical Environment (chemical Shift)

Equivalent H - Hydrogen attached to carbon in particular chemical environment • Equivalent H in same chemical environment have no splitting effect on each other • All Equivalent H will produce same signal/peak

O ║ CH3-C-O-CH2-CH3

HO-CH2-CH3

O ║ HO-C-CH2-CH3

O ║ CH3-C-CH2-CH2-CH3

Equivalent Hydrogen in same chemical Environment (chemical Shift)

4 different chemical environment • 4 absorption peak /chemical shift

3 equivalent H

2 equivalent H 2 equivalent H

3 equivalent H

2 equivalent H

3 equivalent H

1 equivalent H

3 different chemical environment • 3 absorption peak/chemical shift

3 equivalent H

3 equivalent H

2 equivalent H



3 equivalent H


12

3 2 1 3 2 3 2

3 2 1 3 2 3

Equivalent Hydrogen in molecule with plane of symmetry

Equivalent H - Hydrogen attach to carbon in particular chemical environment • Equivalent H in same chemical environment have no splitting effect on each other • Hydrogen atoms on neighbouring carbon can be equivalent if they are in the same environment • All Equivalent H in the same chemical environment/shift will produce a same peak /signal.

CH3

| CH3 – C -CH3

| CH3

1 chemical environment • 1 absorption peak/chemical shift

12 equivalent H O ║ CH3-CH2-C-CH2- CH3



CI | CH3-C-CH3

| H


1 equivalent H 6 equivalent H CH3

| HO-CH2- HC

| CH3


1 equivalent H


6 equivalent H

2

4 2

3 2 12

6 1 2 1 6 1

Splitting Pattern by neighbouring H


HO-CH2-CH3

O ║ HO-C-CH2-CH3


4 chemical environment • 4 absorption peak




12

• Equivalent H in same chemical environment have no splitting effect on each other • Equivalent H do not split each other • All Equivalent H in the same chemical environment will produce a same peak /signal.

Triplet

2 adj H

Septet 5 adj H

Singlet

No H

Triplet

2 adj H

Triplet

2 adj H

Quartet

3 adj H

Singlet OH – No split

Triplet

2 adj H

Singlet

No H

Quartet 3 adj H

Triplet

2 adj H

Quartet 3 adj H

Singlet No H


3 2 1 3 2 3 2

3 2 1 3 3 2

Singlet Splitting Pattern

• Equivalent H in same chemical environment have no splitting effect on each other • All Equivalent H in the same chemical environment will produce a same peak /signal. • Singlet can be due to presence of OH or no adjacent H

Singlet due to • Equivalent H in same chemical environment • No adj H

CH3

| CH3 – C -CH3

| CH3

Singlet No H

O CH3

║ | H-C- C-CH3

| CH3

Singlet No H


9.7

Singlet No H

H CH3

| | CI- C- C- CH3

| | H CH3

Singlet No H

Singlet No H


H H | | CI- C- C- CI

| | H H

Singlet due to • Equivalent H in same chemical environment • Equivalent H do not split each other

Singlet No H

9 2 4

12 9 1

Singlet Splitting Pattern

• Equivalent H in same chemical environment have no splitting effect on each other • All Equivalent H in the same chemical environment will produce a same peak /signal. • Singlet can be due to presence of OH or no adjacent H

Singlet No H

Singlet No H


Singlet No H

Singlet due to • Equivalent H in same chemical environment • Equivalent H do not split each other

H H | | H - C- C- H

| | H H

CH3

| CH3 – O-C -CH3

| CH3

O ║ HO-C-CH3

12

Singlet No H

Singlet due to • OH in COOH • No adj H

2

Singlet No H

O ║ HO-C-H

Singlet due to • OH in COOH • H in CHO

Singlet No H

10.6 8.3

Singlet No H

3 1 1 1

6 9 3

Spin Spin Coupling and Chemical Shift

NMR Spectrum

O ║ HO-C-CH2-CH3

3 diff proton enviroment, Ratio H - 3: 3 : 2 • Peak A – split to 3 – 2H on adj C • Peak B - No split – No H on adj C • Peak C – split to 4 – 3H on adj C

3 diff proton enviroment, ratio H - 3:2:1 • Peak A – split to 3 – 2H on adj C • Peak B – split to 4 – 3H on adj C • Peak C – No split – No H on adj C

A B

C

B

A

C


12

3 2 3

3 2 1

HO-CH2-CH3

NMR Spectrum


3 diff proton enviroment, Ratio H - 3:2:1 • Peak A – split to 3 – 2H on adj C • Peak B – split to 4 – 3H on adj C • Peak C – No split for OH

4 diff proton enviroment, Ratio H - 3:2:2:3 • Peak A – split to 3 – 2H on adj C • Peak B – split to 6 – 5H on adj C • Peak C – No split – No H on adj C • Peak D – split to 3 – 2H on adj C

A

B C

3

B

A C D

2 1

3 2 2 3

O

║

H-C-CH3

NMR Spectrum

O ║

CH3-C-O-CH2-CH2-CH3

4 diff proton enviroment, Ratio H – 3:2:2:3 • Peak A – split to 3 – 2H on adj C • Peak B – split to 6 – 5H on adj C • Peak C – No split – No H on adj C • Peak D – split to 3 – 2H on adj C

A

B C D

2 diff proton enviroment, Ratio H - 3:1 • Peak A – split to 2 – 1H on adj C • Peak B – split to 4 – 3H on adj C

9.8

A

B

3 2 2 3

3 1

NMR Spectrum

Molecule with plane of symmetry

3 diff proton enviroment, Ratio H - 6:1:1 • Peak A – split to 2 – 1H on adj C • Peak B – No split for OH • Peak C – split to 7 – 6H on adj C

CH3

| H-C-OH

| CH3

O CH3

║ |

CH3-C-O-C-H

|

CH3

A

B

C

A B

C

3 diff proton enviroment, Ratio H - 6:3:1 • Peak A – split to 2 – 1H on adj C • Peak B – No split – 0H on adj C • Peak C – split to 7 – 6H on adj C


6 1 1

6 3 1

NMR Spectrum


O

║

CH3-CH2-C-CH2-CH3

O CH3

║ |

H-C-C-CH3

|

CH3

2 diff proton enviroment, Ratio H – 6:4 • Peak A – split to 3 – 2H on adj C • Peak B – split to 4 – 3H on adj C

A

B

A

B

6 4

9 1

2 diff proton enviroment, Ratio H – 9:1 • Peak A – No split – No H on adj C • Peak B – No split – No H on adj C


NMR Spectrum


4 diff proton enviroment, Ratio H – 6:1:1:2 • Peak A – split to 2 – 1H on adj C • Peak B – split to 7 – 6H on adj C • Peak C – No split for OH • Peak D – split to 2 – 1H on adj C

CH3

|

HO-CH2-CH

|

CH3

A

B D C

2 diff proton enviroment, Ratio H – 6:1 • Peak A – split to 2 – 1H on adj C • Peak B – split to 7 – 6H on adj C

CH3-CH-CH3

| CI

A

B


6 1 1 2

6 1

NMR Spectrum

2 diff proton enviroment, Ratio H – 3:5 • Peak A – No split – No H on adj C • Peak B – split to 3 – 2H on adj C • Peak C – split to 3 – 2H on adj C • Peak D – split to 2 – 1H on adj C

A B

Molecule with benzene ring

3


5

2 1 2

C D

7.3 8

All H in benzene are consider • as 1 proton environment


7.3 8

2

E

1

D

2 5

C

2

3 2

A

B

3 diff proton enviroment, Ratio H – 3 : 2 :5 • Peak A – split to 3 – 2H on adj C • Peak B – split to 4 – 3H on adj C • Peak C – split to 3 – 2H on adj C • Peak D – split to 3 – 2H on adj C • Peak E – split to 2 – 1H on adj C

NMR Spectrum

A C


3


5

2 1 2

D E

7.3 8



7.3 8

2

F

1

E

2 5

D

3

1 2

A

B

4 diff proton enviroment, Ratio H – 1 : 2 : 2 :5 • Peak A – No split for OH • Peak B – split to 3 – 2H on adj C • Peak C – split to 3 – 2H on adj C • Peak D – split to 3 – 2H on adj C • Peak E – split to 3 – 2H on adj C • Peak F – split to 2 – 1H on adj C

2

B

3 diff proton enviroment, Ratio H – 3 : 2 : 5 • Peak A – split to 3 – 2H on adj C • Peak B – split to 4 – 3H on adj C • Peak C – split to 3 – 2H on adj C • Peak D – split to 3 – 2H on adj C • Peak E – split to 2 – 1H on adj C

3

4

C

2

NMR Spectrum

A C

6


5

2 1 2

D E

7.3 8


1

B

3 diff proton enviroment, Ratio H – 6 : 1 : 5 • Peak A – split to 2 – 1H on adj C • Peak B – split to 7 – 6H on adj C • Peak C – split to 3 – 2H on adj C • Peak D – split to 3 – 2H on adj C • Peak E – split to 2 – 1H on adj C

5

ib chemistry on nuclear magnetic resonance (nmr) spectroscopy and spin spin coupling

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