NUCLEAR MAGNETIC RESONANCE (NMR)

NUCLEAR MAGNETIC RESONANCE

(NMR)WIDIASTUTI AGUSTINA ES, S.Si., M.Si.

Nuclear Magnetic Resonance Spectroscopy (NMR) :

Spectroscopic technique that provide information about amount and type of atomic molecule• Hydrogen atoms 1H NMR• Carbon atoms 13C NMR• Phosphor atoms 31P NMR

NUCLEAR SPIN ATOM- Electron have quantum number ½ with a

value of +1/2 and -1/2- Spin Charge generates magnetic field so

that electron act as a tiny magnet called a magnetic moment

- This effect also valid for another atom. An atomic nucleus has an odd number and atomic number of the odd or both will have to have spin and produced magnetic moment

- Nuclear Spin Rate depends on the quantum spin number , l, of nuclei

NUCLEAR SPIN NUMBER

1H 2H 12C 13C 14N 16O 31P 32S15N 19FElementNuclear spinquantum number (I )

Number ofspin states

1/2 1 0 0 01/2 1

2 3 1 2 3 1

1/2

2 1

1/2

2

1/2

2

Number of spin state = 2 l +1l = nuclear spin quantum number

+ 1/2 - 1/2

+ +

m

m

Nuclear atomic spin with + charge, generating a magnetic moment vector

Without magnetic field, both spin state have the

same energy

SPIN STATE

IN MAGNETIC FIELD (BO)

RESONANCEIn NMR spectroscopy, resonance is the energy absorption by the core-precision results in a change of spin nuclei from lower energy level to a higher energy level

The precision results in a magnetic field oscillations and produce a "signal"

Bo

+1/2

-1/2

+1/2

-1/2

DE = hnDE

quantized

In a strong magnetic field,

a rotating nuclei absorbs

radio frequency (resonance

phenomena)Magnetic Field

gn = 2p

Bo

LARMOR EQUATION

n= frequency of the radiation that comes, which will cause the transitiong = giromagnetic ratio different for each atom (H, C, N)B0 = magnetic field

In organic compounds, hydrogen atoms are surrounded by electrons moving in the presence of a magnetic field.

The movement of electrons around the nuclei of hydrogen atoms in the magnetic field result in Diamagnetic Current

The area around the atomic nucleus that is formed by electrons are called Diamagnetic Shielding

B Induced(opposed Bo)

Bo Applied

Magnetic Field

MEASUREMENT Liquid Sample Sample volume 0,5 mL Solvent 1H NMR = deuterated solvent

CDCl3, CDOH3, Acetone-d6, Benzene-d6Piridin-d5, DMSO-d6, D2O

13C NMR = CHCl3, CHOH3, Acetone, BenzenePiridin, DMSO, H2O

Sampel Amount = ≤ 50 mg

1H NMR

INFORMATION FROM 1H NMR

1. Chemical Shift (, ppm), expressed as ppm (per million) functional group

2. Integration number of proton3. Multiplicity (s, d, t, q, qi, sext., hept.)

proton relationship4. Coupling Constant (J, Hz) type of proton

relationship stereochemistry or position of proton

5. Proton Signal: 0-15 ppm

OCH2CH3Brmultiplicity

Chemical shift

Coupling constante

ppm

standart TMS

integration

H group = amount & type of proton

HYDROGEN EQUIVALENTHydrogen Equivalent : Hydrogen that have a same

chemical environtment

- Compounds that have one hydrogen equivalent, producing one peak of proton NMR

H3CC C

CH3

H3C CH3

CH3CCH3 ClCH2CH2Cl

Propanone(Acetone)

1,2-Dichloro-ethane

Cyclopentane 2,3-Dimethyl-2-butene

O

- Compounds that have two/three hydrogen equivalent, producing two/three peak of proton NMR

CH3CHClCl Cl

C CCH3

H HO

Cyclopent-anone

(2 signals)

1,1-Dichloro-ethane

(2 signals)

(Z)-1-Chloro-propene

(3 signals)

Cyclohexene (3 signals)

How many proton signal??

H3C COCCH3

CH3CH3

CH2 CH2 O COCH3

CH3 CH2 CH2 NO2

Cl(CH2)3Cl

CH3CH2 O CO

(CH2)2 COO CH3

CHEMICAL SHIFTNMR signal is not measured by resonance position, but based on how far to shift from TMS, called CHEMICAL SHIFT

Tetramethylsilane (TMS)

CH3Si CH3CH3

CH3Has a highly protected proton and carbon (appears on upfield region)

PROTON CHEMICAL SHIFTProton chemical shift depends on the frequency of tool used (shear difference for protons appear the same but measured in different tools)

chemical shift = =

shift in Hz

spectrometer frequency in MHz= ppm

Any specific protons in a molecule will always appear at the same chemical shift (constant value)

TMS

shift in Hz

0ndownfield

PROTON CHEMICAL SHIFT

PROTON CHEMICAL SHIFT

RCH2 OR

(CH3 )4Si

ArCH3

RCH3

RC CH

RCCH3

ROHRCH2 OH

ArCH2 R

O

O

RCH2 RR3 CH

R2 NH

RCCH2R

R2 C=CRCHR2

R2 C=CHR

RCH

O

RCOH

O

RCH2 ClRCH2 BrRCH2 I

RCH2 F

ArHO

O

R2 C=CH2

RCOCH3

RCOCH2R

ArOH

9.5-10.1

3.7-3.9

3.4-3.6

Type of Hydrogen

0 (by definition)

Type of Hydrogen

Chemical Shift ()

1.6-2.62.0-3.0

0.8-1.01.2-1.41.4-1.7

2.1-2.3

0.5-6.0

2.2-2.6

3.4-4.0

Chemical Shift ()

3.3-4.0

2.2-2.52.3-2.8

0.5-5.0

4.6-5.05.0-5.7

10-13

4.1-4.73.1-3.3

3.6-3.84.4-4.5

6.5-8.5

4.5-4.7

Factors affecting proton chemical shift :1. Electronegatifity of the neighbour atoms2. Hibridisation from the adjacent atoms3. Diamagnetic Effect from the adjacent

phi bond

PROTON CHEMICAL SHIFT

ELECTRONEGATIFITY

Shielding protons, appears at high field

Deshielding protons, appears at low field

more deshielding

C HCl•Chlorine pull electron density away from carbon , caused electron density around the proton.•Chlorine caused proton to be “deshields” electronegative

NMR CHART

- +

- +

ELECTRONEGATIFITY

CH3X XElectronegativity of XGeseran Kimia d

CH3F CH3OH CH3Cl CH3Br CH3I CH4 (CH3)4SiF O Cl Br I H Si

4.0 3.5 3.1 2.8 2.5 2.1 1.84.26 3.40 3.05 2.68 2.16 0.23 0

Chemical Shift of X on CH3X

TMSMost deshielded

CHCl3 CH2Cl2 CH3Cl 7.27 5.30 3.05 ppm

-CH2-Br -CH2-CH2Br -CH2-CH2CH2Br 3.30 1.69 1.25 ppm

mostdeshielded

mostdeshielded

"deshielding" effect increased with increasing number of electronegative atoms

“deshielding” effect decrease with increasing proton distance of electronegative atoms

ELECTRONEGATIFITY

HIBRIDISATION

RCH3, R2CH2, R3CH

R2C=CHR, R2C=CH2

RCHO

R2C=C(R)CHR2

RC CHAllylic

Type of Hydrogen(R = alkyl)

Name ofHydrogen

Chemical Shift ()

Alkyl

AcetylenicVinylicAldehydic

0.8 - 1.71.6 - 2.6

4.6 - 5.79.5-10.1

2.0 - 3.0

• Magnetic Induction on phi bond causes the formation of pi bonds

• The presence of phi bond (double bond) or phi system will affect the chemical shift of nearby proton

• Accured on alkyne, alkene and benzene ring

DIAMAGNETIC

- ALKYNE

- ALKENE

- BENZENE RING

SPLITTING SIGNAL

• On NMR spectrum, proton signals often do not appear as a single peak (singlet), but appear as doublet, triplet, quartet, and so on

• Spin-spin splitting on the H atom is due to the interaction (coupling) with the neighboring H atom

• Spin-spin splitting followed the (n +1) RULES, if an Atom H has n non-equivalent H atoms which are neighbors, then the NMR spectrum of H atom signal will experience a breakdown as a (n +1) peaks

(n+1) RULES

n = 1, the signal will be splitted as (1+1) peaks, doublet

n = 3, the signal will be splitted as (3+1) peaks, quartet

Equivalent protons due to symmetry effects are usually not mutually spliting each other

CH CHX Y CH2 CH2X Y

no splitting if x=y no splitting if x=y

1)

2) Protons in the same group (tied to the same C) are usually not mutually splitting each other

CH

HH or C

H

H

EXCEPTIONAL FOR (n+1) RULES

EXEPTIONAL FOR (n+1) RULES3) N +1 rule applied to the protons in the aliphatic

chain (saturated) or cyclic saturated.

CH2CH2CH2CH2CH3CH3Hor

But it is not applied to the protons of the double bond or benzene compounds

CH3

H

H

H

CH3

NO NO

YES YES

• Splitting pattern similar with PASCAL TRIANGLE rule

PASCAL TRIANGLE

CH2 CH2X Y

CH CHX Y

CH2 CH

CH3 CH

CH3 CH2

CH3CH

CH3

( x = y )

( x = y )

SPLITTING PATTERN

SPLITTING