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