Post on 07-Jul-2018
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Nuclear Magnetic Resonance
(NMR) Spectroscopy
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Proses Resonansi• Atom: inti dan elektron
• Inti mempunyai bil. spin momen spin• !il. Spin I" # $ %%$ &'• I"# bila proton dan netron ganil• Inti % and %*+ I: ,%-& dan %-&• Spinning c/arge spinning nucleus /as a
magnetic moment t/at coincides 0it/t/e a1is o2 rotation.• 3nder normal circumstances t/e t0o
spin states are energeticallye4ui5alent.
• Spinning nuclei precesses along a1is o2
spin in concert 0it/ t/e orientation0it/ t/e magnetic 2ield.∀ ω re2ers to angular 2re4uency o2
nuclear precession.
ω
AppliedMagnetic 6ield
Precessional motion of aspinning nucleus
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Not all elements/isotopes are NMR active.
• Nuclei with even mass number and even atomic number have
nuclear spin quantum number (I=0) of zero
• Odd mass number and even/odd atomic number have
I=1/2
• Even mass number but odd atomic number have integer values
I= 1,2, 3, etc
Only nuclei with non zero nuclear spin give NMR spectra
13C vs. 12C The natural abundance of 13C is approximately 1%
The natural abundance of 12C is approximately 99%
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• Keadaan normal (tdk ada medan
magnet) spin inti mempunyai energi yg
sama.
•Dlm medan magnet, terjadi dua orientasienergi
• Perbedaan energi tergantung pada
medan magnet yg digunakan
H0 14100 gauss ∆! "0#H$
H0 %&'00 gauss ∆! 100#H$• Pada keaaan ini bila energi dr luar
diberikan spin inti dapat lip*. +ni
proses esonansi
• nergi luar (gel radio) -arus sama
dengan perbedaan energi yg dibutu-kan.h ν
Applied
Magnetic6ield
.%-&
,%-&
H0
∆ E ∆ E'
E1
E2
E'1
E'2
H0 H'0
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Peralatan CW NMR
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Frequensi Vs Medan magnet
• Proton mempunyai frequensi tertentu padakeadaan resonansi
• Faktor yang mempengaruhi adalah faktorlindungan (shielding) elektron yangmenyelimuti inti
• Lindungan ditentukan oleh induksi danmomen magnet yang disebabkan oleh awanelektron
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+/emical S/i2t
• A molecule may contain multipleprotons that exist in uniqueelectronic environments.
• Therefore not all protons are
shielded to the same extent.• Resonance differences in protons
are very small (ppm).
• Measure differences in resonanceenergy relative to a reference.
• etramet-ylsilane (/H&)4i(#) proides -ig-ly s-ieldedreeren2e (set to 0ppm).
Nuclear Shielding
• Nuclei are shielded by
electrons.•
Induced field associated withorbiting electrons.• Require stronger magnetic field
than H0.
• Increased shielding requires
greater applied field strength to
achieve resonance.
Chemical Shift (δ, ppm) =Observed chemical shift from TMS (Hz)
Sptectrometer frequencey (MHz)
= ppm
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NMR Spectra
• Hypothetical NMR spectra.
• Shows TMS reference.
• Chemical shifts (δ, ppm) given relative to TMS
0123456789101112
Increasing magnetic field strength
δ, ppm
TMS
C
H
H
H
TMS as referenceis set to 0 ppm
Representative peak,3 equivalent protons
Increased sheilding of nuclei
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+/emically 74ui5alent• Protons in the same
environment will have thesame chemical shift.
• Protons in different
environments havedifferent chemical shifts.
• Protons with the samechemical shift are referred
to as chemicallyequivalent.
• Integrated area of peak isproportional to the numberof protons.
H
H
H
H
H
H
C
C
H
H
H
H
H
H
H
C
H
H
H
H
H
H
H
C
C
H
H
H
H
C
H
H H
H
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Sample Spectra
• The first spectra is that
of a symmetric
molecule, all protons are
equivalent.
• Second spectra is that of
a molecule containing
two types of protons.
• Correlation chart for
proton chemical shift
has been studied.
0123456789101112 δ, ppm
TMS
C
C
H
H
H
H
H
H
0123456789101112 δ, ppm
TMS
H
CH
H
HH
H
H
H
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CH3CHCH2CCH3
OCH3
chemical shift = 25 ppm
chemical shift = 209 ppm
chemical shift = 53 ppm
chemical shift = 30 ppm
chemical shift = 23 ppm
Sample Carbon Spectrum: 4-methyl-2-pentanone
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Shielding: Magnetic Fields
1. External Magnetic Field (B0)
2. Induced Magnetic Field Caused by Circulating Electrons
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Proton Chemical Shifts of ethyl !erivatives
Proton Chemical Shifts "ppm#
Compound (CH3)4C (CH3)3N (CH3)2O CH3F
0.9 2.1 3.2 4.1
Compound (CH3)4Si (CH3)3P (CH3)2S CH3Cl
0.0 0.9 2.1 3.0
Cpd. / Sub. X=Cl X=Br X=I X=OR X=SR
CH3X 3.0 2.7 2.1 3.1 2.1
CH2X
2 5.3 5.0 3.9 4.4 3.7
CHX3 7.3 6.8 4.9 5.0
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Tabel pergeseran Kimia
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Nuclear S/ielding-8es/ielding
• Valence electron densitycan shield nucleus fromapplied field.
•Electronegativesubstituents can drawelecron density away.
• Results in deshielding.
• Anisotropy: π-electrons
and induced magneticfield.
• Results in shielding anddeshielding zones.
H
H0
O HH
/H&3 /H&/l /H%/l% /H&/H& /H&/H&
δ (ppm) 4,& &,1 ',4 &,% 0,5
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Spektra 1H NMR
• Spektra CH3CH2OH bila tidak terjadi
spliting
• OH CH2 CH3
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Spektra C2H6O (terjadi pemecahan)
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Spinspin Splitting and n,% Rule
• Each type of proton “senses”
protons on adjacent carbon atoms.
• Spin state of nearby protons
contributes to the proton
evironment and apparent magnetic
field.• General rule is that the signal is
split into n! pea"s. n # number of
e$uivalent neighboring protons.
• Spacing bet%een componentpea"s referred to as coupling
constant &J '.
• J coupling is representative of the
degree to %hich protons interact.
• J usually ()!*H+
n # ,- tripletn # !- doublet
-1/2 +1/2 0 +1 -1
n # - $uartet
-1/2 +1/2
-1 1/2 +1 1/2
Numbers in Italics refer to net spin
Splittin$
n # (- singlet
Cl C
Ha
Cl
C
Hb
Hb
Cl Cl C
Ha
Cl
C
Hb
Hb
Cl
e$uivalentprotons behave
as a group
/%o types of protons in !-!-,)trichloroethane
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n # ,- tripletn # !- doublet
-1/2 +1/2 0 +1 -1
n # .- $uartet
-1/2 +1/2
-1 1/2 +1 1/2
Numbers in Italics refer to net spin
Splittin$
n # (- singlet
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Multiplicity
singlet
Doublet
Triplet
Quartet
Quintet
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struktur
struktur
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%%&tric/loroet/ane
• NMR spectrum for 1,1,2-trichloroethane
• Hb proton signal split into doublet
• Ha proton signal split into triplet
• J couplings are the same for Ha and Hb signals
• Ha integral is 1/2 that of Hb
(!,0123* δ, ppm
TMS
Cl C
Ha
Cl
C
Hb
Hb
Cl
J J
J
Hb
Ha
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Coupling constant J
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Magnitude of Some Typical Coupling Constants
<
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Magnetic 74ui5alence 5s.
+/emical 74ui5alence• NMR differentiates
between nuclei based onenvironment.
• In constrained systems,two protons on the sameC-atom can be in differentenvironments.
• These protons candemonstrate spin-spinsplitting.
• Geminal coupling
• J geminal ~5Hz
Ha
HbH3C
Br
Br
H3C
X
HcHa
Hb
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Diagram KarplusDiagram Karplus
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4)O)H 5,O 4)O)5 5)O)H
Ikatan Hidrogen
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ig/er 6ield Strengt/s
• At higher field strengths
differences in energy
between spin states is
increases.
• Improved signal
resolution.
• Coupling constants are
independent of fieldstrength.
(!,0123* δ, ppm
(!,0 δ, ppm
/6S
/6S
2( 6H+
!(( 6H+
2( 6H+
!(( 6H+
7hemical Shift &δ- ppm' #Observed chemical shift from /6S &H+'
Sptectrometer fre$uencey &6H+' # ppm
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Chemical shift Reagent
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Pereasi Per$eseran imia
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Integrasi
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Tentukan Struktur senyawa dari spektra NMR proton berikut:
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C10 H14 O
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Tentukan struktur dari data berikut:
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Rumus molekul C3H8O
http://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB1A.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB1A.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB1A.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB1.HTM
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http://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTM
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Rumus molekul C6H12
http://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB2A.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB2A.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB2A.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB2.HTM
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http://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTMhttp://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/IRHELP.HTM
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Rumus Molekul C5H10O
http://www.chem.uic.edu/web1/OCOL-II/WIN/SPEC/PROBLEMS/PROB3.HTM
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+arbon%* NMR
• ~1.08% of C atoms are the 13C isotope.
• Do not usually see C-C spin-spin interactions.
• Can see coupling between C and attached H’s.
• Magnetic moment µ of 13C is low.• Resonances of 13C nuclei are ~6000 fold weaker than 1H
resonances.
• Therefore most useful information is chemical shift.
• Covers a range of 0-200ppm.• Influence chemical shift in proton spectra also influence
in carbon spectra
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Spektra NMR Carbon 4-bromoacetofenon
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Per$eseran imia atom &arbon
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Perbedaan atom arbon dalam 13C '(
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Proton 8ecoupled
• Proton coupling canprovide informationabout number of protons.
• Often useful to decoupleprotons.
• Irradiate sample withbroad spectrum offrequencies.
• Substituents on C canenhance of reduce signal.
• Protons enhance the 13Csignal.
( δ, ppm
TMS
OH,7
H,7
O
7H
,(0(2(*(!((!,(!0(!2(!*(
8ndecoupled
5ecoupled from protons
O 7H, 7H
H,7 7
O12
3
4
5
6
!
,-2-1
07O
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(umus oleul C)*+,2'
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Rumus Molekul C6H8O
R M l k l C H O
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Rumus Molekul C8H8O