lecture nmr 5
TRANSCRIPT
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NMR Lecture 5
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Factors affecting 13C NMR spectra
Proton decoupler always on, no pulse delay
How do you know 3 icrosec ! ""#
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Pulse delay $%% s& gated decoupler'on
only w(en ac)uiring signal
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*ffects of t(e pulse delay +etween pulses, $%% s
Proton decoupler always on N-*.
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/nforation o+tained +y e0aining nr spectra
1 C(eical s(ift identifies nature of nucleus" 2rea identifies relatie nu+er of nuclei.
3 Multiplicity N-*.
"4 NMR +asically proides inforation a+out connectiity and
pro0iity
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2pplications of 1H and 13C NMR
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Molecular
forula CH1%-
/R6 17"% c'1
area6 56 "6 3
CH" CH3
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Molecular forula C7H1$-"
/R 17"% c'1
1H NMR
CCH3 CH"
CCH3
- -CH3
CH336"6368
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F NMR of F3
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CF"$
CF"5H
!CF3'
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F
FF
F
NH"
H
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Returning to 4ynaic Nuclear Magnetic Resonance
For a siple e0c(ange process coalescence ≈ π∆ν9"19"
Most c(eical s(ift differences are of t(e order of a few
(undred H: or less Rate constants are of t(e order of few
(undred sec'1 Large in coparison to k ≈ 1%'$ ; 1%'5 sec'1,
easured +y conentional kinetics +ut sall relatie to anydynaic processes occurring in olecular systes suc( as
rotations a+out +onds
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2ssign t(e spectru and
e0plain t(e coupling o+sered
Let
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=(at would t(e NMR spectru of t(e et(yl resonances of $'
diet(yl'3'(ydro0ycyclo+utenone look like if all t(e et(ine
(ydrogens of t(is olecule (ad t(e sae spin>
H-
-CH3
H
CH3
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H-
-CH3
H
CH3
?13, ?15 are t(e
sae sign
?13 ?15 are of
opposite
sign
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H-
-CH3
H
CH3
?13, ?15 are t(e
sae sign
?13, ?15 are of
oppositesign
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=(at are soe ec(aniss +y w(ic( t(e two et(yl groups can
+ecoe identical>
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H-
-CH3
H
CH3
-
H
CH3
CH3
H
-
-
CH3
H
CH3
-H
H"-
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H-
-CH3
H
CH3
-
CH3
H
CH3
-H
-
-
H
CH3
H
CH3
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H-
-CH3
H
CH3
H- CH3
-HCH3
-
CH3
H
CH3
-H
H"-
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H-
-CH3
H
CH3
-
CH3
H
CH3
-H
H- CH3
-HCH3
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H-
-CH3
H
CH3
-H
- CH3
H
H3C
1,3'(ydrogen s(ift
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H-
-CH3
H
CH3
-H
- CH3
H
H3C
1,3'(ydrogen s(ift
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H-
-CH3
H
CH3
? is t(e sae
sign
? is of
oppositesign
-H
- CH3
H
H3C
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H-
-CH3
H
CH3
H- CH3
-HCH3
-
CH3
H
CH3
-H
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H-
-CH3
H
CH3-
CH3
H
CH3
-H-
-
H
CH3
H
CH3
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1,3'(ydrogen s(ift& ?2@
and ?2M of t(e sae sign -
CH3
H
CH3
-H
H-
-CH3
H
CH3
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H-
-CH3
H
CH3
1,3'(ydrogen s(ift& ?2@
and ?2M of t(e opposite signs-
CH3
H
CH3
-H
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Pro+le Aet 4NMR
By line s(ape analysis, deterine t(e actiation energy for
rotation a+out a car+on nitrogen +ond in an aide
o to y gateway and down load t(e *0cel file
2 plot of ln k s 19D s(ould result in a straig(t line and t(e
slope of t(e line s(ould +e ' *a9R Eour pro+le will +e to fit
t(e lines(apes as +est you can and ealuate k for a series of
teperatures Ree+er t(at t(e ost accurate k alues will +e w(en t(e line s(apes c(ange t(e ost
k ! rate constant