1
IsotopomersIsotopomers
11H NMR of CHH NMR of CH33CHCH22OH : considerOH : consider 11H,H, 22H,H, 1212C,C, 1313C,C, 1616O,O, 1717O,O, 1818OO
Some isotopomers:Some isotopomers:
1212CC11HH33
1212CC11HH22
1616OO11HH System: ASystem: A33BB22CC
1313CC11HH33
1212CC11HH22
1616OO11HH System: XASystem: XA33BB22CC
1212CC11HH33
1212CC11HH22HH1616OO11HH System: ASystem: A33BXCBXC
288 isotopic varieties, 192 of which magnetically distinct288 isotopic varieties, 192 of which magnetically distinct
These give rise to 184These give rise to 184 11H spectra, 184H spectra, 184 22H spectra, 144H spectra, 144 1313C spectra and 96C spectra and 96 1717OO
spectra, all nontrivial and distinct from each otherspectra, all nontrivial and distinct from each other
The least abundant of theseThe least abundant of these isotopomersisotopomers is so rare that one would need overis so rare that one would need over
100 moles of ethanol to have any chance to meet one of its molec100 moles of ethanol to have any chance to meet one of its molecules, butules, but
that can change completely with isotopic enrichmentthat can change completely with isotopic enrichment
2
IsotopeIsotope EEffectsffects
MM –– XX n = 1 primary isotope shiftn = 1 primary isotope shift
MM –– CC –– XX n = 2 secondary isotope shiftn = 2 secondary isotope shift
(D/H)(D/H) nn
ΔΔ((1313
C)C)
Isotope shift of M signal caused by substitution of H by D, n boIsotope shift of M signal caused by substitution of H by D, n bonds awaynds away
Magnitude expressed in ppb, decreases with distance, nMagnitude expressed in ppb, decreases with distance, n
GenerallyGenerally
nn
ΔΔ((AA
MM) =) = δδHEAVYHEAVY –– δδLIGHTLIGHT < 0< 0
Heavy isotope shields moreHeavy isotope shields more
3
IsotopeIsotope EEffectffect
12
C19
F3I 13
C19
F3I
0.149 ppm
19
F NMR
13
C16
O 13
C17
O
0.025 ppm
13
C NMR
CO bond lengthCO bond length
difference 5 fmdifference 5 fm
4
IsotopeIsotope EEffectffect
(D/H)(D/H) nnΔΔ((3131P)P)
ppmppm
DDHH
−− 0.8880.888PDPD33PHPH33
−− 0.8450.845PDPD22HHPHPH33
−− 0.8040.804PDHPDH22PHPH33
5
IIsotope Effectssotope Effects
Occupation ofOccupation of vibrationalvibrational levels changes with temperaturelevels changes with temperature
Level spacing changes with mass of bound atomsLevel spacing changes with mass of bound atoms
6
IsotopeIsotope EEffectffect
1919F NMR spectrum of [NMeF NMR spectrum of [NMe44][TeF][TeF77] in CH] in CH33CN at 30CN at 30 ººCC
[TeF7]-
Fluxional
All F identical
7
IsotopeIsotope EEffectffect
Central line of theCentral line of the 1919F NMR spectrum of [NMeF NMR spectrum of [NMe44][TeF][TeF77]]
8
TelluriumTellurium IIsotopessotopes
ZZ AA NA%NA% II
5252 TeTe 120120 0.09 (1)0.09 (1)
122122 2.55 (12)2.55 (12)
123123 0.89 (3)0.89 (3) ½½
124124 4.74 (14)4.74 (14)
125125 7.07 (15)7.07 (15) ½½
126126 18.84 (25)18.84 (25)
128128 31.74 (8)31.74 (8)
130130 34.08 (62)34.08 (62)
9
SatelliteSatellite SSpectrapectra ofof Si(CHSi(CH33))44
IsotopomersIsotopomers
2828Si(Si(1212CHCH33))44
2929Si(Si(1212CHCH33))44
2828Si(Si(1313CHCH33)()(1212CHCH33))33
OtherOther iisotopomerssotopomers havehave tootoo lowlow
concentrationconcentration
28/2928/29Si(Si(1212CHCH33))44--nn((1313CHCH33))nn
11HH
A
B B
C C
10
SatelliteSatellite SSpectrapectra
[(R2Sn)2(R2SnO)(F)(HONZO)(ONZO)], R = Me
HONZOH = salicylaldoxime,ortho-HO–N=CH–C6H4OH
1919FF
11
SatelliteSatellite SSpectrapectra
Si
C
C
CH3
CH3
C
C
H3C
H3C
2929Si NMRSi NMR
1313C satellitesC satellites
12
IsotopeIsotope EEffectffect onon SatelliteSatellite SSpectrapectra
Me-C≡N
15N signal shows coupling to:
1H 3J(1H-15N) = 1.7 Hz
13C 1J(13C-15N ) = 17 Hz
The signal appears as
a central 1:3:3:1 quartet flanked by 13C
satellites
The unsymmetrical nature of the 13C
satellites arises from 12C/13C isotopic
chemical shift perturbation.
15N NMR
13
Calculation ofCalculation of AAbundancebundance ofof
IIsotopomerssotopomers
O
Pt Pt
O
H
H
11H NMRH NMR spectrumspectrum
195195Pt I =Pt I = ½½, NA = 33.8, NA = 33.8 %%
NMRNMR inactiveinactive PtPt nuclidesnuclides 66.266.2 %%
O
Pt Pt
O
H
H
O
195Pt Pt
O
H
H
O
195Pt 195Pt
O
H
H
14
Calculation ofCalculation of AAbundancebundance ofof
IIsotopomerssotopomers
O
Pt Pt
O
H
H
....zyx
i
i cbaf
σ
σ
=
1H NMR spectrum
195Pt I = ½, NA = 33.8 %
15
Calculation ofCalculation of AAbundancebundance ofof
IIsotopomerssotopomers
Isotopic isomers =Isotopic isomers = isotopomersisotopomers
....zyx
i
i cbaf
σ
σ
=
ffii = the fractional abundance of= the fractional abundance of isotopomerisotopomer ii
σσ == the symmetry number of the parent moleculethe symmetry number of the parent molecule isotopicallyisotopically
pure = the order of rotation grouppure = the order of rotation group CCnn
σσii == the symmetry number of thethe symmetry number of the isotopomerisotopomer
a = abundance of an isotopea = abundance of an isotope occuringoccuring xx--times in atomic %times in atomic %
b = abundance of an isotopeb = abundance of an isotope occuringoccuring yy--times in atomic %times in atomic %
..
..
16
Abundance ofAbundance of IsotopomersIsotopomers
....zyx
i
i cbaf
σ
σ
= W P W
CO
CO
CO
OC
COAr
Ar
Ar
ffiib (0.856)b (0.856)a (0.144)a (0.144)σσii
IsotopomerIsotopomer
0.0210.021bb00aa2211183183
WW≡≡PP−−183183
WW
0.1230.123bb11aa1111183183
WW≡≡PP−−WW
0.1230.123bb11aa1111WW≡≡PP−−183183
WW
0.7330.733bb22aa0011WW≡≡PP−−WW
17
IIsotopomerssotopomers Pt
Pt Pt
OC CO
CO
P P
P
R
R
R
R
R
R
1+
0.0760.076195195**195195FF
0.0760.076195195195195**GG
0.1480.148**195195**CC
0.1480.148****195195BB
0.2900.290******AA
0.0380.038195195195195195195HH
0.0760.076**195195195195EE
0.1480.148195195****DD
ffiiPt3Pt3Pt2Pt2Pt1Pt1IsotopomerIsotopomer
18
Abundance ofAbundance of IsotopomersIsotopomers
MercuracarborandsMercuracarborands
[Me[Me44N]FN]F
[Me[Me44N]N]++
19
Calculation of Abundance ofCalculation of Abundance of
IsotopomersIsotopomers
yx
i
i baf
σ
σ
=
199199 Hg I =Hg I = ½½ NA = 16.8%NA = 16.8%
201201Hg I = 3/2 NA = 13.2%Hg I = 3/2 NA = 13.2%
other Hg inactive in NMRother Hg inactive in NMR
1919F NMRF NMR
Only coupling toOnly coupling to 199199 Hg observedHg observed
No coupling toNo coupling to 201201Hg visibleHg visible
σσ = 4= 4
a = 16.8 %a = 16.8 % 199199 Hg (active)Hg (active)
b = 83.2 % all other nuclidesb = 83.2 % all other nuclides
(inactive)(inactive)
20
IsotopomersIsotopomers
Hg
F
Hg
Hg Hg
Hg
F
Hg Hg
Hg
F
Hg
Hg
F
Hg
Hg
F
F
Hg = 199
Hg
4
4
1 1
1 2
A
B
C
D
E
F
21
IsotopomerIsotopomer AbundancesAbundances
dd0.387030.38703331111EE
ss0.479170.47917440044FF
tt0.078150.07815222222DD
tt0.039070.03907222211CC
dtdt0.015780.01578113311BB
qnqn0.000800.00080004444AA
2nI + 12nI + 1ffiiyyxxσσ ii
isotopomerisotopomer
yx
i
if )832.0()168.0(
4
σ
=
22
BB55HH99
A
A
A
A
A
B
B
A
A
A
B
A
A
A
A
A
B
A
B
A
A
B
A
A
A
A
B
A
A
B
I II III
IV V VI
BH
BH
B
H
HB
H
B
H
H H
H