1
Isotopologues
Molecules of ISOTOPOLOGUES have different isotopic composition
1H NMR of CH3CH2OH : consider 1H, 2H, 12C, 13C, 16O, 17O, 18O
Some isotopologues:
12C1H3
12C1H2
16O1H System: A3B2C
13C1H3
12C1H2
16O1H System: XA3B2C
12C1H3
12C1H2H16O1H System: A3BXC
288 isotopic varieties, 192 of which magnetically distinct
These give rise to 184 1H spectra, 184 2H spectra, 144 13C spectra and 96 17O
spectra, all nontrivial and distinct from each other
The least abundant of these isotopologues is so rare that one would need over
100 moles of ethanol to have any chance to meet one of its molecules, but that
can change completely with isotopic enrichment
2
Isotopomers
Molecules of ISOTOPOMERS have the same isotopic composition,
the isotope sits at different positions - isotopic isomers
Some isotopomers:
13C1H3
12C1H2
16O1H
12C1H3
13C1H2
16O1H
13C1H3
13C1H2
16O1H - Isotopologue
12C1H3
12C1H2H16O2H Constitutional Isotopomers
12C1H3
12C1H2H16O1H
12C1H3
12C2H1H16O1H Stereo Isotopomers (R/S)
3
Isotope Effects
M – X n = 1 primary isotope shift
M – C – X n = 2 secondary isotope shift
(D/H) n(13C)
Isotope shift of M signal caused by substitution of H by D, n bonds away
Magnitude expressed in ppb, decreases with longer distance, n
Generally
n(AM) = HEAVY – LIGHT < 0
Heavy isotope shields more
4
Isotope Effect
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 length
difference 5 fm
5
Isotope Effect
H D (D/H) n(31P)
ppm
PH3 PDH2  0.804
PH3 PD2H  0.845
PH3 PD3  0.888
6
Isotope Effects
Occupation of vibrational levels changes with temperature
Level spacing changes with mass of bound atoms
7
Isotope Effect
19F NMR spectrum of [NMe4][TeF7] in CH3CN at 30 ºC
[TeF7]-
Fluxional
All F identical
8
Isotope Effect
Central line of the 19F NMR spectrum of [NMe4][TeF7]
9
Tellurium Isotopes
Z A NA% I
52 Te 120 0.09 (1)
122 2.55 (12)
123 0.89 (3) ½
124 4.74 (14)
125 7.07 (15) ½
126 18.84 (25)
128 31.74 (8)
130 34.08 (62)
10
Satellite Spectra of Si(CH3)4
Isotopomers
28Si(12CH3)4
29Si(12CH3)4
28Si(13CH3)(12CH3)3
Other isotopomers have too low
concentration
28/29Si(12CH3)4-n(13CH3)n
1H
A
B B
C C
11
Satellite Spectra
[(R2Sn)2(R2SnO)(F)(HONZO)(ONZO)], R = Me
HONZOH = salicylaldoxime, ortho-HO–N=CH–C6H4OH
19F
Satellite Spectra
12
Resolution enhanced 195Pt-NMR spectrum of K2PtCl4 in D2O showing isotopomers
35Cl 75.5 %
37Cl 24.5 %
13
Satellite Spectra
Si
C
C
CH3
CH3
C
C
H3C
H3C
29Si NMR
13C satellites
14
Isotope Effect on Satellite Spectra
CH3-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
12C 13C
Isotope Effect on Satellite Spectra
15
Isotope Effect on Satellite Spectra
16
17
Calculation of Abundance of
Isotopologues
O
Pt Pt
O
H
H
1H NMR spectrum
195Pt I = ½, NA = 33.8 %
NMR inactive Pt nuclides 66.2 %
O
Pt Pt
O
H
H
O
195Pt Pt
O
H
H
O
195Pt 195Pt
O
H
H
18
Calculation of Abundance of
Isotopologues
O
Pt Pt
O
H
H
....zyx
i
i cbaf



1H NMR spectrum
195Pt I = ½, NA = 33.8 %
19
Calculation of Abundance of
Isotopologues
Isotopologues and isotopomers
....zyx
i
i cbaf



fi = the fractional abundance of isotopomer i
 = the symmetry number of the parent molecule isotopically
pure = the order of rotation group Cn
i = the symmetry number of the isotopomer
a = abundance of an isotope occuring x-times (in atomic %)
b = abundance of an isotope occuring y-times (in atomic %)
20
Abundance of Isotopologues
....zyx
i
i cbaf


 W P W
CO
CO
CO
OC
COAr
Ar
Ar
Isotopomer i a (0.144) b (0.856) fi
WPW 1 a0 b2 0.733
WP183W 1 a1 b1 0.123
183WPW 1 a1 b1 0.123
183WP183W 1 a2 b0 0.021
21
Isotopologues Pt
Pt Pt
OC CO
CO
P P
P
R
R
R
R
R
R
1+
Isotopomer Pt1 Pt2 Pt3 fi
A * * * 0.290
B 195 * * 0.148
C * 195 * 0.148
D * * 195 0.148
E 195 195 * 0.076
F 195 * 195 0.076
G * 195 195 0.076
H 195 195 195 0.038
22
Abundance of Isotopologues
Mercuracarborands
[Me4N]F
[Me4N]+
23
Calculation of Abundance of
Isotopologues
yx
i
i baf



199 Hg I = ½ NA = 16.8%
201Hg I = 3/2 NA = 13.2%
other Hg inactive in NMR
19F NMR
Only coupling to 199 Hg observed
No coupling to 201Hg visible
 = 4
a = 16.8 % 199 Hg (active)
b = 83.2 % all other nuclides
(inactive)
24
Isotopologues/Isotopomers
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
25
Isotopologue Abundances
Isotopologue  i x y fi
2nI + 1
A 4 4 0 0.00080 qn
B 1 3 1 0.01578 dt
C 1 2 2 0.03907 t
D 2 2 2 0.07815 t
E 1 1 3 0.38703 d
F 4 0 4 0.47917 s
yx
i
if )832.0()168.0(
4


26
B5H9
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