Transcript Document

Nuclear Magnetic Resonance (NMR)
Spectroscopy
basic theory
1. properties of nucleus
spin of nucleus nuclear spin quantum number
I = n/2
n : integer
atomic mass
number number
Z
A
I
example
1
12C, 16O, 28Si, 56Fe
even
even
0
odd
even n : even 2H, 10B, 14N, 50V
odd
odd
n : odd 1H, 13C, 19F, 55Mn
* NMR properties of some nuclei with I = 1/2
* NMR properties of some quadrupolar nuclei
(I > 1/2)
number of possible spin states = 2I + 1
magnetic quantum number
m = +I, +(I-1), ……., -I
without a magnetic field, the spin states are
degenerate
nucleus I No. of states
m values 1
1H
1/2
2
+1/2, -1/2
11B
3/2
4
+3/2, +1/2, -1/2, -3/2
1
12C
0
1
0
14N
1
3
+1, 0, -1
1
NMR properties of some nuclei with I = 1/2
2
NMR properties of some quadrupolar nuclei (I > 1/2)
3
2. nuclear Zeeman effect
a nucleus with I≠0 in a magnetic field, 2I+1
spin states are not degenerate; they separate in
energy with the largest positive m value
corresponding to the lowest-energy state
ex. I = 1/2
m = -1/2
Bo
E
DE
m = +1/2
Bo
spin state energy
gh
Ei = -miBo ——
g : magnetogyric ratio
2p
transition Dm = -1
for a nucleus with I = 1/2, the energy difference
g h Bo
DE = ————
2p
precession – some sort of uniform periodic
motion, the magnetic moment wobble
around the axis of applied field
Lamar frequency
w = gBo
linear Lamar frequency u = w/2p = gBo/2p 4
Boltzmann distribution
Pm=-1/2
ghBo
–DE/kT
——— = e
DE = ———
Pm=+1/2
2p
If Bo = 2.35 T
DE = 6.63 x 10-26 J
Pm= -1/2
Pm=-1/2 =0.4999959
———— = 0.999984
Pm= +1/2
Pm=+1/2 =0.5000041
experimental considerations
sample
solution solid (magic-angle spin)
magnet
radio-frequency transmitter
spectrometer
receiver
decoupler
recording device
5
magnet : permanent magnet (1 – 2 T)
electromagnet (1.8 – 2.3 T)
superconducting magnet (up to 13 T)
two important characteristics of magnet
• stability – sensitive to temperature
• homogeneity
continuous wave experiment
1. frequency-sweep
2. field-sweep
6
Fourier transform technique
relaxation processes
spin-lattice relaxation T1
Peq – P = (Peq – Po) e
-t/T1
spin-spin relaxation T2
much faster than spin-lattice relaxation
T2 < T1
7
information from NMR spectrum
(1) chemical shift
the nuclei are screen from the magnetic field
Bo, the net field effective at a nucleus is
Beff = Bo (1 – s) s : the shielding constant
each chemically distinct nucleus is
associated with a characteristic frequency
ex. B10H14
4 distinct B nuclei
chemical shift d
relative to a standard for the isotope concerned
uobs - uref
6
d = 10 × ——————————
spectrometer frequency
unit: ppm
a shift to higher frequency than standard
==> positive d
decrease in shielding ≡
increase in chemical shift
8
relative NMR
frequency (MHz) standard
nucleus (B0 = 4.7 T)
reference
1H
200.0 (CH3)4Si
13C
50.2
(CH3)4Si
19F
188.2 CFCl3
29Si
39.8
(CH3)4Si
31P
81.0
85% aq. H3PO4
77Se 38.2
(CH3)2Se
119Sn 74.5
(CH3)4Sn
195Pt
43.0
[Pt(CN)6]2-
compound common
range (ppm)
1
-30 – 20
-100 – 400
-200 – 200
-350 – 40
-100 – 250
-300 – 200
-1000 – 8000
-200 – 15000
(2) intensity integration of the area
not for 13C
(3) spin-spin coupling
non-equivalent magnetically active nuclei
couple each other
chemically equivalent
magnetically equivalent
9
notation
Dd >> J
Dd small
A, X, M, Q
A, B, C
splitting pattern 2nI + 1
coupling constant J
ex. 1H, 13C NMR spectra of H13CO2-
(i) first-order
(ii) satellites
(iii) second-order
(4) exchange
10
11
number of lines splitting determined by Pascal’s
triangle
number of equivalent name of
coupling nuclei
pattern
0
1
2
3
4
5
singlet
doublet
triplet
quartet
quintet
sextet
ratio of integration
1
1
1
1
1
1
2
3
4
5
1
1
3
6
10 10
1
4
1
5
1
12
AX2 ??
classification of the nuclei
• I = 1/2, 100%abundance 1H, 31P, 19F, 103Rh
• I = 1/2, low abundance
13C, 15N, 29Si, 77Se,
109Ag, 119Sn, 125Te,
183W, 195Pt, 199Hg
• I > 1/2, 100% abundance 14N, 27Al, 51V, 59Co
• I > 1/2, low abundance
(I) 1H
11B, 121Sb, 193Ir
13
14
Sn(CH3)4
1H
119Sn
52 Hz
54 Hz
expanded 1H
13C
1J119
Sn-13C =
329
Sn-13C =
317
Hz
1J117
Hz
15
GeH4
Si2H6
(29Si I = ½, 4.7%)
16
CH3–CH2–S–PF2
K[BH4]
17
1H
3J
NMR spectrum of PF215NHSiH3
PH
= 8 Hz, 3JHH = 4 Hz, 2JNH = 2 Hz, 4JFH = 2 Hz
1H{15N}
NMR spectrum of PF215NHSiH3
18
[HV(CO)5]2-
doublet of doublet of triplet
J Pt-H = ?
J Pc-H = ?
19
for CH3 (or C(CH3)3) group in tertiary
phosphine complexes, doublet 1H spectra
indicate mutually cis arrangements and
triplet spectra mutually trans
PMe2Ph
PtCl2(PMe2Ph)2
20
21
22
23
MCl3‧xH2O
L
KH
MCl3L3
D
(M: Rh, Ir)
(L: PR3, AsR3)
MHCl2L3 (I)
EtOH, 1h
MHCl2L3 (II)
(i) Ir, PEt2Ph
158 Hz
19 Hz
18 Hz
12 Hz
24
(ii) Rh, AsMePh2
4 Hz
9 Hz
25
(iii) Rh, PMePh2
206 Hz
2J
1J
HP =
9 Hz
RhH = 4 Hz
2J
1J
HP =
14.5, 9 Hz
RhH = 13.5 Hz
26
(II) 13C
M-CO
M=C
27
1J
Pt-C
1J
Pt-C
= 35 Hz
2J
Pt-C = 0 Hz
= 1936 Hz
2J
Pt-C = 180 Hz
28
DEPT
29
20 lines
5 lines
[Ti(13CO)6]213C
47,49
Ti
30
(III) 31P
31
31P NMR
spectrum of P(OMe)3
31P NMR
spectrum of [Cu(PMe)3]+
31P NMR
spectrum of PHF2(15NH2)2
32
31P NMR
spectra of the mixed products from
the reaction of
trans-[PtCl4(PEt3)2] + trans-[PtBr4(PEt3)2]
[PxFy]-
x=?
y=?
33
(IV) 19F
19F
NMR spectrum of the products from the
reaction: UF6 + Me3SiCl (halogen exchange)
34
(V) 29Si
29Si NMR spectrum of SiMe
4
(VI) 195Pt
35
2-D NMR
1. correlated spectroscopy (COSY)
provide information about couplings
between nuclei of a single isotopes
the off-diagonal peak at a frequency (f1, f2)
implies that there is a coupling between
the nuclei resonating at f1 and f2
ex. COSY 11B spectrum for B10H14
B(2), B(4) (-35 ppm)
B(6), B(9) (11 ppm)
B(1), B(3) (13 ppm)
B(5), B(7), B(8), B(10)
(1 ppm)
36
ex. COSY 11B spectrum for B9H11NH
2. heteronuclear correlation spectroscopy
(HETCOR or HCOR)
ex. HETCOR 11B/1H spectra for B10H14
37
3. nuclear Overhauser effect spectroscopy
(NOSEY)
identify a NOE which arises from the
proximity of the two nuclei in space
heteronuclear NOSEY (HOSEY)
ex. 2D 1H/6Li HOSEY spectrum for tmeda
adduct of 2-lithio-1-phenylpyrrole
38
ex. homonuclear 2D 13C scalar coupling
(COSY) and chemical exchange
(NOSEY) spectra for [Os3H2(CO)10]
ex.
CH2CH2Br
O=P
OCH2CH2
OCH2CH2
expanded 1H NMR spectra
39
COSY (1H—1H)
COSY (1H—13C)
40
exchange reactions
ex. 1 31P{1H} NMR spectrum of the
products derived from [Rh4(CO)9{P(OPh)3}3]
under 400 atm of CO at 300 K
Rh4 cluster broke down to 2 dinuclear
complexes
41
ex. 2
19F
NMR at 180 K
chemical shift pattern
intensity
d 68 ppm
doublet of triplets
2
of doublets
d -61 ppm triplet of doublets
1
of narrow triplets
d 68 ppm
triplets of quartets
1
230 K two higher-frequency resonances
broaden and lose detail
300 K coalesced to a single broad line
the lowest-frequency peak remained
unchanged
42
ex. 3
13C{1H}
spectrum of Rh5(13CO)15under pressure of 13CO (5 bar)
43
ex. 4
13C{1H}
spectrum of the CO region of
(h5-C5H5)2Rh2(13CO)3
44
ex. 5
31P{1H}
NMR spectra of
[Ru2Cl5(PEtPh2)4•Ag(PEtPh2)]
45
ex. 6 trans-[IrCl(CO)(PMe3)2] + SF4 ―→
Cl
F
Ir
P
CO
P
SF3
d 68
(2F)
-61
(1F)
-383 ppm
(1F)
46
ex. 7 variable-temperature 1H NMR spectra
of [Ru3W(C5H5)(CO)11H3]
47
ex. 8 EXSY 2D 1H NMR of Pt complex
48
solid state NMR spectroscopy
difficulties – immobility of the nuclei in
solids
(i) dipolar coupling are not averaged to zero
==> very broad resonance
(ii) chemical shift anisotropy in solids is not
averaged out
==> line broadening
(iii) relaxation time T1 is very long
==> good signal-to-noise ratio is difficult
to get
solution:
(i) magic angle sample spinning (MASS,
MAS) technique
an angle q = 54.7o to the magnetic field,
the effect of chemically anisotropy can be
averaged out
(ii) cross-polarization (CP) technique
overcome the problem of long relaxation
time
49
ex. 1 13C NMR spectra of 2Ca(CH3CO2)2•H2O
ex. 2 119Sn chemical shift of Ph3SnOH in
solution d –80 ppm
==> 4-coordinated, tetrahedral
in solid phase d –298 ppm
==> 5-coordinated similar to Me3SnF
50
ex. 3
31P chemical
shift of phospha-alkene
complex
in solution d –31 ppm, JPt-P = 498 Hz
==> p-bonded ligand
in solid phase d 247 ppm, JPt-P = 4720 Hz
==> s-bonded ligand
51
52