Chemistry Reference
In-Depth Information
200 K
300 K
400
500
600
700
666
668
670
wavelength / nm
m/z
(a)
(b)
Figure 3.8
(a) Temperature-dependent electronic spectra showing thermochromism of
TBPLY
in a hexane
solution. (b) Cold-spray ionization mass spectrometry (CSI-MS) spectrum of the
π
dimer formed in a solution
stateatlowtemperature.
B
143
128
123
34.6
signals
due to
solvent
*
1.48
signal intensity
A:B=6:27
signals
due to
solvent
a
-protons
120
tert
-Bu
protons
*
6.47
A
*
180 K
180 K
185 K
190 K
200 K
210 K
230 K
250 K
270 K
*
*
*
*
*
270 K
*
*
*
7
6
5
chemical shift
4
3
2
1
200
150
100
chemical shift
50
0
ppm
ppm
(a)
(b)
Figure 3.9
Temperature dependences of (a)
1
Hand(b)
13
C NMR spectra of
TBPLY
in hexane-d
14
. These
spectraclearlyshowaformationofahighlysymmetricallystructureddimeratlowtemperature.(Reprintedwith
permissionfrom[15].Copyright2006AmericanChemicalSociety.)
-dimeric structure with a high symmetry was accomplished by
low temperature
1
Hand
13
C NMR measurements and chemical shift simulations by quantum chemical
calculations (Figure 3.9).
15
In the
1
H NMR spectrum in hexane-
d
14
at a high temperature (270 K), a
broad signal attributed to the protons of the
tert
-butyl groups is observed at around 3.2 ppm due to the
downfield shift by an effect of radical spin. This broad signal shifts to the high field region with a decreasing
temperature, indicating the formation of the
The definite determination of the
π
π
dimer (Figure 3.9a). At low temperature regions (
T
<
190 K),
the
dimer becomes dominant and the
tert
-butyl protons shift to 1.48 ppm (
B
in Figure 3.9a), and a signal
originating from the
π
protons on the phenalenyl ring emerges in the aromatic region (6.47 ppm,
A
in
Figure 3.9a). The integral intensity ratio of
α
protons to the
tert
-butyl protons is 6:27. In the
13
CNMR
spectra, almost no signal is found at room temperature due to the presence of paramagnetic species.
At low temperature, four signals attributable to the phenalenyl skeleton are clearly observed, since the
paramagnetic spins are quenched by the
α
π
dimerization (Figure 3.9b). A definite
π
-dimeric structure is
Search WWH ::
Custom Search