Laser Flash Photolysis of [3,n]Paracyclophan-2-ones
the effects are dramatically smaller for 2c and 2d ,
suggesting that lifetimes are controlled by a different
parameter. This, combined with the detection of magnetic
field effects for 2c and 2d makes a compelling case for
ISC as the key parameter for these systems.
In conclusion, laser flash photolysis of ketones 1b-d
has allowed the generation, detection and study for the
first time of the 4,4′-(1,n-alkanediyl)bisbenzyl biradicals
(500 mL) and 30% aqueous NaOH solution (60 mL) was added
a mixture of the corresponding 1,n-bis(4-bromomethylphenyl)-
alkane (2 mmol) and TosMIC (0.4 g, 2 mmol) in CH Cl (60
2 2
mL) over a period of 2 h. After the solution was refluxed for
an additional 3 h and allowed to cool, water (100 mL) was
added. The organic layer was concentrated under vacuum. To
2 2
the residue in CH Cl (10 mL) was added concentrated
hydrochloric acid (10 mL) and the mixture stirred for 10 min
at room temperature. After the usual workup, the residue was
chromatographed on silica gel with CH
2
Cl
2
to afford the
(2b-d ) in solution at room temperature. Conformations
ketones 1b-d .
of the biradicals, and the factors that determine their
decay dynamics, have been found to be affected by the
length of the chain linking the benzyl radical moieties.
This is reflected in the chemical behavior of the biradi-
cals; with longer tethers leading to behavior approximat-
ing that of true radical pairs.
1
[3,3]Paracyclophan-2-one (1b): H NMR (CDCl
3
) δ 2.0-2.2
(
4
1
m, 2 H), 2.7 (t, J ) 5 Hz, 4 H), 3.7 (s, 4H), 6.7 (d, J ) 8 Hz,
H), 6.8 (d, J ) 8 Hz, 4 H); 13C NMR (CDCl
40.0 (s), 133.3 (s), 130.2 (d), 129.9 (d), 51.9 (t), 36.0 (t) 29.2
) δ 208.2 (s),
3
+
(t); MS m/z 250 (M , 90), 222 (18), 117 (100), 91 (22). Anal.
Calcd for C H O: C, 86.36; H, 7.25. Found: C, 86.33; H, 7.12.
1
8
18
1
[
3,4]Paracyclophan-2-one (1c): H NMR (CDCl
m, 4 H), 2.3 (t, J ) 5 Hz, 4 H), 3.7 (s, 4 H), 6.6 (d, J ) 8 Hz,
H), 6.7 (d, J ) 8 Hz, 4 H); 13C NMR (CDCl
) δ 207.0 (s),
140.4 (s), 131.4 (s), 129.5 (d), 129.0 (d), 51.4 (t), 35.5 (t), 29.0
(t); MS m/z 264 (M , 100), 236 (18), 208 (22), 104 (70). Anal.
Calcd for C H O: C, 86.32; H, 7.63. Found: C, 86.51; H, 7.69.
3
) δ 1.5-1.7
(
4
Exp er im en ta l Section
3
Gen er a l P r oced u r e. 1H and 13C NMR spectra were re-
corded in a 200 MHz spectrometer; chemical shifts (δ) are
reported in ppm relative to TMS. GC/MS measurements were
made on a quadrupole mass selective detector connected to a
gas chromatography equipped with DB-5 capillary column (30
m × 0.32 mm i.d.; film thickness 0.25 µm). Combustion
analyses were performed at M-H-W Laboratories, Phoenix,
AZ. The external magnetic field source was a “homemade”
magnet that can achieve fields of up to 3000 G. Continuous
variation in the magnetic field was possible through the use
of a Hewlett-Packard 6282A DC power supply.
+
1
9
20
1
[
3,5]Paracyclophan-2-one (1d ): H NMR (CDCl
3
) δ 0.6-0.8
(
6
m, 2 H), 1.3-1.5 (m, 4 H), 2.4 (t, J ) 6 Hz, 4H), 3.7 (s, 4 H),
13
.7 (d, J ) 8 Hz, 4 H), 6.9 (d, J ) 8 Hz, 4 H); C NMR (CDCl
3
)
δ 207.0 (s), 140.0 (s), 130.9 (s), 128.9 (d), 128.6 (d), 51.2 (t),
+
3
3.8 (t), 28.7 (t), 22.5 (t); MS m/z 278 (M , 100), 250 (12), 117
(
46), 104 (50), 91 (28), 77 (18). Anal. Calcd for C20 22O: C,
H
8
6.29; H, 7.97. Found: C, 86.20; H, 7.76.
Con ven t ion a l La m p Ir r a d ia t ion of Com p ou n d s 1b-
Rea gen ts. TEMPO and cis,cis-1,3-cyclooctadiene were com-
mercially available. The substrates 427 and 5 were prepared
following procedures described in the literature.
d . Deaerated 1 mM cyclohexane or benzene solutions of 1b-d
were irradiated for 1 h at 254 nm with a prototype of a
Luzchem photoreactor equipped with eight UV lamps. The
28
Syn th esis of 1-(4-Ch lor om eth ylp h en yl)-2-(4-m eth yl-
1
photolysis mixture was analyzed by GC-MS and H NMR.
2
9
p h en yl)eth a n e (6). 1-(4-Hydroxymethylphenyl)-2-(4-meth-
La ser F la sh P h otolysis. These experiments were carried
out using a Nd:YAG laser using the fourth laser harmonic (266
nm, <10 ns, <20 mJ /pulse). Transient signals were captured
with a Tetronix-2440 digital oscilloscope which was interfaced
to a computer that also controlled the experiment. The system
was operated with software written in the LabVIEW 4.1
environment from National Instruments.32 Other aspects of
3
0
ylphenyl)ethane was added to thionyl chloride (10 mL), and
the solution was allowed to stand at room temperature for 12
h; after this time, thionyl chloride was removed under reduced
pressure. The residue was submitted to semipreparative HPLC
using hexane as eluent to obtain the chloro compound 6
1
(
92%): H NMR (CDCl
3
) δ 2.3 (s, 3 H), 2.9 (s, 4 H), 4.6 (s, 2
1
3
H), 7.2 (d, J ) 8 Hz, 4 H), 7.3 (d, J ) 8 Hz, 4 H); C NMR
CDCl ) δ 142.1 (s), 138.3 (s), 135.2 (s), 134.8 (s), 128.9 (d),
28.7 (d), 128.5 (d), 128.1 (d), 46.1 (t), 37.6 (t), 37.2 (t), 20.9
3
3
this instrument are similar to those described earlier. All
experiments were carried out using Luzchem cuvettes con-
structed from 7 × 7 mm quartz tubing. Samples were purged
with a slow stream of either nitrogen or oxygen, as required.
(
1
(
3
+
q); MS m/z 244 (M , 95), 209 (42), 139 (38), 105 (100), 77 (65).
Syn th esis of [3.2]P a r a cyclop h a n -2-on e (1a ).31 This com-
pound was obtained upon photolysis of [3.3]paracyclophane-
1
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada and the
Spanish DGES (M.A.M., Project No. PB97-0339) for
generous support of this work. Thanks are also due to
Drs. A. St. Amant and Wei Quan Tian for their help
with the calculations.
2
(
2
,11-dione (5): H NMR (CDCl
d, J ) 8 Hz, 4 H), 6.7 (d, J ) 8 Hz, 4 H); C NMR (CDCl
07.0 (s), 140.0 (s), 133.3 (s), 133.1 (d), 131.0 (d), 51.5 (t), 33.7
3
) δ 3.0 (s, 4 H), 3.7 (s, 4 H), 6.4
13
3
) δ
+
(t); MS m/z 236 (M , 85), 208 (72), 104 (100), 77 (28).
Syn th esis of [3.n ]P a r a cyclop h a n -2-on es 1b-d . These
compounds were synthesized in low yield (9-15%) by the
reaction of p-toluenesulfonylmethyl isocyanide (TosMIC) with
the corresponding 1,n-bis(4-bromomethylphenyl)alkanes. Thus,
J O025776S
4 2 2
to a refluxed mixture of n-Bu NBr (1.6 g, 5 mmol) in CH Cl
(
30) Camaioni, D. M.; Franz, J . A. J . Org. Chem. 1984, 49, 1607-
1613.
(31) Isaji, H.; Sako, K.; Takemura, H.; Tatemitsu, H.; Shinmyozu,
(
27) Otsubo, T.; Kitasawa, M.; Misumi, S. Bull. Chem. Soc. J pn.
979, 52, 1515-1520.
28) Kurosawa, K.; Suenaga, M.; Inazu, T.; Yoshino, T. Tetrahedron
Lett. 1982, 23, 5335-5338.
29) Amatore, C.; Gaubert, F.; J utand, A.; Utley, J . H. P. J . Chem.
Soc., Perkin Trans. 2 1996, 11, 2447-2452.
1
(
T. Tetrahedron Lett. 1998, 39, 4303-4304.
(32) Scaiano, J . C. J . Am. Chem. Soc. 1980, 102, 7747-7753.
(33) Scaiano, J . C.; Tanner, M.; Weir, D. J . Am. Chem. Soc. 1985,
107, 4396-4403.
(
J . Org. Chem, Vol. 67, No. 17, 2002 6135