Photochemistry of 5-phenyl-1-pentene in the gas phase

Article abstract of DOI:10.1021/ja044504z

The photochemistry of the title compound has been studied in the gas phase using 254-nm irradiation. In addition to meta cycloadducts analogous to those observed in solution, population of S₁^vib in the gas phase gives several products, the relative amounts of which depend on quencher gas pressure but not on excitation wavelength. For example, in the absence of butane, the major photoproduct is compound 5. This product is formed by a [1,5] hydrogen shift in the primary photoproduct, compound 4. Compound 4 is an intramolecular meta cycloadduct that is generated in the gas phase with sufficient excess vibrational energy to undergo rearrangement unless quencher gas is present. Likewise, there is evidence that two other meta cycloadducts (2 and 3) are also formed with appreciable vibrational energy in the absence of a quencher gas. A unique intramolecular ortho cycloadduct is also formed from 1 but only within a narrow range of quencher gas pressures. This is a two-photon product, with the initial cycloadduct (11) ring opening to a cyclooctatriene (12) that photochemically closes to 6. The pressure dependence of this ortho cycloaddition may be due to a requirement for vibrational deactivation of 11 (Scheme 5) or a precursor species (Scheme 6). The overall chemistry is outlined in Scheme 7.

Full text of DOI:10.1021/ja044504z

Published on Web 02/01/2005
Photochemistry of 5-Phenyl-1-pentene in the Gas Phase
Chang-Dar D. Ho and Harry Morrison*
Contribution from the Department of Chemistry, Purdue UniVersity,
West Lafayette, Indiana 47907
Received September 10, 2004; E-mail: hmorrison@purdue.edu
Abstract: The photochemistry of the title compound has been studied in the gas phase using 254-nm
irradiation. In addition to meta cycloadducts analogous to those observed in solution, population of S1vib in
the gas phase gives several products, the relative amounts of which depend on quencher gas pressure
but not on excitation wavelength. For example, in the absence of butane, the major photoproduct is
compound 5. This product is formed by a [1,5] hydrogen shift in the primary photoproduct, compound 4.
Compound 4 is an intramolecular meta cycloadduct that is generated in the gas phase with sufficient excess
vibrational energy to undergo rearrangement unless quencher gas is present. Likewise, there is evidence
that two other meta cycloadducts (2 and 3) are also formed with appreciable vibrational energy in the
absence of a quencher gas. A unique intramolecular ortho cycloadduct is also formed from 1 but only
within a narrow range of quencher gas pressures. This is a two-photon product, with the initial cycloadduct
(11) ring opening to a cyclooctatriene (12) that photochemically closes to 6. The pressure dependence of
this ortho cycloaddition may be due to a requirement for vibrational deactivation of 11 (Scheme 5) or a
precursor species (Scheme 6). The overall chemistry is outlined in Scheme 7.
substituted benzenoid compounds with ethenes.4-7 The proposed
Introduction
mechanism involves the formation of a pair of exciplexes (EX1
The study of the photochemistry of nonconjugated arylalkenes
has been a source of interest for several decades. A particularly
fascinating early observation was that a double bond three car-
bons removed from a benzene ring is highly successful in
trapping the phenyl S1 excited state.1 On the basis of the
reduction in lifetime of the phenyl S1 state from 35 ns (toluene)
to 2.5 ns, these workers proposed that the alkene traps the phenyl
S1 excited state to form an exciplex. They suggested that the
exciplex then converts to the intramolecular meta(1,3)-cycload-
ducts that were observed as the primary products.1 The intra-
molecular meta photocycloaddition reaction was subsequently
extended, analyzed, and utilized by numerous workers.2 Gilbert
and co-workers studied the effect of aryl and alkene substituents
and proposed a more detailed mechanism3 that was analogous
to proposals to rationalize the intermolecular photoreactions of
and EX2) followed by the generation of a pair of diradical inter-
mediates (BR1 and BR2). Using 5-phenyl-1-pentene (1) as an
example (Scheme 1), the 2,4 closure of BR1 forms meta cyclo-
adduct 3 while the formation of a 2,6 bond in this biradical
gives 2. Likewise, there are two modes of closure for BR2.
One, 1,3 closure, leads to adduct 4, but closure of the 1,5 bond
in BR2 would give a severely strained product that is rarely
observed.
Though the diradical mechanism explained products formed
in the parent system, it did not rationalize the difference in
regioselectivity seen in the presence of electronegative and
electropositive substituents nor the effect of solvent polarity.
Through the efforts of numerous workers, the mechanism was
therefore extended to involve partially zwitterionic intermediates
instead of full diradicals.2b,8 However, the regioselectivity of
meta cycloadduct formation is basically predetermined by the
conformations of the exciplexes,2b,3 an aspect that was exten-
sively studied by Wender’s group.2a,2c With the proper design
of substituents on the benzene and alkene moieties, photoinduced
(1) (a) Morrison, H.; Ferree, W. I., Jr. J. Chem. Soc., Chem. Commun. 1969,
268-269. (b) Ferree, W. I., Jr.; Grutzner, J. B.; Morrison, H. J. Am. Chem.
Soc. 1971, 93, 5502-5512.
(2) For reviews, see: (a) Wender, P. A.; Siggel, L.; Nuss, J. M. In Com-
prehensiVe Organic Synthesis. SelectiVity, Strategy and Efficiency in
Modern Organic Chemistry; Trost, B. M., Fleming, I., Paquette, L. A. Eds.;
Pergamon Press: Oxford, 1991; Vol. 5, pp 645-673. (b) Cornelisse, J.
Chem. ReV. 1993, 93, 615-669. (c) Wender, P. A.; Dore, T. M. CRC
Handbook of Organic Photochemistry and Photobiology; Horspool, W. M.,
Song, P. S., Eds; CRC Press: Boca Raton, FL, 1995; pp 280-290. (d)
Mizuno, K.; Maeda, H.; Sugimoto, A.; Chiyonobu, K. In Molecular and
Supramolecular Photochemistry. Understanding and Manipulating Excited-
State Processes; Ramamurthy, V., Schanze, K. S., Eds.; Marcel Dekker:
New York, 2001; Vol. 8, pp 127-241. (e) Gilbert, A. CRC Handbook of
Organic Photochemistry and Photobiology, 2nd ed.; Horspool, W. M.,
Lenci, F., Eds; CRC Press: Boca Raton, FL, 2004; pp 41-1-41-11. (f)
Hoffmann, N. Synthesis 2004, 481-495.
(4) (a) Cornelisse, J.; Merrit, V. Y.; Srinivasan, R. J. Am. Chem. Soc. 1973,
95, 6197-6203. (b) Merrit, V. Y.; Cornelisse, J.; Srinivasan, R. J. Am.
Chem. Soc. 1973, 95, 8250-8255. (c) Srinivasan, R.; Ors, J. A. Chem.
Phys. Lett. 1976, 42, 506-508. (d) Ors, J. A.; Srinivasan, R. J. Org. Chem.
1977, 42, 1321-1327.
(5) Sheridan, R. S. Tetrahedron Lett. 1982, 23, 267-270.
(6) Bryce-Smith, D.; Fenton, G. A.; Gilbert, A. Tetrahedron Lett. 1982, 23,
2697-2700.
(7) Mattay, J.; Runsink, J.; Leismann, H.; Scharf, H. D. Tetrahedron Lett. 1982,
23, 4919-4922.
(3) (a) Gilbert, A.; Taylor, G. N. J. Chem. Soc., Perkin Trans. 1 1980, 1761-
1768. (b) Ellis-Davies, G. C. R.; Gilbert, A.; Heath, P.; Lane, J. C.;
Warrington, J. V.; Westover, D. L. J. Chem. Soc., Perkin Trans. 2 1984,
1833-1841.
(8) Cornelisse, J.; de Haan, R. Molecular and Supramolecular Photochemistry,
Vol. 8; Ramamurthy, V., Schanze, K. S., Eds.; Marcel Dekker: New York,
2001; pp 1-126.
9
2114
J. AM. CHEM. SOC. 2005, 127, 2114-2124
10.1021/ja044504z CCC: $30.25 © 2005 American Chemical Society

Photochemistry of 5-Phenyl-1-pentene in the Gas Phase
A R T I C L E S
Scheme 1. Biradical Mechanism for Intramolecular Meta
Cycloaddition of 5-Phenyl-1-pentene (1) in Solution
Table 1. Quantum Yields for the Photolysis of 1 in Cyclohexane
as a Function of Excitation Wavelength
2
2
2
2
λex (nm)
Φcyc
(×
10-
)
Φ2
(×
10-
)
Φ3
(×
10-
)
Φ4 (× )
10-
255
266
13.0 ( 1.0
11.0 ( 0.8
1.7 ( 0.2
1.4 ( 0.2
2.2 ( 0.4
1.9 ( 0.3
9.1 ( 0.4
7.7 ( 0.3
vib
about the benzene S1 states or about transients derived from
these states. We chose the simplest model, compound 1, and
have, in fact, observed photochemistry not seen in solution.
Time-course studies, and the effects of quencher gases and
excitation wavelengths, have been used to understand the origin
of this new gas-phase photochemistry.
Results
Preparation of 5-Phenyl-1-pentene (1). 5-Phenyl-1-pentene
was prepared by the Grignard coupling of 1-bromo-2-phenyl-
ethane with allylmagnesium bromide. Distillation, silica gel flash
chromatography, and finally preparative GLC provided samples
of g99% purity. The compound has been prepared previously
and its 1H NMR spectrum was consistent with that in the
literature.14 The UV absorption spectrum for 1 in cyclohexane
(Supporting Information) shows structured absorption between
230 and 280 nm. This corresponds to the first electronic
intramolecular meta cycloaddition has become a powerful tool
in the synthesis of polycyclic natural products.2f
Ortho cycloaddition often competes with meta cycloaddi-
tion in intermolecular photocycloaddition reactions involving
benzene derivatives and alkenes.2e,8 Through studies of the
effect of the ionization and redox potentials of various ben-
zenes and alkenes on the photochemistry, it has been dem-
onstrated that the difference in these potentials for the reac-
tion pair plays an important role in the competition between
meta and ortho cycloaddition.2b,8 Using the Rehm-Weller
equation to estimate the degree of charge transfer in the
exciplexes, it was noted that cycloaddition involving reactant
pairs having little charge transfer generally leads to meta
cycloadducts, while those reactions in which charge transfer is
energetically favored are dominated by ortho cycloaddition.9,10
This rule is followed even more strictly in intramolecular
cycloaddition. The photocycloaddition between a simple alkyl
substituted benzene and an internal alkene always leads to meta
cycloadducts.2d,8
transition (S0 f S1), and the λmax at 260 nm (ꢀ, 215 M-1cm-1
)
is unexceptional. The spectrum is quite similar to the absorption
spectrum reported for cis-6-phenyl-2-hexene in hexane.1 The
UV absorption spectrum for toluene in the gas phase also shows
a λmax at 260 nm with ꢀ ) 103 M-1cm-1 15
.
Solution Phase Photolysis of 1. As noted in the Introduction,
the photolysis of 1 in solution has been extensively studied.3
We reproduced those results and found that irradiation with 254
nm light gave the three products (2, 3, 4) previously reported,
with a comparable product ratio (eq 1).
Our interest in examining the photochemistry of 5-phenyl-
1-pentene (1) in the gas phase stemmed from the fact that the
alkene group in 1 is capable of intercepting the aryl singlet
excited state with a rate constant of 0.37 × 109 s-1 in solution.1
Photochemistry in the gas phase is useful for probing reactions
that occur in upper electronic excited states (i.e., S2) or
vibrationally excited states (S1vib), and we have made some novel
observations upon applying this technique to several aromatic
hydrocarbons.11 For example, the gas-phase photochemistry of
3-methyl-1,2-dihydronaphthalene leads to several new products
unique to the gas phase that derive from the “hot” vibronic
excited states of S2 or S1.12 In benzene itself, upper vibronic
states of S1 are involved in the so-called “channel-three”
radiationless decay that occurs when benzene is excited with
∼3000 cm-1 of excess vibrational energy above the S1 origin.13
We thus thought it of interest to see if the rapid interaction of
an alkene appended to a benzene ring could provide information
The quantum yields for loss of 1 were determined by
excitation into the long- and short-wavelength portions of the
first electronic absorption band using lasers. The values (Fcyc
)
we determined at 266 nm (0.11) and at 255 nm (0.13) are
comparable to that (0.15) reported in Gilbert’s work3 using 254-
nm low-pressure mercury arc light. GLC analysis using an
internal standard confirmed that the observable products account
for 100% of the starting material lost. The complete set of data
16
is listed in Table 1.
Gas Phase Photolysis of 1 under Flowing Conditions.
Compound 1 was photolyzed in the gas phase under low-
pressure, “flowing conditions” (see Experimental) at 254 nm.
The photolysis produced a new compound, 5, and traces of
compounds 2 and 3. Compound 5 was shown by mass spectral
(9) (a) Mattay, J. Tetrahedron 1985, 41, 2393-2404. (b) Mattay, J. Tetrahedron
1985, 41, 2405-2417.
(10) Mu¨ller, F.; Mattay, J. Chem. ReV. 1993, 93, 99-117.
(11) Waugh, T.; Morrison, H. J. Am. Chem. Soc. 1999, 123, 3083-3092, and
references therein.
(12) Duguid, R. J.; Morrison, H. J. Am. Chem. Soc. 1991, 113, 1271-1281.
(13) (a) Callomon, J. H.; Parkin, J. E. Chem. Phys. Lett. 1972, 13, 125-131.
(b) Riedle, E.; Weber, Th.; Schubert, U.; Neusser, H. J.; Schlag, W. J.
Chem. Phys. 1990, 93, 967-978. (c) Palmer, I. J.; Ragazos, I. N.; Bernardi,
F.; Olivucci, M.; Robb, M. J. Am. Chem. Soc. 1993, 115, 673-682. (d)
Chachisvilis, M.; Zewail, A. H. J. Phys. Chem. A 1999, 103, 7408-7418.
1
analysis to be isomeric with 1, and its H NMR spectrum was
identical with that reported3a for the structure shown in eq 2.
(14) Gamage, S. A.; Smith, R. A. J. Tetrahedron 1990, 46, 2111-2128.
(15) Hipper, H.; Troe, J.; Wendelken, H. J. J. Chem. Phys. 1983, 78, 5351-
5357.
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J. AM. CHEM. SOC. VOL. 127, NO. 7, 2005 2115

A R T I C L E S
Ho and Morrison
Compound 5 is formed by a [1,5] H-shift in 4 which earlier
workers had observed during GLC analysis (see eq 3).3a We
too observed this rearrangement when the GLC column oven
temperature was >150 °C or the injection port temperature was
>220 °C.
Figure 1. Effect of added butane on the conversion of 1 in the static gas-
phase photolysis.
Effect of Butane on the Gas-Phase Photochemistry of 1.
Compound 1 was photolyzed in the presence of varying
pressures of butane gas under “static” (see Experimental)
conditions. The loss of starting material is plotted in Figure 1,
and the formation of compounds 2-5 are plotted in Figures 2
and 3. All area percentages represent the fraction of the total
integrated area for products and starting material since mass
balance analyses in several static photolysis experiments using
an internal standard indicated that >98% of the disappearing 1
was converted to these products.
Figure 3 includes a new product, 6, that has not been
discussed. This product is not observed in the absence of butane
and is seen primarily at medium pressures (ca. 10 Torr) of the
quencher gas (see Figure 3). It is also formed in trace amounts
(<0.5%) in solution upon prolonged photolysis (>60 min). In
fact, compound 6 was eventually isolated from a series of
preparative, prolonged, solution-phase photolyses of 1. Its
Figure 2. Effect of added butane on the formation of 4 and 5 in the static
gas-phase photolysis of 1.
1
structure assignment was based on an analysis of its H and
Effect of Ar on the Gas-Phase Photochemistry of 1. Argon
was also used as a quencher gas in the photolysis of 1. The
product distribution, using 13 Torr of argon, is compared with
that seen with the same pressure of butane in Table 2.
Time-Dependence Studies on the Gas-Phase Photochem-
istry of 1. Time-dependence plots for the 254-nm light-initiated
gas-phase photochemical reactions of 1 under static conditions
with 13 Torr of butane are shown in Figures 4-6. The plots
for the loss of starting material (Figure 4) and for the appearance
of 2, 3, and the sum of 4 + 5 (Figure 5) all show good linearity
(R2 values of 0.997, 0.999, 0.998, and 0.995, respectively) with
slopes of 0.96, 0.16, 0.16, and 0.42, respectively. There is an
induction period for the formation of 6 (Figure 6).
13C NMR, UV-vis, and mass spectra. The assignment of
structure is discussed in detail in the Discussion section.
In addition to the major products described above, a trace
(e1%) amount of an unidentified material (7) was also detected
under medium butane pressure conditions. This compound was
not seen in the absence of butane nor in the solution-phase
photolysis. It was not isolated because of its low yield, but a
GLC/mass spectrum indicated that it is an isomer of 1 (m/e )
146). The gas-phase photolysis of 1 in the presence of ca. 10
Torr butane is summarized in eq 4.
Wavelength Effects on the Gas-Phase Photochemistry of
1. The effect of excitation wavelength on the gas-phase
photochemistry of 1 was studied under static conditions, both
with and without butane present. Excitation with 254-nm light
was achieved using a low-pressure mercury lamp, while 260,
266, and 270 nm excitation involved the use of lasers. The
results are reported in Tables 1 and 2 in the Supporting
Information section. The data for 254-nm irradiation are in terms
of the relative amounts of the products, whereas an internal
standard was used in the laser experiments. Thus, data for the
latter are in absolute terms, and over 98% of the disappearance
of 1 can be accounted for by the formation of the previously
(16) There is clearly no wavelength effect on this photochemistry in solution.
This contradicts an earlier report of a wavelength effect in the photochem-
istry of 6-phenyl-2-hexene.1 That work was done with a grating mono-
chromator with limited light intensities.
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Photochemistry of 5-Phenyl-1-pentene in the Gas Phase
A R T I C L E S
Figure 3. Effect of added butane on the formation of 2, 3, and 6 in the static gas-phase photolysis of 1.
Table 2. Product Distributions from Photolysis of 1 with and
photoproducts formed in a typical “static” experiment at 300
mTorr of reactant is shown in Table 2. Here again 5 dominates,
but the meta cycloaddition products, 2-4, now also appear.
Compounds 2-4 are the major products from photolysis in
solution, as has been reported earlier3a and confirmed in this
work. Compound 5 was seen earlier as an artifact from the
solution-phase photochemistry that appeared upon the insertion
of 4 into a gas chromatograph at high temperature.3a
without 13 Torr Butane or Argona
quencher conversion %
2
3
4
5
6
none
21.0 ( 1.0 1.4 ( 0.1 1.4 ( 0.1 2.0 ( 0.1 11.6 ( 0.6 0.0
butane 29.0 ( 1.5 4.7 ( 0.1 4.6 ( 0.1 11.1 ( 0.3 1.1 ( 0.2 6.4 ( 0.3
Ar
30.0 ( 1.1 4.8 ( 0.1 4.6 ( 0.1 10.0 ( 0.4 2.2 ( 0.3 7.3 ( 0.5
a Thirty-minute irradiation time; numbers represent area percents from
GLC; Σ 2 - 6 * conversion because of minor products.
Mechanistic Discussion Concerning the Formation of 5
in the Gas Phase. We rigorously confirmed that the formation
of compound 5 was not due to thermal chemistry during our
GLC analysis; we could readily lower the temperature of the
injector and the column to a point where compound 4 was
demonstrably stable and yet observe 5 as a photolysis product.
We also have found compounds 2-4 to be photostable under
flowing conditions, consistent with 5 being a primary photo-
product. However, it is obviously relevant that thermal excitation
of 4 leads to 5, through a mechanism that involves an
unexceptional 1,5 hydrogen shift (see eq 3).3a
The quencher gas experiments clearly indicate that vibra-
tionally excited 4 is forming in the low-pressure gas-phase
photolysis. The presence of butane or argon suppresses the
formation of 5 and concomitantly increases the formation of 4
(see Figure 2 and Table 2). As one might expect, argon is
modestly less effective as a collisional quencher than butane
(Table 2). The overall conversion of 1 to photoproducts is
significantly higher with a quencher gas present (see Figure 1
and Table 2). This will be discussed further below. The yield
of 4 effectively plateaus when the butane pressure exceeds 50
Torr, and no 5 is observed at a butane pressure >500 Torr.
Analysis of the data in Figure 2 indicates that the sum of 4 +
5 is relatively constant and minimally dependent on the butane
pressure.
Figure 4. Time-dependence study for the loss of 1 upon photolysis with
13 Torr butane.
cited products in these photolyses. No wavelength effect on the
product distribution was observed.
Photochemistry of Cycloadducts 2-4. The products 2-4
were isolated from preparative solution photolyses and individu-
ally photolyzed under flowing and static gas-phase conditions
with 254-nm excitation. No photochemistry was observed in
any of these photolyses.
Though one could conceive that the S1 state of 1 also needs
to be vibrationally excited for “hot” 4 to be formed, there are
good reasons to believe that this is not the case. The ground-
state energies for compounds 1 and 4 were estimated by using
electronic structure calculations at the B3LYP/6-31G*//B3LYP/
3-21G* level of theory.17 These indicate that the ground-state
Discussion
Photoproducts Formed in the Gas Phase in the Absence
of a Quencher Gas. Only one photoproduct, compound 5, is
formed when 1 is photolyzed under flowing, that is, low-pressure
(ca. 30 mTorr), conditions (see eq 2). The distribution of the
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J. AM. CHEM. SOC. VOL. 127, NO. 7, 2005 2117

A R T I C L E S
Ho and Morrison
Figure 5. Time-dependence study for the formation of products 2-5 upon photolysis of 1 with 13 Torr butane. Though traces of 5 were detected by GLC
at 5 and 10 min, the peaks were too small to be accurately integrated.
Scheme 2. The Proposed Mechanism for the Formation of 5 in
the Gas Phase
The results of the study of the effect of excitation wavelength
on the photochemistry of 1, under static conditions without
quencher gas, also indicate that S1vib is not required to convert
4 to 5. Excitation into the 0-0 transition of S0 f S1 (270 nm)
gives a ratio of 4 to 5 that is comparable to that observed with
254-nm irradiation. Clearly, the conversion of 4 to 5 is not
Figure 6. Time-dependence study for the formation of 6 upon photolysis
of 1 with 13 Torr butane.
adversely affected by reducing the excess vibrational energy in
energy of 4 sits ca. 34 kcal/mol above that of 1. By analogy
the S1 excited state of 1.
with the spectroscopy of toluene vapor,18 we assign the 0,0
We therefore propose the mechanism for the formation of 5
transition for 1 to ca. 267 nm (37500 cm-1), which leads one
shown in Scheme 2. This mechanism correctly predicts that the
to estimate that S1° of 1 sits ca. 107 kcal/mol above the ground
ratio of 5 to 4 should diminish as quencher gas is added
state. Thus, there could be as much as 73 kcal/mol of vibrational
(ultimately going to zero in solution) but that the sum of 4 +
energy available to 4 upon its formation from S1° of 1. Since
5 should be independent of quencher gas pressure.
thermolysis at ca. 200 °C suffices to efficiently convert 4 to 5,
Mechanistic Discussion Concerning the Formation of 2
one can estimate the activation energy for this transformation
and 3 in the Gas Phase. It is clear that the reactions leading to
to be ca. 30-35 kcal/mol. This is well below that which is
the formation of these two meta cycloadducts are coupled, as
available by electronic excitation of 1.
has been noted earlier for the solution-phase studies (see Scheme
1). This is most evident in the time-course plot in Figure 5 where
the two products show identical slopes. Interestingly, these two
products are formed in essentially identical amounts in the gas
phase (see Table 2 and Tables in the Supporting Information)
but 3 is modestly favored over 2 in solution (Table 1).
(17) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J.
A. Gaussian 03, Revision B.03; Gaussian, Inc.: Pittsburgh, PA, 1998. (b)
We thank Professor Paul Wenthold for carrying out these calculations.
These products differ from 4 in that they do not undergo
thermolysis during gas chromatography. This may partly be a
(18) (a) Ginsburg, N.; Robertson, W. W.; Matsen, F. A. J. Chem. Phys. 1946,
14, 511-517. (b) Burton, C. S.; Noyes, W. A., Jr. J. Chem. Phys. 1968,
49, 1705-1714.
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Photochemistry of 5-Phenyl-1-pentene in the Gas Phase
A R T I C L E S
Scheme 3. The Proposed Mechanism for the Formation of
Cycloadducts 2 and 3 in the Gas Phase
irradiations that this material was eventually isolated. As shown
in Figure 3, 6 is not observed at all in the absence of a quencher
gas. Formation of 6 is optimized at ca. 13 Torr butane and then
rapidly falls off as the quencher gas pressure is increased. In
contrast with the linear time-course plots characteristic of the
formation of 2, 3, and 4 + 5 (see Figure 5), the formation of 6
shows a pronounced induction period (Figure 6). It becomes a
major product (exceeding 2 + 3) with photolysis times longer
than 10 min (for example, see Table 2). This induction period
suggests that one or more transient intermediates are the source
of 6.
Structure Assignment of 6: an Ortho Photocycloaddition
Product. GLC-mass spectral analysis showed the product to
have a molecular ion at m/e ) 146, isomeric with 1. Its
UV-vis absorption spectrum shows no absorption beyond 230
nm, an indication that the highly conjugated character of the
benzene moiety in 1 has been destroyed. A comprehensive NMR
spectral analysis clearly indicated that the structure of 6 is
fundamentally different from the meta cycloadducts, and on the
basis of the reasoning outlined below, we assign the structure
of this compound to the ortho cycloadduct shown below. Also
shown are three structures (8-10) that proved useful in
interpreting the NMR spectra.
Figure 7. (a-c): Low-energy conformations for 2, 3, and 4 from MM+
calculations. (d) The low-energy conformation for 4 with the six-member
ring highlighted.
consequence of their greater stability. The electronic structure
calculations17 place the energies of 2 and 3 at 26 and 28
kcal/mol above that of 1; recall that 4 is computed to lie 34
kcal/mol above 1. Compound 4 is also better configured for
the [1,5] hydrogen shift chemistry, as can be seen in the opti-
mized structures shown in Figure 7a-c that were derived from
MM+ molecular mechanics calculations. The distances between
the key atoms, C* and H*, in 2, 3, and 4 are 3.15, 3.32, and
2.86 Å, respectively. The proximity of C* and H* in 4 is
facilitated by the six-membered ring highlighted in Figure 7d
that is unique to this adduct.
The formation of products 2 and 3 is modestly increased when
a quencher gas is added (Figure 3). The effect is greater than
for the sum of 4 + 5 (Table 2) and accounts for part of the
increased conversion of 1 to photoproducts in the presence of
quencher gas (Figure 1 and Table 2). The enhancement is maxi-
mized at a butane pressure of ca. 10 Torr (Figure 3). A study
of the effect of excitation wavelength on product formation
indicates that the yields of 2 and 3 are not improved by exci-
tation with lower excess vibrational energy (table in Supporting
Information). By the same argument as that used for the for-
mation of 5, this suggests that the excess vibrational energy in
vib
S1 is unnecessary for the formation of 2 and 3. This is con-
sistent with their formation in the solution phase. However, the
enhancement in their formation as a quencher gas is added
indicates that either these products or some precursor species
must be vibrationally cooled for 2 and 3 to be efficiently formed.
There appears to be no chemical process that traps the hot prod-
uct, since we see no set of related products akin to the 4/5 pair.
The most logical alternative would be that the hot species re-
turns to 5-phenyl-1-pentene. Employing Occam’s Razor, we
show “hot” 2 and 3 as the species returning to the starting ma-
terial in Scheme 3 (however, see also further discussion below).
Compound 6. The most novel observation made during the
butane-quenching studies was the appearance of a new product,
6. By contrast with compounds 2-5, there is no product reported
in the solution-phase studies that would appear to correlate with
this product. In fact, a reexamination of the solution-phase
photochemistry showed that a trace amount of 6 is formed in
solution with long photolysis times, and it was from such
1
The NMR data available to us included H and 13C NMR
spectra as well as spectra from APT, H-13C HMQC, and
1
1H-1H COSY experiments. The H and 13C NMR spectra are
1
shown in Figures 8 and 9, respectively. The 1H chemical shifts
of 6, as well as chemical shift data for reference compounds
8,19,20 9,21 and 10,22 are summarized in Table 3. The J values
for 6, 9, 10, and cyclobutene are compiled in Table 4.21-23
(19) Baldwin, J. E.; Kaplan, M. S. J. Am. Chem. Soc. 1971, 93, 3969-3977.
(20) Allred, E. L.; Beck, B. R.; Voorhees, K. J. J. Org. Chem. 1974, 39, 1426-
1427.
(21) V´ızva´rdi, K.; Toppet, S.; Hoornaert, G. J.; Keukeleire, D. D.; Bako´, P.;
Van der Eycken, E. J. Photochem. Photobiol., A: Chem. 2000, 133, 135-
146.
(22) Al-Qaradawi S. Y.; Cosstick K. B.; Gilbert A. J. Chem. Soc., Perkin Trans.
1 1992, 1145-1148.
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A R T I C L E S
Ho and Morrison
Figure 8. 1H NMR spectrum of 6 in CDCl3; peaks marked with × are due to impurities.
Table 4. The J Values for the 1H NMR Resonances of 6, 9, 10,
and Cyclobutenea
6
9
10
cyclobutene
J1,2
J1,9
J2,7
J10,11
J’s of H4
5.7
4.2
6.3
5
4
2.5
4.65
2.85
2.4b
2.5
2.4/2.7c
21.3,d 12.3
a Coupling constants in Hz. b This coupling constant is obtained from
1
the resonance in the H NMR spectrum that corresponds only to H2. The
peak corresponding to H7 is embedded in a multiplet that includes H7 plus
one of the H6s. The J2,7 could not be resolved from this peak. The
c
assignment of this coupling constant is based on the reference values. J10,11
is 2.4 Hz in H11 and 2.7 Hz in H10. d This large J value may be due to the
geminal coupling between the H4s. The J6gem in 10 is reported as 20 Hz.22
Figure 9. 13C NMR and APT 13C NMR spectra of 6 in CDCl3.
Table 3. 1H NMR Data for 6, 8, 9, and 10
those in reference compound 10 suggests a cis-H1,H9 config-
uration for 6. This result is confirmed by a previous study of
the coupling constants between the protons in cyclobutene,23
which reported values of 4.65 Hz for Jcis and 1.75 Hz for Jtrans
between the vicinal methylene protons. The coupling constant
between the vinyl protons in cyclobutene was also reported as
2.85 Hz in the same reference, which is consistent with our
observation of 2.4 and 2.7 Hz from the H NMR spectrum of
6. In sum, the spectral data are consistent with the assignment
of photoproduct 6 to the structure shown above.
Mechanistic Discussion Concerning the Formation of 6
in the Gas Phase. Considering the bonding present in 6, the
most logical origin for this compound is through intramolecular
ortho cycloaddition of the alkene with the aromatic ring. Such
[2+2] cycloaddition is a known photochemical reaction for
certain, appropriately substituted, aryl alkenes.8 Two additional
steps are necessary to generate 6 after the primary photoproduct
is formed, but both are well-precedented.2e,8 The mechanism is
shown in Scheme 4.
6
8
9
10
δH1 3.38 (dd)
δH2 5.67 (dd)
δH4 2.33 (dd)
δH5 1.40-1.70 (m)
3.20-3.35 (br s) 2.92-3.02 (m)
3.2 (dd)
4.89 (dd)
5.70-5.90
4.87 (dd)
4.17 (t) (exo)
3.92 (ddd) (endo) 3.50 (m) (endo)
1.65 (ddd) (exo) 1.5 (exo)
2.00-2.50 (endo) 1.08 (m) (endo)
2.00-2.50
1.07 (ddd) (exo)
4.89 (dds) (exo)
1
δH6 1.14-1.39 (m)
δH7 2.10-1.95 (m) 1.20-2.10
δH8 0.99 (m) 1.20-2.10
1.90-2.05 (m)
δH9 3.18 (dd)
δH10 5.90 (d)
δH11 6.14 (d)
1.76 (m)
0.64 (m) (exo)
2.00-2.50 (endo) 1.5 (endo)
3.05-3.20 (br s) 3.20-3.30 (m)
2.56 (m)
6.00 (d)
5.70-5.90
6.00-6.15 (d)
5.64 (br s)
The 1H-13C HMQC and 1H-1H COSY spectra (Supporting
Information) provided the carbon connectivity. The assignment
of the configuration between H1 and H9 is based on the coupling
constant J1,9. The consistency between the J1,9 value in 6 and
With regard to the initial cycloaddition reaction, intermo-
lecular ortho photocycloaddition between benzene and ethene
(23) Hill, E. A.; Roberts, J. D. J. Am. Chem. Soc. 1967, 89, 2047-2049.
9
2120 J. AM. CHEM. SOC. VOL. 127, NO. 7, 2005

Photochemistry of 5-Phenyl-1-pentene in the Gas Phase
A R T I C L E S
Scheme 4. Proposed Mechanism for the Formation of 6 in the
Gas Phase
The pronounced induction period we observe for the forma-
tion of 6 (Figure 6) is consistent with the mechanism in Scheme
4. However, all attempts to detect intermediates 11 or 12, by
either GLC or by UV-vs absorption spectroscopy, have been
unsuccessful. The precursors to 17 and 18 were likewise
undetectable.25
in solution has been reported (eq 5).24 The primary cycloadduct,
13, readily isomerizes in its ground state to its tautomer,
cyclooctatriene (14). These are formed together with meta
cycloadducts, which are, in fact, the major photoproducts. Only
small amounts of 13 and 14 are present at high conversions;
secondary photochemistry converts 14 to 8 and 15.
We are left with the question of why ortho cycloaddition of
an unsubstituted phenylalkene such as 1 is readily observable
in the gas-phase photolysis but minimally so in solution. We
believe the quencher gas requirements for observing 6 provide
some insight. This compound is unique among our products in
that it is not observed at all in the absence of butane. It does
resemble 5, however, in that it is rapidly quenched by higher
pressures of butane, in this case with pressures in excess of
100 Torr (Figure 3).30 Collisional quenching ultimately reduces
the formation of 6 to the point where it is found in only trace
amounts, as in solution. As with the other products, the
wavelength studies give no evidence of a wavelength effect on
the formation of 6. With these results in mind, and by analogy
with our proposals to explain the effects of butane on the
formation of the meta cycloadducts, one can extend the
mechanism proposed in Scheme 4 to that shown in Scheme 5.
When the first intermediate, 11, is formed with appreciable
vibrational excitation, it may simply revert back to 1 in what
is, in effect, a mode of radiationless decay. Compound 11 must
be deactivated before it stable enough to survive. However, some
degree of vibrational excitation is required for 11 to ring-open
to 12; the optimal range is ca. 13 Torr of butane. In solution,
or with high pressures of butane, 11 is quenched to the point
where its conversion to 12 is minimal. Under either set of
conditions, one might then anticipate detecting or isolating the
cyclohexadiene, 11, but as already noted, we have not yet been
successful in doing so.
However, attempts to see intramolecular ortho cycloaddition
with unsubstituted alkenyl benzenes in solution have generally
been unsuccessful. Meta cycloaddition always dominates.2b,2d,8
One can achieve ortho cycloaddition by adding electron-donating
and withdrawing substituents to the aryl and olefinic moieties,
respectively, in substrates analogous to 1.8,21,22,25,26 Success here
is apparently due to the intervention of singlet exciplexes with
appreciable charge-transfer character.25,27
Exciplexes in which the olefin approaches the excited benzene
in an exofacial manner are favored, since an endofacial approach
would result in the formation of an excessively strained
cycloadduct.28 In Scheme 4, this leads to the exciplexes labeled
as EX3 and EX4, where the bolded bonds are those exo to the
fused ring formed between the benzene ring and the olefin.
Closure results in 11, with the bolded bond now clearly
occupying an exo-orientation. The subsequent steps mirror those
proposed for the intermolecular system.
The primary cycloadducts are often labile and undergo facile
thermal electrocyclic ring opening to bicyclo[6.3.0]undeca-
trienes.8,29 Secondary photochemistry then leads to disrotatory
ring closure or electrocyclic ring opening. For example, irradia-
tion of compound 16 gives 17 and 18 as the isolable products.25
The analogy between compound 17 and our photoproduct, 6,
is evident; however, we have not observed a product equivalent
to 18.
Alternatively, theoretical analyses of the ortho cycloaddition
reaction suggest that this reaction is forbidden and that there is
a barrier between the excited state of the reactants and the
ultimate products.8,31,32 It is therefore plausible that the gas-
(25) Nuss, J. M.; Chinn, J. P.; Murphy, M. M. J. Am. Chem. Soc. 1995, 117,
6801-6802.
(26) Or by using carbonyl groups to induce intersystem crossing; see Wagner,
P. J. Acc. Chem. Res. 201, 34, 1-8.
(27) See ref 8 for a critical discussion of the necessity for invoking an exciplex
in the ortho cycloaddition mechanism.
(28) Wender, P. A.; Siggel, L.; Nuss, J. M. Org. Photochem. 1989, 10, 357.
(29) Marvell, E. N. Thermal Electrocyclic Reactions; Academic Press: New
York, 1980; p 260.
(30) This observation may explain why ortho cycloaddition was not observed
in early studies of the intermolecular cycloaddition of photoexcited benzene
to 2-butene. We estimate that that the pressures in these studies were at
least 34-fold greater than the optimal (13 Torr) pressure for seeing ortho
product. See: Kaplan, L.; Wilzbach, K. E. J. Am. Chem. Soc. 1968, 90,
3291-3292. Morikawa, A.; Brownstein, S.; Cvetanovic, R. J. Am. Chem.
Soc. 1970, 92, 1471-1476.
(24) Mirbach, M. F.; Mirbach, M. J.; Saus, A. Tetrahedron Lett. 1977, 11, 959-
(31) Van der Hart, J. A.; Mulder, J. J. C.; Cornelisse, J. J. Photochem. Photobiol.,
A: Chem. 1995, 86, 141-148.
962.
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A R T I C L E S
Ho and Morrison
Scheme 5. A Possible Mechanism for Formation of 6 Taking into
Account the Butane-Quenching Results
However, the ortho exciplex cannot give a significant amount
of ortho cycloadduct in the absence of vibrational excitation
(as in solution) nor if the vibrational energy is too great (as in
the gas phase in the absence of quencher gas).
It is interesting to speculate on the possibility of observing
more extensive ortho cycloaddition in solution using fluorinated
solvents that may less effectively deactivate the ortho exciplex
species.
Experimental Section
The detailed experimental procedures for this work may be found
in the doctoral dissertation of C. H. D. H.33 The salient features are
summarized below.
Scheme 6. An Alternative Mechanism for the Formation of 6
1
Instrumentation. Routine H and 13C NMR spectra were obtained
using Varian Gemini 200 MHz or Varian INOVA 300 MHz spectrom-
eters. Chemical shifts are reported in deuteriochloroform in ppm rela-
tive to TMS or residual chloroform. Attached proton test (APT) and
1H-1H COSY spectra were acquired on a Varian INOVA 300 MHz
Spectrometer. High resolution and 1H-13C HMQC spectra were
obtained on a Bruker DRX-500 (500 MHz) spectrometer. Mass spectra
were recorded on a Finnigan 4000 mass spectrometer interfaced to a
gas chromatograph containing either packed or capillary columns.
Electron impact (EI) and chemical ionization (CI) mass spectra were
recorded at 70 eV. Ultraviolet absorption spectra were collected in
matched 1 cm2 quartz cells using a Cary 100 spectrometer interfaced
to a Pentium 100 MHz PC controlled by the Cary Scan Package
software.
Analytical separations were performed on two capillary gas chro-
matographs: a Varian model Star 3400 CX and a Hewlett-Packard
model 5890 series II. Both of the chromatographs were equipped with
flame ionization detectors (FID). The chromatographs were integrated
using either a Hewlett-Packard model 3390A or a model 3393A digital
integrator. Preparative separations were performed using a Varian model
3300 TCD gas chromatograph equipped with a Hewlett-Packard model
3390A digital integrator. Columns used: A (J & W DB-1 30 m ×
0.25 mm id., 0.25 µm), B (J & W Carbowax 30 m × 0.25 mm id.,
0.25 µm), C (6 m ×0.25 in, 15% Carbowax 20M on 60/80 AW-DMCS
Chromosorb W).
phase reaction succeeds because the vibrational energy available
to the reactants allows them to pass over this barrier. This would
explain why the reaction is minimal in solution or with high
pressures of butane but would not explain why the reaction is
unobservable in the absence of butane. Reversion of “hot” 11
to 1 could explain the latter observation. This scenario is shown
in Scheme 6.
Summary Mechanism. There continues to be debate about
the exact description of the excited intermediates (exciplexes
or otherwise) in these photochemical reactions.8 However, incor-
porating these species Schemes 3 and 4, and adding Scheme 6,
we derive the summary mechanism shown in Scheme 7.
Computations. Molecular conformational optimizations were con-
ducted on 2-4 using the MM+ force field found in HyperChem 6.03
(Hypercube). The steepest descent algorithm was used in all calcula-
tions. All geometries were optimized at the level with the root-mean-
square gradient (RMS) of 0.1 kcal/mol. A maximum of 5000 cycles
was set for each optimization if the calculation did not converge at the
RMS level above. The ground-state energies for compounds 1-4 were
estimated by using electronic structure calculations at the B3LYP/
6-31G*//B3LYP/3-21G* level of theory. These calculations are reliable
to ca. (4 kcal/mol.
Solution-Phase Photochemistry. Experiments were done with
matched quartz tubes (1-cm o.d.) in a Rayonet Model RPR-100
reactor (New England Ultraviolet Company) equipped with 16 254-
nm low-pressure mercury lamps. All solution experiments were
conducted in cyclohexane and degassed with argon for 30 min prior
to photolysis. Quantum efficiencies at 255 and 266 nm were mea-
sured using a YAG-pumping dye laser (Continuum ND-60) oper-
ated with Coumarin 500 dye (Exciton Inc.) and a BBO (beta barium
borate) doubling crystal. A 2× beam enlarger was used in front
of the photolysis cell to avoid cell damage. The solutions were
magnetically stirred during photolysis. The laser power passing
through the sample cells was measured using an Ophir model AN/2
power meter. A power of 2-3 mW was used for the solution-phase
photolyses.
Conclusion
Photolysis of 1 in the gas phase produces meta cycloadducts
common to the solution-phase photochemistry but also leads
to products unique to the vapor phase. One such product, 5,
can be attributed to the initial formation of a meta cycloadduct
(4) with excess vibrational energy. There is evidence that excess
vibrational energy in two other meta cycloadducts (2 and 3)
also lessens their formation. An intramolecular ortho cycloadduct
(6) is also produced in the gas phase but only under a rather
specific set of quencher gas pressures. This is the first time that
intramolecular meta and ortho cycloaddition products have been
seen simultaneously upon irradiation of a simple arylalkene
hydrocarbon.
A mechanism for the formation of the cycloadducts is
proposed (Scheme 7) on the basis of the results from buffer
gas quenching and wavelength effect studies. In this mechanism,
the alkene intercepts the excited aryl moiety to form a set of
ortho and meta exciplexes, both in solution and in the gas phase.
(32) For a different view, see: Clifford, S.; Bearpark, M. J.; Bernardi, F.;
Olivucci, M.; Robb, M. A.; Smith, B. R. J. Am. Chem. Soc. 1996, 118,
7353-7360.
(33) Ho, C.-D. D. Doctoral Dissertation, Purdue University, August, 2004.
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2122 J. AM. CHEM. SOC. VOL. 127, NO. 7, 2005

Photochemistry of 5-Phenyl-1-pentene in the Gas Phase
A R T I C L E S
Scheme 7. Summary Mechanism for Photolysis of 1 in the Gas Phase
Gas-Phase Photochemistry. The apparatus has been described in
detail elsewhere.34 Exploratory and preparative experiments were
performed under flowing conditions. Briefly, a liquid sample was
distilled (typically at pressures of 30 mTorr at 0 °C for 1) through a
quartz tube (33 cm in length × 14.7 cm in circumference) surrounded
by 16 254-nm low-pressure mercury lamps. The photolyzed vapor was
collected in a liquid-nitrogen trap. After warming to room temperature,
the trap was washed twice with 10 mL pentane, and the combined
washings were concentrated under a stream of nitrogen. Exploratory
experiments utilized 10-20 mg while preparative work employed
30-300 mg. The products were isolated by prep GLC equipped with
column C.
Qualitative and quenching studies were performed under static
conditions which involved filling a cylindrical quartz vessel (length
34 cm × 4.7 cm o.d.) with the desired vapor to pressures of ca. 300
mTorr. The vessel was removed from the vacuum line and placed in a
modified RPR-100 Rayonet reactor containing one 254-nm lamp for
photolysis times of 30 min at 25 °C. Collection of the photolyzed sample
required immersion of the vessel in liquid nitrogen and the injection
of 5 mL pentane. After the vessel warmed to room temperature, the
solution was removed and the vessel was again washed with pentane
(5 mL). In the time-course study, the photolysis time was varied from
2 to 30 min in the presence of 13 Torr butane.
pentane (5 mL) containing an internal standard. The combined pentane
washings were concentrated under a stream of nitrogen and analyzed
on columns A (80-100 °C) and B (90-110 °C). The gas-phase
apparatus was designed with apertures to allow the introduction of a
quencher gas (butane and Ar). Samples were degassed prior to flowing
and static experiments by at least five freeze-pump-thaw cycles using
5 mTorr vacuum.
Solution Phase Photolysis of 1. Solutions of 30-60 mM (0.5-1%
w/v) 1 in cyclohexane were photolyzed at 254 nm for 20 min. Three
products were identified as 2, 3, and 4 on the basis of the GLC retention
times and by comparison of products to that reported in the literature.3b
Compound 6 was produced in a GLC detectable amount in photolyses
longer than 60 min. Compounds 2-4 were isolated from preparative
photolyses of 1 (60 mM, 114 mL) using AgNO3-impregnated silica
gel chromatography35 followed by preparative GLC. Compound 6 was
isolated using AgNO3-impregnated silica gel chromatography. The 1H
NMR spectral data of 2-4 are consistent with those published in the
literature.3a
Photolysis of 1 in the Gas Phase under Flowing Conditions. A
24-mg sample of 1 was photolyzed in the gas phase under flowing
conditions with 254-nm light. The sample was kept at 0 °C, resulting
in a pressure of 30 mTorr. Compound 5 was isolated by preparative
GLC and found to have 1H NMR spectral data consistent with the those
published.3a
The samples were also photolyzed at different wavelengths using
lasers. The laser power was always less than 13 mW to avoid two-
photon excitation. The photolyses lasted from 20 min to 6 h depending
on the laser power. The laser-photolyzed samples were washed with
Photolysis of 1 in the Gas Phase under Static Conditions. A static
photolysis cell with 300 mTorr of 1 was prepared. The sample was
kept at 0 °C to provide the proper vapor pressure for photolysis. The
(34) Suarez, M. L.; Duguid, R. J.; Morrison, H. J. Am. Chem. Soc. 1989, 111,
6384-6391.
(35) Li, T. S.; Li, J. T.; Li, H. Z. J. Chromatogr., A 1995, 715, 372-375.
9
J. AM. CHEM. SOC. VOL. 127, NO. 7, 2005 2123

A R T I C L E S
Ho and Morrison
Supporting Information Available: 1H-13C HMQC and
1H-1H COSY NMR spectra for compound 6. Tables (1 and 2)
showing the effect of excitation wavelength on product dis-
tribution. The UV absorption spectrum of 1 in cyclohexane.
This material is available free of charge via the Internet at
http://pubs.acs.org.
isolated product mixture in pentane was concentrated and analyzed by
GLC. Each product was identified by GLC retention time, GLC co-
injection with the product isolated from preparative solution phase
photolysis, and GLC-mass spectrometry.
Acknowledgment. We thank Professor Paul Wenthold for
carrying out the electronic structure calculations and for helpful
discussions.
JA044504Z
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2124 J. AM. CHEM. SOC. VOL. 127, NO. 7, 2005