Surface photochemistry of alkyl aryl ketones: Energy transfer and the effect of a silica-gel surface on electronic states of excited molecules

Article abstract of DOI:10.1002/1099-1395(200008)13:8<437::AID-POC252>3.0.CO;2-1

Alkyl aryl ketones undergo Type II photoreaction both on a silica-gel surface and in solution. The amount of acetophenone produced from valerophenone increases linearly with increase in the amount of valerophenone loaded at coverage below ca 60%. The effect of the alkyl chain length on the Type II photoreactivity of alkyl phenyl ketones on the surface is weak. The relative quantum yields Φ_MeAp/Φ_AP and Φ_MeOAP/Φ_ΛP on the surface are lower than those in benzene containing 0.5 M pyridine. A silica-gel surface provides a polar reaction medium that makes the energy difference between the lowest n,π* and the upper π,π* triplet states small and may cause the inversion of the nearby n,π* and π,π* triplet states. The filter effect is trivial in surface photochemistry when all loaded molecules are in the monomolecular layer. The energy transfer processes are observed in the valerophenone-p-methylvalerophenone and valerophenone-p-methoxyvalenophonone systems in which the internal filter effects are so strong that the energy transfer processes cannot be observed directly in solution. Although the Stern-Volmer quenching kinetics would be applicable to the photoreaction on the surface, a correction for the probability of excitation of a molecule should be made. Copyright

Full text of DOI:10.1002/1099-1395(200008)13:8<437::AID-POC252>3.0.CO;2-1

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2000; 13: 437–442
Surface photochemistry of alkyl aryl ketones: energy
transfer and the effect of a silica-gel surface on electronic
states of excited molecules
Tadashi Hasegawa,* Masaaki Kajiyama and Yuko Yamazaki
Department of Chemistry, Tokyo Gakugei University, Nukuikitamachi, Koganei, Tokyo 184-8501, Japan
Received 6 September 1999; revised 17 December 1999; accepted 9 February 2000
ABSTRACT: Alkyl aryl ketones undergo Type II photoreaction both on a silica-gel surface and in solution. The
amount of acetophenone produced from valerophenone increases linearly with increase in the amount of
valerophenone loaded at coverage below ca 60%. The effect of the alkyl chain length on the Type II photoreactivity of
alkyl phenyl ketones on the surface is weak. The relative quantum yields ΦMeAP/ΦAP and ΦMeOAP/ΦAP on the surface
are lower than those in benzene containing 0.5 M pyridine. A silica-gel surface provides a polar reaction medium that
makes the energy difference between the lowest n,p* and the upper p,p* triplet states small and may cause the
inversion of the nearby n,p* and p,p* triplet states. The filter effect is trivial in surface photochemistry when all
loaded molecules are in the monomolecular layer. The energy transfer processes are observed in the valerophenone–
p-methylvalerophenone and valerophenone–p-methoxyvalenophonone systems in which the internal filter effects are
so strong that the energy transfer processes cannot be observed directly in solution. Although the Stern–Volmer
quenching kinetics would be applicable to the photoreaction on the surface, a correction for the probability of
excitation of a molecule should be made. Copyright  2000 John Wiley & Sons, Ltd.
KEYWORDS: surface photochemistry; Type II reaction; alkyl aryl ketones; silica gel; Stern–Volmer quenching
kinetics; energy transfer
INTRODUCTION
photoreactions observed on the surface are fundamentally
the same as those seen in solution, large differences in
9
Photochemical processes of organic molecules have been
widely studied and a growing understanding of the
underlying mechanisms has greatly stimulated develop-
ments in organic photochemistry. Although the synthetic1
value of photoreactions is now well recognized,
selectivity in the reactions is still an important problem
in synthetic and industrial chemistry. Recently, photo-
chemical interest has been focused on the behavior of
product distributions have been observed in some
8,10
cases
and a few examples of novel photoreactions
unique to the non-homogeneous environment have been
11–14
reported.
However, a general rule for the prediction
of novel photoreactions has not been established because
the origin of the novel photoreactivity has not yet been
completely clarified. There must be more than one factor
involved in the origin, and some might govern the
2
3–6
11–14
molecules in a crystalline state and on a solid surface.
behavior of excited molecules
whereas others might
1
2,13
Non-reactive solid surfaces, such as silica gel or alumina,
provide an ordered two-dimensional environment for
effecting and controlling chemical reactivity as a
function of the polarity or molecular associations
control the activity of intermediates.
The photo-
chemistry of alkyl aryl ketones in solution has been
15
widely studied and is now well understood. Thus, the
Type II photoreaction of the ketones has been used as a
surface probe. We report here the effect of the polarity of
a silica-gel surface causing a change in the property of the
lowest excited state of adsorbed ketone molecules and the
energy transfer between the ketones.
4
enhanced or inhibited by the microscopic surface. The
conformation of organic molecules may be distorted and
conformational flexibility may be restricted by adsorp-
7
,8
tion on the surface.
Although the types of most
*
Correspondence to: T. Hasegawa, Department of Chemistry, Tokyo
Gakugei University, Nukuikitamachi, Koganei, Tokyo 184-8501,
Japan.
E-mail: tadashi@u-gakugei.ac.jp
Copyright  2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 437–442

4
38
T. HASEGAWA, M. KAJIYAMA AND Y. YAMAZAKI
RESULTS AND DISCUSSION
Dependence of molecular coverage on the extent
of acetophenone formation from the Type II
photoreaction of valerophenone
Valerophenone (VP) undergoes a Norrish Type II
reaction to give acetophenone (AP) and 2-methyl-1-
1
6
phenylcyclobutanols in solution and on a dry silica-gel
9
d,10g
surface.
The molecular coverage of the surface is an
important factor for surface photoreactions because the
character of the reaction environment should change
dramatically at 100% coverage. Monolayer coverage has
been determined from the Langmuir adsorption iso-
Figure 2. Relative quantum yields for production of
acetophenone from alkyl phenyl ketones PhCO(CH ) CH
2
n
3
in benzene containing 0.5 M pyridine (s) and on a silica-gel
surface (.)
1
0abe,13
therm
or by calculation based on the surface area
of silica gel used and the area occupied by one molecule
9
c,10be,12–14
estimated from space-filling models.
A photo-
Conformational ¯exibility of alkyl phenyl ketones
on a silica-gel surface
reaction on the surface can also be used for the
1
2,14
determination of monolayer coverage.
The values
of the coverage obtained from these different methods
1
0be,12,13
Conformational flexibility is an important factor for
determining the photoreactivity of alkyl phenyl ketones in
generally show good agreement.
Thus, the
monolayer coverage of VP was determined from its
Type II reaction on the surface.
1
7
solution and may be a critical factor for molecules
8
adsorbed on the surface. The relative quantum yields for
Figure 1 shows the relationship between the amount of
VP loaded on 1 g of silica gel and the amount of AP
formed from the Type II reaction of VP under the same
irradiation conditions. The amount of AP initially
increased with increase in the amount of VP loaded and
then levelled off to a constant value. The coverage must
AP production from the Type II reaction of caprophenone
(CP), octanophenone (OP), decanophenone (DP) and
laurophenone (LP) with respect to that of VP (ΦAP/
VP
ΦAP ) were determined in order to clarify the effect of
the alkyl chain length on the Type II photoreactivity of the
alkyl phenyl ketones on the surface. The results are shown
in Fig. 2. The relative quantum yields on the surface were
�
4
be 100% when 5.7 Â 10 mol of VP was loaded on 1 g
of the silica gel. When multiple layers are formed on the
surface, the VP molecules in the outermost layer should
be responsible for the photoreaction. The filter effect
should be trivial when all loaded VP molecules are in the
monomolecular layer. The surface area of the silica gel
similar to those in benzene containing 0.5
M pyridine. A
Lewis base such as pyridine is known to maximize the
Type II quantum yield by suppressing reverse hydrogen
transfer in the 1,4-biradical intermediate, thus ensuring
that product ratios are actually equal to the ratios of the
2
� 1
used is 477 m g , so that the area occupied by one VP
1
6b
�
18
2
reaction rates from the triplet states. As the absorption
coefficients of the alkyl phenyl ketones were nearly equal
to each other and within an experimental error both in
benzene (ꢀ313 = 50–53) and in methanol (ꢀ313 = 73–76),
the ratios of the relative quantum yields on the surface
should be equal to the ratios of the reaction rates from
their triplet states as in solution. Reverse hydrogen
transfer is prevented on the surface as well as in benzene
containing pyridine. The surface provides a strong polar
reaction medium. Leermakers et al. reported that silica
molecule is 1.4 Â 10
m . This value was in accord
with that obtained from calculation on the basis of a
space-filling model (1.4 Â 10� 18 m ).
2
18
gel approximates to methanol on the Kosower Z scale.
Despite the surface having strong polarity, the effect of
the alkyl chain length on the Type II photoreactivity of the
alkyl phenyl ketones on the surface is weak and is nearly
the same as that in solution.
Effect of the surface on photoreactivity of para-
substituted phenyl alkyl ketones
Figure 1. Dependence of the extent of acetophpenone
formation on amount loaded in the surface photoreaction of
valerophenone
The photoreactivity of para-substituted phenyl alkyl
Copyright  2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 437–442

SURFACE PHOTOCHEMISTRY OF ALKYL ARYL KETONES
439
ketones depends on the properties of their lowest excited
states. Ketones having the lowest n,p* state undergo the
Type II photoreaction with moderate to high quantum
efficiency, whereas ketones having the lowest p,p* state
undergo the reaction with low efficiency. The Type II
quantum yield of the ketones in which the energy gap
between the lowest n,p* and the upper p,p* triplet state is
small in non-polar solvents depends on the solvent
polarity because the polarity affects the energy level of
the triplet states. Polar solvents may produce an inversion
of the n,p* and p,p* triplet state because the p,p* state is
more polar and the n,p* state less polar than the ground
Figure 3. Effect of added valerophenone (VP) on relative
quantum yields for formation of MeAP from 0.05 M MeVP in
benzene containing 0.5 M pyridine. The curved line was
1
9a
state in terms of changes in dipole moment. Since a
silica-gel surface provides a strong polar environment,
the surface should cause changes in the properties of the
obtained from the equation [MeAP]/[MeAP] = "MeVP/("MeVP
‡
0
" [VP]/[MeVP]), where [MeAP] = 1.63, " = 51 and
VP 0 VP
= 72
1
0a
"
MeVP
lowest excited state. The deviation of the photoreac-
tivity of organic compounds on the surface from that in
solution may be responsible for the change in the
properties of the lowest excited state. Hence the
photoreactivity of para-substituted phenyl alkyl ketones
was studied.
20
its upper n,p* triplet state. As the polarity of the silica-
gel surface is fairly high, the energy difference of the two
triplet states becomes large and the contribution of the
photoreactive upper triplet state in excited molecules
becomes low on the surface.
Valerophenone, p-methylvalerophenone (MeVP) and
p-methoxyvalerophenone (MeOVP) underwent the Type
II photoreaction to give the corresponding acetophenone
1
9
both in solution and on a silica-gel surface. The
quantum yield for the formation of p-methylacetophe-
none (MeAP) from MeVP in benzene containing 0.5 M
pyridine was equal to that for AP formation from VP
Energy transfer between ketones on a silica-gel
surface
The change in the energy level might affect the rate of the
bimolecular energy transfer. If two kinds of photoreactive
ketones co-exist in solution and absorb the same
irradiation line, each of the ketones acts as an internal
(ΦMeAP /ΦAP = 1). However, the ΦMeAP /ΦAP values for
the photoreaction in methanol and on the surface were
less than unity (Table 1). On the other hand, the quantum
yield for the formation of p-methoxyacetophenone
16b,21
filter for the photoreaction of the other.
Figure 3
(MeOAP) from MeOVP was lower than that for AP
shows the internal filter effect of VP on the production of
MeAP from MeVP. The experimental results fit the curve
obtained from calculation assuming the internal filtering
by VP. The internal filter effect may be trivial in surface
photochemistry when all loaded molecules are in the
monomolecular layer, and the process of energy transfer
from VP even in benzene containing 0.5 M pyridine. The
ΦMeOAP /ΦAP value was only 0.2. The low photo-
reactivity of MeOVP is responsible to the p,p* character
of its lowest excited state. The ΦMeOAP /ΦAP values for
photoreactions in methanol and on the surface were low
(Table 1). These results can be reasonably explained in
terms of the polar medium effect. The character of the
lowest triplet state of MeVP should change from n,p* to
p,p* when the solvent is changed from benzene to
methanol. The Type II photoreaction should occur from
Table 1. Relative quantum yields for acetophenone forma-
tion
Conditions
ΦMeAP/ΦAP ΦMeOAP/ΦAP
c
In benzene containing 0.5 M
1.0
0.2
a
pyridine
a
In methanol
0.5
0.5
0.004
0.003
b
On the silica-gel surface
a
� 3
Figure 4. Relative quantum yields for production of
acetophenone in the Type II reaction of VP on a silica-gel
surface in the presence of MeVP. In all runs 1.64 Â 10 mol
of VP were loaded on 1 g of silica gel. The surface coverage
of VP is ca 25%
The solution contained 0.05 mol dm of VP, MeVP, or MeOVP.
The amount of VP, MeVP or MeOVP loaded on silica gel was
b
�
4
�
4
� 1
1
.64 Â 10 mol (1g of SiO
2
)
(coverage ca 25%).
The quantum yield for disappearance of VP was unity and formation
c
19b
of AP (ΦAP) was 0.85 in benzene containing a Lewis base.
Copyright  2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 437–442

4
40
T. HASEGAWA, M. KAJIYAMA AND Y. YAMAZAKI
Table 1, and its photoreaction is negligible compared
with that of VP, the following simple scheme for the
photoreaction of VP can be written;
h ꢁ
Ã
VP �ꢀ VP
ꢁ1†
ꢁ2†
ꢁ3†
ꢁ4†
k r
Ã
VP �ꢀ 1,4-biradical�ꢀ AP
k d
Ã
VP �ꢀ VP
kET
Ã
Ã
VP ‡ MeOVP �ꢀ VP ‡ MeOVP
#
Figure 5. Relative quantum yields for production of MeAP in
the Type II reaction of MeVP on a silica-gel surface in the
MeOVP
�
4
presence of VP. In all runs 1.64 Â 10 mol of MeVP were
loaded on 1 g of silica gel. The surface coverage of MeVP is
ca 25%
An equation similar to the Stern–Volmer equation can be
obtained by applying the steady-state approximation to
the scheme:
ꢂ0
kET
may be observable because of separation from the
internal filtering even in the case where the internal filter
effect is so strong that the energy transfer process cannot
be observed directly in solution photochemistry.
ˆ
1 ‡
‰MeOVPŠ
ꢁ5†
ꢂ
kr ‡ kd
The concentration of MeOVP may be defined as the
amount of MeOVP on a unit square or a 1 g of silica
22
A constant amount of VP and an appropriate amount of
MeVP were loaded on 1 g of silica gel and irradiated. The
amount of AP from the Type II reaction of VP decreased
with increase in MeVP added (Fig. 4). On the other hand,
when a mixture of a constant amount of MeVP and an
appropriate amount of VP on the surface was irradiated,
the amount of MeAP produced from the Type II reaction
of MeVP increased with increase in VP (Fig. 5). These
results provide strong evidence for energy transfer from
VP to MeVP on the surface. The triplet energies of VP
and MeVP in an ethanol matrix are measured to be 74.5
22,23
gel.
The two definitions are convertible. Hence the
definition based on the amount on 1 g of silica gel was
adopted to analyze of the effect of MeOVP on the
photoreactivity of VP.
The relationship between the relative quantum yield
(f /f) and the amount of MeOVP on 1 g of silica gel is
shown in Fig. 7 [line (a)]. The gradient of line (a)
increases from its initial value. Hence the linear relation-
ship expected from Eqn. (5) could not be observed. Most
VP molecules are in the monomolecular layer at less than
100% coverage and the amount of AP produced from VP
increases linearly with increase in the amount of VP
loaded on the silica gel and reaches a constant value as
shown in Fig. 1. The molecular length of MeOVP is
nearly the same as that of VP, so the coverage must be
less than 40% under the experimental conditions and
0
�
1
19a
and 73 kcal mol , respectively
(1 kcal = 4.184 kJ).
The triplet energy of VP should be higher than that of
MeVP on a polar silica-gel surface.
When a mixture of a constant amount of VP and an
appropriate amount of MeOVP on the surface was
irradiated, the amount of AP produced from VP
decreased with increase in MeOVP (Fig. 6). As the
photoreactivity of MeOVP is fairly low, as shown in
Figure 6. Relationship between the amount of AP from the
Type II reaction of VP on a silica-gel surface and the amount
Figure 7. Dependence of relative quantum yields for
production of AP from the Type II reaction of VP (s) and
its corrected from (.) on the amount of co-adsorbed
�
4
of co-present MeOVP. In all runs 1.64 Â 10 mol of VP were
�
4
loaded on 1 g of silica gel. The surface coverage of VP is ca
2
MeOVP. In all runs 1.64 Â 10 mol of VP were loaded on
5%
1 g of silica gel. The surface coverage of VP is ca 25%
Copyright  2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 437–442

SURFACE PHOTOCHEMISTRY OF ALKYL ARYL KETONES
441
multiple layers must not be formed. Molecules in the
monomolecular layer would be expected not to act as a
filter for each other. Therefore, the filtering effect should
not be responsible for lowering the photoreactivity of VP.
Similar upward curves have been observed in the
Stern–Volmer plots of the fluorescence quenching of
observed in solution because of the inversion. The
internal filter effect is trivial in surface photochemistry
when all loaded molecules are in the monomolecular
layer, and the process of energy transfer is observable
even in the case when the internal filter effect is so strong
that the energy transfer process cannot be observed
directly in solution photochemistry. Although the Stern–
Volmer quenching kinetics would be applicable to the
photoreaction on the surface, a correction for the
probability of excitation of a molecule should be made.
23
pyrene adsorbed on silica gel by 2-bromonaphthalene.
Upward curvature of the Stern–Volmer plots seems to be
essential in surface photochemistry. There must be a
process other than normal quenching and it lowers the
photoreactivity of molecules on the surface by quencher
molecules. There may be fewer strong-binding sites
available for the quencher at a high concentration. This
may result in an increase in quenching rate as implied by
EXPERIMENTAL
2
3
the upward curvature of the Stern–Volmer plot.
Silica gel (Merck Kieselgel 60, Art. 7734) was used as
received. Benzene was washed with sulfuric acid and
then water, dried and fractionally distilled over phos-
phorus pentoxide. Pyridine was dried over potassium
hydroxide and then fractionally distilled. Alkyl aryl
ketones were prepared by Friedel–Crafts acylation
However, the upward tendency is observed even at low
quencher concentration as in Fig. 7. There seems to be a
factor involved other than the availability of strong-
binding sites. The probability of excitation of molecules
on a surface would be different from that in solution.
Silica gel particles may be regarded as impenetrable
spheres. When VP molecules on a hemisphere are
irradiated, the molecules on the other hemisphere should
be in the dark. Then, the probability of excitation of a
molecule should be proportional to the probability of
occupying a special site where the molecule absorbs
light. If the molecular lengths and strength of adsorption
of molecules are nearly the same, the probability should
be defined as the ratio of the numbers of molecules under
consideration to the whole numbers of molecules
presented. The following equation can be written for
the VP–MeOVP system:
24
according to the method given in the literature.
A
Taika 100 W high-pressure mercury lamp was used as an
irradiation source. A potassium chromate filter solution
25
was used for isolation of the 313 nm line. Gas–liquid
chromatographic (GLC) analysis was performed with a
Shimadzu GC-8A gas chromatograph equipped with a
flame ionization detector which was connected to a
Shimadzu C-R6A Chromatopac integrator, using a 2 m
column containing 15% propylene glycol succinate on
Uniport B. Hexadecane was used as a calibrant for the
GLC analysis.
Photolysis of VP on silica gel at different coverages. A
1 g amount of silica gel and 5 cm of dichloromethane
ꢀ
ꢁꢀ
ꢁ
3
ꢂ0
ꢂ
NVP ‡ N
kET
MeOVP
ˆ
1 ‡
‰MeOVPŠ
ꢁ6†
N
kr ‡ kd
containing appropriate amounts of VP were placed in a
VP
3
5
0 cm round-bottomed flask. The mixture was sonicated
where NVP and NMeOVP are the numbers of VP and
MeOVP molecules, respectively.
for 5 min and then the solvent was evaporated under
reduced pressure. The coated silica gel was placed in an
1
8 Â 180 mm Pyrex culture tube. The tubes were rotated
When the corrected relative quantum yields [NVP/
and irradiated with 313 nm radiation from a 100 W high-
pressure mercury lamp. After the irradiation, 4 cm of
3
(
NVP ‡ N
)] (f /f) were plotted against the amount
MeOVP
0
of MeOVP on 1 g of silica gel, a linear relationship was
observed [line (b) in Fig. 7]. The slope of line (b) was
8
indicates that a correction for the probability of excitation
is needed for the Stern–Volmer equation for surface
photoreactions.
acetone containing a known amount of hexadecane as a
calibrant were added and the mixture was sonicated for
10 min. The supernatant solutions were analyzed to
determine the amounts of AP. The results are shown in
Fig. 1.
4
� 1 � 1
.53 Â 10 [mol (1g of SiO ) ] . This result strongly
2
General procedure for determination of relative
quantum yields for formation of AP from alkyl phenyl
ketones in benzene containing 0.5 M pyridine.
�
3
CONCLUSION
Benzene containing 0.5 mol dm pyridine solutions of
�
3
a mixture of ca 0.05 mol dm of an alkyl phenyl ketone
A silica gel surface provides a polar reaction medium that
makes the energy difference between the lowest n,p* and
the upper p,p* triplet states small and may cause the
inversion of the nearby n,p* and p,p* triplet states. The
surface may bring about new reactions that are not
(VP, CP, OP, DP or LP) and a known concentration of
�
3
hexadecane (ca 0.0025 mol dm ) as a calibrant were
placed in 15 Â 150 mm Pyrex culture tubes. The tubes
were degassed by three freeze–pump–thaw cycles and
then sealed. Irradiation with 313 nm radiation was
Copyright  2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 437–442

4
42
T. HASEGAWA, M. KAJIYAMA AND Y. YAMAZAKI
performed on a ‘merry-go-round’ apparatus with an
Ushio 450 W high-pressure mercury lamp. The amounts
of AP formed were determined from the results of GLC
analyses. The relative quantum yields are shown in Fig.
3. (a) Fox MA, Dulay MT. Chem. Rev. 1993; 93: 341–357; (b)
Hoffmann MR, Martin ST, Choi W, Bahnemann DW. Chem. Rev.
1
995; 95: 69–96.
. Kamat PV. Chem. Rev. 1993; 93: 267–300.
5. Thomas JK. Chem. Rev. 1993; 93: 301–320.
4
6
. Hasegawa T, Yamazaki Y. Recent Res. Dev. Photochem. Photo-
biol. 1997; 1: 19–39.
2.
7
. Oelkrug D, Flemming W, Fullerman R, Gunter R, Honnen W,
Krabichler G, Schafer S, Uhl S. Pure Appl. Chem. 1986; 58: 1207–
General procedure for determination of relative
quantum yields for production of AP from alkyl phenyl
1
218.
. Hasegawa T, Yamazaki Y, Yoshioka M. J. Phys. Org. Chem. 1995;
: 31–34.
8
�
5
ketones on a silica-gel surface. After 5.0 Â 10 mol of
8
an alkyl phenyl ketone (the surface coverage for LP is ca
9. (a) Johnston LJ, de Mayo P, Wong SK. J. Chem. Soc., Chem.
Commun. 1982; 1106–1108; (b) Aoyama H, Miyazaki K,
Sakamoto M, Omote Y. Chem. Lett. 1983; 1583–1586; (c)
Johnston LJ, de Mayo P, Wong SK. J. Org. Chem. 1984; 49:
20–26; (d) Hasegawa T, Moribe J, Yoshioka M. Bull. Chem. Soc.
Jpn. 1988; 61: 1437–1439.
25%) had been loaded on 1.0 g of silica gel and irradiated
at 313 nm, the amount of AP was determined as described
in the procedure for the photolysis of VP on silica gel at
different coverages. The relative quantum yields for the
formation of AP from alkyl phenyl ketones are shown in
Fig. 2 together with those in solution. In the case of the
determination of the relative quantum yields for the
formation of acetophenones from para-substituted alkyl
1
0. (a) Weis LD, Evans TR, Leermarkers PA. J. Am. Chem. Soc. 1968;
9
0: 6109–6118; (b) Avnir D, Johnston LJ, de Mayo P, Wong SK. J.
Chem. Soc., Chem. Commun. 1981; 958–959; (c) de Mayo P,
Nakamura A, Tsang PWK, Wong SK. J. Am. Chem. Soc. 1982;
1
1
04: 6824–6825; (d) Baretz BH, Turro NJ. J. Am. Chem. Soc.
983; 105: 1309–1316; (e) Frederick B, Johnston LJ, de Mayo P,
�
4
phenyl ketones, 1.64 Â 10 mol of the ketones were
loaded on 1.0 g of silica gel. The relative quantum yields
are shown in Table 1.
Wong SK. Can. J. Chem. 1984; 62: 403–410; (f) de Mayo P,
Ramnath N. Can. J. Chem. 1986; 64: 1293–1296; (g) Turro NJ.
Tetrahedron 1987; 43: 1589–1616; (h) Su J-J, Dai G-S, Wu S-K. J.
Photochem. Photobiol. A: Chem. 1994; 83: 49–53, and references
cited therein.
1
1. (a) Farwaha R, de Mayo P, Toong YC. J. Chem. Soc., Chem.
Commun. 1983; 739–740; (b) Dave V, Farwaha R, de Mayo P,
Stothers JB. Can. J. Chem. 1985; 63: 2401–2405.
General procedure for determination of relative
quantum yields for production of Type II cleavage
product from alkyl aryl ketones on a silica gel surface in
the presence of the second ketone. After a mixture of
12. Hasegawa T, Imada M, Yoshioka M. J. Phys. Org. Chem. 1993; 6:
94–498.
3. Hasegawa T, Imase Y, Imada M, Yoshioka M. J. Phys. Org. Chem.
996; 9: 677–682.
4
1
�
4
1.64 Â 10 mol of VP or MeVP and an appropriate
1
amount of the second ketone (MeVP or MeOVP for VP,
VP for MeVP) had been loaded on 1.0 g of silica gel and
irradiated at 313 nm, the amount of AP or MeAP was
determined as described in the procedure for the
photolysis of VP on silica gel at different coverages.
The relative quantum yields for the formation of AP or
MeAP from VP or MeVP with respect to the ratio of VP
or MeVP to the second ketone, respectively, are shown in
Figs. 4–7.
14. Hasegawa T, Imada M, Imase Y, Yamazaki Y, Yoshioka M. J.
Chem. Soc., Perkin Trans 1 1997; 1271–1273.
1
5. Wagner PJ, Park B-S. In Organic Photochemistry, Padwa A (ed).
Marcel Dekker: New York, 1991; vol. 11, Chapt. 4, 227–366.
16. (a) Wagner PJ. J. Am. Chem. Soc. 1967; 89: 5898–5901; (b)
Wagner PJ, Kemppainen AE, Jellinek T. J. Am. Chem. Soc. 1972;
9
4: 7489–7494.
1
7. Wagner PJ. Acc. Chem. Res. 1983; 16: 461–467.
18. Leermakers PA, Thomas HT, Weis LD, James FC. J. Am. Chem.
Soc. 1966; 88: 5075–5083.
1
9. (a) Wagner PJ, Kemppainen AE, Schott HN. J. Am. Chem. Soc.
973; 95: 5604–5614; (b) Wagner PJ, Frerking HW. Jr., Can. J.
1
Chem. 1995; 73: 2047–2061.
0. Wagner PJ, Nakahira T. J. Am. Chem. Soc. 1973; 95: 8474–8475.
1. (a) Hasegawa T, Arata Y, Endoh M, Yoshioka M. Tetrahedron
2
2
REFERENCES
1
985; 41: 1667–1673; (b) Hasegawa T, Nishimura M, Yoshioka
M. J. Phys. Org. Chem. 1990; 3: 230–234; (c) Hasegawa T,
Ohkanda J, Kobayashi M, Yoshioka M. J. Photochem. Photobiol.
A: Chem. 1992; 64: 299–306.
1
2
. Horspool WM (ed). Synthetic Organic Photochemistry. Plenum
Press: New York, 1984.
. (a) Caswell L, Garibay MA, Scheffer JR, Trotter J. J. Chem. Educ.
22. de Mayo P. Pure Appl. Chem. 1982; 54: 1623–1632.
23. de Mayo P, Natarajan LV, Ware WR. Chem. Phys. Lett. 1984; 107:
187–192.
24. Layraud ME. Bull. Soc. Chim. Fr. 1906; [3] 35: 223–234.
25. Murov SL. Handbook of Photochemistry. Marcel Dekker: New
York, 1973; 99.
1
993; 11: 785–787; (b) Leibovich M, Olovsson G, Scheffer JR,
Trotter J. J. Am. Chem. Soc. 1998; 120: 12755–12769; (c)
Takahashi M, Sekine N, Fujita T, Watanabe S, Yamaguchi K,
Sakamoto M. J. Am. Chem. Soc. 1998; 120: 12770–12776, and
references cited therein.
Copyright  2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 437–442