Rodlike molecules and singlet energy transfer

Article abstract of DOI:10.1021/jo0003145

In continuing our investigations on rodlike molecules composed of bicyclo[2.2.2]octane units, we studied the effect of interposing a single aromatic ring in the rod. Thus, two [3]-rods were synthesized with the two outer units being bicyclooctyls, the central unit being benzenoid, and with one terminal unit bearing an α-naphthyl moiety and the other terminus bearing an acetyl or benzoyl group. Excitation of the α-naphthyl group led to fluorescence emission by both the naphthyl and the acetyl units. However, compared to the [1]- and [2]-rods previously studied, transmission of singlet excitation proved to be less efficient as determined by the fluorescence emission and also by the singlet lifetimes obtained from single photon counting measurement. Transmission to the benzoyl group proved more rapid than to the acetyl moiety. In assessing the factors controlling energy transmission, Δ-density determinations were employed to describe the distribution of electronic excitation in such systems. It was observed that despite most of the energy being located in the terminal chromophores, some is distributed in the bicyclooctyl units. The extent of this distribution provides a guide to the facility of through-bond energy transfer. Evidence is presented that energy transfer in the short rods is mainly through-bond while in the longer rods Forster through-space transfer is involved.

Full text of DOI:10.1021/jo0003145

7740
J . Org. Chem. 2000, 65, 7740-7746
Rod lik e Molecu les a n d Sin glet En er gy Tr a n sfer 1,2
Howard E. Zimmerman,* Yuri A. Lapin, Evgueni E. Nesterov, and Grigoriy A. Sereda
Chemistry Department of the University of Wisconsin, Madison, Wisconsin, 53706
zimmerman@chem.wisc.edu
Received March 6, 2000
In continuing our investigations on rodlike molecules composed of bicyclo[2.2.2]octane units, we
studied the effect of interposing a single aromatic ring in the rod. Thus, two [3]-rods were synthesized
with the two outer units being bicyclooctyls, the central unit being benzenoid, and with one terminal
unit bearing an R-naphthyl moiety and the other terminus bearing an acetyl or benzoyl group.
Excitation of the R-naphthyl group led to fluorescence emission by both the naphthyl and the acetyl
units. However, compared to the [1]- and [2]-rods previously studied, transmission of singlet
excitation proved to be less efficient as determined by the fluorescence emission and also by the
singlet lifetimes obtained from single photon counting measurement. Transmission to the benzoyl
group proved more rapid than to the acetyl moiety. In assessing the factors controlling energy
transmission, ∆-density determinations were employed to describe the distribution of electronic
excitation in such systems. It was observed that despite most of the energy being located in the
terminal chromophores, some is distributed in the bicyclooctyl units. The extent of this distribution
provides a guide to the facility of through-bond energy transfer. Evidence is presented that energy
transfer in the short rods is mainly through-bond while in the longer rods Fo¨rster through-space
transfer is involved.
In tr od u ction
acetyl S1,6 while for the triplet the converse is true. In
these papers we described the molecular rods as “light
pipes” since emission could be observed from the acceptor
moiety. Additionally, the rates of singlet energy transfer
were obtained by use of a single photon counting tech-
nique and dissection of the emission rate constant data.
We have not been alone in studying energy transfer
through saturated moieties. For example, there is the
elegant work by Michl with Staffane rods.7 In some
instances, irregularly shaped separators have also been
termed rods (vide infra). Finally, more recently we have
extended our synthesis to prepare [3]-rod and [4]-rod
compounds.5 It was of interest to ascertain the effect of
interposing an aromatic ring. This study involves four
aspects: (a) The synthesis of [3]-rods with the interposed
aromatic ring, (b) measurement of energy transfer by use
of single photon counting, (c) a new theoretical tool for
prediction of through-bond energy transfer, and (d)
correlation of through-bond and through-space contribu-
tions with rod length.
Our interest in the transmission of electronic excitation
as well as electron transfer through saturated rodlike
moieties goes back very close to three decades.3 Through-
out, these studies have employed bicyclo[2.2.2]octyl
moieties fused bridgehead to bridgehead as separators
between two chromophores at the terminal bridgehead
sites.3-5 The rod compounds most commonly had a
naphthyl group bonded to the bridgehead carbon at one
end of a [1]- or [2]-rod and a keto group (e.g., as in acetyl,
benzoyl, cyclohexanecarbonyl) at the other terminus. In
our original publication,3 evidence was adduced for
singlet energy transfer from a naphthyl group at one end
to the acetyl group at the other while triplet energy
transfer was found to occur in the reverse direction. The
directionality of transfer is controlled by the excited-state
energetics. Thus naphthyl S1 energy > benzoyl S1 and
(1) This is Paper 192 of our photochemical series and Paper 258 of
our general series.
(2) For Paper 257, see: Zimmerman, H. E.; Alabugin, I. V.; Smo-
lenskaya, V. N. Tetrahedron Symposium-in-Print, 2000, 56, 6821-
6831.
(3) Zimmerman, H. E.; McKelvey, R. D. J . Am. Chem. Soc. 1971,
93, 3638-3645.
(4) (a) Zimmerman, H. E.; Goldman, T. D.; Hirzel, T. K.; Schmidt,
S. P. J . Org. Chem. 1980, 45, 3933-3951. (b) Zimmerman, H. E.; Penn,
J . H.; Carpenter, C. W. Proc. Natl. Acad. Sci. U.S.A. 1982, 79, 2128-
2132.
(5) Zimmerman, H. E.; King, R. K.; Meinhardt, M. B. J . Org. Chem.
1992, 57, 5484-5492.
(6) (a) For benzoyl and naphthyl singlet energies there is general
agreement.6b,c (b) Benzoyl, 79 kcal/mol, Murov, S. L. Handbook of
Photochemistry, 2nd. ed.; Marcel Dekker: New York, 1993. (c) Naph-
thyl, 90 kcal/mol, Idem. (d) Acetyl, 84 kcal/mol, Dalton, J . C.; Turro,
N. J . Annu. Rev. Phys. Chem. 1970, 21 499-560. (e) Contrast the 102
kcal/mol acetyl value given by Dewar, M. J . C. et al. J . Comput. Chem.
1984, 5, 480-485. (d) In any case, the more favorable exothermic
naphthyl to benzoyl compared with naphthyl to acetyl transfer
accounts for the greater rate in the benzoyl example. A greater
transition dipole for benzoyl excitation is an added factor; the extinction
coefficient for acetophenone is 40 and for acetone is 14 (both n-π*).6b
Resu lts
Syn th esis. The synthesis of [3]-rods is outlined in
Schemes 1 and 2. In these syntheses the inverse addition
of bicyclic iodides to tert-butyllithium was important,
since the role of the second equivalent of the lithium
compound was to destroy tert-butyl iodide formed and
thus tert-butyllithium needed to be in excess throughout
to avoid consumption of bridgehead lithium reactant. One
example is the conversions of the 4-benzoyl-1-iodobicyclo-
[2.2.2]octane ketal 12 and its acetyl counterpart 13 to
the bridgehead lithium derivatives which required in-
verse addition. In another difficult step the conversion
(7) (a) See ref 7b for an excellent review of rod-chemistry; (b)
Schwab, P. F. H.; Levin, M. D.; Michl, J . Chem. Rev. 1999, 1863,
3-1933.
10.1021/jo0003145 CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/21/2000

Rodlike Molecules and Singlet Energy Transfer
J . Org. Chem., Vol. 65, No. 23, 2000 7741
Ta ble 1. Absor p tion a n d Em ission Da ta
Sch em e 1. Syn th esis of [3]-Rod P r ecu r sor s
cbsorption maxima (nm)
fluorescence
compound
and extinction coefficients maxima (nm)a
naphthyl-[1]-rod 26
228 (20600)
282 (12400)
226 (27000)
282 (2600)
226 (24000)
282 (6900)
325 (340)
325 (340)
325 (340)
benzoyl-[3]-rod 14
acetyl-[3]-rod 16
a
The 0-0 fluorescence peaks are followed by the fluorescence
maxima in parentheses.
The singlet lifetimes were measured using the ap-
paratus described in our earlier publication.4 The fluo-
rescence emission data were subjected to deconvolution
as earlier8 but with modifications. Thus, a 916A EG&G
Ortec multichannel analyzer board with 2048 channels
was used with a PC for data collection in the form of
counts per channel. Also note the Experimental and
Supporting Information Sections. These data were trans-
mitted to a VAX. Deconvolution programming, termed
“Photon”, was written in Fortran based on the algorithm
described in our earlier study.8 The results obtained for
singlet lifetimes and decay rates are summarized in Table
2.
In Table 2, the 1-naphthyl-[1]-rod 26 is a reference
compound and its lifetime is very close to that of typical
1-substituted alkyl naphthalenes. The decay rate of the
benzoyl rod compound was more rapid than this reference
compound. This difference is due to energy transfer to
the carbonyl energy acceptor. Quantitatively, the rate
difference gives the rate of energy transfer (i.e., kET).4
Quite often it is convenient to think in terms of the
reciprocals of the decay rate constants, namely the
excited-state lifetimes. Here we note that the 58 ns
lifetime of 26 is close to the 67 ns value reported9 for
1-methylnaphthalene but shorter than the 97 ns reported
for naphthalene itself.9 The lifetimes and rates of decay
for the 1-naphthyl-[1]-rod 26 and the acetyl-[3]-rod 16
are virtually within experimental error of one another
(i.e., 58 and 55 ns, respectively). In contrast, the benzoyl-
[3]-rod 14 has a shorter lifetime (41 ns) and a more rapid
rate of decay which is approximately 1.4 times that of
the reference compound.6
Sch em e 2 Th e F in a l Step s in th e Acetyl a n d
Ben zoyl [3]-Rod Syn th eses
of the γ-hydroxyketone 3 to enone 4 required optimization
to obtain reasonable yields. Still another reaction which
required optimization was the deprotection of ketal 15
where the normal mild conditions used for ketals did not
suffice and more strenuous conditions were required. This
presumably arises from the conformation of the ketal
enforced by considerable steric hindrance. Finally, the
known4 1-bicyclooctylnaphthalene (26) was needed as a
reference compound.
Com p u ta tion a l a n d Discu ssion . To understand
better the electronic interaction of bridgehead groups
with the bicyclooctane units, we carried out ab initio
computations of the rods of interest. For this we employed
the delta-density matrix approach10 which gives the
distribution of excitation. The method takes the differ-
ence between the excited state and ground-state density
Em ission a n d Sin gle P h oton Cou n tin g Mea su r e-
m en t of Lifetim es. Absorption and fluorescence spectra
for the 1-naphthyl-[1]-rod 26, the acetyl-[3]-rod 16, and
the benzoyl-[3]-rod 14 were obtained. In the absorption
spectra, the strong maxima at 230 and 280 nm are
characteristic of naphthyl compounds. Fluorescence emis-
sion strong peaks were seen at 340 nm, again charac-
teristic of naphthyl emission. No acetyl or benzoyl
fluorescence emission peaks were observed; these n-π*
bands are anticipated to be weak and, if present, would
be obscured by the intense naphthyl absorption and
emission. These spectroscopic data are listed in Table 1.
(8) Zimmerman, H. E.; Werthemann, D. P.; Kamm, K. S. J . Am.
Chem. Soc. 1973, 95, 5094-5095.
(9) Berlman, I. B. Handbook of Fluorescence Spectra of Aromatic
Molecules, 2nd ed.; Academic Press: New York, 1971.
(10) (a)Zimmerman, H. E.; Alabugin, I. V. J . Am. Chem. Soc. 2000,
121, 952-953. (b) Zimmerman, H. E.; Gruenbaum, W. T.; Klun, R. T.;
Steinmetz, M. G.; Welter, T. R. J . Chem. Soc., Chem. Commun. 1978,
228-230.

7742 J . Org. Chem., Vol. 65, No. 23, 2000
Zimmerman et al.
Ta ble 2. Sin gle P h oton Cou n tin g Da ta a
lifetime (τ1/2),
decay rate,
s-1
no. of
runs
compound
ns
naphthyl-[1]-rod 26
acetyl-[3]-rod 16
benzoyl-[3]-rod 14
57.9 ( 0.5
55.0 ( 0.8
40.5 ( 0.4
(1.73 ( 0.02) × 107
(1.82 ( 0.03) × 107
(2.47 ( 0.02) × 107
6
7
5
a
All runs in cyclohexane; Concentrations: 1-naphthalene-[1]-
rod 9.3 × 10-5 M, acetyl-[3]-rod 7.2 × 10-5 M, benzoyl-[3]-rod 7.0
× 10-5 M; Relative std deviations are 0.01, 0.02, and 0.01,
respectively.
matrixes obtained for a reactant by ab initio computation.
D*rt and Do terms are the excited and ground-state local
rt
electron densities and r and t refer to two Weinhold NHO
hybrid orbitals.11 The Srt terms are overlap integrals
which take into account both distance effects and also
the orientation of hybrids. The matrix elements, ∆Drt, of
the Delta Density Matrix are defined as in eq 1. Each
element gives fractional electron density increase or
decrease resulting from excitation.
∆Drt ) D*rtS*rt - DortSo
(1)
rt
The diagonal terms afford one-center electron density
changes, and each off-diagonal ∆D term gives the change
in electron density between a pair of orbitals on excita-
tion. The off-diagonal terms may be thought of as
modified bond orders and indications of the excitation
energies of the various bonds. For the most part these
terms will be negative (i.e., antibonding compared with
ground state) indicating concentration of the energy of
excitation. A few bonds may be strengthened with lower-
ing of that local energy but most have to be negative as
a consequence of the increase in total energy on excita-
tion. Where ∆D elements are zero, there is no excitation.
Accordingly, the method is useful in giving the distribu-
tion of electronic excitation energy in a molecule. In the
present instance of intrarod energy transfer the method
then gives an indication of the role of the through-bond
component.
For the systems of present interest, the ∆-Density
values are given in Figure 1. Computations were carried
out for the simple 1,4-dibicyclooctylbenzene 19, i.e., the
basic [3]-rod, the 1-acetyl-4-R-naphthyl-[1]-rod 17, the
1-benzoyl-4-R-naphthyl-[1]-rod 18, the 1-benzoyl-4-R-
naphthyl-[3]-rod 14, and the 1-acetyl-4-R-naphthyl-[3]-
rod 16. In the cases of the [1]-rods, 6-31G* was used as
a basis in CASSCF with an active space of (6,6). For the
[3]-rods, we employed 3-21G* as a practical and reason-
able choice. The choice of basis sets and active space was
predicated on accessible computation times. However, the
adequacy of active space was checked by variation in
configurations included, and the choice of basis sets was
checked by comparison with earlier computations using
more primitive basis sets (e.g., 3-21G with no polarized
contributions). In both instances, the ∆-Density values
varied only minimally.
F igu r e 1. Delta-density values for rod compounds. Where
bonds have no values indicated, these are vanishing. “/” gives
σ- and π-values in that order. ∆D matrix values are expanded
by 10000.
which are close to coplanar with the p-orbitals of the
π-systems. Hence, we find delocalization of excitation,
albeit small, throughout the system.12 Appreciable exci-
tation distribution is seen in all of the different rod
compoundssnamely the [1]-rods, [2]-rods, and [3]-rods.
Thus, the much smaller diminution of lifetime of the
naphthyl group in the [3]-rods of the present study cannot
be attributed solely to diminished delocalization. The
remaining factor is the dependence of transition dipole
(i.e., Fo¨rster coupling) on distance between the chro-
mophores. In the case of the [1]-rod previously studied4
the very rapid singlet energy transfer was shown to be
too fast to result purely from transition dipole coupling
(vide infra). We concluded that both through-bond and
through-space electronic transmission occurs with through-
bond being dominant at short distances and through-
space at long distances.4a
a
kET(1) )
+ be-âR(1) ) A1 + B1
+ be-âR(2) ) A2 + B2
+ be-âR(3) ) A3 + B3
(2)
(3)
(4)
R(1)6
a
k
k
ET(2) )
ET(3) )
R(2)6
What these computations revealed (Figure 1) is that
excitation is not localized in the terminal chromophores
of the 1,n-disubstituted rods nor in the central aromatic
ring of the simple [3]-rod 19. Small but real ∆-Density
Matrix elements are found in the bicyclooctyl spacer
units. The larger sigma contributions come from bonds
a
R(3)6
Equations 2, 3, and 4 give the total rate of energy
transfer for each of the rods - [1]-rod, [2]-rod or [3]-rod,
respectively. These are given as having two components,
the Fo¨rster through-space portion with an inverse sixth
power dependence on chromophore distance, R, and the
through-bond component, having a negative exponential
(11) (a) Foster, J . P.; Weinhold, F. J . Am. Chem. Soc. 1980, 102,
7211-7218. (b) Reed, A.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988,
88, 899-926.

Rodlike Molecules and Singlet Energy Transfer
J . Org. Chem., Vol. 65, No. 23, 2000 7743
Ta ble 3. Deca y a n d En er gy Tr a n sfer Ra tes for Th r ee
Ben zoyl Rod s
through-bond transfer being dominant in short rods while
the Fo¨rster transfer becomes dominant for long rods.
With both mechanisms being operative, there is no
controversy remaining.
through-
space
through-
bond
distance,
Å
compd
kET, s-1
(A) kET, s-1 (B) kET, s-1
A:Bb
[1]-roda 3.98 × 109 7.78 × 108 3.20 × 109
7.14
11.23
15.70
20:80
50:50
93:7
Exp er im en ta l Section
[2]-roda 1.03 × 108 5.14 × 107 5.16 × 107
[3]-rod 7.4 × 106
6.9 × 106
5.2 × 105
1,4-Dioxa sp ir o[4.5]d eca n -8-on e (20). (a) Utilization of the
method of Crombie et al.18a gave 20 as a white solid after
recrystallization from hexane (yield 26%), mp 72-73 °C (lit.18a
mp 72.5-73.5 °C).
a
From ref 4. b Ratio of through-space to through-bond contribu-
tions as given in eqs 2, 3, and 4. c Values for a, b, and â are 1.03
× 1014, 4.36 × 1012, and 1.01 Å-1, respectively.
(b) The method of Salau¨n et al.18b was employed to give 20
as a white solid after recrystallization from hexane, mp 72-
73 °C (lit.18b 73 °C). From 7.36 g (36.8 mmol) of cyclohexane-
1,4-dione bisethylene ketal, 3.27 g of anhydrous FeCl3, 41 g of
SiO2, and 10 mL of 41% aqueous formaldehyde solution mixed
for 1 h, ether extracted, and chromatographed with silica gel
was obtained 4.94 g (86%) of 20: 1H NMR (300 MHz, CDCl3)
δ 4.04 (s, 4H), 2.52 (t, 4H, J ) 7.2 Hz), 2.02 (t, 4H, J ) 7.2
Hz).
1-Iodo-4-(r-n aph th yl)bicyclo[2.2.2]octan e (1) an d 1-Iodo-
4-(â-n a p h th yl)bicyclo[2.2.2]octa n e (21). A mixture of 8.87
g (35.2 mmol) of 4-iodobicyclo[2.2.2]octan-1-ol4 22, 21.3 g (166.2
mmol) of naphthalene, and 8.8 mL of CH3SO3H was stirred
at 110 °C for 3 h. After the mixture was cooled, water was
added and the aqueous phase was neutralized with solid
sodium bicarbonate and ether extracted. The combined organic
materials were water washed, dried, and concentrated in
vacuo. The majority of the naphthalene was removed by
sublimation. The remaining mixture was chromatographed on
a silica gel column with hexane to give 9.69 g (76%) of a
mixture of the isomers 1 and 21 in ratio 1.5:1.0. The crystal-
lization from hexane formed two different kinds of crystals:
the R-isomer 1 gave colorless prisms while the â-isomer 21
formed colorless needles. Two of these cycles afforded 5.0 g
(39%) of pure 1-iodo-4-(R-naphthyl)bicyclo[2.2.2]octane 1, mp
164 °C (lit.4 164-165.5 °C); 1H NMR (300 MHz, CDCl3) δ 8.38
(dm, 1H, J ) 8.4 Hz),7.86 (dd, 1H, J 1 ) 7.8, J 2 ) 1.8 Hz), 7.70
(dm, 1H, J ) 7.8 Hz), 7.46 (m, 2H), 7.41 (t, 1H, J ) 7.8 Hz),
7.28 (dd, 1H, J 1 ) 7.2, J 2 ) 1.2 Hz), 2.71 (m, 6H), 2.35 (m,
6H); and 3.3 g (26%) of pure 1-iodo-4-(â-naphthyl)bicyclo-
[2.2.2]octane 24, mp 167-168 °C (lit.4 168.5-169 °C); 1H NMR
(300 MHz, CDCl3) δ 7.77 (m, 3H), 7.60 (s, 1H), 7.42 (m, 3H),
2.64 (m, 6H), 2.08 (m, 6H).
4-H y d r o x y -4-(4-(r-n a p h t h y l)b ic y c lo [2.2.2]o c t y l)-
cycloh exa n -1-on e 1,2-eth a n ed iyl Keta l (2). (a) A 0.62 mL
(1.054 mmol) portion of 1.7 M solution of tert-butyllithium in
pentane was added with a syringe to a stirred suspension of
0.2 g (0.552 mmol) of 1-iodo-4-(R-naphthyl)bicyclo[2.2.2]octane
1 in 9.3 mL of ether at -70 °C. After the pale yellow solution
was stirred for 45 min, a solution of 0.083 g (0.53 mmol) of
cyclohexane-1,4-dione 1,2-ethanediyl ketal 20 in 2.4 mL of
ether was added with a syringe. The yellow color immediately
disappeared, and the mixture was allowed to warm to -50 °C
for 30 min, kept at this temperature for 1.5 h, and left at room-
temperature overnight. A 10 mL portion of saturated aqueous
ammonium chloride was added, and the aqueous layer was
ether extracted (3 portions of 10 mL) and combined with the
ether layer. The precipitate formed was filtered off, connected
with the combined organic phase, and chromatographed on a
silica gel 5 × 30 cm column eluted subsequently with hexane,
F igu r e 2. Plot of through-space (A) and through-bond (B)
contributions versus number of rod units.
dependence. With three equations of this form and three
unknownssa, b, and âsat most two solutions are pos-
sible;13 note Supporting Information. In this case of the
two solutions, only one was physically real. The solution
obtained is given in Table 3. Here A gives the weighting
of the inverse sixth power Fo¨rster contribution while B
gives the negative exponential through-bond Dexter
transmission.14 The details of the computations are given
in the Supporting Information. Interestingly, a plot of
the through-space and through-bond contributions, A and
B, against number of rod units is linear; note Figure 2.
Furthermore, we see that for the short rod, through-bond
energy transmission dominates while for the longer rod
through-space is the major contributor. For the [2]-rod,
both factors seem to contribute equally.15
Con clu sion
The energy transfer studies begun nearly three decades
ago have been fruitful and have stimulated studies with
many different types of systems. The present study
reveals that both Fo¨rster (through-space) and Dexter
exchange (through-bond) transfer participate with the
(12) The ∆D values are meaningful to five significant figures as the
density matrix elements arise from multiplication of two four digit
numbers. It needs to be recognized that the ∆-density elements derive
from products of two MO coefficients, each with an absolute value less
than zero. Thus these elements rapidly decrease as the effect of
excitation on the wave function decreases. Our contention is that such
small elements account for leakage from chromophore to chromophore.
(13) The basis of this conclusion comes from Dr. Olga Holtz of the
Mathematics Department, University of Wisconsin, to whom we are
indebted.
(16) (a) Closs, G. L., Piotrowiak, P.; MacInnis, J . M.; Fleming, G. R.
J . Am. Chem. Soc. 1988, 110, 2652-2653. (b) Oevering, H.; Verhoeven,
J . W.; Paddon-Row, M. N.; Cotsaris, E. Chem. Phys. Lett. 1988, 143,
488-495. (c) Schlicke, B.; Belser, P.; De Cola, L.; Sabbioni, E.; Balzani,
V. J . Am. Chem. Soc. 1999, 121, 4207-4214. (d) Kroon, J .; Oliver, A.
M.; Paddon-Row, M. N.; Verhoeven, J . W. J . Am. Chem. Soc. 1990,
112, 4868-4873. (e) The studies in refs 16a,c deal with triplet energy
transfer while those in refs 16b,d involve singlet energy transfer.
(17) (a) It needs to be noted that the idea that delocalization involves
both σ- and π-systems derives heavily from the pioneering observations
of Hoffmann;17b (b) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397-1412.
(18) (a) Crombie, W. M. L.; J amieson, S. V.; Tuchinda, P.; Whitaker,
A. J . J . Chem. Soc., Perkin Trans. 1982, 1485-1496. (b) Fadel, A.;
Yefsah, R.; Salau¨n, J . Synthesis 1987, 37-40.
(14) (a) Note, the work of Dexter14b involved triplet energy transfer
by an electron exchange mechanism while the singlet counterpart has
been treated theoretically with parallel theory by the present author.4
We also note that despite different terminology, “through-bond mech-
anisms” correspond to the “exchange processes”. (b) Dexter, D. L. J .
Chem. Phys. 1953, 21, 836-850.
(15) The linearity of each contribution with number of spacer units
is of real interest. Some precedence is seen in the work of Closs16a who
used number of coplanar sigma bonds to correlate with through-bond
interaction. Further authors16b-d have used the same approach with
respect to through-bond interactions.17

7744 J . Org. Chem., Vol. 65, No. 23, 2000
Zimmerman et al.
ether, and chloroform. The first fraction contained 0.063 g
(48%) of 1-(R-naphthyl)bicyclo[2.2.2]octane 26. The spectral
data of 26 were the following: 1H NMR (CDCl3, 250 MHz) δ
8.45 (m, 1H), 7.90-7.50 (m, 2H), 7.50-7.20 (m, 4H), 2.00-
2.02 (m, 6H), 2.90-1.60 (m, 7H). The second fraction after
evaporation of the solvent afforded 0.074 g (34%) of 4-hydroxy-
4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)cyclohexan-1-one 1,2-eth-
anediyl ketal 2. Crystallization from 50% benzene in hexane
gave colorless crystals, mp 245-246 °C. The spectral data were
the following: 1H NMR (CDCl3, 250 MHz) δ 8.45 (m, 1H), 7.85
(m, 1H), 7.70 (m, 1H), 7.60-7.30 (m, 4H), 3.95 (s, 4H), 2.20
(m, 6H), 2.05-1.50 (m, 14H), 1.05 (s, 1H); MS m/e 392.2362
(calcd for C26H32O3, 392.2351). Anal. Calcd for C26H32O3: C,
79.56; H, 8.22. Found: C, 80.11; H, 8.38.
(b) To a mixture of 4.2 mL (7 mmol) of 1.7 M solution of
tert-butyllithium in pentane and 14 mL of ether stirred at -70
°C was added a solution of 1.22 g (3.37 mmol) of 1-iodo-4-(R-
naphthyl)bicyclo[2.2.2]octane 1 in 50 mL of ether (benzo-
phenone ketyl dried) dropwise with a syringe. After the
resulting pale yellow solution was stirred for 30 min, a solution
of 0.6 g (3.8 mmol) of cyclohexane-1,4-dione 1,2-ethanediyl
ketal 20 in 15 mL of ether was added dropwise with a syringe.
The mixture was allowed to warm to -50 °C for 30 min, kept
at this temperature for 1 h, and then left at room-temperature
overnight. A 10 mL portion of saturated aqueous ammonium
chloride was added, and the aqueous layer was ether extracted
(3 portions of 10 mL) and combined with the organic layer.
The precipitate formed was filtered off, connected with the
combined organic phase, and chromatographed on a silica gel
5 × 60 cm column eluted subsequently with hexane, ether,
and chloroform. The first fraction contained 0.288 g (36%) of
1-(R-naphthyl)bicyclo[2.2.2]octane 26. The second fraction after
evaporation of the solvent afforded 0.814 g (62%) of 4-hydroxy-
4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)cyclohexan-1-one 1,2-eth-
anediyl ketal 2. The compounds obtained were identical those,
described by method a.
(m, 1H), 7.40-7.20 (m, 4H), 5.15 (m, 1H), 2.65 (m, 2H), 2.2-
1.9 (m, 10H), 1.5-1.35 (m, 6H); MS m/e 330.1976 (calcd for
C24H26O, 330.1984). Anal. Calcd for C24H26O: C, 87.23; H, 7.93.
Found: C, 87.46; H, 8.08. Crystallization of 4-(4-(R-naphthyl)-
bicyclo[2.2.2]octyl)cyclohex-2-enone 4 from hexane gave color-
less crystals, mp 138-140 °C. The spectral data were the
following: 1H NMR (CDCl3, 250 MHz) δ 8.43 (m, 1H), 7.87
(m, 1H), 7.71 (m, 1H), 7.50-7.35 (m, 4H), 7.12 (dt, 1H, J 1
)
10.5, J 2 ) 1.9 Hz), 6.07 (dd, 1H, J 1 ) 10.5, J 2 ) 2.9 Hz), 2.57
(dt, 1H), 2.37 (ddd, 1H, J 1 ) 16.5, J 2 ) 14.2, J 3 ) 5.0 Hz), 2.23
(m, 6H, J ) 7.7 Hz), 2.12 (m, 1H), 1.72 (m, 8H); MS m/e
330.1995 (calcd for
C24H26O, 330.1984). Anal. Calcd for
C
24H26O: C, 87.23; H, 7.93. Found: C, 86.98; H, 8.33.
4-Iod o-1-m eth oxybicyclo[2.2.2]octa n e (5). The method
of Zimmerman et al.4 was employed to give 5 as a white solid,
mp 78-79 °C (lit.4 mp 77.4-79.4 °C); 1H NMR (300 MHz,
CDCl3) δ 3.14 (s, 3H), 2.54(m, 6H), 1.76 (m, 6H).
(4-Meth oxybicyclo[2.2.2]octyl)p h en ylca r bin ol (6). To a
stirred suspension of 0.207 g (0.77 mmol) of 1-iodo-4-meth-
oxybicyclo[2.2.2]octane (5) in 5 mL of ether at -70 °C was
added 0.90 mL (1.55 mmol) of 1.7 M pentane solution of tert-
butyllithium with a syringe. The solution was stirred at -70
°C for 45 min, and 0.79 mL (0.824 g, 7.77 mmol) of benzalde-
hyde (freshly distilled from calcium hydride) was added with
a syringe. The mixture was allowed to warm to room temper-
ature for 30 mi and then was poured into 5.0 mL of saturated
aqueous ammonium chloride. The aqueous layer was extracted
with chloroform (3 × 10 mL). The combined organic phase was
water washed, dried with sodium sulfate, and concentrated
in vacuo to give an oil, which was chromatographed on a silica
gel 5 × 30 cm column and eluted subsequently with hexane
and 25% ether in hexane. The obtained material (119 mg) was
crystallized from hexane to give 0.060 g of (4-methoxybicyclo-
[2.2.2]octyl)phenylcarbinol 6, mp 114-115 °C. The mother
solution was chromatographed under the same conditions to
give additional 0.030 g of the alcohol 6. The total yield of (4-
methoxybicyclo[2.2.2]octyl)phenylcarbinol 6 was 0.090 g (47%).
The spectral data for 6 were the following: 1H NMR (CDCl3,
250 MHz) δ 7.4-7.1 (m, 5H), 4.35 (s, 1H), 3.15 (s, 3H), 1.9-
1.4 (m, 13H); MS m/e 246.1618 (calcd for C16H22O2, 246.1620).
Anal. Calcd for C16H22O2: C, 78.00; H, 9.01. Found: C, 78.12;
H, 9.18.
4-Ben zoyl-1-m eth oxybicyclo[2.2.2]octa n e (8). (a) To a
stirred suspension of 0.138 g (0.50 mmol) of 4-iodo-1-meth-
oxybicyclo[2.2.2]octane (5) in 5.0 mL of ether at -70 °C was
added 0.6 mL (1.00 mmol) of 1.7 M pentane solution of tert-
butyllithium with a syringe. The mixture was stirred at -70
°C for 45 min, and 0.062 mL (0.50 mmol) of methylbenzoate
(freshly distilled from calcium hydride) was added. The tem-
perature rose to -50 °C, and the mixture was stirred at this
temperature for 3 h, allowed to warm to room temperature,
and stirred overnight. Then 10 mL of saturated aqueous
ammonium chloride was added, and the aqueous layer was
extracted with chloroform (3 × 5 mL). The combined organic
phase was water washed, dried with sodium sulfate, and
concentrated in vacuo to give an oily mixture, which was
chromatographed on a 5 × 30 cm silica gel column eluted
subsequently with hexane and 20% ether in hexane. Fraction
2 afforded 0.072 g (59%) of 4-benzoyl-1-methoxybicyclo-
[2.2.2]octane 8 as a colorless oil, identical that described below.
(b) A mixture of 0.0235 g (0.1 mmol) of (4-methoxybicyclo-
[2.2.2]octyl)phenylcarbinol 6, 0.0175 g (0.1 mmol) of potassium
chlorochromate, and 3.0 mL of acetic acid was heated on a
steam bath until it became green (approximately 5 min). It
was then poured into 20 mL of water, neutralized with solid
sodium bicarbonate until no foaming was observed, and
extracted with chloroform (3 × 10 mL). The chloroform layer
after drying with sodium sulfate was concentrated in vacuo
to give 0.019 g (82%) of 4-benzoyl-1-methoxybicyclo[2.2.2]-
octane 8 as a colorless oil.
4-H y d r o x y -4-(4-(r-n a p h t h y l)b ic y c lo [2.2.2]o c t y l)-
cycloh exa n -1-on e (3). A suspension of 0.344 g (0.875 mmol)
of 4-hydroxy-4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)cyclohexan-
1-one 1,2-ethanediyl ketal 2 in 10 mL of ether was stirred with
10 mL of 50% aqueous sulfuric acid for 2 h and neutralized
with solid sodium bicarbonate until no foaming was observed,
and the ether was removed by evaporation. The precipitate
formed was filtered off, water washed, and dried on air. It gave
0.306 g (100%) of 4-hydroxy-4-(4-(R-naphthyl)bicyclo[2.2.2]-
octyl)cyclohexan-1-one 3, which was crystallized from benzene
as colorless crystals, mp 223-225 °C. The spectral data were
the following: 1H NMR (CDCl3, 250 MHz) δ 8.42 (m, 1H), 7.87
(m, 1H), 7.71 (m, 1H), 7.51-7.35 (m, 4H), 2.78 (dt, 2H), 2.35-
2.15 (m, 8H), 2.15-1.70 (m, 10H), 1.35 (s, 1H); MS m/e
348.2089 (calcd for
24H28O2: C, 82.72; H, 8.10. Found: C, 82.65; H, 8.19.
4-(4-(r-N a p h t h y l)b i c y c lo [2.2.2]o c t y l)c y c lo h e x -2-
C24H28O2, 348.2089). Anal. Calcd for
C
en on e (4) a n d 4-(4-(r-Na p h th yl)bicyclo[2.2.2]octyl)cyclo-
h ex-3-en on e (23). A 0.048 g (0.14 mmol) portion of 4-hydroxy-
4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)cyclohexan-1-one 3 was
stirred with 2.0 g (20 mmol) of 85% phosphoric acid for 5.5 h
at 75 °C. The mixture was treated with 1 mL of water,
neutralized with saturated aqueous sodium hydrocarbonate
until no foaming was observed, and ether extracted (3 × 10
mL). The organic phase was dried with sodium sulfate. The
solvent was evaporated, and the residue was chromatographed
on a silica gel 5 × 30 cm column eluted subsequently with
hexane, 20% ether in hexane, 50% ether in hexane, and pure
ether. Fraction 1 gave 0.0079 g (17%) of 4-(4-(R-naphthyl)-
bicyclo[2.2.2]octyl)cyclohex-3-enone 23. Fraction 2 gave 0.024
g (52%) of 4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)cyclohex-2-enone
4. Fraction 3 contained 0.0077 g (16%) of the starting alcohol
3, identical to the authentic sample. Crystallization of 4-(4-
(R-naphthyl)bicyclo[2.2.2]octyl)cyclohex-3-enone 23 from 20%
ether in hexane gave colorless crystals, mp 157 °C. The
spectral data were the following: 1H NMR (CDCl3, 300 MHz)
δ 8.45(m, 1H), 7.90 (m, 1H), 7.70 (m, 1H), 7.50-7.30 (m, 4H),
5.50 (m, 1H), 2.90 (m, 2H), 2.6-2.0 (m, 10H), 1.9-1.6 (m, 6H);
1H NMR (C6D6, 250 MHz) δ 8.50(m, 1H), 7.75 (m, 1H), 7.60
(c) To a stirred suspension of 0.927 g (3.48 mmol) of 4-iodo-
1-methoxybicyclo[2.2.2]octane 5 in 40 mL of ether at -78 °C
was added 4.1 mL (6.96 mmol) of 1.7 M tert-butyllithium in
pentane. The resulting yellow mixture was stirred for 45 min,
and then 1.09 mL (1.323 g, 9.40 mmol) of freshly distilled

Rodlike Molecules and Singlet Energy Transfer
J . Org. Chem., Vol. 65, No. 23, 2000 7745
benzoyl chloride was added which discharged the color. The
cooling bath was removed, and after 4 h of further stirring
the mixture was quenched with saturated solution of am-
monium chloride. The aqueous phase was ether extracted, and
the combined organic materials were water washed and dried.
Removal of solvent in vacuo gave an oil, which was chromato-
graphed on a silica gel column (elution with hexanes-ether,
3:1) to give 0.527 g (62%) of 4-benzoyl-1-methoxybicyclo-
MHz, CDCl3) δ 3.19 (s, 3H), 2.09 (s, 3H), 1.84 (m, 6H), 1.68
(m, 6H); IR (neat) 1689 cm-1; MS m/e 182.1300 (calcd for
C11H18O2, 182.1307).
4-Acetyl-1-iod obicyclo[2.2.2]octa n e (11). A 210 mg (1.15
mmol) amount of 4-acetyl-1-methoxybicyclo[2.2.2]octane 9 was
treated with 20 mL of 57% HI. The mixture was heated, and
methyl iodide and water were distilled out. The distillation
head was replaced with a condenser, and reflux was continued
overnight. The mixture was poured onto ice, chloroform
extracted, neutralized with dry sodium bicarbonate, and
extracted further. The extracts were washed with aqueous
saturated sodium bicarbonate, sodium thiosulfate, and water,
dried over calcium chloride, and concentrated in vacuo to give
263 mg of white solid. It was chromatographed on a silica gel
column (hexanes-ether, 5:1) to yield 208 mg (65%) of pure
4-acetyl-1-iodobicyclo[2.2.2]octane 11 as a white solid, Rf 0.21;
mp 80-81 °C; 1H NMR (300 MHz, CDCl3) δ 2.46 (m,6H), 2.06
(s, 3H), 1.84 (m, 6H); IR (film) 1699 cm-1; MS m/e 278.0166
(calcd for C10H15IO, 278.0164). Anal. Calcd for C10H15IO: C,
43.18; H, 5.44. Found: C, 43.06; H, 5.37.
1
[2.2.2]octane 8 as a colorless oil, Rf 0.1; H NMR (300 MHz,
CDCl3) δ 7.61 (m, 2H), 7.39 (m, 3H), 3.20 (s, 3H), 2.07 (m, 6H),
1.74 (m, 6H); IR (neat) 1653 cm-1; MS m/e 244.1465 (calcd for
C16H20O2, 244.1463).
4-Ben zoyl-1-iod obicyclo[2.2.2]octa n e (10). A 400 mg
(1.64 mmol) amount of 4-benzoyl-1-methoxybicyclo[2.2.2]octane
8 was treated with 45 mL of 57% HI. The mixture was heated,
and methyl iodide and water were distilled out. The distillation
head was replaced with a condenser, and reflux was continued
overnight. The mixture was poured onto ice, ether extracted,
neutralized with solid sodium bicarbonate, and extracted
further. The extracts were washed with aqueous saturated
sodium bicarbonate, sodium thiosulfate, and water, dried over
calcium chloride, and concentrated to give 459 mg of white
solid. It was chromatographed on silica gel (elution with
hexanes-ether, 9:1) to yield 395 mg (71%) of 4-benzoyl-1-
iodobicyclo[2.2.2]octane 10 as a white solid, Rf 0.28; mp 82-
84 °C; 1H NMR (300 MHz, CDCl3) δ 7.60 (m, 2H), 7.43 (m,
3H), 3.19 (s, 3H), 2.07 (m, 6H), 1.74 (m, 6H); IR (film) 1662
cm-1; MS m/e 340.2089 (calcd for C15H17IO, 340.0320). Anal.
Calcd for C15H17IO: C, 52.96; H, 5.04. Found: C, 53.21; H,
4.96.
4-Acetyl-1-iodobicyclo[2.2.2]octan e 1,2-Eth an ediyl Ket-
a l (13). The mixture of 170 mg (0.6 mmol) of 4-acetyl-1-
iodobicyclo[2.2.2]octane 11, 401 µL (446 mg, 7.2 mmol) of
ethylene glycol, and 4 mg of p-toluenesulfonic acid in 12 mL
of benzene was refluxed with a Dean-Stark adapter for 4 h.
The mixture was washed with saturated solution of sodium
bicarbonate, dried, and evaporated to give 193 mg (quantita-
tive yield) of ketal 13 as a white solid, pure by NMR, mp 117-
1
118 °C; H NMR (300 MHz, CDCl3) δ 3.92 (m, 2H), 3.84 (m,
2H), 2.44 (m, 6H), 1.72 (m, 6H), 1.13 (s, 3H); MS m/e 322.0432
(calcd for C12H19IO2, 322.0426). Anal. Calcd for C12H19IO2: C,
44.74; H, 5.94. Found: C, 44.51; H, 5.97.
4-Ben zoyl-1-iod ob icyclo[2.2.2]oct a n e 1,2-E t h a n ed iyl
Keta l (12). A solution of 320 mg (0.94 mmol) of 4-benzoyl-1-
iodobicyclo[2.2.2]octane 10, 524 µL (583.5 mg, 9.4 mmol) of
ethylene glycol, and 10 mg of p-toluenesulfonic acid in 10 mL
of benzene was refluxed with a Dean-Stark adapter for 4.5
h. The mixture was washed with saturated solution of sodium
bicarbonate, dried, and evaporated to give 332 mg (92%) of 12
as a white solid, pure by NMR. Purification by column
chromatography (silica gel, hexanes-ether, 14:1) and recrys-
tallization from hexane gave an analytical sample of 4-benzoyl-
1-iodobicyclo[2.2.2]octane 1,2-ethanediyl ketal 12: Rf 0.32; mp
1-(4-Be n zoylb icyclo[2.2.2]oct yl)-4-(4-(r-n a p h t h yl)-
bicyclo[2.2.2]octyl)ben zen e 1,2-eth a n ed iyl Keta l (15). To
a stirred suspension of 0.192 g (0.5 mmol) of 1-benzoyl-4-
iodobicyclo[2.2.2]octane 1,2-ethanediyl ketal 12 in 10 mL of
absol ether, cooled to -70 °C under nitrogen, a 0.47 mL (0.8
mmol) portion of 1.7 M solution of tert-butyllithium in pentane
was added dropwise. The resulting slightly yellow solution was
allowed to warm to -50 °C and stirred at this temperature
for 30 min. Then a solution of 0.111 g (0.34 mmol) of 4-(4-(R-
naphthyl)bicyclo[2.2.2]octyl)cyclohex-2-enone 4 in 25 mL of
absol ether was added dropwise with a syringe. The mixture
was stirred at -60 to -70 °C for 2 h, allowed to warm to room
temperature, and stirred overnight, followed by quenching
with 5 mL of aqueous saturated ammonium chloride, extract-
ing with chloroform (3 × 5 mL), drying with sodium sulfate,
and concentrating in vacuo. The residue was chromatographed
on a 3 × 30 cm silica gel column and eluted subsequently with
hexane, 10% ether in hexane, 20% ether in hexane, 50% ether
in hexane, and pure ether. Fraction 2 (the richest of the desired
material) was concentrated in vacuo to give 90 mg of a white
solid. A 10 mg portion of this material was refluxed with 20
mg (0.088 mmol) of 2,3-dicyano-5,6-dichloro-1,4-benzoquinone
in 2.0 mL of benzene for 1.25 h, cooled to room temperature,
and chromatographed on a 3 × 30 cm silica gel column, eluted
subsequently with hexane, 50% ether in hexane, and pure
ether. It gave 7.0 mg (0.012 mmol) of 1-(4-benzoylbicyclo[2.2.2]-
octyl)-4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)benzene 1,2-ethanediyl
ketal 15 as a white solid. The yield of 15 counting on initial
enone 4 was 32%, mp 301-303 °C. The spectral data were the
following: 1H NMR (CDCl3, 250 MHz) δ 1.9-1.7 (m, 12H), 2.00
(m, 6H), 2.30 (m, 6H), 3.65 (m, 2H), 3.95 (m, 2H), 7.5-7.2 (m,
13H), 7.70 (m, 1H), 7.85 (m, 1H), 8.50 (m, 1H).
1
200-202 °C; H NMR (300 MHz, CDCl3) δ 7.31 (m, 5H), 3.89
(m, 2H), 3.63 (m, 2H), 2.38 (m, 6H), 1.74 (m, 6H); IR (film)
1068 cm-1; MS m/e (M+ - I) 257.1529 (calcd for C17H21O2,
257.1542). Anal. Calcd for C17H21IO2: C, 53.14; H, 5.51.
Found: C, 53.49; H, 5.58.
4-(1-Hyd r oxyeth yl)-1-m eth oxybicyclo[2.2.2]octa n e (7).
To a stirred suspension of 2.007 g (7.54 mmol) of 4-iodo-1-
methoxybicyclo[2.2.2]octane 5 in 50 mL of ether at -78 °C 8.87
mL (15.08 mmol) of 1.7 M tert-butyllithium in pentane was
added. After 45 min, 4.2 mL (75.4 mmol) of acetaldehyde
(freshly distilled from calcium hydride) was added. Over 1 h
the mixture was allowed to warm to room temperature,
saturated aqueous ammonium chloride was added, and the
aqueous layer was extracted with chloroform. The organic
layers were water washed, dried, and concentrated in vacuo
to give 2.01 g of yellowish oil. The oil was chromatographed
on a silica gel column. Elution with hexanes-ether, 1:1 gave
1.13 g (89%) of 4-(1-hydroxyethyl)-1-methoxybicyclo[2.2.2]-
octane 7 as a colorless oil, Rf 0.24; 1H NMR (300 MHz, CDCl3)
δ 3.43 (q, 1H, J ) 6.6 Hz), 3.18 (s, 3H), 1.63 (m, 12H), 1.25
(m, 1H), 1.07 (d, 3H, J ) 6.6 Hz); IR (neat) 3446 cm-1; MS m/e
184.1450 (calcd for C11H20O2, 184.1463).
4-Acetyl-1-m eth oxybicyclo[2.2.2]octa n e (9). To the com-
plex formed from 8.29 mL (105.7 mmol) of pyridine and 5.18
g (51.8 mmol) of CrO3 in 145 mL of methylene chloride was
added 1.25 g (6.78 mmol) of 4-(1-hydroxyethyl)-1-methoxybi-
cyclo[2.2.2]octane 7 in 50 mL of methylene chloride. A black
precipitate formed immediately. After 20 min, solvent was
removed, and the remaining solid was washed alternately with
ether and 5% solution of sodium hydroxide. The organic layer
was washed with 5% hydrochloric acid and saturated solution
of sodium bicarbonate. Then it was dried and concentrated in
vacuo to give the quantitative yield (1.23 g) of 4-acetyl-1-
methoxybicyclo[2.2.2]octane 9 as colorless oil, 1H NMR (300
1-(4-Be n zoylb icyclo[2.2.2]oct yl)-4-(4-(R-n a p h t h yl)-
bicyclo[2.2.2]octyl)ben zen e (14). A 7.0 mg (0.012 mmol)
portion of 1-(4-benzoylbicyclo[2.2.2]octyl)-4-(4-(R-naphthyl)-
bicyclo[2.2.2]octyl)benzene 1,2-ethanediyl ketal 15 was heated
with stirring at 100 °C under nitrogen with 1.0 mL of acetic
acid and 0.20 mL of concentrated HCl for 30 min. The mixture
was then diluted with 5 mL of water, extracted with ethyl
acetate (3 × 2 mL), washed with water (2 × 3 mL) and then
with aqueous saturated sodium hydrocarbonate (2 × 3 mL),
dried over sodium sulfate, and evaporated. The residue was
chromatographed on a silica gel column, eluted subsequently

7746 J . Org. Chem., Vol. 65, No. 23, 2000
Zimmerman et al.
with 4:1 hexanes-ether, ether, chloroform. It gave 6 mg of a
solid, which was washed with ether (3 × 0.5 mL) and dried.
This procedure afforded 5 mg (83%) of 1-(4-benzoylbicyclo-
[2.2.2]octyl)-4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)benzene 14, mp
Sin gle P h oton Cou n tin g P r oced u r e. The single photon
counting equipment is that largely described.4a,8 Nitrogen lamp
pressure of 70 psi and 6 kV gave a pulse width of 3 ns.
Wavelengths: excitation 270 nm, emission 320 nm. Details of
the instrumental settings are given in the Supporting Infor-
mation.
1
301-303 °C. H NMR (300 MHz, CD2Cl2) δ 8.44 (d, 1H, J )
8.4 Hz), 7.79 (d, 1H, J ) 7.2 Hz), 7.63 (d, 1H, J ) 7.2 Hz),
7.55 (d, 2H, J ) 6.9 Hz), 7.44-7.25 (m, 7H), 7.24 (s, 4H), 2.24
(m, 6H), 1.98 (m, 12H), 1.83 (m, 6H); IR (film) 1676 cm-1; MS
m/e 524.3094 (calcd for C39H40O, 524.3079).
Com p u ta tion a l Meth od ology. Computations were run
using Gaussian98.19 Initially the ground-state geometry was
optimized using RHF/3-21G. This was followed by CASSCF
single point computations. The CASSCF active space (n,n) was
adjusted to parallel the rod molecule being studied. The first
singlet excited state was run using ground-state geometry. S0
and S1 computations produced density matrixes. The DelDen
program20 was used to subtract the ground-state density
matrix from the corresponding first excited-state one and to
print out the matrix elements.
1-(4-Acetylbicyclo[2.2.2]octyl)-4-(4-(r-n aph th yl)bicyclo-
[2.2.2]octyl)ben zen e (16). To a stirred mixture of 0.18 mL
(0.30 mmol) of 1.7 M pentane solution of tert-butyllithium and
3 mL of ether at -70 °C was added a solution of 0.115 g (0.36
mmol) of 4-acetyl-1-iodobicyclo[2.2.2]octane 1,2-ethanediyl
ketal 13 in 5 mL of ether dropwise with a syringe. The mixture
was stirred for 45 min at -70 °C, and 5 mL of ether solution
of 0.081 g (0.24 mmol) of 4-(4-(R-naphthyl)bicyclo[2.2.2]octyl)-
cyclohex-2-enone (4) was added with a syringe. The resulting
solution was kept at -70 °C for 1 h, allowed to warm to room
temperature for 1 h, poured into 5 mL of aqueous saturated
ammonium chloride, extracted with chloroform (3 × 5 mL),
dried over sodium sulfate, and concentrated in vacuo. The
residue was chromatographed on a 3 × 30 cm silica gel column,
eluted subsequently with hexane, 10% ether in hexane, 20%
ether in hexane, 50% ether in hexane, and pure ether. Fraction
1 contained 0.039 g (34%) of starting compound 13. Fraction
2 contained 0.014 g (18%) of starting enone 4. Fraction 4 gave
0.045 g of a white solid; a portion of 0.033 g of this solid was
stirred with 1 mL of 50% sulfuric acid and 3 mL of ether for
4 h, sodium hydrocarbonate neutralized, ether extracted, and
dried over sodium sulfate. Concentration of the solution gave
0.016 g of a white solid. A mixture of 0.016 g of this solid, 0.024
g (0.106 mmol) of 2,3-dicyano-5,6-dichloro-1,4-benzoquinone,
and 2.0 mL of benzene was refluxed for 15 min, cooled to room
temperature, and chromatographed on a 3 × 30 cm silica gel
column, eluted with 20% ether in hexane to give 0.012 g of
1-(4-acetylbicyclo[2.2.2]octyl)-4-(4-(R-naphthyl)bicyclo[2.2.2]-
octyl)benzene 16. Totally 0.081 g (0.24 mmol) of 4-(4-(R-
naphthyl)bicyclo[2.2.2]octyl)cyclohex-2-enone 4 gave 0.012 g
(0.026 mmol, 11%) of 16. Crystallization from 20% ether in
hexane gave colorless crystals, mp 288-289 °C; the spectral
data were the following: 1H NMR (CDCl3, 250 MHz) δ 8.50
(m, 1H), 7.9 (m, 1H), 7.7 (m, 1H), 7.5-7.2 (m, 8H), 2.4-2.3
(m, 6H), 2.2-2.0 (m, 9H), 2.0-1.8 (m, 12H); MS m/e 462.2921
(calcd for C34H38O, 462.2923). Anal. Calcd for C34H38O: C,
88.26; H, 8.28. Found: C, 88.24; H, 8.52.
Ack n ow led gm en t. Support of this research by the
National Science Foundation is gratefully acknowledged
with special appreciation for its support of basic re-
search.
Su p p or t in g In for m a t ion Ava ila b le: Includes single
photon counting details, evidence on the adequacy of the basis
set selection; details on the solution of the eqs 2-4, a general
analysis of the number of solutions anticipated from equations
as 2-4, and NMR spectra of key compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O0003145
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