Influence of alkyl substitution on the gas-phase stability of 1-adamantyl cation and on the solvent effects in the solvolysis of 1-bromoadamantane

Article abstract of DOI:10.1021/jo0015265

1-Adamantyl cations having three methyl groups or one, two, or three isopropyl groups on the 3-, 5-, and 7-positions were found by FT ICR to be more stable than the 1-adamantyl cation and that the stability increases with the number of isopropyl group. The relative stabilities calculated by PM3 were in good agreement with the experimental results. In contrast, the sequence of the rates for the solvolysis in nonaqueous solvents are 3,5,7-(Me)₃-1-AdBr < 1-bromoadamantane (1-AdBr) < 3,5,7-(n-Pr)₃-1-AdBr < 3,5,7-(i-Pr)₃-1-AdBr. The rates of solvolysis of 3,5,7-(i-Pr)₃-1-AdBr and 3,5,7-(n-Pr)₃-1-AdBr relative to 1-AdBr at 25 °C are 15 and 3.8 in EtOH, respectively, but markedly decreases with the increase in the amount of added water, reaching 0.84 and 0.15, respectively, in 60% EtOH. Reflecting these effects of water, the Grunwald-Winstein (GW) relationship for 3,5,7-(i-Pr)₃-1-AdBr and 3,5,7-(n-Pr)₃-1-AdBr against Y_Br is linear for nonaqueous alcohols (EtOH, MeOH, TFE-EtOH, TFE, 97% HFIP), but marked downward deviations are observed for aqueous organic solvents, in particular, aqueous ethanol and aqueous acetone. The effect of the alkyl substituents to diminish relative solvolytic reactivity in EtOH-H₂O mixtures may be ascribed to a blend of steric hindrance to Bronsted base-type hydration to the β-hydrogens and hydrophobic interaction of the alkyl groups with ethanol to make the primary solvation shell less ionizing. The introduction of one nonyl group to the 3-position showed much smaller deviations in the GW relationship than the case of 3,5,7-(n-Pr)₃-1-AdBr. The markedly decelerated solvolysis of alkylated 1-bromoadamantanes in aqueous organic solvents is a kinetic version of anomalously diminished dissociation of alkylbenzoic acids in aqueous ethanol and aqueous tert-butyl alcohol that was demonstrated by Wepster and co-workers a decade ago and ascribed to hydrophobic effects.

Full text of DOI:10.1021/jo0015265

2
034
J . Org. Chem. 2001, 66, 2034-2043
In flu en ce of Alk yl Su bstitu tion on th e Ga s-P h a se Sta bility of
-Ad a m a n tyl Ca tion a n d on th e Solven t Effects in th e Solvolysis of
1
1
-Br om oa d a m a n ta n e
Ken’ichi Takeuchi,* Takao Okazaki,* Toshikazu Kitagawa, Takuhiro Ushino, Kenji Ueda, and
Tadasuke Endo
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University,
Sakyo-ku, Kyoto 606-8501, J apan
Rafael Notario
Instituto de Qu ı´ mica Fisica, “Rocasolano”, C. S. I. C. E-28006 Madrid, Spain
okazaki@scl.kyoto-u.ac.jp
Received October 27, 2000
1
5
-Adamantyl cations having three methyl groups or one, two, or three isopropyl groups on the 3-,
-, and 7-positions were found by FT ICR to be more stable than the 1-adamantyl cation and that
the stability increases with the number of isopropyl group. The relative stabilities calculated by
PM3 were in good agreement with the experimental results. In contrast, the sequence of the rates
for the solvolysis in nonaqueous solvents are 3,5,7-(Me)
3,5,7-(n-Pr) -1-AdBr < 3,5,7-(i-Pr) -1-AdBr. The rates of solvolysis of 3,5,7-(i-Pr)
,5,7-(n-Pr) -1-AdBr relative to 1-AdBr at 25 °C are 15 and 3.8 in EtOH, respectively, but markedly
decreases with the increase in the amount of added water, reaching 0.84 and 0.15, respectively, in
0% EtOH. Reflecting these effects of water, the Grunwald-Winstein (GW) relationship for 3,5,7-
i-Pr) -1-AdBr and 3,5,7-(n-Pr) -1-AdBr against YBr is linear for nonaqueous alcohols (EtOH, MeOH,
3
-1-AdBr < 1-bromoadamantane (1-AdBr)
<
3
3
3
3
-1-AdBr and
3
6
(
3
3
TFE-EtOH, TFE, 97% HFIP), but marked downward deviations are observed for aqueous organic
solvents, in particular, aqueous ethanol and aqueous acetone. The effect of the alkyl substituents
to diminish relative solvolytic reactivity in EtOH-H O mixtures may be ascribed to a blend of
2
steric hindrance to Βrφnsted base-type hydration to the â-hydrogens and hydrophobic interaction
of the alkyl groups with ethanol to make the primary solvation shell less ionizing. The introduction
of one nonyl group to the 3-position showed much smaller deviations in the GW relationship than
3
the case of 3,5,7-(n-Pr) -1-AdBr. The markedly decelerated solvolysis of alkylated 1-bromoadaman-
tanes in aqueous organic solvents is a kinetic version of anomalously diminished dissociation of
alkylbenzoic acids in aqueous ethanol and aqueous tert-butyl alcohol that was demonstrated by
Wepster and co-workers a decade ago and ascribed to hydrophobic effects.
In tr od u ction
Substituent effects on the rates of solvolysis of bridge-
head compounds and on the stability of bridgehead
carbocations have been a long-standing subject in physi-
cal organic chemistry. The bridgehead systems that have
substrates. Among various substituents, simple alkyl
groups sometimes show peculiar behavior. Schleyer and
co-workers found that the order of solvolysis rates is Me
1b
<
H ∼ Et < i-Pr < t-Bu for 3-alkyl-1-bromoadamantanes
and Me < Et < i-Pr < t-Bu < H for 4-alkyl-1-bicyclo-
2.2.2]octyl brosylates. Grob and co-workers and Per-
kins et al. carried out similar studies. The variable
behavior of hydrogen has been ascribed to differential
1b
1c
[
1
a-h
been actively studied are 1-adamantyl,
octyl, 1-bicyclo[1.1.1]pentyl,
1-bicyclo[2.2.2]-
1f
1
a,i
2a-d
2e,f
1-bicyclo[2.2.1]heptyl,
and cubyl3 systems. In particular, the 1-adamantyl
system containing a substituent on one of the other three
equivalent bridgehead positions has been subjected to
extensive studies because of the wide availability of
1c
solvation, steric effects of the alkyl groups on molecular
1b,f
1a
geometry,
and possible electron-withdrawing effect
of a methyl substituent. Introduction of three methyl
groups to the 3-, 5-, and 7-positions of 1-bromoadaman-
*
To whom correspondence should be addressed. (T.O.) Tel: +81
5 7535714; Fax: +81 75 7533350; (K.T.) Fax: +81 75 7533350.
1) (a) Fort, R. C., J r.; Schleyer, P. v. R. J . Am. Chem. Soc. 1964,
6, 4194-4195. (b) Schleyer, P. v. R.; Woodworth, C. W. J . Am. Chem.
(2) (a) Grob, C. A.; Yang, C. X.; Della, E. W.; Taylor, D. K.
Tetrahedron Lett. 1991, 32, 5945-5948. (b) Wiberg, K. B.; McMurdie,
N. J . Am. Chem. Soc. 1991, 113, 8995-8996. (c) Adcock, J . L.; Gakh,
A. A. Tetrahedron Lett. 1992, 33, 4875-4878. (d) Adcock, J . L.; Gakh,
A. A. J . Org. Chem. 1992, 57, 6206-6210. (e) Adcock, W.; Clark, C. I.;
Schiesser, C. H. J . Am. Chem. Soc. 1996, 118, 11541-11547. (f) Garc ´ı a
Mart ´ı nez, A.; Os ´ı o Barcina, J .; Rodr ´ı guez Herrero, M. E.; Iglesias de
Dios, M.; Teso Vilar, E.; Subramanian, L. R. Tetrahedron Lett. 1994,
35, 1793-1796.
(3) (a) Moriarty, R. M.; Tuladhar, S. M.; Penmasta, R.; Awasthi, A.
K. J . Am. Chem. Soc. 1990, 112, 3228-3230. (b) Kevill, D. N.; D′Souza,
M. J .; Moriarty, R. M.; Tuladhar, S. M.; Penmasta, R.; Awasthi, A. K.
J . Chem. Soc., Chem. Commun. 1990, 623-624. (c) Eaton, P. E.; Zhou,
J .-P. J . Am. Chem. Soc. 1992, 114, 3118-3120.
7
(
8
Soc. 1968, 90, 6528-6530. (c) Grob, C. A.; Schwarz, W.; Fischer, H. P.
Helv. Chim. Acta 1964, 47, 1385-1401. (d) Fischer, W.; Grob, C. A.
Helv. Chim. Acta 1978, 61, 1588-1608. (e) Grob, C. A.; Schaub, B.
Helv. Chim. Acta 1982, 65, 1720-1727. (f) Perkins, R.; Tibbo, P.; Reid,
K.; Dornan, Chem. Ind. 1981, 571-572. (g) Grob, C. A.; Sawlewicz, P.
Tetrahedron Lett. 1987, 28, 951-952. (h) Grob, C. A.; Gr u¨ ndel, M.;
Sawlewicz, P. Helv. Chim. Acta 1988, 71, 1502-1507. (i) Bielmann,
R.; Grob, C. A.; K u¨ ry, D.; Guo-Wei, Y. Helv. Chim. Acta 1985, 68, 2158-
2
164. (j) Sunko, D. E.; Hir sˇ l-Star cˇ evi c´ , S.; Pollack, S. K.; Hehre, W. J .
J . Am. Chem. Soc. 1979, 101, 6163-6170.
1
0.1021/jo0015265 CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/01/2001

Gas- and Liquid-Phase Stability of 1-Adamantyl Cations
J . Org. Chem., Vol. 66, No. 6, 2001 2035
Ch a r t 1
Sch em e 1a
tane (1Br) decelerates the solvolysis rate by a factor of
1
a,c
3
.
Meanwhile, the three methyl groups in the 3,5,7-
+
trimethyl-1-adamantyl cation (2 ) causes upfield shift of
the bridgehead cationic carbon of 1 by 5.9 ppm, from δ
+
3
00 to 294.1, showing that the methyl substituents
4
actually behave as electron-donating groups. Calcula-
tions (STO-3G) indicate that the methyl group on the
3
-position stabilizes the 1-adamantyl cation by 1.23 kcal
-
1 1j
mol . To our knowledge, the above anomalous effect of
the alkyl substituents on solvolytic reactivity has not
been clarified. We wished first to obtain unambiguous
evidence for the effect of alkyl substituents on the
stability of 1-adamantyl cation by the Fourier Transform
Ion Cyclotron Resonance Spectroscopy (FT ICR) tech-
nique and theoretical calculations.
much different from that of 1-bromoadamantane that is
the standard compound for the YBr scale9 of the GW
relationship.
The second objective was to examine how the size of
the alkyl substituents affect the Grunwald-Winstein
GW) relationship. Recently, one of us (K.T.) reported that
5
(
highly crowded tertiary alkyl chlorides show downward
dispersions of aqueous ethanol data points in the GW
Resu lts
6
relationship. As a possible cause, steric hindrance to the
1. Syn th esis. Among the eight alkylated 1-bromoada-
7
1a,c,f
Brφnsted base-type solvation of water to â-hydrogens
mantanes used in this work, the 3,5,7-trimethyl,
6
a
1b,c
10
was proposed. Meanwhile, two different explanations
were suggested. Bentley’s interpretation was related to
possible mechanistic change to one-step olefin forming
reaction.8 Actually, the major product was a mixture of
olefins (without skeletal rearrangement). The other com-
ment by Kevill included possible reduced ion pair return.8b
Although the extent of ion-pair return was unknown, the
major formation of olefins led Kevill to an interpretation
that the fast deprotonation from ion pair by the chloride
ion would be much faster than its nucleophilic attack
toward the cationic carbon.8b Consequently, we decided
to examine the GW relationship in the solvolysis of
3-isopropyl, and 3-propyl derivatives (2Br, 3a Br, and
4a Br, respectively) had been reported. In the present
work, 3a Br, 4a Br, and the other new bromides were
prepared by the following routes.
a
1
.1. 3-Isop r op yl-, 3,5-Diisop r op yl-, a n d 3,5,7-Tr i-
isop r op yl-1-br om oa d a m a n ta n es (3a Br, 3bBr, and
cBr). The synthesis of 3a OH and 3bOH starting from
-adamantanecarboxylic acid was reported by Kovalev
et al. We converted 3bOH to the corresponding car-
boxylic acid, which was then subjected to the process that
had been employed for the synthesis of 3bOH to give
cOH (Scheme 1). The three alcohols were converted to
the corresponding bromides with PBr
.2. 3-P r op yl-, 3,5-Dip r op yl-, 3,5,7-Tr ip r op yl-, a n d
3
1
11
3
1
3
-bromoadamantanes having alkyl substituents on the
-, 5-, and 7-positions, which never give olefinic products,
3
.
1
and the extent of ion pair return was thought not to be
3
5
-Non yl-1-br om oa d a m a n ta n es (4a Br, 4bBr, 4cBr, and
Br). An efficient alkylation method of 1-bromoadaman-
(
4) Olah, G. A.; Surya Prakash, G. K.; Shih, J . G.; Krishnamurthy,
tane with alkyl Grignard reagents was reported by
Eguchi et al., which was used here to synthesize
V. V.; Mateescu, G. D.; Liang, G.; Sipos, G.; Buss, V.; Gund, T. M.;
Schleyer, P. v. R. J . Am. Chem. Soc. 1985, 107, 2764-2772.
12
1
-propyl-, 1,3-dipropyl-, and 1,3,5-tripropyl-adamantanes
(4a H, 4bH, and 4cH) (Scheme 2). 1-Nonyladamantane
5H) was prepared similarly. These were converted to
a Br, 4bBr, 4cBr, and 5Br by direct bromination with
Br
(
5) (a) Grunwald, E.; Winstein, S. J . Am. Chem. Soc. 1948, 70, 846-
8
1
54. (b) Bentley, T. W.; Llewellyn, G. Prog. Phys. Org. Chem. 1990,
7, 121-158. (c) Kevill, D. N. In Advances in Quantitative Structure-
Property Relationships; Charton, M., Ed.; J AI Press: Greenwich, CT,
(
4
1
996; Vol. 1, pp 81-115.
(
6) (a) Takeuchi, K.; Ohga, Y.; Ushino, T.; Takasuka, M. J . Org.
2
.
Chem. 1997, 62, 4904-4905. (b) Takeuchi, K. Pure Appl. Chem. 1998,
7
0, 2025-2032.
7) (a) Bentley, T. W.; Schleyer, P. v. R. J . Am. Chem. Soc. 1976,
8, 7658-7666. (b) Bentley, T. W.; Bowen, C. T. J . Chem. Soc., Perkin
(
(9) (a) Bentley, T. W.; Carter, G. E. J . Am. Chem. Soc. 1982, 104,
9
5741-5747. (b) Raber, D. J .; Bingham, R. C.; Harris, J . M.; Fry, J . L.;
Schleyer, P. v. R. J . Am. Chem. Soc. 1970, 92, 5977-5981. (c) Liu,
K.-T.; Sheu, H.-C. J . Chin. Chem. Soc. 1991, 38, 29-33.
(10) Henkel, J . G.; Hane, J . T. J . Med. Chem. 1982, 25, 51-56.
(11) Kovalev, V. V.; Rozov, A. K.; Shokova, E. A. Tetrahedron 1996,
52, 3983-3990.
Trans. 2 1978, 557-562. (c) Bentley, T. W.; Bowen, C. T.; Parker, W.;
Watt, C. I. F. J . Chem. Soc., Perkin Trans. 2 1980, 1244-1252. (d)
Richard, J . P.; J agannadham, V.; Amyes, T. L.; Mishima, M.; Tsuno,
Y. J . Am. Chem. Soc. 1994, 116, 6706-6712.
(8) (a) Bentley, T. W.; Llewellyn, G.; Ryu, Z. H. J . Org. Chem. 1998,
6
3
3, 4654-4659. (b) Kevill, D. N.; D’Souza, M. J . Tetrahedron Lett. 1998,
9, 3973-3976.
(12) Ohno, M.; Shimizu, K.; Ishizaki, K.; Sasaki, T.; Eguchi, S. J .
Org. Chem. 1988, 53, 729-733.

2
036 J . Org. Chem., Vol. 66, No. 6, 2001
Takeuchi et al.
Sch em e 2a
F igu r e 1. Summary of the experimental standard Gibbs
energy for reaction 1 obtained by FT ICR at experimental
-1
uncertainty (0.4 kcal mol . The stability of the ions increases
-
1
downward. All values in kcal mol
.
Ta ble 1. Exp er im en ta l Sta n d a r d Gibbs En er gy Ch a n ges
2
. ICR Exp er im en ts. The experiments were per-
of Rea ction 3, ∆G°(3)a
formed on a modified Bruker CMS-47 Fourier Transform
ICR mass spectrometer1 used in previous studies.
3a
13b,14
cation
∆G°(3)/kcal mol-1
+
(0.0)b
The substantial field strength of its superconducting
magnet (4.7 T) easily allows the storage and study of ions
1
+
c
2
-2.2c
+
3
3
a
-2.2
for periods of 20-30 s. The experimental method is based
+
c
b
-3.8
on the classical gas-phase bromide exchange1
two different carbocations, reaction 1:
5,16
between
3c+
-5.6c
a
All values in kcal mol-1. b Reference value. c Estimated un-
-
1
certainty, (0.4 kcal mol
.
R1+(g) + R Br(g) a R2 (g) + R Br(g) [K , ∆G°(1) (1)
+
2
1
p
Ta ble 2. Ga s-P h a se Sta bilities of Alk yl Su bstitu ted
+
1
-Ad a m a n tyl Ca tion s Rela tive to 1 [∆H°(3,th eor )]
Ca lcu la ted by P M3
The standard Gibbs energy change for reaction 1,
G°(1), was obtained through eq 2:
∆H°(3,theor)/kcal mol-
1
∆
substituent (R)
3-(R)
3,5-(R)2
3,5,7-(R)3
∆
G°(1) ) -RT ln Kp
(2)
(0.0)a
(0.0)a
(0.0)a
H
Me
Et
i-Pr
n-Pr
t-Bu
-0.76
-1.43
-2.07
-1.65
-2.86
-1.47
-2.76
-3.95
-3.48
-5.34
-2.13
-4.07
The partial pressures of the neutral reagents, as
-5.68
b
determined by a Bayard-Alpert gauge, were corrected
(-5.0 ( 0.1)
-7.64
according to Bartmess and Georgiadis17 using the average
a
Reference value. b Estimated from a plot of ∆H°(3,theor)
against the number of the substituent. See Figure S1 in Support-
ing Information.
molecular polarizabilities, R(ahc) calculated according to
Miller.18 Uncertainties on the ∆G°(1) values are esti-
-
1
mated at 0.4 kcal mol . A significant part of this
uncertainty originates in the adsorption of these com-
pounds onto the inner surface of the vacuum system. The
direct comparison of 2 and 3a could not be carried out
because they are isomeric species. The experimental
results are summarized in Figure 1.
∆G°(3) is a quantitative measure of the relative
thermodynamic stabilities of the carbocations with re-
spect to 1-adamantyl cation (1 ) in the gas phase. The
∆G°(3) values are presented in Table 1.
+
+
+
3. P M3 Ca lcu la t ion s. PM3 calculations were car-
ried out on the heat of exchange reaction for eq 3
[∆H°(3,theor)] for mono-, di-, and trisubstituted 1-ada-
mantyl cations having Me, Et, i-Pr, n-Pr, or t-Bu sub-
stituents through the MOPAC system.19 The most stable
conformers were sought; however, because of too many
The results in Figure 1 can be used to obtain experi-
mental, averaged values of ∆G°(3).
+
+
1
Br(g) + R (g) a 1 (g) + RBr(g) [∆G°(3) (3)
+
+
conformations of 4c and 4cBr, the energy of 4c was
obtained not by calculations, but by estimation as -5.0
(
13) (a) For a detailed description of the instrument and its
capabilities, see, e.g., Laukien, F. H.; Allemann, M.; Bischofberger, P.;
Grossmann, P.; Kellerhals, H. P.; Kopfel, P. In Fourier Transform Mass
Spectormetry. Evolution, Innovation and Applications; Buchanan, M.
V., Ed.; ACS Symposium Series 359; American Chemical Society:
Washington, DC, 1987; Chapter 5. (b) Abboud, J .-L. M.; Casta n˜ o, O.;
Della, E. W.; Herreros, M.; M u¨ ller, P.; Notario, R.; Rossier, J .-C. J .
Am. Chem. Soc. 1997, 119, 2262-2266. (c) Abboud, J .-L. M.; Esseffar,
M.; Herreros, M.; M o´ , O.; Molina, M. T.; Notario, R.; Y a´ n˜ ez, M. J . Phys.
Chem. A, 1998, 102, 7996-8003.
14) Abboud, J .-L. M.; Casta n˜ o, O.; Herreros, M.; Elguero, J .;
J agerovic, N.; Notario, R.; Sak, K. Int. J . Mass Spectrom. Ion. Processes
998, 175, 35-40.
15) Staley, R. H.; Wieting, R. D.; Beauchamp, J . L. J . Am. Chem.
Soc. 1977, 99, 5964-5972.
16) Sharma, R. B.; Sen Sharma, D. K.; Hiraoka, K.; Kebarle, P. J .
Am. Chem. Soc. 1985, 107, 3747-3757, and references therein.
-
1
( 0.1 kcal mol by comparing a plot of ∆H°(3,theor)
against the number of the n-Pr group with those for the
other substituents (see Supporting Information). All the
calculated results are summarized in Table 2. Calcula-
tions on 3a , 3b , and 3c by AM1 gave energies about
4% larger than the values in Table 2. Comparisons with
+
+
+
1
(
the FT ICR data in Table 1 reveal that PM3 calculations
show very good agreement.
1
(
(17) Bartmess, J . E.; Georgiadis, R. M. Vacuum 1983, 33, 149-153.
(18) Miller, K. J . J . Am. Chem. Soc. 1990, 112, 8533-8542.
(19) Stewart, J . J . P. J . Comput. Chem. 1989, 10, 209-263.
(

Gas- and Liquid-Phase Stability of 1-Adamantyl Cations
J . Org. Chem., Vol. 66, No. 6, 2001 2037
Ta ble 3. Ra te Con sta n ts of Solvolysis of 1-Br om o-3,5,7-tr ia lk yla d a m a n ta n es a n d Ra te Ra tios to 1-Br om oa d a m a n ta n e
(
1Br ) a t 25.0 °Ca
kc/s-1
rate rel to 1Br
3cBr/1Br
solventb
00E
3,5,7-(Me)3 (2Br)
9.7 × 10-
3,5,7-(i-Pr)3 (3cBr)
3,5,7-(n-Pr)3 (4cBr)
4.9 × 10-9 d,g
1-AdBr (1Br)
2Br/1Br
4cBr/1Br
10 d
-8 d,f
-9 h
1
9
8
7
6
5
3
1
9
8
7
6
1
9
7
5
8
6
9
8
7
2.0 × 10
1.6 × 10
5.3 × 10
1.3 × 10
0.75
15
3.8
-
7 d,i
-7 d,l
-6 o,p
-8 j
0E-10W
0E-20W
0E-30W
0E-40W
0E-50W
0E-70W
00M
0M-10W
0M-20W
0M-30W
0M-40W
00T
4 × 10
4.0
1.9
1.1
0.84
-
-
8 d,k
-7 d,m
-7 j
8.0 × 10
7.8 × 10
1.37 × 10
2.8 × 10
0.29
0.59
0.49
0.30
0.15
7 d,n
-7 o
-6 j
1.73 × 10
4.29 × 10
3.94 × 10
1.33 × 10
-
6 o
-7 o
-6 j
7.72 × 10
5.1 × 10
-
-
6 o,q
-5 j
5.49 × 10
1.57 × 10
2.12 × 10
0.26
0.22
0.95
4 d,r
-4 j
6.98 × 10
-
8 d,r,s
-7 d,t
8.6 × 10-8 d,u
2.39 × 10-6 o,r
-8 j
2.0 × 10
3.40 × 10
1.63 × 10
7.31 × 10
2.83 × 10
1.01 × 10
1.24 × 10
2.1 × 10
16
4.1
1.7
-
6 o,r
-7 j
2.0 × 10
8.2
5.2
3.9
3.3
14
7.8 × 10-
7 d,v
-6 o,r
1.40 × 10
-6 j
0.56
-
-
-
5 o
-6 j
7.3 × 10
4 o,r
3 q
-5 o,r
-5 j
3.11 × 10
3.1 × 10
1.0
3.2
-4 o
-5 w
2.98 × 10
9.22 × 10
-
-
5 o
5 o
-5 j
7T
4.59 × 10
5.60 × 10
9.5 × 10
0.50
0.33
-4 o,r
2.66 × 10-4 o,r
-4 w
0T-30W
0T-50W
0T-20E
0T-40E
7HFIP-3W
0A-20W
0A-30W
9.51 × 10
9.81 × 10
1.03 × 10
8.82 × 10
1.31 × 10
1.10 × 10
5.16 × 10
1.71 × 10
5.6
3.2
14
12
14
1.6
-
4 o,r
-4 w
3.10 × 10
-
-
-
6 o
-4 o
-5 o
-6 w
3.90 × 10
4.28 × 10
7.02 × 10
2.91 × 10
7.32 × 10
0.53
0.56
0.77
4.0
1.9
4.6
7 d,x
3 q,r
-6 o
-6 o
-7 w
1.48 × 10
7.64 × 10
-1 q,r
-2 q,r
-3 j
4.19 × 10
9.1 × 10
-
-
7 d,y
7 d,z
-8 j
6 × 10
1.8
1.0
1.48 × 10-7 d,aa
5 × 10
-7 j
0.3
a
-4
mol L-1
Solvolysis was generally conducted in the presence of 25% excess of 2,6-lutidine for titrimetric runs and (2∼10) × 10
b
2
,6-lutidine for conductometric runs. E, M, A, T, and W denote ethanol, methanol, acetone, 2,2,2-trifluoroethanol, and water, respectively,
and the preceding figures denote vol % of each component at 25 °C except for T-W and 97HFIP systems, which are expressed by wt %.
c
Most of the data were obtained from duplicate runs within experimental errors of (2% and (0.5% in titrimetric and conductometric
d
e
-7 -1
-5 -1
measurements, respectively. Extrapolated from data at higher temperatures. k: 9.51 × 10
s
(75.0 °C); 1.49 × 10
s
(100.0 °C);
‡
-1
‡
-1 -1
f
-5 -1
-4 -1
‡
-1
‡
∆
H
) 27.8 kcal mol ; ∆S ) -6.5 cal mol
K
.
k: 1.19 × 10
s
(75.0 °C); 1.53 × 10
s
(100.0 °C); ∆H ) 25.8 kcal mol ; ∆S
)
-
1
-1
g
-6 -1
-5 -1
(100.0 °C); ∆H ) 25.8 kcal mol ; ∆S‡ ) -9.9 cal mol K-1
‡
-1
-1
h
-
7.2 cal mol
K
.
k: 2.98 × 10
s
(75.0 °C); 3.86 × 10
s
.
For
-
9
-1
i
-5 -1
-4 -1
estimation of this value, see text. Bentley estimated a value 1 ×10
s
(ref 9a). k: 7.38 × 10
s
(75.0 °C); 8.47 × 10
s
(100.0 °C);
‡
-1
‡
-1 -1
j
Ref 9a. k k: 2.39 × 10
-6 -1
-5 -1
‡
-1
∆
∆
∆
H ) 24.6 kcal mol ; ∆S ) -7.0 cal mol
K
.
s
(50.0 °C); 4.40 × 10
s
(75.0 °C); ∆H ) 25.5 kcal mol
;
‡
-1 -1
-5 -1
(ref 1c). k: 1.55 × 10 s-1 (50.0 °C); 2.78 × 10
l
-5
-4 -1
S
H
) -5.6 cal mol
K
. A reported value at 75.0 °C is 6.93 × 10
s
s
(75.0 °C);
‡
-1
‡
-1 -1
m
-6 -1
-5 -1
‡
-1
‡
) 25.2 kcal mol ; ∆S ) -2.6 cal mol
K
.
k: 4.31 × 10
s
(50.0 °C); 8.22 × 10
s
(75.0 °C); ∆H ) 25.8 kcal mol ; ∆S )
-
1
-1
n
-5 -1
-4 -1
‡
-1
‡
-1 -1
o
-
3.4 cal mol
K
.
k: 1.74 × 10
s
(50.0 °C); 2.48 × 10
s
(75.0 °C); ∆H ) 24.8 kcal mol ; ∆S ) -5.2 cal mol
K
.
Determined
p
-6 -1 q
titrimetrically. The specific rate in the absence of 2,6-lutidine was 1.76 ×10
s . Extrapolated from data determined conductometrically
-
4
-1
-3 -1
‡
-1
‡
-1 -1 r
in the absence of 2,6-lutidine. k: 9.83 × 10
s
(40.0 °C); 3.03 × 10
s
(50.0 °C); ∆H ) 22.1 kcal mol ; ∆S ) -1.8 cal mol K . In
‡
s
-7 -1
-5 -1
(75.0 °C); ∆H ) 25.2 kcal mol ; ∆S‡ ) -9.0 cal mol-1K . k:
u
-1
-1 t
the absence of 2,6-lutidine. k: 5.78 × 10
s
(50.0 °C); 1.04 × 10
s
-
5
-1
-4 -1
(75.0 °C); ∆H ) 25.3 kcal mol ; ∆S‡ ) -3.1 cal mol
‡
-1
-1 -1
-5 -1
1
.01 × 10
s
(50.0 °C); 1.83 × 10
s
K
.
k: 4.21 × 10s
s
(75.0 °C); 5.02
(75.0 °C); ∆H )
-
4
-1
‡
-1
‡
-1 -1
v
-5 -1
-4 -1
‡
×
10
s
(100.0 °C); ∆H ) 25.0 kcal mol ; ∆S ) -7.1 cal mol
K
.
k: 1.74 × 10
s
(50.0 °C); 2.48 × 10
-
1
‡
-1 -1
w
x
-6 -1
-4 -1
‡
-1
2
3.1 kcal mol ; ∆S ) -8.8 cal mol
K
.
Reference 9c. k: 8.85 × 10
s
(50.0 °C); 1.18 × 10
s
(75.0 °C); ∆H ) 22.6 kcal mol ;
‡
-1 -1
y
-5 -1
-4 -1
‡
-1
‡
-1 -1 z
∆
1
×
S ) -11.8 cal mol
K
.
k: 4.98 × 10
s
(75.0 °C); 5.72 × 10
s
(100.0 °C); ∆H ) 24.6 kcal mol ; ∆S ) -7.8 cal mol
K
. k:
-
5
-1
-4 -1
(75.0 °C); ∆H ) 25.5 kcal mol ; ∆S‡ ) -1.7 cal mol
‡
-1
-1 -1 aa
-6 -1
.56 × 10
s
(50.0 °C); 2.89 × 10
s
K
.
k: 4.22 × 10
s
(50.0 °C); 7.41
-
5
-1
‡
-1
‡
-1 -1
10
s
(75.0 °C); ∆H ) 25.0 kcal mol ; ∆S ) -5.8 cal mol
K
.
Ta ble 4. Ra te Con sta n ts of Solvolysis of 1-Br om o-3,5-d ia lk yla d a m a n ta n es a n d Ra te Ra tios to 1-Br om oa d a m a n ta n e (1Br )
a t 25.0 °Ca
kc/s-1
rate rel to 1Brd
solventb
3,5-(i-Pr)2 (3bBr)
3,5-(n-Pr)2 (4bBr)
3bBr/1Br
4bBr/1Br
-
9 e,f
-9 e,g
1
8
7
8
6
8
00E
8.3 × 10
4.0 × 10
6.4
2.9
1.7
4.6
5.4
5.1
3.1
-
-
-
-
-
7 e,h
-7 e,i
0E-20W
0E-30W
0M-20W
0T-40E
0T-20E
8.10 × 10
2.26 × 10
6.41 × 10
4.12 × 10
3.76 × 10
1.9 × 10
0.68
0.41
1.3
1.8
1.9
6
6
6
5
-7
5.40 × 10
-6
1.84 × 10
-6
1.34 × 10
-5
1.38 × 10
a
b
Solvolysis was conducted titrimetrically in the presence of 25% excess of 2,6-lutidine E, M, T, and W denote ethanol, methanol,
,2,2-trifluoroethanol, and water, respectively, and the preceding figures denote vol % of each component at 25 °C. Most of the data
c
2
d
e
were obtained from duplicate runs within experimental error of (2%. For the specific rates of 1Br, see Table 1. Extrapolated from
f
-6 -1
(75.0 °C); 1.52 × 10 s-1 (100.0 °C); ∆H ) 28.5 kcal mol ; ∆S‡ ) -0.4 cal mol
-4
‡
-1
-1 -1
data at higher temperatures. k: 9.22 × 10
s
K .
g
-7 -1
-6 -1
(75.0 °C); ∆H ) 27.5 kcal mol ; ∆S‡ ) -4.5 cal mol
‡
-1
-1 -1
h
-5 -1
k: 1.58 × 10
s
(50.0 °C); 3.68 × 10
s
K
.
k: 1.77 × 10
s
(50.0 °C);
-
4
-1
‡
-1
‡
-1 -1
i
-6 -1
-4 -1
‡
2
)
.47 × 10
s
(75.0 °C); ∆H ) 23.1 kcal mol ; ∆S ) -9.3 cal mol
K
.
k: 5.58 × 10
s
(50.0 °C); 1.01 × 10
s
(75.0 °C); ∆H
-
1
‡
-1 -1
25.3 kcal mol ; ∆S ) -4.4 cal mol K .
4
4
. Solvolysis Stu d ies
.1. Ra te Stu d ies. The rates of solvolysis were deter-
slow for direct measurements at 25 °C were obtained by
extrapolation from data at higher temperatures. The rate
constants at 25.0 °C are summarized in Tables 3-5. The
rate of 1Br in EtOH at 25.0 °C had been roughly
mined titrimetrically or conductometrically. Generally,
the solvolysis was conducted in the presence of 25%
excess of 2,6-lutidine, but some rate runs in several
aqueous solvents were conducted in its absence, since the
titrimetric end-point became obscured or conductometric
measurements became difficult. The rates that are too
-9
-1 9a
estimated by Bentley and Carter to be 1 × 10
s . We
found that a logarithmic plot of the rate constants for
3cBr against those for 1Br for the solvolysis in nonaque-
ous solvents, 97% HFIP, 100% TFE, 80% TFE-20%

2
038 J . Org. Chem., Vol. 66, No. 6, 2001
Takeuchi et al.
Ta ble 5. Ra te Con sta n ts of Solvolysis of 1-Br om o-3-a lk yla d a m a n ta n es a n d Ra te Ra tios to 1-Br om oa d a m a n ta n e (1Br ) a t
2
5.0 ˚C a
kc/s-1
rate rel to 1Brd
4a Br/1Br
solventb
3-i-Pr (3a Br)
3-n-Pr (4a Br)
3-n-C9H19 (5Br)
3a Br/1Br
5Br/1Br
-
-
9 e,f
7 e,i
-9 e,g
-9 e,h
1
8
7
8
6
8
00E
3.5 × 10
5.4 × 10
2.1 × 10
2.2 × 10
2.7
1.9
2.2
2.5
2.5
2.6
1.6
1.7
-7 e,j
-7 e,k
0E-20W
0E-30W
0M-20W
0T-40E
0T-20E
2.6 × 10
2.1 × 10
0.93
0.89
1.6
1.4
1.4
0.75
0.61
1.0
1.2
1.1
-
-
-
-
6
6
6
5
-6
-7
2.87 × 10
3.44 × 10
1.93 × 10
1.93 × 10
1.19 × 10
8.17 × 10
-6
-6
2.24 × 10
1.40 × 10
-6
-7
1.08 × 10
8.85 × 10
-5
-6
1.01 × 10
8.39 × 10
a
b
Solvolysis was conducted titrimetrically in the presence of 25% excess of 2,6-lutidine. E, M, T, and W denote ethanol, methanol,
,2,2-trifluoroethanol, and water, respectively, and the preceding figures denote vol % of each component at 25 °C. Most of the data
c
2
d
e
were obtained from duplicate runs within experimental error of (2%. For the specific rates of 1Br, see Table 1. Extrapolated from
f
-7 -1
-6 -1
(75.0 °C); ∆H ) 28.5 kcal mol ; ∆S‡ ) -1.5 cal mol
‡
-1
-1 -1
data at higher temperatures. k: 1.57 × 10
s
(50.0 °C); 4.08 × 10
s
K .
g
-8 -1
-6 -1
(75.0 °C); ∆H ) 28.1 kcal mol ; ∆S‡ ) -3.6 cal mol
‡
-1
-1 -1
h
-8 -1
k: 9.18 × 10
s
(50.0 °C); 2.30 × 10
s
K
.
k: 9.19 × 10
s
(50.0 °C);
(75.0 °C); ∆H
-
6
-1
‡
-1
‡
-1 -1
i
-5 -1
-4 -1
‡
2
)
.25 × 10
s
(75.0 °C); ∆H ) 28.0 kcal mol ; ∆S ) -4.2 cal mol
K
.
k: 1.28 ×10
s
(50.0 °C); 1.94 × 10
s
-
1
‡
-1 -1
j
-6 -1
-4 -1
‡
-1
‡
23.7 kcal mol ; ∆S ) -7.8 cal mol
K
.
k: 7.03 ×10
s
(50.0 °C); 1.20 × 10
s
(75.0 °C); ∆H ) 24.7 kcal mol ; ∆S ) -5.6 cal
-
1
-1
k
-6 -1
-4 -1
‡
-1
‡
-1 -1
mol
K
.
k: 6.06 ×10
s
(50.0 °C); 1.06 × 10
s
(75.0 °C); ∆H ) 25.0 kcal mol ; ∆S ) -5.2 cal mol
K
.
EtOH, 60% TFE-40% EtOH, and MeOH, give a good
straight line. Extrapolation to the EtOH data point for
3
cBr in this plot gave an estimated rate constant for 1Br
-
9
-1
of (1.3 ( 0.1) × 10
s . The details are given in the
Supporting Information.
4
.2. P r od u cts of Solvolysis of 1Br a n d 3cBr in 80%
EtOH. To examine if isopropyl substituents on the 3-,
-, and 7-positions exert effects on the product partition
selectivity) in an ethanol-water mixture, the distribu-
5
(
tion of ethyl ether and alcohol products was determined
for the solvolyis in 80% ethanol-20% water (v/v) in the
presence of excess 2,6-lutidine at 25 and 75 °C.20 The
product distributions at 75 °C were determined at 10
half-lives, but those at 25 °C were analyzed at 1.5 or 2.9
half-lives. The ethyl ether/alcohol product ratios at 75
°
4
2
C were 37 ( 2/63 ( 2 and 36 ( 1/64 ( 1 for 1Br and
cBr, respectively. The corresponding product ratios at
5 °C were 38 ( 1/62 ( 1 and 40 ( 1/60 ( 1, respectively,
F igu r e 2. A plot of experimental ∆G°(3) obtained by FT ICR
against ∆H°(3,theor) calculated by PM3 for various 1-ada-
which are similar to those at 75 °C. The product distribu-
tions from 1Br afford selectivity ratios k /k of 0.50 at
5 °C and 0.48 at 75 °C: reported values are 0.74 at 25
+
mantyl cations. The energies are relative to 1 . Slope: 0.97;
E
W
r: 0.999.
2
2
1a
21b
21c
°
C, 0.53 at 75 °C, and 0.48 at 100 °C.
respective stability differences by PM3 calculation are
-
1
2
.07, 1.88, and 1.73 kcal mol
.
Discu ssion
2
. Solvolysis Ra te Ra tios a n d Ga s-P h a se Sta bili-
ties of Ca r boca tion s. The solvolysis rate ratios between
alkylated 1-bromoadamantanes and 1-bromoadamantane
1
. Effects of Alk yl Su bstitu en ts on Rela tive Sta -
bilities of 1-Ad a m a n tyl Ca tion s in Ga s-P h a se a n d
(
1Br) are summarized in Tables 3-5. First, as previously
in Solu tion . As previously estimated from STO-3G
1a,c
calculations on the 3-methyl-1-adamantyl cation,1j the
reported for a few solvents,
1-bromo-3,5,7-trimethyl-
adamantane (2Br) solvolyzes slower than 1Br in all the
solvents examined (Table 3). Besides, it was revealed that
the addition of water to ethanol, methanol, and TFE
decreases the rate ratio of 2Br/1Br, although rigorous
comparison may not be permitted since the rate data
include extrapolation from data at higher temperatures.
Thus, the rate ratio changes in the following manner;
present FT ICR experiments reveal that the introduction
of three methyl or one to three isopropyl substituents to
the 3- (and 5-, 7-) position(s) stabilizes the 1-adamantyl
cation (Table 1). As evident from a plot of limited
numbers of experimental gas-phase stabilities [∆G°(3)]
for eq 3 against the stabilities obtained by PM3 calcula-
tions [∆H°(3,theor)] (Figure 2), the gas-phase substituent
0
.75 (100% EtOH), 0.29 (80% EtOH), 0.59 (70% EtOH),
effect obtained by FT ICR is nearly additive within the
experimental error (0.4 kcal mol-1. Notwithstanding the
0.26 (50% EtOH), and 0.22 (30% EtOH); 0.95 (100%
MeOH) and 0.56 (80% MeOH); 0.50 (97% TFE) and 0.33
experimental uncertainty, the first substituent appears
most effective. From the data in Table 1, the differences
(70% TFE).
-
1
+
+
in stability (kcal mol ) are 2.2 ( 0.4 for 3a vs 1 , 1.6 (
The effect of water on the rate ratio is more marked
+
+
+
+
0
.4 for 3b vs 3a , and 1.8 ( 0.4 for 3c vs 3b . The
when isopropyl or propyl substituents are introduced. For
example, the rate ratio of 15 for 3cBr/1Br in EtOH
decreases with increase in water content in such a way
to 4.0 (90% EtOH), 1.9 (80% EtOH), 1.1 (70% EtOH), and
finally below unity, 0.84 (60% EtOH) (Table 3). A similar
(
20) For a review on solvent selectivity, see, Ta-Shma, R.; Rap-
poport, Z. Adv. Phys. Org. Chem. 1992, 27, 239-291.
(
21) (a) McManus, S. P.; Zutaut, S. E. Isr. J . Chem. 1985, 26, 400-
4
5
2
03. (b) Karton, Y.; Pross, A. J . Chem. Soc., Perkin Trans. 2 1978,
95-598. (c) Luton, P. R.; Whiting, M. C. J . Chem. Soc., Perkin Trans.
1979, 646-647.
trend is also found in MeOH-H
2
2
O and TFE-H O. The
4cBr/1Br rate ratio also shows a similar trend: it is noted

Gas- and Liquid-Phase Stability of 1-Adamantyl Cations
J . Org. Chem., Vol. 66, No. 6, 2001 2039
‡
F igu r e 4. A plot of -δ∆G () RT ln(k
R
/k
H
)) for the solvolysis
of 3,5,7-trialkyl-1-bromoadamantanes in EtOH, TFE, 80%
TFE-20% EtOH, 97% HFIP, and 80% EtOH at 25 °C against
-∆H°(3,theor) of 3,5,7-trialkyl-1-adamantyl cations calculated
by PM3. The energies are relative to those of the 1-adamantyl
system: TFE (9); EtOH (2); 97% HFIP (b); 80% TFE-20%
EtOH (O); 80% EtOH (×).
F igu r e 3. A plot of logarithms of specific rates for the
solvolysis of 1Br, 3a Br, 3bBr, and 3cBr in various solvents
against the number of isopropyl group: EtOH (b); 60% TFE-
points of each substrate for the first four nonaqueous
solvents fall very close to each other to give a roughly
linear correlation with a slope 0.5. In contrast, the points
for 80% EtOH scatter below the correlation line.
4
0% EtOH (9); 80% EtOH (0); 70% EtOH (4).
that the rate ratio of 3.8 in EtOH decreases to 0.15 in
6
0% EtOH.
The upward deviation of the data point for 1Br by 1.4
In the long history of solvolysis studies, “80% ethanol”
-
1
kcal mol from the correlation line (Figure 4) suggests
that 1Br is subject to extra stabilization in the transition
state of ionization, which is not evident in the 3,5,7-
trialkyl systems. Βrφnsted base-type solvation toward
relatively positive hydrogens on the 3-, 5-, and 7-posi-
tions23 might be operative.
has been used as a convenient solvent. In the Grunwald-
Winstein relationship,5 80% ethanol is used as the
standard solvent. However, the data of the present study
suggest that aqueous ethanol might result in a wrong
conclusion regarding the stability of incipient carboca-
tions and electron-donating ability of alkyl substituents.
Representative situations are illustrated in Figure 3 by
using the rate constants of Tables 3-5. The isopropyl-
substituent effect on log k is essentially additive in
nonaqueous solvents, such as 100% EtOH and 60% TFE-
3
. Gr u n w a ld -Win stein Rela tion sh ip . In the revised
Grunwald-Winstein (GW) equations [log(k/k ) ) mY
for solvolytic reactions of alkyl halides, the ionizing power
) of solvent is defined by log(k/k ) for the solvolysis of
-haloadamantanes, with m ) 1 by definition. The k and
are rate constants in a given solvent and 80% ethanol-
0% water (v/v), respectively, at 25 °C, and X is a halogen
o
X
]
(Y
X
o
1
k
2
4
0% EtOH, whereas in 80% EtOH and 70% EtOH the
o
introduction of the second or the third isopropyl sub-
stituent results in decreased solvolysis rates. This sort
of anomaly is reflected in dispersion in the Grunwald-
Winstein relationship. The probable causes are discussed
leaving group. Many tertiary alkyl halides have been
examined by the revised GW equations, and any disper-
sions in the log(k/k ) vs Y plot ascribed to solvent effects
o X
other than polarity and electrophilic nature (toward
the leaving group) of solvents, or possible mechanistic
changes.
6
in the following section. It is recommended that when-
ever the solvolytic reactivity is to be related with car-
bocation stability, the rates should be examined in
nonaqueous solvents such as ethanol, methanol, TFE,
TFE-EtOH, and 97% HFIP, and the use of aqueous
mixtures should be avoided.
5
b,c
For example, nucleophilic solvent participation,
6
Brφnsted base-type solvation to â-hydrogens, ion-pair
return,8b and concerted elimination have been proposed
as possible causes for various kinds of dispersion in the
GW relations of simple and highly congested open-chain
alkyl chlorides. In this respect, 3,5,7-trialkyl-1-bromoad-
amantanes were thought as one of ideal candidates for
8a
The Gibbs energies of activation relative to 1Br in
solvolysis [δ∆G‡solv] can be obtained by eq 4, where k
o
and
k are rate constants of 1Br and other bromides in
question, respectively.
‡
solv
δ∆G
) -RT ln(k/ko)
(4)
(
22) (a) Bingham, R. C.; Schleyer, P. v. R. J . Am. Chem. Soc. 1971,
3, 3189-3199. (b) Parker, W.; Trauter, R. L.; Watt, C. I. F.; Chang,
L. W. K.; Schleyer, P. v. R. J . Am. Chem. Soc. 1974, 96, 7121-7122.
c) Abboud, J .-L. M.; Casta n˜ o, O.; Della, E. W.; Herreros, M.; M u¨ ller,
P.; Notario, R.; Rossier, J .-C. J . Am. Chem. Soc. 1997, 119, 2262-
2266. (d) M u¨ ller, P.; Mareda, J .; Milin, D. J . Phys. Org. Chem. 1995,
9
The relation between δ∆G‡solv and gas-phase stability
(
of carbocations [∆G°(3)] has been one of central subjects
in carbocation chemistry since the pioneering work by
Schleyer and co-workers on the solvolytic reactivities of
8
, 507-528. (e) M u¨ ller, P.; Mareda, J . In Cage Hydrocarbons; Olah,
G. A., Ed.; J ohn Wiley & Sons: New York, 1990; Chapter 6. (f)
Takeuchi, K.; Takasuka, M.; Shiba, E.; Kinoshita, T.; Okazaki, T.;
Abboud, J .-L. M.; Notario, R.; Casta n˜ o, O. J . Am. Chem. Soc. 2000,
cage compounds. Figure 4 shows a plot of -δ∆G‡solv for
2
2
2
Br, 3cBr, and 4cBr relative to 1Br against PM3
1
22, 7351-7357.
calculated ∆H°(3,theor) for the corresponding carboca-
tions in Table 2. The solvents are EtOH, TFE, 80% TFE-
0% EtOH, 97% HFIP, and 80% EtOH. Notably, the data
(
23) The 1H NMR δ values for H(3) and H(2) of the 1-adamantyl
cation are 5.19 and 4.19 ppm, respectively, indicating that H(3) is more
positively charged than H(2) (ref 4).
2

2
040 J . Org. Chem., Vol. 66, No. 6, 2001
Takeuchi et al.
more congested 3cBr is subject to less effective hydration
than 1Br in the transition state for ionization.
The notion of preferential solvation on the cation side
has long been suggested,7 but has not been clearly
demonstrated in the GW type relationship. Aqueous
ethanol solvents show such a sign. The GW plot of the
rate data for 3cBr in aqueous ethanol shows a greater
downward dispersion than in aqueous methanol, and the
line connecting EtOH, aq ethanol mixtures, and water
points obviously results in a downward bulge. This
behavior may be due to the hydrophobic interaction of
the highly alkylated structure with ethanol in aqueous
ethanol. Presumably, the first solvation shell contains
more ethanol and less water than the bulk phase, making
the ionization less easy.
,25
Previously, Wepster and co-workers found that the
Hammett σ constants of bulky alkyl groups, such as tert-
butyl and 1,1-diethylpropyl (Et3C), become significantly
more minus in aqueous ethanol or aqueous tert-butyl
alcohol than in water, and the results were ascribed to
the hydrophobic effect.26 They reported that dispersions
in various Hammett relations for the systems having
bulky alkyl groups in aqueous organic solvents could be
markedly improved by incorporation of an “hπ” term,
2
7
where π is Hansch’s hydrophobic constant. In the
present solvolyses, a plot of log(k70E-30W/k60T-40E) for the
eight substrates included in Tables 3-5 for the two
solvents (70E-30W and 60T-40E) having comparable
F igu r e 5. A plot of log k values against YBr for the solvolysis
of 2Br (9, 0), 3cBr (b, O), and 4cBr (2, 4) at 25 °C. The closed
and open symbols denote nonaqueous and aqueous solvents,
respectively. A, E, M, T, and HFIP stand for acetone, ethanol,
methanol, 2,2,2-trifluoroethanol, and 1,1,1,3,3,3-hexafluoro-
Br values (0.689 and 0.436 , respectively) against the
a
9c
Y
2
7
total value of hydrophobic parameters for substituents
(Σπ) is roughly linear (excluding the data point for
-bromo-3-nonyladamantane) with a negative slope (see
1
2
%
-propanol, respectively, and the preceding numbers mean vol
, whereas 50T, 70T, 97T, and 97HFIP are mixtures with
Supporting Information).
Recently, the effects of added ethanol on the rates of
the benzoin condensation, Diels-Alder reactions, and S 2
N
water in wt %. The plots of 2Br and 4cBr are shifted by 2
units downward and 4 units upward, respectively, for clarity.
For YBr values, see refs 5b and 9c.
reactions in aqueous solutions have been extensively
studied by Breslow and co-workers, and the important
role of ethanol as “antihydrophobic agent” has been
pointed out.28 The nearly linear behavior of aqueous
methanol solvents (Figure 5) is in line with the notion
that methanol is a much less effective antihydrophobic
agent than ethanol. This is in accord with the much
smaller microscopic hydrophobicity parameter for a
methyl group (0.41) than that for an ethyl group (0.73);
the parameters were obtained from the accelerating
investigation of the above possibilities, since they give
no elimination products and â-hydrogens are somewhat
hindered to the Brφnsted base-type solvation. It was also
supposed that the extent of ion-pair return would be
almost similar to the parent 1-bromoadamantane (1Br).
Figure 5 shows the GW plot against YBr5
b,9a,c
for the rates
of solvolysis of 1-bromo-3,5,7-trimethyl-, 1-bromo-3,5,7-
triisopropyl-, and 1-bromo-3,5,7-tripropyl-adamantanes
+
-
effects of added RNMe
3
X (R ) Me or Et) on the rate of
(2Br, 3cBr, and 4cBr, respectively).
hydrolysis of p-nitrophenyl laurate.29
The GW plot for 2Br shows fairly good linear relation-
ship. However, the data points for aqueous ethanol (80E,
0E, 50E, and 30E) obviously fall slightly below the
straight line that passes through the points for nonaque-
24) The reported rate constant of 1Br in water of 7.7 × 10 s-1
9
a
-3
(
7
-3 -1
and the estimated one for 3cBr of 6 × 10
s
(see text) were used.
(25) Leading references: (a) J orgensen, W. L.; Buckner, J . K.;
Huston, S. E.; Rossky, P. J . J . Am. Chem. Soc. 1987, 109, 1891-1899.
b) McClelland, R. A.; Kanagasabapathy, V. M.; Banait, N. S.; Steen-
ous solvents (100E, 100M, 97T, 97HFIP, 60T-40E, 80T-
(
2
0E) (m ) 0.99, r ) 0.999). This trend is more marked
ken, S. J . Am. Chem. Soc. 1989, 111, 3966-3972. (c) Reichardt, C.
Solvents and Solvent Effects in Organic Chemistry, 2nd ed.; VCH:
Weinheim, 1988; pp 35-38.
for 3cBr and 4cBr. Their rates in nonaqueous solvents
show good linear relations: m ) 0.99 and r ) 0.999 for
(
26) (a) Hoefnagel, A. J .; Wepster, B. M. J . Chem. Soc., Perkin Trans.
3
cBr and m ) 1.00 and r ) 0.999 for 4cBr.
2 1989, 977-986. (b) Hoefnagel, A. J .; Wepster, B. M. Collect. Czech.
Chem. Commun. 1990, 55, 119-135. (c) Hoefnagel, A. J .; Wepster, B.
M. Recl. Trav. Chim. Pays-Bas 1990, 109, 455-462. (d) Hoefnagel, A.
J .; de Vos, R. H.; Wepster, B. M. Recl. Trav. Chim. Pays-Bas 1992,
11, 22-28.
27) (a) Leo, A., Hansch, C.; Elkins, D. Chem. Rev. 1971, 71, 525-
16. (b) Hansch, C.; Leo, A.; Unger, S. H.; Kim, K.-H.; Nikaitani, D.;
Similarly to nonaqueous solvents, methanol and aque-
ous methanol solvents also give good linear relations, but
with smaller m values; m ) 0.78 (r ) 0.999) and m )
1
(
0
.80 (r ) 0.999) for 3cBr and 4cBr, respectively. A linear
6
extrapolation of the aqueous methanol line for 3cBr in
Lien, E. J . J . Med. Chem. 1973, 16, 1207-1216. (c) Marcus, Y. The
Properties of Solvents; J ohn Wiley & Sons: Chichester, 1998; Ch. 4.
Figure 5 to the YBr value (4.44)9a for water suggests the
(
28) (a) Breslow, R.; Connor, R.; Zhu, Z. Pure Appl. Chem. 1996,
rate constant of 3cBr in water of approximately 0.006
68, 1527-1533. (b) Mayer, M. U.; Breslow, R. J . Am. Chem. Soc. 1998,
120, 9098-9099, and previous publications cited therein. (c) Breslow,
R.; Groves, K.; Mayer, M. U. Pure Appl. Chem. 1998, 70, 1933-1938.
-
1
24
s
at 25 °C, which gives the 3cBr/1Br rate ratio of ∼0.8.
We assume that the Brφnsted-base type hydration to the
â-hydrogens is so sensitive to steric encumbrance that
(
29) Menger, F. M.; Venkataram, U. V. J . Am. Chem. Soc. 1986,
108, 2980-2984.

Gas- and Liquid-Phase Stability of 1-Adamantyl Cations
J . Org. Chem., Vol. 66, No. 6, 2001 2041
Ta ble 6. Con tr ibu tion s of th e En th a lp y a n d En tr op y
Ter m s of Activa tion in th e Solvolysis of 1Br , 3cBr , a n d
a
4
cBr in 80% EtOH a t 25.0 °C
compound
term
H‡
1Brb
3cBrc
4cBrc
∆
24.5
1.8
26.3
25.2
0.8
26.0
25.8
1.0
26.8
‡
-
T∆S
‡
∆G
a
All values are in kcal mol-1. b The data were taken from ref
9
a. c See footnote to Table 3.
The similar product patterns for 1Br and 3cBr indicate
that the introduction of the isopropyl groups may not
induce much change in the structure of ion pairs and also
the solvent composition around the C(1) cationic carbon
-
and the Br counterion. However, there might be sig-
nificant difference in solvent composition around the
hydrophobic hydrocarbon moiety between 1Br and 3cBr
in the transition state of ionization. The extent of ion pair
return would also be assumed to be similar between 1Br
and 3cBr because of structural similarity and insignifi-
cant difference in solvolytic reactivity. It would not be
reasonable to ascribe the decreased solvolytic reactivity
of 3cBr and 4cBr in aqueous ethanol to possible increase
in ion pair return, since the ion pair return is expected
to decrease in aqueous ethanol that is more nucleophilic
than fluorinated alcohols.30
F igu r e 6. Plots of log k values against YBr for the solvolysis
of (a) 3a Br (9), 4a Br (b), and 5Br (2), and (b) 3bBr (9) and
4
bBr (b) at 25 °C. The data points for 4a Br and 4bBr, and
those for 5b are shifted downward by 2 and 4 units, respec-
tively, for clarity.
sentially no influence. As shown in Figure 6b for the GW
plot for 3bBr and 4bBr, both bromides exhibit similar
dispersions whose deviations are between their mono-
and trisubstituted homologues.
4
. En th a lp y a n d En tr op y of Activa tion . The con-
tributions of the enthalpy and entropy terms of activation
for the solvolysis of 1Br, 3cBr, and 4cBr in 80% EtOH
are summarized in Table 6.
Con clu sion s
The ∆H value (kcal mol-1) changes in the manner 1Br
‡
(
24.5) < 3cBr (25.8) > 4cBr (25.2). This trend is similar
FT ICR experiments showed that the introduction of
three methyl or three isopropyl substituents into the 3-,
5-, and 7-positions of 1-admantyl cation increases the
stability of the cation in the gas phase. The experimental
standard Gibbs energy changes of the cation formation
(reaction) were in very good agreement with PM3 calcu-
lations. However, 1-bromo-3,5,7-trimethyladamantane
(2Br) solvolyzes slower than 1-bromoadamantane (1Br)
in all the nonaqueous alcoholic solvents examined. The
faster rate of 1Br has been ascribed to the Brφnsted base-
type solvation toward relatively positive hydrogen atoms
on the 3-, 5-, and 7-positions in the transition state of
ionization. When isopropyl or propyl groups are intro-
duced in place of the methyl groups to give 3cBr or 4cBr,
respectively, the respective rate ratio to 1Br in nonaque-
ous alcoholic solvents increases to 12-15 or 2-4, owing
to the greater electron-donating abilities of the substit-
uents than the methyl group. However, the rate ratios,
3cBr/1Br and 4cBr/1Br, in aqueous organic solvents
showed a trend to decrease with increase in the amount
of water, reaching 0.84 and 0.15, respectively, in 60%
ethanol. In the long history of solvolysis studies, “80%
ethanol” has been used as a convenient solvent. However,
the present data suggest that aqueous ethanol might
result in a wrong conclusion regarding the stability of
incipient carbocations and electron-donating ability of
alkyl substituents. It is recommended that whenever the
solvolytic reactivity is to be related with carbocation
stability, the rates should be examined in nonaqueous
solvents such as ethanol, methanol, TFE, TFE-EtOH,
and 97% HFIP.
‡
to that for ∆G , 1Br (26.3) < 3cBr (26.8) > 4cBr (26.0).
Clearly, the introduction of the three n- or isopropyl
substituents is unfavorable by 1.3 or 0.7 kcal mol with
-
1
‡
respect to the ∆H term, but favorable by about 1 kcal
-
1
‡
mol regarding the -T∆S term. The former effect may
be explained by assuming the decreased stability of the
cation side in more ethanolic solvation shell with in-
creased hydrophobicity, and the latter by the concomitant
decrease in the fraction of water that would be sterically
more easily solvating than ethanol at the transition state.
5
. Beh a vior of Mon o- a n d Dia lk yl-1-br om oa d a -
m a n ta n es in th e Gr u n w a ld -Win stein Rela tion sh ip .
The greater dispersions in the GW plots for 3,5,7-trialkyl-
1
5
factor than the shape of the alkyl group. To examine if a
n-nonyl group exerts an effect similar to that of the three
n-propyl groups of 4cBr, 5Br was subjected to solvolysis.
In this investigation, only five solvents were selected.
From the plots in Figure 5, it appears convenient to
examine downward dispersions of the data points for 80%
EtOH, 70% EtOH, 80% MeOH from a line connecting
those for 80% TFE-20% EtOH and 60% TFE-40%
EtOH. In Figures 6a are shown the GW plots for
-bromoadamantanes, 3cBr and 4cBr, than 2Br (Figure
) indicate that the carbon number is a more important
3
-isopropyl-, 3-propyl-, and 3-nonyl-1-bromoadamantanes
(3a Br, 4bBr, and 5Br, respectively). Evidently, the nonyl
group causes only slightly greater dispersions than the
propyl group, suggesting that the solvent composition at
the place distant from the adamantyl moiety has es-
(30) An examination of ion pair return by using the chloroformate
Because of unexpectedly decreased rates of solvolysis
of alkylated 1-bromoadamantanes having isopropyl or
propyl substituents relative to 1Br in aqueous organic
of 3cOH was attempted, but it was too unstable for isolation. For the
use of the chloroformate of 1OH, see, Kevill, D. N.; Kyong, J . B.; Weitl,
F. L. J . Org. Chem. 1990, 55, 4304-4311.

2
042 J . Org. Chem., Vol. 66, No. 6, 2001
Takeuchi et al.
solvents, those data points for 3cBr and 4cBr show
downward dispersions in the Grunwald-Winstein (GW)
relationship. In contrast to aqueous ethanol, aqueous
methanol mixtures do not show an appreciable downward
bulge in the GW plot. Linear extrapolation of the aqueous
methanol line to the YBr value for water (4.44) suggests
the rate ratio 3cBr/1Br of ∼0.8. It is assumed that the
Brφnsted-base type hydration to the â-hydrogens is so
sensitive to steric encumbrance that more congested 3cBr
is subject to less effective hydration than 1Br in the
transition state of ionization. This type of solvation by
methanol and larger molecules may not be so significant
as water since the GW plot for the nonaqueous solvents
with ether and then washed with water and saturated
NaHCO
fication by MPLC (SiO
8% yield. Anal. Calcd for C16
Found: C, 64.39; H, 8.83.
,5-Diisop r op yl-1-a d a m a n ta n eca r bon yl Ch lor id e (3b-
3
and dried (MgSO
) gave 3bBr (0.46 g) as a viscous oil in
27Br: C, 64.21; H, 9.09.
4
). Evaporation of ether and puri-
2
3
H
3
COCl). Thionyl chloride (3.10 mL, 43.3 mmol) was slowly
added to 3bCO H (1.60 g, 6.05 mmol), and then the mixture
2
was warmed with stirring at 70 °C for 2 h. Excess thionyl
chloride was distilled off to give essentially pure 3bCOCl (1.69
g) as a yellow oil in 98% yield, which was used for the next
step without further purification.
2
-(3,5-Diisop r op yl-1-a d a m a n tyl)-2-p r op a n ol (6). A solu-
tion of 3bCOCl (1.69 g, 5.97 mmol) in anhydrous diethyl ether
50 mL) was added over 30 min to methylmagnesium iodide
(
shows a very good linear relation with YBr
.
which had been prepared from methyl iodide (2.1 mL, 34
mmol) and magnesium turnings (0.85 g, 35 mmol) in anhy-
drous diethyl ether (25 mL), and then the mixture was refluxed
The markedly slower rates of solvolysis of 3cBr and
cBr in aqueous ethanol and aqueous acetone than in
4
for 4 h. The reaction mixture was treated with saturated NH
Cl and worked up as usual to afford essentially pure 6 (1.63
g) as a yellow oil in 98% yield. HRMS (FAB+) calcd for C19
78.2610, found 278.2609.
,5,7-Tr iisop r op yl-1-a d a m a n ta n ol (3cOH). Following the
4
-
nonaqueous organic solvents having a same YBr value
may be explained by hydrophobic interaction of the highly
alkylated structure with the organic component in the
aqueous organic mixtures. The first solvation shell
containing greater amounts of the organic component
than the bulk phase would make the ionization less easy.
The present markedly decelerated solvolysis of 3cBr and
34
H O
2
3
11
procedure reported for the preparation of 3a OH and 3bOH,
trifluoroacetic acid (26.0 mL, 337 mmol) was added with
stirring to 6 (1.54 g, 5.53 mmol), and the reaction mixture was
stirred at 65 °C for 4 h. To the stirred mixture was added
4
cBr in aqueous organic solvents is a kinetic version of
saturated aqueous Na
addition, a reddish brown oil separated, and its color changed
to yellow when 90 mL of saturated aqueous Na CO was
added. The reaction mixture was refluxed for 3.5 h and then
extracted with diethyl ether. The extract was washed with H
and dried (MgSO ) and the solvent evaporated. The residue
2 3
CO (170 mL) dropwise. During the
anomalously diminished dissociation of alkylbenzoic acids
in aqueous ethanol and aqueous tert-butyl alcohol that
was demonstrated by Wepster and co-workers a decade
ago and ascribed to hydrophobic effects.
2
3
2
O
4
was subjected to MPLC (hexane-ether) to give 3cOH (0.88 g)
Exp er im en ta l Section
as slowly solidifying, colorless crystals in 57% yield: mp 81.5-
Melting points are uncorrected. 1H NMR spectra were
82.5 °C. Anal. Calcd for C19
C, 81.66; H, 12.22.
H34O: C, 81.95; H, 12.31. Found:
1
3
recorded at 270 or 400 MHz. C NMR spectra were recorded
at 67.5, 75.5, or 100 MHz. The spectral data for all new
compounds are summarized in the Supporting Information.
GLC analyses were conducted on a PEG 20M column (3 mm
1-Br om o-3,5,7-tr iisop r op yla d a m a n ta n e (3cBr ). To a
solution of 3cOH (0.81 g, 2.91 mmol) in anhydrous benzene
(10 mL) was added a solution of PBr (0.90 g, 9.5 mmol) in
3
×
2 m) or a PEG 20 M capillary column (0.22 mm × 25 m).
anhydrous benzene (10 mL) over 3 min at 0 °C. The reaction
mixture was stirred at r.t. for 0.5 h and then refluxed for 2.5
h. The reaction mixture was poured into ice and extracted with
diethyl ether. The extract was washed with saturated aqueous
NaHCO and dried (MgSO ), and the solvent was evaporated
3 4
to give 3cBr (0.85 g) as slowly solidifying, pale yellow crystals
Mass spectra were recorded on a GC-MS spectrometer. El-
emental analyses were performed by the Microanalytical
Center, Kyoto University, Kyoto. 1-Bromo-3,5,7-trimethylada-
1
a,c,f
1b,c
mantane (2Br),
1-bromo-3-isopropyladamantane (3a Br),
1
1
3
-isopropyl-1-adamantanol (3a OH), 3,5-diisopropyl-1-ada-
1
1
10
mantanol (3bOH), and 1-bromo-3-propyladamantane (4aBr)
in 86% yield: mp 40.0-40.5 °C. Anal. Calcd for C19H33Br: C,
were reported previously. 1-Propyladamantane (4a H),10,31
which had been synthesized by the Wolff-Kishner reduction
66.85; H, 9.74. Found: C, 66.56; H, 9.85.
1
0
1-P r op yla d a m a n ta n e (4a H). This known compound was
1
0
12
of 1-(1-adamantyl)-2-propanone, was prepared by the direct
alkylation of 1Br with PrMgBr in CH
were purified by previously described methods. Anhydrous
solvents used for synthesis were purified by the standard
2
procedures. 2,6-Lutidine was distilled over CaH . Other com-
prepared by a different method than that used originally. A
1
2
-1
2
Cl
2
.
Solvolysis solvents
solution (50 mL) of 2.24 mol L propylmagnesium bromide
3
2
in ether was placed in a 300 mL flask, and the ether was
distilled off until the residual PrMgBr became white crystals.
A solution of 1-bromoadamantane (1Br) (12.1 g, 56.4 mmol)
mercially available reagents were of a reagent-grade quality
and used as received. Medium-pressure liquid chromatography
in dry CH
refluxed under N
2
Cl
2
(134 mL) was added, and the mixture was
for 15 h. The reaction mixture was worked
2
(
MPLC) was conducted on Merck silica gel 60 (230-400 mesh).
Recycle preparative HPLC was performed with GPC columns
J AIGEL 1H and 2H, 20 × 600) using CHCl as eluent.
,5-Diisop r op yl-1-a d a m a n t a n eca r b oxylic Acid (3b -
H). To a mixture of CCl (80 mL) and H SO (100 mL)
was added with stirring a solution of 3,5-diisopropyl-1-ada-
up in a usual manner to give an oil (9.25 g), which on
treatment by MPLC (hexane) gave 4a H as a colorless oil (6.45
g) in 64% yield.
1,3-Dip r op yla d a m a n ta n e (4bH). Treatment of 4a Br (7.93
g, 30.8 mmol) with propylmagnesium bromide (63 mmol) in
(
3
3
2
CO
4
2
4
CH
2 2
Cl (70 mL) in the manner described for 4a H gave crude
1
1
mantanol (3bOH) (4.92 g, 20.8 mmol) in formic acid (70 mL,
.8 mol) over 210 min at 8-17 °C by cooling in an ice-water
bath. The reaction mixture was poured into ice-water and
extracted with CCl . The aqueous layer was extracted with
CCl , and the organic layer was dried (MgSO ). Evaporation
of solvent gave 3bCO H as a colorless solid (5.55 g) in 100%
yield: mp 81.0-82.0 °C (from hexane). Anal. Calcd for
: C, 77.22; H, 10.67. Found: C, 76.96; H, 10.58.
-Br om o-3,5-diisopr opyladam an tan e (3bBr ). To a chilled
solution of 3bOH (0.96 g, 4.06 mmol) in benzene (6.0 mL) was
added PBr (0.30 mL, 3.16 mmol) in benzene (6.0 mL) over 2
4bH (6.34 g) as a yellow oil, which was then purified by MPLC
1
(hexane). Anal. Calcd for C16
C, 87.19; H, 12.81.
H28: C, 87.36; H, 12.92. Found:
4
1-Br om o-3,5-d ip r op yla d a m a n ta n e (4bBr ). A mixture of
4bH (500 mg, 2.26 mmol) and Br (2.3 mL, 45 mmol) in CCl
4
4
2
4
2
(45 mL) was refluxed for 18 h. The reaction mixture was
treated as usual to give a yellow oil, which was purified by
MPLC (hexane) to give 4bBr (480 mg) in 71% yield. Anal.
17 28 2
C H O
1
Calcd for C16
9.23.
H27Br: C, 64.21; H, 9.09. Found: C, 64.13; H,
3
1,3,5-Tr ip r op yla d a m a n ta n e (4cH). Treatment of 4bBr
min. The mixture was stirred for 55 min at 0 °C, 18 min at
r.t. and then refluxed for 2 h. The reaction mixture was diluted
(9.71 g, 32.4 mmol) with propylmagnesium bromide (72 mmol)
in CH Cl (50 mL) in the manner described for 4a H gave crude
2 2

Gas- and Liquid-Phase Stability of 1-Adamantyl Cations
cH (7.5 g) as a yellow oil, which was shown by GLC to contain
J . Org. Chem., Vol. 66, No. 6, 2001 2043
4
Br/R
2
Br. In all cases, double-resonance-like experiments were
about 30% of 4cH and 60% of 4bH. Treatment of the mixture
by MPLC (hexane) afforded fractions containing 4bH and 4cH,
which were not investigated further. Treatment of a fraction
performed in order to confirm the exchange of bromide anion.
Kin etic Meth od s. The preparation of solvents and kinetic
3
2
studies followed the methods described previously.
P r od u ct Stu d ies. The solutions of 0.01 and 0.005 mol L
of 1Br and 3cBr, respectively, in 80% ethanol-20% water
-
1
by GPC gave pure 4cH. Anal. Calcd for C19
3.05. Found: C, 86.97; H, 12.76.
-Br om o-3,5,7-tr ip r op yla d a m a n ta n e (4cBr ). A mixture
of 4cH (174 mg, 0.66 mmol) and Br (0.4 mL, 7.8 mmol) in
CCl (0.1 mL) was refluxed for 39 h. The reaction mixture was
H34: C, 86.95; H,
1
-
1
1
containing 0.025 mol L 2,6-lutidine were kept at 25 or 75
°C. The solvolyses at 75 °C were carried out for 10 half-lives,
but those at 25 °C were conducted for 1.5 and 2.9 half-lives
for 1Br and 3cBr, respectively. The reaction solutions were
2
4
treated as usual to give a yellow oil, which was purified with
GPC to give 4cBr (135 mg) in 60% yield. The elemental
analysis data were unsatisfactory because of difficulty in
2 3
treated with solid K CO , and the organic layer separated by
salting-out was dried over Drierite and subjected to GLC
analysis using a PEG 20M capillary column and an FID
detector. The calibration of the peak area was performed by
using factors 0.83 for 1OEt vs 1OH and 0.90 for 3cOEt vs
3cOH.
complete removal of solvent. Anal. Calcd for C19
6.85; H, 9.74. Found: C, 65.82; H, 9.71.
-Non yla d a m a n ta n e (5H). Treatment of 1Br (300 mg, 1.40
mmol) with nonylmagnesium bromide (2.9 mmol) in CH Cl
6 mL) at reflux for 12 h followed by usual work up gave 5H
220 mg) in 59% yield after purification by MPLC (hexane).
H33Br: C,
6
1
2
2
(
(
Ack n ow led gm en t. We thank Professor J os e´ -Luis
M. Abboud and Professor Emeritus J ohn Shorter for
valuable suggestions. Work at Kyoto University was
supported in part by the J apanese Ministry of Educa-
tion, Science, Sports and Culture through a Grant-in-
Aid for Scientific Research (10440188), and that at CSIC
was supported by Grant PB-96-0927-C02-01 of the
Spanish DGES.
Anal. Calcd for C19
H, 13.33.
H34: C, 86.95; H, 13.05. Found: C, 86.80;
1
-Br om o-3-n on yla d a m a n ta n e (5Br ). A mixture of 5H
2.83 g, 10.8 mmol) and Br (5 mL, 98 mmol) in CCl (5 mL)
was heated at 70 °C for 12 h. The reaction mixture was treated
as usual to give a yellow oil, which was purified with a SiO
column (hexane) to give 5Br (2.95 g) as a yellow oil in 80%
(
2
4
2
yield. Calcd for C16
H, 9.99
H27Br: C, 66.85; H, 9.74. Found: C, 66.40;
Su p p or tin g In for m a tion Ava ila ble: Estimations of ∆H°-
F T ICR Exp er im en ts. Typically, mixtures of two carefully
degassed bromides, R Br and R Br, with total pressures in the
+
(
3,theor) of 4c and the rate constant of ethanolysis of 1Br,
1
2
plot of log(k70E-30W/k60T-40E) vs Σπ, and NMR data for new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
-7
-6
range 5 × 10 to 2 × 10 mbar were introduced into the high
vacuum section of a modified Bruker CMS-47 Fourier Trans-
1
3a
form ICR mass spectrometer
and subjected to electron
J O0015265
ionization under mild conditions (nominal energies of 11-12
+ +
1 2
and R thus obtained were allowed to react and
eV). Ions R
(
31) For 13C NMR data, see, Shokova, E. A.; Luzikov, Yu. N.;
Kovalev, V. V. J . Org. Chem. USSR, Engl. Transl. 1984, 20, 2104-
108.
32) Takeuchi, K.; Ikai, K.; Shibata, T.; Tsugeno, A. J . Org. Chem.
1988, 53, 2852-2855.
equilibrate, the reaction being monitored for some 20 s, with
samplings every 1-2 s. The ratios of the partial pressures of
the neutral reagents were varied as much as possible. At least
2
(
1
six different experiments were performed for each couple R -