Cases of pronounced extended π,n-participation in solvolysis of tert-butyl and benzyl chloride derivatives

Article abstract of DOI:10.1002/poc.853

Solvolysis rates of chlorides that share the same side-chain comprising two neighboring groups [tertiary chloride 10, 2-chloro-2,6-dimethyl-9-methoxy-(6E)- nonene, and benzyl chlorides 11, 1-chloro-1-aryl-5-methyl-8-methoxy-(5E)octene, with various phenyl substituents (Y=p-OCH₃, p-CH₃, H, p-Br and m-Br)], were measured in 80% (v/v) aqueous ethanol. Both the tertiary substrate 10 and the benzyl substrates 11 solvolyze with smaller entropy and enthalpy of activation than the corresponding reference analogs with one neighboring group, 6 and 8, respectively (ΔΔH≠ = -34 ± 6kJ mol^-1, ΔΔ≠ S = -122 ± 19 JK^-1 mol^-1 with 10; ΔΔH≠ = -33 ± 6kJ mol ^-1, ΔΔS≠ = -95 ± 17 J K^-1 mol ^-1 with 11), indicating that in addition to the double bond, the methoxy group also participates in the rate-determining step. Chloride 10 has a significantly reduced secondary β-deuterium kinetic isotope effect (k _H/k_D= 1.07 ± 0.01 in 80E; k_H/k _D = 1.05 ± 0.1 in 97T) in comparison with the typical value for the tertiary chlorides (k_H/k_D = 1.80), as a consequence of the less positive charge on the reaction center in the transition state. The slope of the Hammett plot σ ⁺ value obtained with the series of 11 is considerably smaller than that obtained with the reference chlorides 8-Y (σ⁺ = -1.29 ± 0.11 vs -3.93 ± 0.10), confirming that benzyl substrates also solvolyze with extended π,n-participation. On both types of substrates, 10 and 11, the kinetic parameters indicate that very pronounced assistance of both neighboring groups occurs in the rate-determining step. Copyright

Full text of DOI:10.1002/poc.853

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2005; 18: 368–372
Published online 6 September 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.853
Cases of pronounced extended p,n-participation in
solvolysis of tert-butyl and benzyl chloride derivatives
´
Sandra Juric and Olga Kronja*
ˇ ´
Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovacica 1, P. O. Box 156, 10000 Zagreb, Croatia
Received 02 May 2004; revised 07 July 2004; accepted 13 July 2004
ABSTRACT: Solvolysis rates of chlorides that share the same side-chain comprising two neighboring groups [tertiary
chloride 10, 2-chloro-2,6-dimethyl-9-methoxy-(6E)-nonene, and benzyl chlorides 11, 1-chloro-1-aryl-5-methyl-8-
methoxy-(5E)-octene, with various phenyl substituents (Y ¼ p-OCH3, p-CH3, H, p-Br and m-Br)], were measured in
80% (v/v) aqueous ethanol. Both the tertiary substrate 10 and the benzyl substrates 11 solvolyze with smaller
entropy and enthalpy of activation than the corresponding reference analogs with one neighboring group, 6 and 8,
¼
¼
¼
respectively (ÁÁH ¼ ꢀ34 ꢁ 6 kJ molꢀ1, ÁÁS ¼ ꢀ122 ꢁ 19 J Kꢀ1 molꢀ1 with 10; ÁÁH ¼ ꢀ33 ꢁ 6 kJ molꢀ1
,
ÁÁS ¼ ꢀ95 ꢁ 17 J Kꢀ1 molꢀ1 with 11), indicating that in addition to the double bond, the methoxy group also
participates in the rate-determining step. Chloride 10 has a significantly reduced secondary ꢀ-deuterium kinetic
isotope effect (kH/kD ¼ 1.07 ꢁ 0.01 in 80E; kH/kD ¼ 1.05 ꢁ 0.1 in 97T) in comparison with the typical value for the
tertiary chlorides (kH/kD ¼ 1.80), as a consequence of the less positive charge on the reaction center in the transition
state. The slope of the Hammett plot ꢁþ value obtained with the series of 11 is considerably smaller than that obtained
with the reference chlorides 8-Y (ꢁþ ¼ ꢀ1.29 ꢁ 0.11 vs ꢀ3.93 ꢁ 0.10), confirming that benzyl substrates also
solvolyze with extended ꢂ,n-participation. On both types of substrates, 10 and 11, the kinetic parameters indicate that
very pronounced assistance of both neighboring groups occurs in the rate-determining step. Copyright # 2004 John
Wiley & Sons, Ltd.
¼
KEYWORDS: secondary ꢀ-deuterium isotope effects; tertiary chlorides; benzyl chlorides; extended ꢂ,n-participation;
Hammett correlation; solvolysis
INTRODUCTION
electrons of the methoxy group take part in the reaction,
hence the reaction proceeds by way of extended ꢂ,n-
participation.
The outstanding problem with the biomimetic cyclization
mechanism is whether cyclization occurs in a stepwise or
concerted manner upon the formation of the carbocation
intermediate. We have reported on numerous squalene
derivatives1 and model compounds2 that solvolyze by
way of the kÁ process in which two neighboring groups
take part in the rate-determining step, i.e. extended
participation occurs. For example, in solvolysis of chlo-
rides 1,3 24,5 and 3,6 both double bonds participate
their electrons in the rate-determining displacement
of chloride ion. We have also demonstrated that in
chlorides 47 and 5,8 which have a methoxy group as
second neighboring group, the double bond and the n-
Kinetic data are considered to provide an indication of
the extended participation mechanism if they show spe-
cific variations from those obtained with the correspond-
ing model compound lacking the second neighboring
group (e.g. chlorides 6–9). Typically, the most pertain
variations are as follows: (a) decrease of ÁH and ÁS ;
(b) depression of the secondary ꢀ-deuterium kinetic
isotope effect (KIE) (two deuteromethyl groups, as
*Correspondence to: O. Kronja, Faculty of Pharmacy and Biochem-
ˇ ´
istry, University of Zagreb, A. Kovacica 1, P. O. Box 156, 10000
Zagreb, Croatia.
E-mail: kronja@pharma.hr
Contract/grant sponsor: Ministry of Science and Technology of the
Republic of Croatia; Contract/grant number: 0006451.
¼
¼
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 368–372

EXTENDED ꢂ,n-PARTICIPATION IN SOLVOLYSIS
369
shown in, e.g. structures 1, 3 and 5); and (c) lowering
the slope of Hammett ꢁþ plot for benzyl derivatives
(substrates 2 and 4).
RESULTS AND DISCUSSION
The protio and hexadeuterated isotopomers of chloride
10 and benzyl chlorides 11 (Y ¼ p-OCH3, p-CH3, H, p-Br
and m-Br) were prepared according to procedures pre-
sented in detail in the Experimental section.
Chlorides 10, 10-d6 and the series of 11 were subjected
to solvolysis in 97% (w/w) aqueous 2,2,2-trifluoroethanol
(97T) and/or 80% (v/v) aqueous ethanol (80E). Solvolysis
rates were followed by means of a pH-stat. The extrapo-
lated or measured rate constants and the activation para-
meters are presented in Table 1. The activation parameters
were calculated from the rate constants determined at
different temperatures. The rates for the corresponding
unsaturated compound were calculated according to the
empirical equation presented earlier that takes into account
the length of the side-chain of tertiary and benzyl chlo-
rides.12 The Hammett ꢁþ values for the chlorides 11 were
calculated using simple regression analysis. Rate effects
(kU/kS, where kU is the rate for the unsaturated compound
and kS is the rate for the saturated reference compound),
secondary ꢀ-deuterium KIEs (kH/kD) or reaction constants
(ꢁþ ) of 10 and 11, along with the same data for some
relevant reference compounds are given in Table 2.
Both substrates 10 and 11 show a moderate rate
enhancement relative to saturated analogs (Table 2).
However, the simple participation cannot be distin-
guished from the extended participation mechanism, so
these results are not conclusive.
Even though the participation of the second neighbor-
ing group in 1–5 has been proved without ambiguity, its
assistance is not the same in magnitude in all substrates. It
generally appears that the delocalization of the second
neighboring group is more efficient in substrates which
have the first participating group (double bond) located at
C-5 from the reaction center (as in 1 and 2) than in the
substrates which have the double bond located at C-4 (as
in 3–5). For example, the depression of the ꢀ-deuterium
KIE in the solvolysis of 1 is much more pronounced
[kH/kD ¼ 1.01 ꢁ 0.02 vs 1.37 ꢁ 0.03 for the reference
compound 6 in 80% (v/v) ethanol at 50 ꢂC]3,9 than that
of 3 and 5, respectively [kH/kD ¼ 1.14 ꢁ 0.01 and 1.16 ꢁ
0.03, respectively, vs kH/kD ¼ 1.30 ꢁ 0.03 for the refer-
ence compound 7 in 80% (v/v) ethanol at 50 ꢂC],6,8
indicating less positive charge on the reaction center in
the transition structure of 1 than that of 3 and 5, i.e.
more extensive charge delocalization in 1. Similarly, the
slope of Hammett plot is 2.3 units less for 2 than for
the reference chloride 8,10 whereas it is only 1.1 units less
for 4 than for reference compound 9.
Since, to the best of our knowledge, substrates 4 and 5
are the only cases reported in which the methoxy group as a
second neighboring group acts with the double bond in a
concerted manner, in a logical extension of our work we set
out to design substrates in which we predict very distinct
extended charge delocalization of ꢂ- and n-electrons in the
transition state. According to the above considerations, a
suitable candidate for a structure is one in which the double
bond is located on C-5 from the reaction center, which
leads to the formation of a cyclohexyl-like transition
structure. It is known that methoxy group participation is
very efficient if the transition state is a tetrahyrofuran-like
structure.11 Therefore, we assumed that the tertiary chloride
10 and the benzyl chlorides 11 should unambiguously give
kinetic evidence of a very pronounced extended ꢂ,n-
participation mechanism.
A concerted bicyclization mechanism for 10 and all
derivatives of 11 can be deduced with great certainty on
the basis of the activation parameters. It is well known
¼
that neighboring group participation lowers ÁH . Also,
the kÁ process involves bridging and loss of some
degrees of rotational freedom of the alkenyl chain in
the transition state, which results in a more negative
¼ 13
ÁS . Therefore, we compared the activation para-
meters of tertiary chloride 69 with those of tertiary
chloride 10 and of benzyl chloride 810 with benzyl chloride
11, respectively. The methoxy group in both types of
substrate has an substantial influence on activation para-
meters. Thus, the enthalpy and the entropy of activation
are considerably lower for both the tertiary substrate
¼
¼
¼
10 (ÁÁH ¼ ÁH 10 ꢀ ÁH ¼ ꢀ34 ꢁ 6 kJ molꢀ1
,
6
¼
¼
¼
ÁÁS ¼ ÁS 10 ꢀ ÁS ¼ ꢀ122 ꢁ 19 J Kꢀ1 molꢀ1 in
6
¼
¼
¼
¼
80EtOH) and the benzyl substrate 11 (ÁÁH ¼ ÁH
11
ꢀ ÁH ¼ ꢀ33 ꢁ 6kJmolꢀ1; ÁÁS ¼ ÁS 11 ꢀ ÁS
¼
¼
8
8
¼ ꢀ95 ꢁ 17 J Kꢀ1 molꢀ1 in 80EtOH). These values are
consistent with the rate-determining extended participa-
tion mechanism, in which the high degree of order
¼
required in the transition state (large negative ÁS ) is
overcompensated by a rather small ÁH .
¼
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 368–372

´
S. JURIC AND O. KRONJA
370
Table 1. Solvolysis rate constants and activation parameters for chlorides 10 and 11
¼
¼
Compound
Solventa
80E
t/( ꢂC)
k(10ꢀ 4sꢀ1 b
)
ÁH (kJ molꢀ1 c
)
ÁS
(J Kꢀ1 molꢀ1 c
)
10
50
40
30
25
55
45
35
25
50
35
50
40
30
25
60
50
40
25
70
60
50
25
70
60
50
25
70
60
50
25
4.26 (2)
2.37 (5)
1.53 (3)
1.127
65.5 (6)
33.2 (2)
18.6 (1)
9.12
1.43 (2)
1.78 (1)
48.1 (2)
23.5 (1)
11.9 (2)
8.05
16.6 (3)
10.7 (1)
6.69 (9)
3.13
8.72 (5)
5.89 (3)
3.24 (7)
0.805
6.44 (3)
3.88 (9)
2.21 (1)
0.479
5.58 (2)
2.98 (2)
1.68 (2)
0.297
39 ꢁ 4
ꢀ190 ꢁ 13
97T
50 ꢁ 3
ꢀ135 ꢁ 10
10-d6
80E
97T
80E
11-p-OCH3
54 ꢁ 2
36 ꢁ 0.1
43 ꢁ 5
46 ꢁ 1
52 ꢁ 2
ꢀ122 ꢁ 6
ꢀ189 ꢁ 0.2
ꢀ179 ꢁ 14
ꢀ171 ꢁ 2
ꢀ155 ꢁ 7
11-p-CH3
11
80E
80E
80E
80E
11-p-Br
11-m-Br
a 80E is 80% (v/v) aqueous ethanol; 97T is 97% (w/w) aqueous 2,2,2-trifluoroethanol.
b
The uncertainties of the last reported figure (standard deviation of the mean) are given in parentheses. The rate constants lacking standard errors are
extrapolated.
c Uncertainties are standard deviations.
Table 2. Relative solvolysis rates, ꢀ-deuterium secondary
kinetic isotope effects and Hammett ꢁþ values of some
tertiary and benzyl chlorides
Charge delocalization from the reaction center in
benzyl systems can be proved with the Hammett ꢁþ
parameter, which is a measure of the charge ‘seen’ by the
aromatic ring at the reaction center, i.e. a measure of
charge delocalization.14 The assistance of one double
bond in 6 lowers the ꢁþ value by ꢃ2 units in comparison
with the saturated analog 13 (ꢀ3.93 vs ꢀ6.28, Table 2),
while the methoxy group in 11 has a further dramatic
influence, so the ꢁþ value decreases by another 2.5 units.
It is worth noting that the Hammett parameter obtained is
similar to that with substrate 2, which ꢁþ was proposed as
a reference value for the extended participation mechan-
ism.5 The different solvolysis mechanisms of 8 and 11
are supported by the fact that with 8 breakdown of the
Hammett plot occurs, whereas with 11 all data correlate
well with the ꢃþ values. In the case of 8, the double bond
assistance is very attenuated by the strongly electron-
donating p-methoxy substituent, whereas with derivatives
of structure 11 the ‘stronger’ neighboring group partici-
pation is not overcome even by the p-methoxy group.
In conclusion, kinetic parameters obtained with 10 and
11 are fundamentally the same as those obtained earlier
with chlorides 1 and 2, indicating that the side-chain
b
c
Compound Solventa kU/kS
kH/kD
ꢀ ꢁþ d
12
13
6
8
5
80E
97T
80E
97T
80E
97T
80E
80E
97T
80E
1.80 ꢁ 0.03e
1.37 ꢁ 0.03e
6.28 ꢁ 0.25f
3.93 ꢁ 0.10f
32.7
16.1
3.7
1.16 ꢁ 0.1
1.12 ꢁ 0.1
4
10
11.9
10.4
1.45 ꢁ 0.03
1.07 ꢁ 0.01
1.05 ꢁ 0.01
11
55.9
1.29 ꢁ 0.11
a
80E is 80% (v/v) aqueous ethanol; 97T is 97% (w/w) aqueous 2,2,2-
trifluoroethanol.
Rate constant of unsaturated vs the rate constant of the corresponding
b
saturated chloride at 25 ꢂC; rate constants of saturated chlorides having the
same size of the side-chain wereeither measured or calculated according to
the equation given in Ref. 12.
c In 80E determined at 50 ꢂC, in 97T determined at 30 ꢂC; uncertainties are
standard errors of the estimate.
d
Determined from the rate constants extrapolated to 25 ꢂC; uncertainties
are standard errors of the estimate.
e Ref. 9.
f
Ref. 10.
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 368–372

EXTENDED ꢂ,n-PARTICIPATION IN SOLVOLYSIS
371
takes part in a similar manner regardless of whether the
second neighboring group is a double bond or a methoxy
group, i.e. under given conditions the methoxy group and
the double bond have comparable electron-donating
abilities. The results presented for 10 and 11 further
support the observation that in the transition state the
charge is more efficiently delocalized from the reaction
center if the double bond is located at C-5 than at C-4.
Hence the more reduced KIE with 10 than 5 and the more
reduced slope of the Hammett plot with 11 than 5
(Table 2) could be attributed to less charge on the reaction
center. Efficient charge delocalization could occur from
the optimal preorganized structure, which probably can-
not be achieved with 5 and 4 because of the angle strain.
Therefore, in the solvolysis of 10 and 11, the participation
of the second double bond is more important. The results
obtained could also be interpreted in terms of ‘early’ and
‘late’ transition states. The ‘earlier’ transition state exists
in the case of 4 and 5 and the ‘later’ state in the case of
10 and 11.
1.37 (m, 2H), 1.43–1.65 (m, 11H), 1.93–2.08 (m, 4H),
3.54–3.65 (m, 5H), 5.12–5.15 (t, 1H); 13C NMR (CDCl3),
ꢄ (ppm) 14.90, 16.20, 25.97, 34.12, 39.05, 41.15, 53.28,
68.50, 71.55, 122.44, 136.91.
1-Phenyl-8-methoxy-5-methyl-5-octenol. A suspension
of lithium powder (332 mg, 0.048 mol), granulated Li
(332 mg, 0.048 mol), dry THF (5 ml) and very little
(10 mL) CH3I was refluxed under a slow stream of argon
for 10–15 min in an ultrasonic bath, then a solution of
1.1 g (0.005 mol) of 1-bromo-4-methyl-7-methoxy-4-
heptene and benzaldehyde (0.575 g, 0.005 mol) in 20 ml
of dry THF was added dropwise to the stirred mixture at
0 ꢂC. After all the solution had been added, the reaction
mixture was by turns stirred with the magnetic stirrer and
the ultrasonic bath for 3 h. The progress of the reaction
was checked by TLC. The excess of Li was filtered off
and the filtrate was treated with a saturated aqueous
solution of NH4Cl. The alcohol was extracted with
diethyl ether and dried over anhydrous Na2SO4. The
diethyl ether was evaporated and the product was purified
on a silica gel column. Unreacted bromide was removed
with light petroleum and the pure alcohol was eluted with
dichloromethane. The yield of pure alcohol was 0.25 g
EXPERIMENTAL
1
Substrate preparation
(20.2%). H NMR (CDCl3) ꢄ (ppm) 1.38–1.52 (m, 5H),
1.89–1.99 (m, 4H), 2.46–2.50 (q, 2H), 3.26 (s, 3H), 3.54–
3.57 (t, 2H), 4.53–4.57 (t, 1H),5.10–5.13 (t, 1H), 7.17–
7.26 (m, 5H); 13C NMR (CDCl3), ꢄ (ppm) 17.08, 20.57,
26.16, 39.02, 39.29, 51.22, 67.49, 73.88, 123.99, 125.51,
127.84, 134.43, 135.17.
1-Bromo-4-methyl-7-methoxy-4-heptene. To a stirred
solution of primary alcohol (4-methyl-7-methoxy-4-
heptenol, 5 g, 0.032 mol) and carbon tetrabromide
(13.6 g, 0.041 mol) in 50 ml of dry methylene chloride,
a solution of triphenylphosphine (9.95 g, 0.038 mol) in
50 ml of the same solvent was added dropwise at room
temperature. After the addition was completed, the reac-
tion mixture was refluxed and stirred for 2–3 h. After
completion of the reaction (checked with TLC), light
petroleum was added and the volatiles were evaporated.
The crude product was purified by column chromatogra-
phy on silica gel by eluting the product with light
petroleum. The yield of pure bromide was 5.39 g
(76.5%). 1H NMR (CDCl3), ꢄ (ppm) 1.53 (s, 3H), 1.83–
2.08 (m, 6H), 3.28 (s, 3H), 3.59–3.65 (m, 4H), 5.12–5.15
(t, 1H); 13C NMR (CDCl3), ꢄ (ppm) 12.90, 30.44, 32.74,
34.37, 37.39, 51.16, 67.51, 125.39, 134.94.
1-(4-Methoxyphenyl)-8-methoxy-5-methyl-5-octenol. The
procedure is the same as described above. From
221 mg, (32.00 mmol) of Li powder, 221 mg
(32.00 mmol) of granulated Li, 1.10 g (5.00 mmol) of 1-
bromo-7-methoxy-4-methyl-4-heptene
and
0.74 g
(5.00 mmol) of anisaldehyde was obtained 0.27 g
1
(19.4%) of pure alcohol. H NMR (CDCl3), ꢄ (ppm)
1.55–1.58 (m, 2H), 1.66–1.96 (m, 7H), 2.41–2.23
(q, 2H), 3.73–3.97 (m, 8H), 4.60–4.63 (t, 1H), 5.19–
5.21 (t, 1H), 7.12–7.14 (d, 2H), 7.21–7.23 (d, 2H); 13C
NMR (CDCl3), ꢄ (ppm) 16.00, 23.81, 26.33, 39.46,
39.72, 55.00, 59.00, 67.66, 76.47, 118.80, 123.49,
129.75, 143.38, 158.81.
2,6-Dimethyl-9-methoxy-6-nonen-2-ol. Grignard reagent,
prepared from Mg (1.35 g, 54.00 mmol) and 1-bromo-4-
methyl-7-methoxy-4-heptene (3 g, 14.00 mmol) in THF
(10 ml), was cooled to 0 ꢂC and a solution of acetone
(0.80 g, 14.00 mmol) in 10 ml of THF was added drop-
wise. Stirring was continued at room temperature for 1 h.
The Grignard complex was hydrolyzed with saturated
aqueous NH4Cl. The water layer was washed with diethyl
ether three times and the combined ether layers were
washed with brine and dried over Na2SO4. The crude
product was purified by column chromatography on silica
gel. The pure alcohol obtained (1.15 g, 41.1%) was in the
1-(4-Methylphenyl)-8-methoxy-5-methyl-5-octenol. The
procedure is the same as described above. From 221 mg
(32.00 mmol) of Li powder, 221 mg (32.00 mmol) of
granulated Li, 1.10 g (5.00 mmol) of 1-bromo-7-meth-
oxy-4-methyl-4-heptene and 0.65 g (5.00 mmol) of p-
toluylaldehyde was obtained 0.18 g (13.7%) of pure
1
alcohol. H NMR (CDCl3), ꢄ (ppm) 1.35–1.79 (m, 5H),
1.84–2.07 (m, 7H), 3.69–3.978 (m, 5H); 13C NMR
(CDCl3), ꢄ (ppm) 15.50, 20.73, 20.84, 25.36, 39.46,
53.33, 67.72, 74.00, 118.00, 124.00, 124.26, 134.46,
136.63, 141.91.
1
form of a viscous oil. H NMR (CDCl3), ꢄ (ppm) 1.33–
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 368–372

´
S. JURIC AND O. KRONJA
372
1-(4-Bromophenyl)-8-methoxy-5-methyl-5-octenol. The
procedure is the same as described above. From 221 mg
(32.00 mmol) of Li powder, 221 mg (32.00 mol) of
granulated Li, 1.10 g (5.00 mmol) of 1-bromo-7-meth-
oxy-4-methyl-4-heptene and 0.92 g (5.00 mmol) of 4-
bromobenzaldehyde was obtained 0.29 g (17.8%) of
pure alcohol. 1H NMR (CDCl3), ꢄ (ppm) 1.18–1.25
(m, 7H), 1.42–1.45 (t, 2H), 1.63–1.69 (q, 2H), 3.42–
3.50 (m, 5H), 7.18–7.20 (d, 2H), 7.42–7.44 (d, 2H); 13C
NMR (CDCl3), ꢄ (ppm) 15.07, 25.10, 29.26, 30.15,
37.05, 58.57, 64.10, 65.68, 121.07, 125.33, 131.33,
131.77, 131.91.
the chloride 1 was dissolved in 20 ml of the solvent at the
required temperature thermostated to ꢁ 0.05 ꢂC, and the
liberated HCl was continuously titrated by using a 0.008
M solution of NaOH in the same solvent mixture. In-
dividual measurements could be described by the first-
order law from 15% up to at least 80% completion. First-
order rate constants were calculated from about 100
determinations by using a non-linear least-squares pro-
gram. Measurements were usually repeated 3–7 times.
Activation parameters were calculated from rate con-
stants at three different temperatures.
1-(3-Bromophenyl)-8-methoxy-5-methyl-5-octenol. The
procedure is the same as described above. From
62.5 mg (9.00 mmol) of Li powder, 62.5 mg (9.00 mol)
of granulated Li, 0.44 g (2.00 mmol) of 1-bromo-7-meth-
oxy-4-methyl-4-heptene and 0.35 g (52 mmol) of 3-bro-
mobenzaldehyde was obtained 0.18 g (27.5%) of pure
Acknowledgement
We gratefully acknowledge the financial support of this
research by the Ministry of Science and Technology of
the Republic of Croatia (Grant No. 0006451).
1
alcohol. H NMR (CDCl3) ꢄ (ppm) 1.29–1.35 (m, 2H),
1.52–1.60 (m, 5H),1.95–2.06 (m, 4H), 3.27 (s, 3H), 3.51–
3.54 (t, 2H), 5.05–5.09 (t, 1H), 7.20–7.42 (m, 4H); 13C
NMR (CDCl3), ꢄ (ppm) 13.02, 24.93, 26.83, 39.50,
55.21, 64.00, 66.02, 121.20, 122.55, 124.50, 126.33,
129.45, 130.95, 139.52, 141.20.
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´
3. Borcic S, Humski K, Kronja O, Imper V, Orlovic M, Polla E.
Chlorides 10, 10-d6 and 11. The parent alcohol was
dissolved in 10–15 ml of light petroleum, the solution
was cooled to ꢀ15 ꢂC and SOCl2 was added dropwise.
The reaction mixture was stirred for 2 h under reduced
pressure (about 520–560 mmHg) to remove the liberated
HCl and SO2 continuously. The light petroleum was then
evaporated and the crude chloride was used for kinetic
measurements. Further purification proved to be unne-
cessary because the solvolysis rates were found to be
independent on contamination.
J. Chem. Soc., Perkin Trans. 1 1989; 1861.
ˇ ´
4. Kronja O, Polla E, Borcic S. J. Chem. Soc., Chem. Commun 1983;
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7. Juric; S, Filipovic A, Kronja O. J. Phys. Org. Chem. 2003; 16:
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8. Juric S, Kronja O. J. Phys. Org. Chem. 2002; 15: 556–560.
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´ ˇ ´
10. Mihel I, Orlovic M, Polla E, Borcic S. J. Org. Chem. 1979; 44:
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4086–4090.
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Kinetic measurements
1–13.
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´
51: 3253–3256.
ˇ ´
Solvolysis rates were followed in 80% (v/v) aqueous
ethanol (80E) and 97% (w/w) aqueous 2,2,2-trifluor-
oethanol (97T) titrimetrically by means of a pH-stat
(end-point titration, pH ¼ 6.85). Typically, 0.02 mmol of
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(b) Johnson CD. Tetrahedron 1980; 36: 3461–3480; (c) Pross A.
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Copyright # 2004 John Wiley & Sons, Ltd.
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