Low-temperature x-ray structural studies of the ester and ether derivatives of cis- and trans-4-tert-butyl cyclohexanol and 2-adamantanol: Application of the variable oxygen probe to determine the relative σ-donor ability of C-H and C-C bonds

Article abstract of DOI:10.1039/b303453d

Results of low-temperature X-ray structural studies for five cis-, and three trans-4-tert-butyl cyclohexanol, and six 2-adamantanol ester and ether derivatives are reported. Plots of C-OR bond distance against pK_a(ROH) for derivatives of axial alcohol (5), equatorial alcohol (6) and 2-adamantanol derivatives (7) give slopes of -2.77 × 10^-3, -2.86 × 10^-3 and -3.05 × 10^-3, respectively. Given that the relative differences in the slopes are modest, no clear distinction can be made about the relative σ-donor ability of a C-H bond and a C-C bond.

Full text of DOI:10.1039/b303453d

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Low-temperature X-ray structural studies of the ester and ether
derivatives of cis- and trans-4-tert-butyl cyclohexanol and
2-adamantanol: application of the variable oxygen probe to
determine the relative ꢀ-donor ability of C–H and C–C bonds
Marisa Spiniello and Jonathan M. White*
School of Chemistry, The University of Melbourne, Victoria, 3010, Australia.
E-mail: whitejm@unimelb.edu.au
Received 31st March 2003, Accepted 26th June 2003
First published as an Advance Article on the web 28th July 2003
Results of low-temperature X-ray structural studies for five cis-, and three trans-4-tert-butyl cyclohexanol,
and six 2-adamantanol ester and ether derivatives are reported. Plots of C–OR bond distance against pKa(ROH)
for derivatives of axial alcohol (5), equatorial alcohol (6) and 2-adamantanol derivatives (7) give slopes of
Ϫ2.77 × 10Ϫ3, Ϫ2.86 × 10Ϫ3 and Ϫ3.05 × 10Ϫ3, respectively. Given that the relative differences in the slopes are
modest, no clear distinction can be made about the relative σ-donor ability of a C–H bond and a C–C bond.
other 2-substituted-1-fluoroethanes. They concluded that the
Introduction
gauche conformation of 1-fluoropropane 1a was preferred
because it maximises overlap between the C–H σ-donor and the
C–F σ* acceptor orbital. The anti conformation 1b, although
sterically more favourable, was proposed to be disfavoured
because it has the weaker C–C donor orbital interacting with
the C–F σ* orbital. From their calculations they established the
following ranking of hyperconjugative electron donor abilities:
C–Si > C–H > C–C > C–F.
Baker and Nathan1 reported that reaction of p-alkyl-substi-
tuted benzyl bromides with a solution of pyridine in acetone
follows the reactivity order of; Me > Et > Pri > But. This same
order of reactivity was observed for many other reactions which
were believed to involve electron deficient centres either directly
on, or immediately adjacent to the aromatic ring. Baker and
Nathan attributed this order of reactivity to C–H hyper-
conjugation, which was proposed to be superior to C–C hyper-
conjugation. This was supported by Taft and Lewis2 who
separated the contributions of inductive effects and resonance
effects for several alkyl substituents for reactions ranging
from the ionisation of alkyl-substituted benzoic acid deriv-
atives, to the solvolysis rates of benzyl hydryl chlorides
(Ar(C6H5)CHCl), and came to the conclusion that C–H hyper-
conjugation is about 1.3 times more effective than C–C
hyperconjugation.
Nevertheless both the origin of the Baker–Nathan effect and
the relative merits of C–H and C–C hyperconjugation is still
subject to much controversy. It has been suggested that the
original Baker–Nathan effect is a solvation phenomenon and
does not necessarily reflect differing merits of C–H and C–C
hyperconjugation. For example Glyde and Taylor3 measured
the pyrolysis rates of alkyl-substituted 1-aryl ethyl esters. This
reaction has been shown to proceed via formation of a partial
carbocation at the side-chain α-carbon,4 and therefore provided
an ideal system to investigate the electron-releasing effects of
alkyl substituents in the gas phase. They found the tert-butyl
group to be significantly more electron releasing than the
methyl group (σϩ(But)/σϩ(Me) = 1.26), and furthermore σpϩ–σI
for t-butyl (0.291) is greater than σpϩ–σI for methyl (0.244). The
data suggested that indeed the Baker–Nathan order of electron
release by alkyl groups was a solvation phenomenon, and
also that C–C hyperconjugation is greater than C–H hyper-
conjugation. However, Happer and Cooney5 determined the
electronic effect of alkyl substituents by measuring their influ-
ence on the 13C NMR chemical shifts of the β-carbon of
β-substituted styrenes. They found that the order of electron
release by p-alkyl substituents was Me > Et > Pri > But, which is
the original Baker–Nathan order. Furthermore they found that
this order was maintained in solvents ranging from CCl4,
CDCl3 to Me2SO and EtOH and concluded that the Baker–
Nathan order can justifiably be attributed to superior C–H
hyperconjugation. Rablen and co-workers6 reported a theor-
etical investigation on the gauche effect in 1-fluoropropane and
Despite the fact that the relative σ-donor abilities of C–H
and C–C bonds is still a matter of some dispute, Cieplack7
hypothesises that the preferred axial approach (2a) of small
nucleophiles to cyclohexanone derivatives arises because of
superior C–H hyperconjugation of the axial hydrogens with the
developing Nu–C antibonding orbital.
Given the conflicting data on the relative merits of C–H and
C–C hyperconjugation, we were interested to establish whether
useful information could be obtained from accurate X-ray
structural studies of cis and trans ester derivatives of 4-tert-
butyl cyclohexanol at low temperature.
It has been demonstrated that C–O bond distances are sensi-
tive to the effects of hyperconjugative electron donation into
the C–O antibonding orbital.8–12 For example, the C–OPNB
bond distances in the β-trimethylsilyl ester 3 is 1.492(2) Å,10 this
is significantly lengthened with respect to the corresponding
silicon-free analogue 4 which has a C–O distance of 1.473(2)
Å.13 In 3 the C–Si bond, which is a strong σ-donor, overlaps and
interacts with the C–OPNB σ* orbital. Whereas in 4 the C–Si
bond is replaced by a weaker C–H σ-donor orbital and as a
result the C–OPNB bond is shorter.
In axial cyclohexanol derivatives 5 the C–O σ* orbital over-
laps with two antiperiplanar C–H bonds whereas in equatorial
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 9 4 – 3 1 0 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 1 C–O Bond distances in selected axial and equatorial cyclohexyl ester and ether derivatives
a
pKa
R
rC–O/Å
rC–O/Å
3.4317
4-NO2C6H4CO
5a 1.473(2)
6a 1.463(2)
Molecule 1
6a 1.468(2)
Molecule 2
2.0018
0.42b 17
Ϫ3.8019
2,4-(NO2)2C6H3SO
2,4,6-(NO2)3C6H2
4-NO2C6H4SO2
5b 1.476(2)
5c 1.497(2)
5d 1.492(2)
6b 1.473(2)
6c 1.491(2)
6d 1.487(2)
a All pKa values were measured in water at 25ЊC. b This pKa value was measured at 24ЊC.
structural method for detecting the presence of electronic inter-
actions between electron donors and oxygenated substituents in
the ground state. Kirby and co-workers8,9 established that the
C–O bond distance in the C–OR fragment increases with
increasing electron demand of the OR substituent, reflecting an
increasing contribution of the Cϩ ϪOR valance bond form to
the ground state structure. If the electron demand of a substi-
tuent OR is quantified as the pKa value for the parent acid
(ROH), then a plot of C–OR bond distance vs. pKa(ROH) is
linear, and the slope of the resulting plot is sensitive to the
effects of electron donation into the C–OR σ* antibonding
orbital. The presence of good donor orbitals vicinal and anti-
periplanar to the C–O bond results in a strong response of the
C–OR distance to the electron demand of OR. This is because
of increased stabilisation of the cation part of the valance bond
form Cϩ ϪOR. For example, the plots of C–OR bond distance
vs. pKa(ROH) constructed for 8,9 918 and 108 give the following
relationships:
derivatives 6 the interaction is with the two antiperiplanar C–C
bonds in the cyclohexane ring.
Do the differing σ-donor abilities of C–H and C–C bonds
(if any) manifest in differences of the C–OR bond distances
between the axial and equatorial derivatives? Although Kirby
and co-workers9 found no evidence for this from room-
temperature structural data, we were hopeful that the increased
accuracy and precision of low-temperature X-ray data would
allow us to determine any differences in axial and equatorial
C–O bond distances (if indeed they exist).
We have previously reported, for different reasons, four pairs
of axial and equatorial cyclohexanol derivatives; the p-nitro-
benzoates 5a13 and 6a,13 the 2,4-dinitrobenzenesulfenates 5b11
and 6b,14 the 2,4,6-trinitrophenoxides 5c15 and 6c,15 and the
p-nitrobenzenesulfonates 5d16 and 6d16 (Table 1). In all
four pairs of structures the axial C–OR bond distance is
slightly longer than the equatorial distance. Although the
differences within each pair of structures is small and barely
significant in some cases, the fact that the same pattern is
observed for all pairs strongly suggested to us that this differ-
ence is real.
The slightly longer C–OR bond distances in the axial
derivatives 5a–d does not necessarily reflect the more effective
σ-donor ability of the antiperiplanar C–H bonds in 5a–d,
compared with the antiperiplanar C–C bonds in 6a–d, but may
simply arise because axially disposed oxygen substituents are in
a different steric environment to equatorial C–O substituents.
We decided to approach this question in two ways; firstly
to determine the structures of ether and ester derivatives of
2-adamantanol 7, in which the oxygen substituent is axial as in
5 but rather than having two C–H bonds antiperiplanar to the
C–OR bond, there are two C–C bonds as in 6.
8: rC–O/Å = 1.475 Ϫ 2.90 × 10Ϫ3pKa(ROH); R2 = 0.999 (1)
9: rC–O/Å = 1.502 Ϫ 5.30 × 10Ϫ3pKa(ROH); R2 = 0.986 (2)
10: rC–O/Å = 1.493 Ϫ 6.49 × 10Ϫ3pKa(ROH); R2 = 0.985 (3)
A strong response of C–OR bond distance to the electron
demand of OR is demonstrated for 10 which has oxygen lone
pair (nO) orbital antiperiplanar to the OR substituent (this is
the basis of the well known anomeric effect),8 a strong response
is also observed for 9 which has a C–Si bond antiperiplanar to
the OR substituent (this is the basis of the silicon β-effect),10 but
a weaker response is obvious in 8 which has either a σ C–H or
C–C bonding orbital, which are both weaker donor orbitals
situated antiperiplanar to the OR bond.
In this study we proposed to construct plots of C–OR bond
distance vs. pKa(ROH) for a range of ester and ether derivatives
of 5, 6 and 7 in the hope the electronic interaction between the
donor and acceptor orbitals, which is reflected in the slopes
obtained, might give some information about the σ-donor
abilities of C–H and C–C bonds.
The second approach was to apply the variable oxygen
probe10,11 to determine any differences in the σ-donor abilities
of C–H and C–C bonds. The variable oxygen probe is an X-ray
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 9 4 – 3 1 0 1
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Table 2 Ester and ether derivatives of 5, 6 and 7 suitable for low temperature X-ray analysis
a
pKa
pKa
pKa
7.1517
3.2922
2.8523
1.4323
0.66b 17
5e 4-NO2C6H4
2.1717
6e 2-NO2C6H4CO
6f 4-CH3C6H5SO2
6g C6H5SO2
7.1517
7a 4-NO2C6H4
7b 3-NO2C6H4CO
7c 2,4-(NO2)2C6H3CO
7d CH3SO2
7e 4-CH3C6H5SO2
7f C6H5SO2
5f 3-NO2-4-ClC6H3CO
5g 3,5-(NO2)2C6H3CO
5h 2,4-(NO2)2C6H3CO
5i Cl3CCO
Ϫ2.7019
Ϫ2.8019
3.4617
1.4317
Ϫ1.9019
Ϫ2.7019
Ϫ2.8019
a All pKa values were measured in water at 25ЊC. b This pKa value was measured at 20ЊC.
Results and discussion: synthesis
The alcohols 5 and 6 were prepared according to Scheme 1 by
reduction with either lithium aluminium hydride20 giving the
equatorial alcohol 6 as the major product, or by reduction with
L-selectride21 giving the axial alcohol 5. 2-Adamantanol is
commercially available.
Fig. 2 ORTEP-336 representation of the molecular structure of 6e.
Thermal ellipsoids are drawn at the 30% probability level.
Scheme 1
The alcohols 5, 6 and 7 were converted to a wide range of
ester and ether derivatives using standard techniques, those
derivatives which gave crystals suitable for X-ray analysis and
which could be cooled to low temperature without destructive
phase changes are given in Table 2.
The chloronitrobenzoate 5f was unexpectedly prepared from
3,4-dinitrobenzoic acid, which upon treatment with oxalyl
chloride gave 3-nitro-4-chlorobenzoyl chloride by apparent dis-
placement of the nitrite ion from 3,4-dinitrobenzoyl chloride,
Scheme 2.
Fig. 3 ORTEP36 representation of the molecular structure of 7a.
Thermal ellipsoids are drawn at the 30% probability level.
Scheme 2
Results and discussion: molecular structures
All structures were determined at 130 K to minimise the effects
of thermal motion. Thermal ellipsoid plots for 5h, 6e, 7a and 7c
are presented in Figs. 1, 2, 3 and 4, respectively (the remaining
structures which have the same numbering system for the
Fig. 4 ORTEP-336 representation of the molecular structure of 7c,
indicating the N ؒ ؒ ؒ O distances (O(4) ؒ ؒ ؒ N(2Ј)
= 2.789(2) Å;
O(4Ј) ؒ ؒ ؒ N(2) = 2.851(2) Å) by dashed lines. Thermal ellipsoids are
drawn at the 20% probability level.
cyclohexyl and adamantly fragments are omitted for the
purposes of brevity). Selected structural parameters for the
axial derivatives 5a–5i, the equatorial derivatives 6a–6g, and
the 2-adamantanyl derivatives 7a–7f are presented in Tables 3, 4
and 5, respectively.
Structures 6g and 7c occur in the solid state with two
independent molecules in the asymmetric unit. The two mole-
cules of 6g differ with respect to the conformation of the
benzenesulfonate group; in one molecule the aromatic ring
eclipses one of the S᎐O double bonds (Cortho–Cipso–SO = 3.1(2)Њ)
᎐
whereas in the second molecule the equivalent dihedral angle is
34.9(2)Њ. In 7c the two independent molecules in the asymmetric
unit are held together by a combination of π-stacking between
the benzene rings, and nitro–nitro interactions (Fig. 4). The
overall ‘complex’ has an approximate, non-crystallographic
2-fold axis of symmetry. The distance between the aromatic
Fig. 1 ORTEP-336 representation of the molecular structure of 5h.
Thermal ellipsoids are drawn at the 30% probability level.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 9 4 – 3 1 0 1
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Table 3 Selected bond distances (Å) for the axial derivatives 5a–5i
Compound
C(1)–O(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(1)
5a
5b
5c
5d
5e
5f
5g
5h
5i
1.473(2)
1.476(2)
1.497(2)
1.492(2)
1.460(2)
1.466(2)
1.471(2)
1.479(2)
1.478(3)
1.514(2)
1.512(2)
1.496(2)
1.514(2)
1.516(2)
1.513(3)
1.516(2)
1.514(3)
1.510(4)
1.512
1.532(2)
1.530(2)
1.522(2)
1.531(2)
1.529(2)
1.523(3)
1.525(2)
1.525(3)
1.529(4)
1.527
1.538(2)
1.534(2)
1.532(2)
1.537(2)
1.533(2)
1.536(3)
1.535(2)
1.532(3)
1.531(4)
1.534
1.533(2)
1.530(2)
1.535(2)
1.536(2)
1.534(2)
1.529(3)
1.533(2)
1.537(3)
1.529(4)
1.533
1.529(2)
1.527(2)
1.529(2)
1.528(2)
1.530(2)
1.530(3)
1.524(2)
1.524(3)
1.532(4)
1.528
1.516(2)
1.517(2)
1.507(2)
1.517(2)
1.520(2)
1.520(3)
1.515(2)
1.515(3)
1.515(4)
1.516
Mean
Table 4 Selected bond distances (Å) for the equatorial derivatives 6a–6g
Compound
C(1)–O(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(1)
6a
1.463(2)
1.514(2)
1.529(2)
1.537(2)
1.536(2)
1.535(2)
1.514(2)
Molecule 1
6a
1.468(2)
1.512(2)
1.526(2)
1.541(2)
1.539(2)
1.537(2)
1.514(2)
Molecule 2
6b
6c
6d
6e
6f
1.473(2)
1.491(2)
1.487(2)
1.471(2)
1.488(2)
1.487(2)
1.514(2)
1.504(2)
1.510(2)
1.503(2)
1.506(2)
1.510(2)
1.531(2)
1.533(2)
1.534(2)
1.530(2)
1.525(2)
1.532(2)
1.533(2)
1.539(2)
1.527(2)
1.537(2)
1.531(2)
1.534(2)
1.536(2)
1.525(2)
1.537(2)
1.522(2)
1.533(2)
1.531(2)
1.529(2)
1.531(2)
1.528(2)
1.534(2)
1.528(2)
1.532(2)
1.511(2)
1.503(2)
1.511(2)
1.516(2)
1.504(2)
1.510(2)
6g
Molecule 1
6g
1.492(2)
1.510(2)
1.509
1.529(2)
1.530
1.536(2)
1.535
1.533(2)
1.532
1.529(2)
1.531
1.509(2)
1.510
Molecule 2
Mean
Table 5 Selected bond distances (Å) for the 2-adamantyl derivatives 7a–7f
Compound C(2)–O(1) C(1)–C(7) C(3)–C(9) C(1)–C(6) C(3)–C(4) C(1)–C(2) C(2)–C(3) C(7)–C(8) C(8)–C(9) C(8)–C(10)
7a
7b
7c
1.456(1)
1.478(2)
1.481(2)
1.533(2)
1.552(2)
1.545(3)
1.539(2)
1.554(2)
1.537(3)
1.534(2)
1.538(2)
1.530(3)
1.534(2)
1.543(2)
1.528(3)
1.526(2)
1.518(2)
1.513(3)
1.534(2)
1.488(2)
1.520(3)
1.534(2)
1.499(2)
1.531(3)
1.532(2)
1.529(2)
1.538(3)
1.535(2)
1.539(2)
1.531(3)
Molecule 1
7c
1.481(3)
1.535(3)
1.540(3)
1.530(4)
1.508(4)
1.523(4)
1.504(3)
1.540(4)
1.528(3)
1.518(3)
Molecule 2
7d
7e
7f
1.487(2)
1.492(1)
1.485(2)
1.534(2)
1.540(2)
1.536(2)
1.537(3)
1.537(2)
1.538(2)
1.525(3)
1.536(2)
1.534(2)
1.530(3)
1.533(2)
1.533(2)
1.522(2)
1.521(2)
1.516(2)
1.527(2)
1.522(2)
1.526(2)
1.534(2)
1.535(2)
1.535(2)
1.536(3)
1.536(2)
1.533(2)
1.531(3)
1.533(2)
1.537(2)
ring systems of the two molecules of 7c is approximately 3.7 Å.
This brings the nitro groups of the two molecules into close
contact with each other; the O(4) ؒ ؒ ؒ N(2Ј) and O(4Ј) ؒ ؒ ؒ N(2)
distances which are 2.789(2) and 2.851(2) Å, respectively, and
are well within the sum of the van der Waals radii of nitrogen
and oxygen which is 3.05 Å.24 We believe that these short nitro–
nitro distance represent weak bonding interactions, consistent
with this is the observation that N(2Ј) deviates from the plane
of its attached substituents (O(5Ј), O(6Ј) and C(15Ј)) by 0.008 Å
towards O(2), while N(2) deviates from the plane defined by
O(5), O(6) and C(15) by 0.003 Å towards O(2Ј), the smaller
deviation in the latter case is consistent with the greater distance
between the N(2) and O(2Ј). Similar nitro–nitro interactions
have been reported in the crystal structure of the picrates 5c and
6c,15 in the crystal structure of nitromethane25 and in a nitro-
methane solvate26 although in these examples the N ؒ ؒ ؒ O dis-
tances are longer and hence the interactions weaker (3.02–3.05
Å). Weaker nitro-nitro interactions also exist between each pair
of molecules of 7c and other pairs of molecules extending up
the b axis, these secondary interactions are characterised by the
distances; O(3Ј) ؒ ؒ ؒ N(2) of 2.907(2) Å and O(3) ؒ ؒ ؒ N(2Ј) of
3.111(2) Å.
Examination of the structural parameters in Tables 3 and 4
show excellent agreement between those C–C bonds which are
related by the approximate local plane of symmetry bisecting
the C(1)–O(1) and C(4)–C(7) bonds. The C–C bonds of the
cyclohexane rings show systematic variations; the mean C(1)–
C(2) and C(1)–C(6) bonds distances is 1.512 Å. The C(2)–C(3)
and C(5)–C(6) distances are 1.529 Å, and the mean C(3)–C(4)
and C(4)–C(5) are 1.534 Å. These bond distance variations can
be adequately accounted for by hybridisation effects;27 the
electronegative substituent attached to C(1) is expected to
increase the s-character of C(1) which would lead to shortening
of the C(1)–C(2) and C(1)–C(6) bond distances. In addition the
electropositive substituent attached to C(4) may be expected to
decrease the s-character at C(4), leading to lengthening of the
C(3)–C(4) and C(4)–C(5) bonds. The variation in the C–C bond
distances may also have a hyperconjugative component, for
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 9 4 – 3 1 0 1
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example σC–H–σ*C–O interactions in the axial structures and
σC–C–σ*C–O in the equatorial structures would be expected to
result in shortening of the C(1)–C(2) and C(1)–C(6) distances, in
addition, lengthening of the C(2)–C(3) and C(5)–C(6) dis-
tances in the equatorial structures compared with the axial
structures would be expected. However, the C(2)–C(3) and
C(5)–C(6) distances, whose mean values are 1.531 Å in the
equatorial structures and 1.528 Å in the axial structures are
not significantly different from one another, implying that
hyperconjugative effects, if present, are small.
A plot of C–OR bond distance vs. pKa(ROH) has been
constructed for the axial 5, equatorial 6, and 2-adamantyl 7
derivatives,† these are presented in Figs. 5, 6 and 7. From these
plots the following relationships between the C(1)–O(1) bond
distance and pKa were established:
Fig.
7
r(C–O) vs. pKa(ROH) relationship for the 2-adamantyl
derivatives 7a–7f and 2-adamantanol.†
substituent, however the correlation coefficients in all cases is
modest. The slope of eqn. (4) (Ϫ2.77 × 10Ϫ3) represents a
measure of the donor ability of the two axial C–H bonds at
C(2) and C(6) of cis derivatives 5 while the slope of eqn. (5)
(Ϫ2.86 × 10Ϫ3) reflects the donor ability of the antiperiplanar
C–C bonds (C(2)–C(3) and C(5)–C(6)) in the trans derivatives
6. The slope of eqn. (6) (Ϫ3.05 × 10Ϫ3) represents the combined
donor abilities of the bonds C(1)–C(7) and C(3)–C(9) in the
adamantly derivatives 7. Given the modest correlation co-
efficients, and given that the differences in the slope of these
three equations is small no conclusions can be made about
the relative donor abilities of C–H bonds and C–C bonds. The
failure of the variable oxygen probe to distinguish the σ-donor
abilities of C–H and C–C bonds in these systems is very likely
due to these bonds being relatively weak σ-donors and there-
fore the response of the C–OR bond distance to the pKa(ROH)
is relatively weak and is likely masked by statistical variations
and packing effects.28
Fig. 5 r(C–O) vs. pKa(ROH) relationship for the axial cyclohexyl
derivatives 5a–b, 5d–i and the unsubstituted axial alcohol.†
Experimental
General
Anhydrous tetrahydrofuran and diethyl ether were distilled
from sodium benzophenone ketyl and sodium metal under a
nitrogen atmosphere. Anhydrous pyridine was distilled from
calcium hydride and stored over 4Å molecular sieves. Petroleum
ether (petrol) refers to the fraction boiling at 40–60ЊC. Benzoyl
chlorides were prepared by stirring the benzoic acid derivative
and oxalyl chloride (2 equiv.) in CH2Cl2 with a catalytic amount
of DMF at rt overnight. The crude benzoyl chloride derivative
then underwent appropriate purification. 2-Adamantanol was
purchased from the Aldrich Chemical Company and all other
commercial reagents were used as received. Where necessary, all
air- and moisture-sensitive reactions were performed in flame-
dried glassware under a nitrogen atmosphere, which was
purified by passage over activated 4Å molecular sieves and
BASF R3–11 copper catalyst. All melting points were deter-
mined on single crystals using a Reichert–Jung hot stage
melting point apparatus and are uncorrected. All proton
nuclear magnetic resonance (1H NMR) and proton decoupled
carbon nuclear magnetic resonance (13C NMR) spectra were
recorded in deuterochloroform solutions at ambient temper-
ature with residual chloroform as the internal reference.
Fig. 6 r(C–O) vs. pKa(ROH) relationship for the equatorial cyclohexyl
derivatives 6a–b, 6d–g and unsubstituted equatorial alcohol and
equatorial 2,4-dinitrobenzoate derivatives.†
5: rC–O/Å = 1.480 Ϫ 2.77 × 10Ϫ3pKa(ROH); R2 = 0.976 (4)
6: rC–O/Å = 1.487 Ϫ 2.86 × 10Ϫ3pKa(ROH); R2 = 0.968 (5)
7: rC–O/Å = 1.482 Ϫ 3.05 × 10Ϫ3pKa(ROH); R2 = 0.958 (6)
Eqns. (4)–(6) demonstrate a clear relationship between the
C–OR bond distance and the electron demand of the OR
Synthesis
† These plots also include data from previously determined low-
temperature structures of appropriate derivatives; a C–OH bond
distance for the axial alcohol has been estimated from several
low-temperature structures of appropriate derivatives found in the
Cambridge Crystallographic Database,29 the low-temperature structure
of 2-adamtanol has been previously reported,30 and the equatorial
alcohol and 2,4-dinitrobenzoate have also been reported.18
cis-4-tert-Butylcyclohexanol 5. To a stirring solution of
L-selectride (48.7 mL, 0.048 mol) in dry THF (50 mL) at Ϫ78ЊC
was added dropwise a solution of 4-tert-butylcyclohexanone
(5.01 g, 0.032 mol) in dry THF (25 mL). The temperature was
maintained for 2 h before the reaction mixture was allowed to
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stirred overnight at rt. The mixture was cooled to 0ЊC before
careful quenching with water. This was followed by warming
to rt before the addition of sodium hydroxide (20 mL, 3 M)
followed by hydrogen peroxide (20 mL, 30%) and stirring for
2 h. The mixture was extracted with Et2O (3×), and the com-
bined organic fractions were washed with saturated aqueous
NaCl and water, dried (MgSO4), filtered, and concentrated
in vacuo to yield 5 as a white solid (5 g, 98%), mp 80–82.5ЊC
(lit.31 82–83ЊC); δH (300 MHz, CDCl3) 0.85 (9H, s), 1.30–1.85
(9H, m), 4.03 (1H, br t, J 2.5); δC (300 MHz, CDCl3) 20.86,
27.45, 32.53, 33.34, 47.98, 65.89.
dried (MgSO4), filtered, and concentrated in vacuo to the crude
product which was subsequently recrystallised to produce
crystals of X-ray quality.
cis-4-tert-Butylcyclohexyl 4-chloro-3-nitrobenzoate 5f. mp
139–141ЊC (colourless plates from MeOH); δH (300 MHz,
CDCl3) 0.88 (9H, s), 1.10–2.11 (9H, m), 5.28 (1H, br s), 7.64
(1H, d, J 8.4 Hz), 8.14 (1H, dd, J 1.8 and 8.4 Hz), 8.48 (1H, d,
J 1.8 Hz); δC (300 MHz, CDCl3) 21.75, 27.35, 30.47, 32.50,
47.25, 71.74, 126.44, 131.05, 131.23, 132.11, 133.36, 147.89,
162.97.
trans-4-tert-Butylcyclohexanol 6. To a suspension of lithium
aluminium hydride (1.84 g, 0.049 mol) in dry Et2O (40 mL) at
0ЊC was added dropwise a solution of 4-tert-butylcyclo-
hexanone (5.125 g, 0.033 mol) in dry Et2O (25 mL). The reac-
tion mixture was then allowed to stir at 0ЊC for 2 h and then
quenched with water. The suspension was filtered through
Celite and the filtrate was extracted with Et2O (3×), and the
combined organic fractions were washed with water, dried
(MgSO4), filtered, and concentrated in vacuo to yield 6 as a
white solid which was 95% pure (3.95 g, 75%): mp 67–68.5ЊC
(lit.31 81–82ЊC, 100 % pure); δH (300 MHz, CDCl3) 0.78 (9H, s),
0.92–1.96 (9H, m), 3.43 (1H, sept, J 4.5 Hz); δC (300 MHz,
CDCl3) 25.53, 27.55, 32.16, 35.89, 47.10, 70.95.
cis-4-tert-Butylcyclohexyl 3,5-dinitrobenzoate 5g. mp 118–
119.5ЊC (pale yellow needles from MeOH); δH (300 MHz,
CDCl3) 0.91 (9H, s), 1.15–2.16 (9H, m), 5.37 (1H, br t, J 2.5),
9.14 (2H, m), 9.22 (1H, m); δC (300 MHz, CDCl3) 21.74, 27.32,
30.43, 32.53, 47.16, 72.90, 122.11, 129.24, 134.80, 148.65,
161.74.
cis-4-tert-Butylcyclohexyl 2,4-dinitrobenzoate 5h. mp 89.5–
90.5ЊC (pale yellow needles from Et2O); δH (300 MHz, CDCl3)
0.84 (9H, s), 1.04–2.10 (9H, m), 5.34 (1H, br s), 7.99 (1H, d,
J 8.4 Hz), 8.52 (1H, dd, J 1.5 and 8.1 Hz), 8.71 (1H, d, J 1.5
Hz); δC (300 MHz, CDCl3) 21.65, 27.35, 30.31, 32.48, 47.29,
73.82, 119.34, 127.09, 131.58, 133.04, 148.87, 162.93.
cis-4-tert-Butylcyclohexyl 4-nitrophenoxide 5e. A suspension
of NaH (0.3 g, 60%) in dry THF (10 mL) was treated with a
solution of alcohol 5 (500 mg, 3.2 mmol) in dry THF (10 mL).
The resulting solution was stirred at rt for 1 h then cooled to
Ϫ78ЊC before a solution of 1-fluoro-4-nitrobenzene (0.68 g,
0.51 mL, 4.8 mmol) in dry THF (10 mL) was added. The
mixture immediately produced a bright yellow precipitate. The
reaction was stirred at rt for 24 h. Excess NaH was destroyed by
the addition of water, and the resulting mixture was extracted
with Et2O (3×). The combined organic fractions were washed
with water, dried (MgSO4), filtered, and concentrated in vacuo
to yield 5e as a yellow solid (880 mg, 97%), which was recrystal-
lised from MeOH to give pale yellow needles: mp 80–83ЊC;
δH (300 MHz, CDCl3) 0.87 (9H, s), 1.08–2.14 (9H, m), 4.66 (1H,
br s), 6.95 (2H, d, J 9.3 Hz), 8.18 (2H, d, J 9.3 Hz); δC (300
MHz, CDCl3) 20.22, 27.37, 30.02, 32.48, 47.43, 72.44, 115.37,
125.86, 140.82, 163.11.
cis-4-tert-Butylcyclohexyl trichloroacetate 5i. mp 55–57ЊC
(pale brown needles from MeOH); δH (300 MHz, CDCl3) 0.85
(9H, s), 1.03–2.11 (9H, m), 5.14 (1H, br t, J 2.4); δC (300 MHz,
CDCl3) 21.30, 27.32, 30.00, 32.50, 47.08, 76.04, 90.50, 161.16.
trans-4-tert-Butylcyclohexyl 2-nitrobenzoate 6e. mp 88–90ЊC
(pale yellow needles from petrol); δH (300 MHz, CDCl3)
0.83 (9H, s), 0.99–2.16 (9H, m), 4.87 (1H, sept, J 4.5 Hz), 7.87–
7.55 (4H, m); δC (300 MHz, CDCl3) 25.28, 27.48, 31.45, 32.19,
47.86, 76.14, 123.66, 138.11, 129.76, 133.40, 132.70, 148.13,
164.84.
trans-4-tert-Butylcyclohexyl 4-toluenesulfonate 6f. mp 75.5–
77ЊC (colourless needles from petrol); δH (300 MHz, CDCl3)
0.78 (9H, s), 0.93–1.96 (9H, m), 2.42 (3H, s), 4.32 (1H, sept,
J 4.5 Hz), 7.31 (2H, d, J 8.1 Hz), 7.77 (2H, d, J 8.4 Hz); δC (300
MHz, CDCl3) 25.42, 27.41, 32.10, 32.77, 46.43, 82.55, 127.49,
129.64, 134.66, 141.25.
2-Adamantyl 4-nitrophenoxide 7a. A suspension of NaH
(0.1 g 60%) in dry THF (10 mL) was treated with a solution of
2-adamantanol (200 mg, 1.32 mmol) in dry THF (10 mL). The
resulting solution was stirred at rt for 1 h then cooled to Ϫ78ЊC
before a solution of 1-fluoro-4-nitrobenzene (0.29 g, 0.21 mL,
0.2 mmol) in dry THF (5 mL) was added. The reaction was
stirred for 72 h at rt. Excess NaH was destroyed by the addition
of water, and the resulting mixture was extracted with Et2O
(3×). The combined organic fractions were washed with water,
dried (MgSO4), filtered, and concentrated in vacuo to yield 7a as
a yellow solid (326.5 mg, 90%), which was recrystallised from
MeOH to give golden sheets: mp 84.5–85.5ЊC; δH (300 MHz,
CDCl3) 1.5–2.2 (14H, m), 4.50 (1H, br s), 6.91 (2H, d, J 9.3 Hz),
8.12 (2H, d, J 9.3 Hz); δC (300 MHz, CDCl3) 26.84, 26.94,
31.16, 31.21, 36.03, 37.06, 80.27, 115.24, 125.71, 140.70, 162.92.
trans-4-tert-Butylcyclohexyl benzenesulfonate 6g. mp 33–
35ЊC (pale yellow needles from petrol); δH (300 MHz, CDCl3)
0.79 (9H, s), 1.86–1.98 (9H, m), 4.37 (1H, sept, J 4.5 Hz), 7.52
(2H, m), 7.61 (1H, m), 7.90 (2H, m); δC (300 MHz, CDCl3)
25.45, 27.43, 32.13, 32.81, 46.44, 82.90, 127.47, 129.05, 133.35,
137.60.
2-Adamantyl 3-nitrobenzoate 7b. mp 68–70ЊC (colourless
needles from MeOH); δH (300 MHz, CDCl3) 1.55–2.20 (14H,
m), 5.24 (1H, br s), 7.66 (1H, t J 7.95 Hz), 8.41 (2H, d, J 7.8
Hz), 8.88 (1H, s); δC (300 MHz, CDCl3) 26.80, 27.08, 31.84,
31.87, 36.17, 37.13, 78.68, 124.31, 127.05, 129.47, 132.71,
135.10, 148.14, 163.55.
2-Adamantyl 2,4-dinitrobenzoate 7c. mp 134–135.5ЊC (pale
yellow blocks from Et2O); δH (400 MHz, CDCl3) 1.56–2.11
(14H, m), 5.22 (1H, br s), 7.97 (1H, dd, J 2 and 8.4 Hz), 8.50
(1H, dt, J 2 and 8.4 Hz), 8.70 (1H, t, J 2 Hz); δC (400 MHz,
CDCl3) 26.72, 26.87, 31.55, 31.58, 36.17, 37.02, 80.91, 119.30,
127.19, 131.36, 133.08, 148.13, 148.70, 162.87.
General procedure for the esterification of alcohols with
benzoyl, sulfonyl or acetyl chlorides. The alcohol (50 mg) was
stirred in pyridine (5 mL) for 30 min and then treated with
either benzoyl, sulfonyl or acetate chloride (1.5 equiv.), which
was added all at once. The reaction was stirred at rt for 4 h or
until precipitation of pyridine hydrochloride was complete.
Water was then added and undissolved solids were filtered off.
The filtrate was then extracted with Et2O (3×), and the com-
bined organic fractions were washed with saturated aqueous
CuSO4, water, saturated aqueous NaHCO3 and water then
2-Adamantyl methanesulfonate 7d. mp 51–53ЊC (pale yellow
plates from Et2O); δH (300 MHz, CDCl3) 1.55–2.15 (14H, m),
2.99 (3H, s), 4.84 (1H, br s); δC (300 MHz, CDCl3) 26.42, 26.73,
31.04, 32.90, 36.25, 36.93, 38.65, 85.93.
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2-Adamantyl 4-toluenesulfonate 7e. mp 68–70ЊC (pale yellow
plates from MeOH); δH (300 MHz, CDCl3) 1.46–2.14 (14H, m),
2.43 (3H, s), 4.68 (1H, br s), 7.32 (2H, d, J 7.5 Hz), 7.79 (2H, d,
J 6.9 Hz); δC (300 MHz, CDCl3) 21.29, 26.26, 26.52, 30.80,
32.37, 36.06, 36.76, 85.97, 127.14, 129.45, 134.58, 144.03.
Crystal data for 5i. C12H19Cl3O2, M = 301.62, T = 130.0(1) K,
λ = 1.5418 Å, monoclinic, space group P21, a = 9.654(1),
b = 6.026(1), c = 13.044(2) Å, β = 107.09(1)Њ, V = 725.3(3) Å3,
Z = 2, Dc = 1.381 Mg mϪ3, µ(Cu-Kα) = 5.630 mmϪ1, F(000) =
316, max. min. transmission 0.67, 0.22, crystal size 0.60 ×
0.17 × 0.08 mm. 1733 reflections measured, 1636 independent
reflections (Rint = 0.0224) and the final wR(F 2) was 0.0966 and
final R was 0.0371 for 1589 unique data with [I > 2σ(I )].
2-Adamantyl benzenesulfonate 7f. mp 79–82ЊC (pale yellow
blocks from MeOH); δH (300 MHz, CDCl3) 1.46–2.12 (14H,
m), 2.43 (3H, s), 4.72 (1H, br t, J 2.4), 7.53 (2H, m), 7.63 (1H,
m), 7.92 (2H, m); δC (300 MHz, CDCl3) 26.32, 26.59, 30.89,
32.49, 36.16, 36.84, 86.46, 127.22, 128.93, 133.22, 137.66.
Crystal data for 6e. C17H23NO4, M = 305.36, T = 130.0(1) K,
λ = 0.71069 Å, monoclinic, space group P21/n, a = 6.237(1),
b = 12.773(2), c = 20.439(4) Å, β = 97.722(1)Њ, V = 1613.49(5) Å3,
Z = 4, Dc = 1.257 Mg mϪ3, µ(Mo-Kα) = 0.089 mmϪ1, F(000) =
654, crystal size 0.25 × 0.07 × 0.07 mm. 16946 reflections
measured, 3719 independent reflections (Rint = 0.0367) and the
final wR(F 2) was 0.0943 and final R was 0.0463 for 2826 unique
data with [I > 2σ(I )].
Crystallography
Data for structures 5e, 5g–5i, 6f, 7a–7b, 7d and 7f were collected
on an Enraf-Nonius CAD-4 Diffractometer using Mo-Kα
radiation (λ = 0.71069 Å, graphite monochromator) or Ni-
filtered Cu-Kα radiation (λ = 1.5418 Å) at 130.0(1) K, data for
structures 5f, 6e, 6g, 7c and 7e were collected on an Nonius
Kappa CCD Area-Detector Diffractometer at 130.0(1) K. The
crystals were mounted on a glass fibre usually using low-
temperature silicone oil and was then flash frozen by placing
directly on a goniometer head under a stream of nitrogen gas
at 130 K. The temperature was controlled using an Oxford
Cryostream cooling device. The data were corrected for Lorentz
and polarization effects32 for absorption where appropriate
(ABSORB)33 and extinction34 where appropriate. Structures
were solved by direct methods (SHELXS-86)35 and were refined
on F 2 (SHELXL-97).34 All non hydrogens were refined aniso-
tropically, while the treatment of hydrogen atoms depended on
the data/reflection ratio, in some structures hydrogen atoms
were refined isotropically without restraint while in others they
were constrained. Thermal ellipsoids plots were generated using
the program ORTEP-336 all programs were implemented within
the suite WINGX.37
Crystal data for 6f. C17H26SO3, M = 310.44, T = 130.0(1) K,
¯
λ = 1.5418 Å, triclinic, space group P1, a = 6.2680(1), b =
10.409(1), c = 13.190(2) Å, α = 94.300(1), β = 95.040(1),
γ = 98.830(1)Њ, V = 843.6(3) Å3, Z = 2, Dc = 1.222 Mg mϪ3
,
µ(Cu-Kα) = 1.761 mmϪ1, F(000) = 336, crystal size 0.35 × 0.15 ×
0.10 mm. 3519 reflections measured, 3204 independent reflec-
tions (Rint = 0.0158) and the final wR(F 2) was 0.0954 and final R
was 0.0375 for 2819 unique data with [I > 2σ(I )].
Crystal data for 6g. C16H24SO3, M = 296.41, T = 130.0(1) K,
λ = 0.71069 Å, monoclinic, space group P21/c, a = 24.736(3),
b = 6.202(1), c = 20.939(4) Å, β = 100.487(1)Њ, V = 3158.68(9) Å3,
Z = 8, Dc = 1.247 Mg mϪ3, µ(Mo-Kα) = 0.210 mmϪ1, F(000) =
1280, crystal size 0.40 × 0.10 × 0.05 mm. 38021 reflections
measured, 7783 independent reflections (Rint = 0.0579) and the
final wR(F 2) was 0.0989 and final R was 0.0443 for 5301 unique
data with [I > 2σ(I )].
Crystal data for 5e. C16H23NO3, M = 277.36, T = 130.0 (1) K,
λ = 0.71069 Å, triclinic, space group P1, a = 6.179(2), b =
Crystal data for 7a. C16H19NO3, M = 273.32, T = 130.0(1) K,
λ = 1.5418 Å, triclinic, space group P1, a = 6.767(2), b =
¯
¯
11.071(3), c = 11.130(2) Å, α = 100.57(2), β = 90.17(2),
γ = 95.16(2)Њ, V = 745.3(3) Å3, Z = 2, Dc = 1.236 Mg mϪ3
,
9.556(3), c = 10.887(3) Å, α = 99.43(3), β = 90.68(2), γ =
105.38(2)Њ, V = 668.5 (3) Å3, Z = 2, Dc = 1.358 Mg mϪ3
,
µ(Mo-Kα) = 0.085 mmϪ1, F(000) = 300, crystal size 0.50 × 0.40
× 0.12 mm. 2888 reflections measured, 2622 independent
reflections (Rint = 0.0196) and the final wR(F 2) was 0.1252 and
final R was 0.0439 for 2196 unique data with [I > 2σ(I )].
µ(Cu-Kα) = 0.759 mmϪ1, F(000) = 292, max. min. transmission
0.84, 0.73, crystal size 0.50 × 0.38 × 0.26 mm. 2833 reflections
measured, 2689 independent reflections (Rint = 0.0095) and the
final wR(F 2) was 0.0896 and final R was 0.0355 for 2645 unique
data with [I > 2σ(I )].
Crystal data for 5f. C17H22ClNO4, M = 339.81, T =
130.0(1) K, λ = 0.71069 Å, monoclinic, space group P21/n,
a = 6.975(3), b = 36.618(8), c = 7.034(2) Å, β = 107.555(1)Њ, V =
1713.1(1) Å3, Z = 4, Dc = 1.318 Mg mϪ3, µ(Mo-Kα) = 0.242
mmϪ1, F(000) = 720, crystal size 0.20 × 0.20 × 0.10 mm. 10738
Crystal data for 7b. C17H19NO4, M = 301.33, T = 130.0(1) K,
¯
λ = 1.5418 Å, triclinic, space group P1, a = 7.539(3), b =
8.479(2), c = 12.043(3) Å, α = 75.30(2), β = 76.86(2),
γ = 88.83(3)Њ, V = 724.6(4) Å3, Z = 2, Dc = 1.381 Mg mϪ3
,
reflections measured, 2860 independent reflections (Rint
=
µ(Cu-Kα) = 0.809 mmϪ1, F(000) = 320, crystal size 0.50 × 0.40 ×
0.07 mm. 4014 reflections measured, 2761 independent reflec-
tions (Rint = 0.0183) and the final wR(F 2) was 0.1096 and final R
was 0.0402 for 2635 unique data with [I > 2σ(I )].
0.0546) and the final wR(F 2) was 0.1252 and final R was 0.0417
for 1991 unique data with [I > 2σ(I )].
Crystal data for 5g. C17H22N2O6, M = 350.37, T = 130.0(1) K,
λ = 1.5418 Å, monoclinic, space group P21/c, a = 16.441(2),
b = 5.981(1), c = 18.722(2) Å, β = 109.47(2)Њ, V = 1735.7(6) Å3,
Z = 4, Dc = 1.341 Mg mϪ3, µ(Cu-Kα) = 0.856 mmϪ1, F(000) =
744, max. min. transmission 0.95, 0.69, crystal size 0.75 ×
0.25 × 0.06 mm. 3027 reflections measured, 2923 independent
reflections (Rint = 0.0172) and the final wR(F 2) was 0.1014 and
final R was 0.0360 for 2622 unique data with [I > 2σ(I )].
Crystal data for 7c. C17H18N2O6, M = 346.33, T = 130.0(1) K,
λ = 0.71069 Å, monoclinic, space group P21/c, a = 29.189(6),
b = 7.0518(1), c = 15.415(3) Å, β = 93.717(1)Њ, V = 3166.3(1) Å3,
Z = 8, Dc = 1.453 Mg mϪ3, µ(Mo-Kα) = 0.111 mmϪ1, F(000) =
1456, crystal size 0.16 × 0.12 × 0.07 mm. 19999 reflections
measured, 5513 independent reflections (Rint = 0.0638) and the
final wR(F 2) was 0.1377 and final R was 0.0481 for 3597 unique
data with [I > 2σ(I )].
Crystal data for 5h. C17H22N2O6, M = 350.37, T = 130.0(1) K,
λ = 0.71069 Å, monoclinic, space group P21/c, a = 15.388(5),
b = 7.129(1), c = 16.839(6) Å, β = 112.56(3), V = 1705.9(9) Å3,
Z = 4, Dc = 1.364 Mg mϪ3, µ(Mo-Kα) = 0.104 mmϪ1, F(000) =
744, crystal size 0.60 × 0.37 × 0.12 mm. 3114 reflections meas-
ured, 2993 independent reflections (Rint = 0.0203) and the final
wR(F 2) was 0.1032 and final R was 0.0421 for 2323 unique data
with [I > 2σ(I )].
Crystal data for 7d. C11H18SO3, M = 230.31, T = 130.0(1) K,
λ = 0.71069 Å, orthorhombic, space group Pbca, a = 9.000(2),
b = 9.594(4), c = 26.225(7) Å, V = 2264(1) Å3, Z = 8, Dc = 1.351
Mg mϪ3, µ(Mo-Kα) = 0.271 mmϪ1, F(000) = 992, crystal size
0.30 × 0.30 × 0.05 mm. 3002 reflections measured, 2585
independent reflections (Rint = 0.0331) and the final wR(F 2)
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 9 4 – 3 1 0 1
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10 J. M. White and G. B. Robertson, J. Org. Chem., 1992, 57, 4638.
11 V. Y. Chan, C. I. Clark, J. Giordano, A. J. Green, A. Karalis and
J. M. White, J. Org. Chem., 1996, 61, 5227.
was 0.0918 and final R was 0.0375 for 2045 unique data with
[I > 2σ(I )].
12 J. M. White and C. I. Clark, in Stereoelectronic effects of Group IVA
metal substituents in organic chemistry, ed. S. Denmark, New York,
1999.
13 J. M. White and G. B. Robertson, Acta Crystallogr., Sect. C, 1993,
49, 347.
14 J. M. White, J. Giordano and A. J. Green, Acta Crystallogr., Sect. C,
1996, 52, 2783.
15 M. Spiniello and J. M. White, Acta Crystallogr., Sect. C, 2002, 58,
o94.
Crystal data for 7e. C17H22SO3, M = 306.41, T = 130.0(1) K,
λ = 0.71069 Å, monoclinic, space group P21/c, a = 10.124(1),
b = 12.551(2), c = 12.409(1) Å, β = 106.860(1)Њ, V = 1509.13(3)
Å3, Z = 4, Dc = 1.349 Mg mϪ3, µ(Mo-Kα) = 0.222 mmϪ1, F(000)
= 656, crystal size 0.15 × 0.11 × 0.09 mm. 24439 reflections
measured, 3720 independent reflections (Rint = 0.0405) and the
final wR(F 2) was 0.1143 and final R was 0.0377 for 3276 unique
data with [I > 2σ(I )].
16 J. M. White, J. Giordano and A. J. Green, Acta Crystallogr., Sect. C,
1996, 52, 3204.
17 CRC Handbook of Chemistry and Physics, ed. D. R. Lide,
CRC Press, Boca Raton, FL, 2000.
Crystal data for 7f. C16H20SO3, M = 292.38, T = 130.0(1) K,
λ = 1.5418 Å, monoclinic, space group P21/c, a = 11.735(9),
b = 11.125(10), c = 11.132(10) Å, β = 104.382(7)Њ, V = 1407.8(1)
Å3, Z = 4, Dc = 1.379 Mg mϪ3, µ(Cu-Kα) = 2.084 mmϪ1, F(000) =
624, max. min. transmission 0.83, 0.57, crystal size 0.36 ×
0.28 × 0.10 mm. 3055 reflections measured, 2900 independent
reflections (Rint = 0.0142) and the final wR(F 2) was 0.0781 and
final R was 0.0308 for 2612 unique data with [I > 2σ(I )].
18 A. J. Green, J. Giordano and J. M. White, Aust. J. Chem., 2000, 53,
285.
19 J. F. King, in The Chemistry of Sulfonic Acida, Esters and
Derivatives, ed. S. Patai and Z. Rappoport, Interscience,
West Sussex, England, 1991.
20 D. C. Wigfield, Tetrahedron, 1979, 35, 449.
21 H. C. Brown and S. Krishnamurthy, J. Am. Chem. Soc., 1972, 94,
7159.
22 C. Rafols, M. Roses and E. Bosch, Anal. Chim. Acta, 1997, 338,
CCDC reference numbers 205439–205452.
See http://www.rsc.org/suppdata/ob/b3/b303453d/ for crys-
tallographic data in CIF or other electronic format.
127.
23 J. A. Dean, Lange’s Handbook of Chemistry, McGraw-Hill,
New York, 1992.
24 A. Bondi, J. Phys. Chem., 1964, 68, 441.
25 I. Y. Bagryanskaya and Y. V. Gatilov, Zh. Strukt. Khim., 1983, 24,
158.
26 B. F. Abrahams, P. A. Jackson and R. Robson, Angew. Chem.,
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27 L. S. Bartell, Tetrahedron, 1962, 17, 177.
Acknowledgements
We thank Dr Alan R. Happer (Canterbury University,
New Zealand) for helpful discussions and Dr Gary D. Fallon
(Monash University, Australia) for data collection of struc-
tures 5f, 6e, 6g, 7c and 7e. The Australian Research Council is
gratefully acknowledged for its financial support.
28 A. Martin and A. G. Orpen, J. Am. Chem. Soc., 1996, 118,
1464.
29 F. H. Allen, S. Bellard, M. D. Brice, B. A. Cartwright, A. Doubleday,
H. Higgs, T. Hummelink, B. G. Hummelink-Peters, O. Kennard,
W. D. S. Motherwell, J. R. Rogers and D. G. Watson,
Acta Crystallogr., Sect. B, 1979, 35, 2331.
30 J. A. Kanters, R. W. W. Hooft and A. J. M. Duisenberg,
J. Crystallogr. Spectrosc. Res., 1990, 20, 123.
31 S. Winstein and N. J. Holness, J. Am. Chem. Soc., 1955, 77, 5562.
32 R. W. Gable, B. F. Hoskins, A. Linden, I. A. S. McDonald and
R. J. Steen, in Process_data, a program for processing of CAD-4
diffractometer data, The University of Melbourne, Australia,
1994.
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3101