cis- and trans-2-(4-tert-butylcyclohexyloxy)-1,3,5-trinitrobenzene

Article abstract of DOI:10.1107/S0108270101019400

Cyclohexanes substitued with ester and ether derivatives of varying electron demand were investigated at low temperature. The accurate structural parameters were obtained for comparision purposes. It was shown that and axial oxygen substituent posseses two antiperoplanar C-H bonds that donated electron density into the C-O antibonding orbital. The C-O bond distances were 1.497 (2) and 1.491 (2) A for the two derivatives.

Full text of DOI:10.1107/S0108270101019400

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
question, `which is the better donor, a CÐH or a CÐC bond?'.
Thus, we have embarked on a series of structural studies on
ester and ether derivatives of cyclohexane in which the oxygen
substituent is constrained to occupy both axial and equatorial
positions. An axial oxygen substituent has two antiperiplanar
CÐH bonds which can donate electron density into the CÐO
antibonding orbital (see Scheme below), whereas an equa-
torial oxygen substituent has two ring CÐC bonds which can
ISSN 0108-2701
cis- and trans-2-(4-tert-Butylcyclo-
hexyloxy)-1,3,5-trinitrobenzene
Marisa Spiniello and Jonathan M. White*
School of Chemistry, University of Melbourne, Victoria 3010, Australia
Correspondence e-mail: j.white@chemistry.unimelb.edu.au
Received 12 October 2001
Accepted 13 November 2001
Online 23 January 2002
donate electron density into the CÐO antibonding orbital. It
is hoped that a comparison of the plots obtained for a range of
oxygen substituents of varying electron demand will allow the
distinction of the donor abilities of CÐH and CÐC bonds.
The structures of cis- and trans-2-(4-tert-butylcyclohexyloxy)-
1,3,5-trinitrobenzene, C16H21N3O7, (I) and (II), respectively,
were determined at low temperature in order to obtain
accurate structural parameters for comparison purposes. The
Ê
CalkylÐOether bond distances are 1.497 (2) and 1.491 (2) A for
(I) and (II), respectively.
Comment
This report forms part of our structural studies on cyclo-
hexanes substituted with ester and ether derivatives of varying
electron demand (White & Robertson, 1992; White et al., 1996,
2000). Previous work reported by Kirby and co-workers
(Kirby & Allen, 1984; Briggs et al., 1984) has shown that
Csp3ÐO bond distances are sensitive both to the donor ability
of bonds which are antiperiplanar to the oxygen substituent,
and also to the electron demand of the oxygen substituent
itself. The Csp3ÐO bond distance was found to be linearly
related to the electron demand of the oxygen substituent, and
the slope of the plot was sensitive to the donor ability of bonds
Figure 1
A view of the molecule of (I). Displacement ellipsoids are drawn at the
30% probability level and H atoms have been omitted for clarity.
which were antiperiplanar to the CÐO bond and therefore
able to donate electron density into the CÐO antibonding
orbital. This structural method for detecting electronic inter-
actions in the ground state was referred to as the `variable
oxygen probe' (Kirby et al., 1992).
Figure 2
A view of the molecule of (II). Displacement ellipsoids are drawn at the
30% probability level and H atoms have been omitted for clarity.
The present low-temperature structural study is part of our
efforts to apply the variable oxygen probe to the important
o94 # 2002 International Union of Crystallography
DOI: 10.1107/S0108270101019400
Acta Cryst. (2002). C58, o94±o96

organic compounds
Compound (I)
The results for the title compounds, (I) and (II), are presented
here.
Crystal data
The structures of (I) and (II) were determined at 130 K to
minimize the unwanted effects of thermal motion. Selected
structural parameters for (I) and (II) are summarized in
Tables 1 and 2, respectively.
3
C16H21N3O7
Mr = 367.36
Dx = 1.344 Mg m
Mo Kꢁ radiation
Cell parameters from 25
re¯ections
Monoclinic, P21=c
Ê
a = 15.257 (3) A
ꢂ = 10±15ꢀ
ꢃ = 0.11 mm
Ê
b = 8.954 (2) A
The picrate moiety (1,3,5-trinitrobenzene) in both struc-
tures adopts the same conformation with respect to both the
nitro substituents and the O-alkyl substituent. In both struc-
tures, the para-nitro substituent is essentially coplanar with the
aromatic ring, and one of the ortho-nitro substituents is
twisted slightly from the plane of the aromatic ring (ca 30ꢀ),
while the second ortho-nitro substituent is close to orthogonal.
The conformation of the ortho-nitro substituents presumably
represents a compromise between the electron preference of
the nitro group to be coplanar with the aromatic ring and the
need to minimize steric interactions with the neighbouring
oxygen substituent.
1
Ê
c = 13.623 (2) A
ꢀ = 102.71 (2)ꢀ
V = 1815.5 (6) A
Z = 4
T = 130.0 (2) K
Needle, brown
3
Ê
0.6 Â 0.1 Â 0.1 mm
Data collection
Enraf±Nonius CAD-4
diffractometer
ꢂ/2ꢂ scans
3341 measured re¯ections
3191 independent re¯ections
2589 re¯ections with I > 2ꢄ(I)
Rint = 0.071
ꢂmax = 25ꢀ
h = 18 ! 17
k = 10 ! 0
l = 0 ! 16
3 standard re¯ections
frequency: 160 min
intensity decay: 2%
The conformation of the O-alkyl substituent, as de®ned by
the dihedral angles C1ÐO1ÐC11ÐC12 and C1ÐO1ÐC11Ð
C16, is essentially identical in each structure. While this
conformation does not allow effective delocalization of an
oxygen lone pair into the electron-de®cient aromatic ring, a
coplanar conformation would suffer from severe steric inter-
action between atom C1 and one of the ortho-nitro substi-
tuents.
An examination of bond angles O1ÐC1ÐC2 and O1Ð
C1ÐC6 suggests that there is no signi®cant strain associated
with the axial substituent. This is consistent with the ®ndings
of Steiner (Steiner & Saenger, 1998), who examined a number
of oxo-substituted cyclohexanes.
Table 1
Selected geometric parameters (A, ) for (I).
ꢀ
Ê
O1ÐC11
O1ÐC1
O2ÐN1
O3ÐN1
O4ÐN2
O5ÐN2
O6ÐN3
O7ÐN3
N1ÐC12
N2ÐC14
N3ÐC16
C1ÐC6
C1ÐC2
1.3383 (19)
1.4964 (18)
1.2259 (18)
1.2281 (17)
1.217 (2)
C2ÐC3
C3ÐC4
C4ÐC5
C4ÐC7
C5ÐC6
C7ÐC8
C7ÐC9
C7ÐC10
C11ÐC12
C11ÐC16
C12ÐC13
C13ÐC14
1.522 (2)
1.532 (2)
1.535 (3)
1.553 (2)
1.529 (2)
1.526 (3)
1.534 (3)
1.541 (2)
1.403 (2)
1.404 (2)
1.384 (2)
1.378 (2)
1.228 (2)
1.2052 (19)
1.2103 (18)
1.467 (2)
1.471 (2)
1.471 (2)
The C1ÐO1 distances in (I) and (II) are 1.497 (2) and
Ê
1.491 (2) A, respectively. Although the axial picrate moiety
1.507 (2)
1.508 (3)
appears to have a slightly longer CÐO bond than the corre-
sponding equatorial picrate, this is barely signi®cant. The CÐ
C bond distances within the cyclohexane rings of both struc-
tures follow similar patterns, with the C1ÐC2 and C1ÐC6
bonds being shorter than both the C2ÐC3 and C5ÐC6 bonds,
and the C3ÐC4 and C4ÐC5 bonds, re¯ecting the expected
effects of the strongly electron-withdrawing picryl substituent.
There are no signi®cant differences in the C2ÐC3 and C5Ð
C6 bond distances between the two structures. Thus, there are
no observable structural effects of hyperconjugation of the
antiperiplanar CÐC bonds with the C1ÐO1 antibonding
orbital in (II).
C11ÐO1ÐC1
O1ÐC1ÐC6
O1ÐC1ÐC2
C1ÐC2ÐC3
C2ÐC3ÐC4
120.13 (11)
105.18 (13)
108.65 (13)
113.94 (14)
112.56 (14)
C3ÐC4ÐC5
C3ÐC4ÐC7
C5ÐC4ÐC7
C6ÐC5ÐC4
C1ÐC6ÐC5
108.62 (14)
113.40 (15)
114.04 (14)
111.29 (14)
111.69 (14)
C11ÐO1ÐC1ÐC6
C11ÐO1ÐC1ÐC2
O1ÐC1ÐC2ÐC3
O1ÐC1ÐC6ÐC5
C1ÐO1ÐC11ÐC12
C1ÐO1ÐC11ÐC16
O2ÐN1ÐC12ÐC13
O3ÐN1ÐC12ÐC13
O2ÐN1ÐC12ÐC11
155.11 (14)
83.98 (17)
67.89 (17)
66.86 (17)
56.7 (2)
126.24 (15)
144.63 (15)
32.9 (2)
O3ÐN1ÐC12ÐC11
O4ÐN2ÐC14ÐC13
O5ÐN2ÐC14ÐC13
O4ÐN2ÐC14ÐC15
O5ÐN2ÐC14ÐC15
O6ÐN3ÐC16ÐC15
O7ÐN3ÐC16ÐC15
O6ÐN3ÐC16ÐC11
O7ÐN3ÐC16ÐC11
151.64 (14)
12.2 (3)
167.98 (16)
168.67 (17)
11.2 (2)
104.03 (19)
75.94 (18)
76.4 (2)
30.8 (2)
103.64 (17)
Experimental
Compounds (I) and (II) were prepared by reaction of cis- and trans-
cyclohexanol with 2,4,6-trinitro¯uorobenzene in diethyl ether in the
presence of one equivalent of pyridine. cis-4-tert-Butylcyclohexanol
in pyridine±diethyl ether was treated with picryl ¯uoride to afford (I).
Brown needles (m.p. 382±385 K) were grown from methanol. trans-4-
tert-Butylcyclohexanol was treated in the same manner to prepare
(II); recrystallization from pentane gave dark-brown slabs (m.p. 381±
383 K).
Re®nement
Re®nement on F2
R[F2 > 2ꢄ(F2)] = 0.039
wR(F2) = 0.107
S = 1.01
3191 re¯ections
232 parameters
H-atom parameters constrained
w = 1/[ꢄ2(Fo2) + (0.0547P)2
+ 0.7679P]
where P = (Fo2 + 2Fc2)/3
(Á/ꢄ)max = 0.001
3
Ê
Áꢅmax = 0.18 e A
3
Ê
0.21 e A
Áꢅmin
=
ꢁ
Acta Cryst. (2002). C58, o94±o96
Spiniello and White C16H21N3O7 o95

organic compounds
Table 2
Selected geometric parameters (A, ) for (II).
Re®nement
ꢀ
Ê
Re®nement on F2
R[F2 > 2ꢄ(F2)] = 0.047
wR(F2) = 0.112
S = 1.04
3104 re¯ections
w = 1/[ꢄ2(Fo2) + (0.0417P)2
+ 0.7612P]
where P = (Fo2 + 2Fc2)/3
(Á/ꢄ)max < 0.001
O1ÐC1
O2ÐN1
O3ÐN1
O4ÐN2
O5ÐN2
O6ÐN3
O7ÐN3
N1ÐC12
N2ÐC14
N3ÐC16
C1ÐC6
C1ÐC2
C2ÐC3
1.492 (3)
1.218 (3)
1.220 (2)
1.221 (3)
1.226 (3)
1.230 (2)
1.230 (3)
1.476 (3)
1.472 (3)
1.472 (3)
1.503 (3)
1.504 (3)
1.533 (3)
C3ÐC4
C4ÐC5
C4ÐC7
C5ÐC6
C7ÐC10
C7ÐC9
C7ÐC8
C11ÐC12
C11ÐC16
C12ÐC13
C13ÐC14
C14ÐC15
C15ÐC16
1.539 (4)
1.525 (4)
1.565 (3)
1.531 (3)
1.523 (4)
1.530 (4)
1.530 (3)
1.403 (3)
1.403 (3)
1.372 (3)
1.388 (3)
1.377 (3)
1.383 (3)
3
Ê
Áꢅmax = 0.22 e A
3
Ê
0.19 e A
256 parameters
H-atom parameters constrained
Áꢅmin
=
For both compounds, H atoms were placed in geometrical posi-
Ê
tions and treated as riding, with CÐH = 0.95±1.00 A and Uiso(H) =
1.2Ueq(C).
For both compounds, data collection and cell re®nement: CAD-4
Software (Enraf±Nonius, 1989); data reduction: PROCESS_DATA
(Gable et al., 1994); program(s) used to solve structure: SHELXS97
(Sheldrick, 1990); program(s) used to re®ne structure: SHELXL97
(Sheldrick, 1997); molecular graphics: ZORTEP (Zsolnai, 1994).
C11ÐO1ÐC1
O1ÐC1ÐC6
O1ÐC1ÐC2
C1ÐC2ÐC3
C2ÐC3ÐC4
120.24 (17)
107.60 (19)
109.37 (19)
109.4 (2)
C5ÐC4ÐC3
C5ÐC4ÐC7
C3ÐC4ÐC7
C4ÐC5ÐC6
C1ÐC6ÐC5
109.35 (19)
113.8 (2)
113.8 (2)
112.1 (2)
108.8 (2)
112.4 (2)
O1ÐC1ÐC2ÐC3
O1ÐC1ÐC6ÐC5
177.80 (18)
179.92 (19)
131.1 (2)
53.0 (3)
109.7 (2)
69.2 (3)
70.7 (3)
O4ÐN2ÐC14ÐC15
O5ÐN2ÐC14ÐC15
O4ÐN2ÐC14ÐC13
O5ÐN2ÐC14ÐC13
O7ÐN3ÐC16ÐC15
O6ÐN3ÐC16ÐC15
O7ÐN3ÐC16ÐC11
O6ÐN3ÐC16ÐC11
175.5 (2)
4.5 (3)
3.4 (3)
176.7 (2)
144.3 (2)
32.6 (3)
30.5 (3)
152.6 (2)
C1ÐO1ÐC11ÐC12
C1ÐO1ÐC11ÐC16
O2ÐN1ÐC12ÐC13
O3ÐN1ÐC12ÐC13
O2ÐN1ÐC12ÐC11
O3ÐN1ÐC12ÐC11
We acknowledge support from the Australian Research
Grants Scheme.
110.4 (2)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: TA1354). Services for accessing these data are
described at the back of the journal.
Compound (II)
Crystal data
3
C16H21N3O7
Mr = 367.37
Dx = 1.375 Mg m
References
Mo Kꢁ radiation
Cell parameters from 25
re¯ections
Monoclinic, P21=c
Briggs, A. J., Glenn, R., Jones, P. G., Kirby, A. J. & Ramaswamy, P. (1984). J.
Am. Chem. Soc. 106, 6200±6206.
Enraf±Nonius (1989). CAD-4 Software. Version 5.0. Enraf±Nonius, Delft, The
Netherlands.
Ê
a = 14.950 (3) A
ꢂ = 10±15ꢀ
Ê
b = 8.3490 (10) A
1
Ê
c = 14.292 (5) A
ꢃ = 0.11 mm
T = 130 K
ꢀ = 94.22 (3)ꢀ
V = 1779.1 (7) A
Z = 4
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3
Ê
Slab, dark brown
0.50 Â 0.25 Â 0.10 mm
Data collection
Enraf±Nonius CAD-4
diffractometer
ꢂ/2ꢂ scans
3248 measured re¯ections
3108 independent re¯ections
2092 re¯ections with I > 2ꢄ(I)
Rint = 0.015
ꢂ
max = 25ꢀ
È
Sheldrick, G. M. (1997). SHELXL97. University of Gottingen, Germany.
h = 17 ! 17
Steiner, T. & Saenger, W. (1998). J. Chem. Soc. Perkin Trans. 2, pp. 371±375.
White, J. M., Giordano, J. & Green, A. J. (1996). Acta Cryst. C52, 3204±3207.
White, J. M., Giordano, J. & Green, A. J. (2000). Aust. J. Chem. 53, 285±292.
White, J. M. & Robertson, G. B. (1992). J. Org. Chem. 57, 4638±4644.
Zsolnai, L. (1994). ZORTEP. University of Heidelberg, Germany.
k = 9 ! 0
l = 0 ! 16
3 standard re¯ections
frequency: 160 min
intensity decay: 2%
ꢁ
o96 Spiniello and White
C16H21N3O7
Acta Cryst. (2002). C58, o94±o96