4,4′-(4,5-Dimethyl-1,2-phenyl-ene)bis-(2-methyl-but-3-yn-2-ol): Structural variation in vicinal dialkynols

Article abstract of DOI:10.1107/S0108270112013169

The structure of the title compound, C₁₈H₂₂O ₂, contains two non-equivalent mol-ecules which differ primarily in the location of the -OH groups on opposite sides or on the same side of the mol-ecular plane. Inversion-symme

Full text of DOI:10.1107/S0108270112013169

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
synthesized by the treatment of 1,2-diiodo-4,5-dimethyl-
benzene (Hathaway et al., 2009) with excess 2-methyl-3-butyn-
2-ol in the presence of copper(I) and palladium catalysts
(Melissaris & Litt, 1994).
ISSN 0108-2701
4,40-(4,5-Dimethyl-1,2-phenylene)-
bis(2-methylbut-3-yn-2-ol): structural
variation in vicinal dialkynols
Marcus R. Bond,a* Bruce A. Hathawayb and Uriah J.
Kilgorea
aDepartment of Chemistry, Southeast Missouri State University, Cape Girardeau,
MO 63701, USA, and bDepartment of Chemistry and Physics, LeTourneau
University, Longview, TX 75607-7001, USA
The two non-equivalent molecules in the asymmetric unit of
(I) (the first digit of the atom label denotes assignment to
molecule 0 or 1) are each quasi-planar for the core atoms, i.e.
those that are, or are bound to atoms that are, sp- or sp2-
hybridized. Bond lengths and angles within each molecule
conform to expected values (Ladd & Palmer, 1994). The
molecules have no formal site symmetry, although each
approximates mm2 symmetry for the core atoms, with half of
the nominally equivalent bond lengths agreeing within 1 s.u.
and all within 2 s.u. Nominally equivalent bond angles for the
ring atoms agree within 3 s.u. [with one slight exception, for
C06—C01—C011 = 120.46 (10)ꢁ and C03—C02—C021 =
120.15 (9)ꢁ], but the angles in the alkynol groups disagree by
more. Similar bond lengths between non-equivalent molecules
agree [with one slight exception, for the Cx1—Cx11 and Cx2—
Correspondence e-mail: bond@mbond2.st.semo.edu
Received 15 January 2012
Accepted 26 March 2012
Online 31 March 2012
The structure of the title compound, C18H22O2, contains two
non-equivalent molecules which differ primarily in the
location of the –OH groups on opposite sides or on the same
side of the molecular plane. Inversion-symmetric pairs of
molecules form intermolecular O—Hꢀ ꢀ ꢀO hydrogen-bonded
tetrameric synthons that link non-equivalent molecules into
an approximately square double layer parallel to (102).
Recently reported fluorinated analogues [Kane, Meyers, Yu,
Gerken & Etzkorn (2011). Eur. J. Org. Chem. pp. 2969–2980]
have significantly different structures of varying complexity
that incorporate intramolecular hydrogen bonding and
suggest that further study of structure versus substituents in
vicinal dialkynols could be fruitful.
˚
Cx21 bonds which are in the range 1.4353 (15)–1.4400 (15) A]
within 3 s.u. for Csp, Csp2 or O atoms, while the Csp3—Csp3
bonds agree within 4 s.u. The differences in similar bond
angles between non-equivalent molecules are larger and agree
within 3–5 s.u. in the ring, with even greater disagreement in
the alkynol groups. Bonds in the ring between substituents are
elongated compared with the others, with the Cx1—Cx2 bond
between alkynol groups being the longest. The substituents
are scissored outward, as shown by bond angles at the
substituted ring atoms of <120ꢁ for aromatic ring atoms only
and interior angles of >120ꢁ involving the substituent. Angles
Comment
Dialkynols have been extensively studied as part of a broader
survey of gem-alkynol structures (Madhavi, Desiraju et al.,
2000a; Nangia, 2010). Since the gem-alkynol moiety provides
two functional groups, viz. –OH and –C CH, there are
several competing ways in which groups on neighboring
molecules can interact which, in turn, lead to a wide variety of
synthons and structures (Madhavi, Bilton et al., 2000; Banerjee
et al., 2006). One recurring structural motif is a tetrameric
synthon of functional groups that are linked by hydrogen
bonds in a square arrangement (Madhavi, Desiraju et al.,
2000b; Bilton et al., 2001). The di-gem-alkynols studied often
place the alkynol groups on opposite sides of an organic ring,
so intramolecular interactions are inhibited. Vicinal dialkynol
structures have recently been reported in which the alkynol
groups are ortho, but with –C CH groups absent, so the –OH
groups are positioned to act as molecular tweezers in which
intramolecular hydrogen bonding is now possible (Kane et al.,
2011). We report here the structure of the title new vicinal
dialkynol compound, (I), an intermediate obtained in an effort
to prepare cyclic diacetylenes (Zhou et al., 1994), which was
Figure 1
The asymmetric unit of (I), showing the two non-equivalent molecules
with atom labels. Displacement ellipsoids are drawn at the 50%
probability level. The dashed line indicates the hydrogen bond between
non-equivalent molecules.
Acta Cryst. (2012). C68, o179–o182
doi:10.1107/S0108270112013169
# 2012 International Union of Crystallography o179

organic compounds
about the unsubstituted ring atoms of ꢂ122ꢁ indicate a slight
scissoring inward of these atoms with the outward scissoring of
the substituents. The main geometric difference between the
non-equivalent molecules is the –OH group location on
opposite sides of the molecular plane (molecule 0) or on the
same side (molecule 1), which reduces the approximate point-
group symmetry of molecule 0 to 2, and of molecule 1 to m. A
displacement ellipsoid plot of the asymmetric unit of (I) is
presented in Fig. 1.
Inversion-related molecular pairs are formed, with inter-
˚
planar spacings of 3.486 (1) and 3.717 (1) A for molecules 0
and 1, respectively. The aromatic rings within each pair are
offset away from each other, principally along a line parallel to
the alkynol arms of O1 or O11, with distances between the
ring-atom centroids (measured perpendicular to the mean-
˚
plane normal) of 1.394 (2) and 1.547 (2) A for molecules 0 and
1, respectively. Since the interplanar spacings are greater than
the sum of the van der Waals radii (Bondi, 1964) and the large
ring displacements lead to only minor (30–35%) overlap, it is
unlikely that there is a significant attractive interaction
between the molecules of each pair. The long axes of the non-
equivalent molecules are almost perpendicular [angle of
86.17 (7)ꢁ between the least-squares lines formed by the core
atoms], with that of molecule 0 parallel to [201] and that of
molecule 1 almost parallel to b. These vectors demarcate axes
Figure 2
A plot of a portion of the quasi-square layer in (I) (with b vertical and
[201] horizontal) formed by hydrogen bonding between inversion-related
pairs of molecules. Atoms are represented by circles of arbitrary radii and
H atoms have been omitted for clarity, except for those bound to oxygen.
Pairs of type 0 and 1 molecules are identified in the diagram and the inset
shows the detail of the square tetrameric hydrogen-bonded synthon.
˚
1
2
1
2
[Symmetry codes: (ii) x ꢄ 1, ꢄy + 12, z ꢄ ; (iv) ꢄx + 1, y ꢄ , ꢄz + 21.]
for an approximately square grid [23.0784 (3) A along [201]
˚
versus 22.7966 (3) A along b] of inversion-related pairs of
molecules linked by hydrogen bonds to form a double layer in
(102). Different types of molecule pairs alternate along each
repeat axis, with a given molecule forming hydrogen bonds to
molecules of the other type on each side. This results in O—
Hꢀ ꢀ ꢀO hydrogen bonds arranged in square tetrameric
synthons between rows of molecules. Deviations from a true
square within the synthon are small, e.g. neighboring Oꢀ ꢀ ꢀO
distances are in close agreement and the Oꢀ ꢀ ꢀOꢀ ꢀ ꢀO angles
are ꢂ90ꢁ, with the largest due to O—Hꢀ ꢀ ꢀO angles of 164–
171ꢁ that place H atoms outside the square. The mean plane of
molecule 1 is closer to (102), with both –OH groups directed
into the double layer and with the C114 and C125 methyl
groups directed outward. The mean-plane normal of molecule
0 forms an angle of 24.86 (2)ꢁ to that of molecule 1, with the
–OH groups hydrogen bonded to molecules 1 on opposite
sides of the double layer. The differences in geometric para-
meters between the alkynol groups (see above) can thus be
ascribed to strains imposed to accommodate hydrogen
bonding. The double layer is scored by grooves parallel to
[201], generated by the offset of molecules 1, with the tetra-
meric O—Hꢀ ꢀ ꢀO synthons at the floor (or ceiling) of each
groove. A diagram of the quasi-square layer is presented in
Fig. 2 and hydrogen-bonding parameters are presented in
Table 1.
60.80 (1) and 36.22 (1)ꢁ for molecules 0 and 1, respectively.
The stacks of inversion-related molecular pairs are readily
observed when the structure is viewed down a, as shown in the
packing diagram in Fig. 3. However, the double layers are less
obvious from a cursory examination, since the methyl groups
projecting away from the layer are nested into the grooves of
neighboring layers so as to obscure the boundaries between
layers.
The structure is completed by stacking the double layers so
molecule 0 pairs stack along a at the lines of inversion centers
passing halfway through the b and c edges, while molecule 1
pairs stack similarly but along the a edges or passing through
the center of the bc face. The mean planes within the stacks
are tilted relative to a, with the normals forming angles of
Figure 3
A unit-cell packing diagram for (I), viewed along a, showing the stacks of
inversion–related pairs of molecules. Atoms are drawn as circles of
arbitrary radii and H atoms have been omitted for clarity.
ꢃ
o180 Bond et al. C18H22O2
Acta Cryst. (2012). C68, o179–o182

organic compounds
steam bath. Crystals of (I) formed as a sand-colored solid upon slow
cooling of this solution, first to ambient temperature and then to
273 K in an ice bath (yield: 2.67 g, 70.6%; m.p. 414 K). Single crystals
of this sample appeared colorless under microscopic examination and
were suitable for X-ray diffraction.
The few known vicinal dialkynols exhibit a variety in their
structures that is sensitive to molecular geometry and com-
position, as is already well known among the much larger gem-
alkynol family. The structure of (I) is, perhaps, the most
conventional, since it contains the recurring tetrameric O—
Hꢀ ꢀ ꢀO synthon, yet at the same time shows no intramolecular
interactions that might be expected for the tweezer-like ortho
arrangement of the alkynol groups. In contrast, the difluoro
analog [Cambridge Structural Database (Version 5.32; Allen,
2002) refcode OQAZUC (Kane et al., 2011)], in which F
replaces the ring CH3 groups, has quite a complex structure
(Z0 = 9) in which intramolecular O—Hꢀ ꢀ ꢀO interactions are
also found. This striking difference in complexity between the
dimethyl and difluoro analogs raises the question of what
other structures might be observed by replacing substituents
in these positions. Meanwhile, the tetrafluoro analog
(OQEBOC; Kane et al., 2011), in which F replaces the ring
CH3 groups and H atoms, has a simpler structure (Z0 = 1) and
only localized intra- and intermolecular O—Hꢀ ꢀ ꢀO hydrogen
bonding between two molecules in the tetrameric synthon,
although with a more distorted square than in (I). In contrast,
in OQEBIW (Z0 = 1; Kane et al., 2011), the analog to
OQEBOC with alkynol CH3 groups replaced by H, a strictly
intermolecular O—Hꢀ ꢀ ꢀO hydrogen-bonding network of
zigzag chains is found. Thus, a two-dimensional hydrogen-
bonding network with no intramolecular hydrogen bonding is
found in (I), in spite of the presence of alkynol CH3 groups,
the presence of which allows for intramolecular hydrogen
bonding in OQAZUC and OQEBIW and localized inter-
actions only in OQEBIW. [Note that the carboxylic acid
analog of (I) contains both intra- and intermolecular bonding
to form zigzag O—Hꢀ ꢀ ꢀO hydrogen-bonded chains (Sarava-
nakumar et al., 2009).] Two other vicinal dialkynols, octa-2,4,6-
triyne-1,8-diol (LILHUJ, Z0 = 0.5; Enkelmann, 1994) and 2,9-
dimethyldeca-3,5,7-triyne-2,9-diol (LILJAR, Z0 = 1; Enkel-
mann, 1994), contain a –C C– core that dictates a linear
geometry, so the –OH groups are at opposite ends (and
intramolecular hydrogen bonding is impossible) and O—
Hꢀ ꢀ ꢀO hydrogen-bonded networks are present as zigzag single
or double layers, respectively. This variation of structure
within the vicinal dialkynols (in particular ortho-dialkynols),
where small variations in ring or alkynol substituents lead to
large changes in structure from competition between intra-
and intermolecular hydrogen bonding, seems a fruitful area
for further investigation.
Crystal data
3
˚
C18H22O2
Mr = 270.37
V = 3248.58 (7) A
Z = 8
Monoclinic, P21=c
Mo Kꢁ radiation
ꢂ = 0.07 mmꢄ1
T = 100 K
0.36 ꢅ 0.32 ꢅ 0.28 mm
˚
a = 8.4720 (1) A
b = 22.7966 (3) A
˚
˚
c = 16.8592 (2) A
ꢀ = 93.886 (1)ꢁ
Data collection
Nonius KappaCCD area-detector
diffractometer
18231 measured reflections
9466 independent reflections
7185 reflections with I > 2ꢃ(I)
Rint = 0.027
Refinement
R[F2 > 2ꢃ(F2)] = 0.046
wR(F2) = 0.122
S = 1.01
9466 reflections
389 parameters
H atoms treated by a mixture of
independent and constrained
refinement
ꢄ3
˚
Áꢄmax = 0.33 e A
ꢄ3
˚
Áꢄmin = ꢄ0.24 e A
Solution and refinement of the structure were straightforward; all
non-H atoms were found in the initial electron-density map and their
anisotropic displacement parameters were refined. All H atoms were
visible in subsequent electron-density difference maps, and the
positions and isotropic displacement parameters of those bound to O
atoms were refined freely. Other H-atom positions were calculated to
˚
give an idealized geometry, with C—H = 0.96 or 0.93 A and Uiso(H) =
1.5 or 1.2Ueq(C) for CH3 or aromatic H atoms, respectively. The CH3
torsion angle was refined to match the electron density. 11 low-angle
2
2
reflections obscured by the beam stop (as indicated by Fo << Fc )
were omitted from the refinement.
Data collection: COLLECT (Nonius, 1998); cell refinement:
SCALEPACK (Otwinowski
DENZO (Otwinowski
& Minor, 1997); data reduction:
Minor, 1997) and SCALEPACK;
&
program(s) used to solve structure: SIR92 (Altomare et al., 1993);
program(s) used to refine structure: SHELXL97 (Sheldrick, 2008);
molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and
ORTEPIII (Burnett & Johnson, 1996); software used to prepare
material for publication: WinGX (Farrugia, 1999) and PARST
(Nardelli, 1995).
The authors thank the National Science Foundation DUE
CCLI–A&I program (grant No. 9951348) and Southeast
Missouri State University for funding the X-ray diffraction
facility.
Experimental
Nitrogen (N2) was bubbled through triethylamine (75 ml) for 15 min
to remove dissolved oxygen, with the N2 atmosphere maintained
throughout the subsequent reaction. 1,2-Diiodo-4,5-dimethylbenzene
(5.0 g, 0.014 mol), 2-methyl-3-butyn-2-ol (5.88 g, 0.070 mol), tri-
phenylphosphane (0.10 g) and copper(I) iodide (0.03 g) were added,
and the mixture was stirred for 10 min. Dichloridobis(triphenyl-
phosphane)palladium (0.030 g) was added, and the reaction was
heated to ꢂ330 K overnight. The resulting green solution was diluted
with diethyl ether and filtered. The filtrate was evaporated to yield a
green–brown solid that was then redissolved in hot toluene on a
Table 1
Hydrogen-bond geometry (A, ).
ꢁ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
O01—H01ꢀ ꢀ ꢀO12i
O02—H02ꢀ ꢀ ꢀO11ii
O11—H11ꢀ ꢀ ꢀO01iii
O12—H12ꢀ ꢀ ꢀO02
0.886 (18)
0.886 (19)
0.886 (19)
0.904 (18)
1.901 (17)
1.876 (19)
1.892 (19)
1.847 (17)
2.773 (1)
2.752 (1)
2.756 (1)
2.744 (1)
167.5 (16)
169.8 (18)
164.3 (18)
170.7 (17)
1
2
1
2
1
2
1
2
Symmetry codes: (i) ꢄx þ 1; y þ ; ꢄz þ ; (ii) x ꢄ 1; ꢄy þ ; z ꢄ ; (iii) ꢄx þ 2; ꢄy þ 1,
ꢄz þ 1.
ꢃ
Acta Cryst. (2012). C68, o179–o182
Bond et al. C18H22O2 o181

organic compounds
Kane, C. M., Meyers, T. B., Yu, X., Gerken, M. & Etzkorn, M. (2011). Eur. J.
Org. Chem. pp. 2969–2980.
Ladd, M. F. C. & Palmer, R. A. (1994). Structure Determination by X-ray
Crystallography, 3rd ed., pp. 434–435. New York: Plenum Press.
Madhavi, N. N. L., Bilton, C., Howard, J. A. K., Allen, F. H., Nangia, A. &
Desiraju, G. R. (2000). New J. Chem. 24, 1–4.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: KU3064). Services for accessing these data are
described at the back of the journal.
Madhavi, N. N. L., Desiraju, G. R., Bilton, C., Howard, J. A. K. & Allen, F. H.
(2000a). Acta Cryst. B56, 1063–1070.
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o182 Bond et al. C18H22O2
Acta Cryst. (2012). C68, o179–o182