erythro-{1-Bromo-1-[(1-phenylethyl)sulfonyl]ethyl}benzene

Structural analysis of the title diasteromeric sulfone determines this to be the erythro (RR/SS) isomer, and was pivotal in showing that the 1,3-elimination reactions of these compounds, which lead to substituted stilbenes, occur with inversion at each asymmetric carbon atom.


Structure description
In an earlier paper (Bordwell et al., 1970), we described how two monobromo sulfone diastereomers with melting points of 349 and 385 K had been prepared.The final products from a Ramberg-Ba ¨cklung reaction on these compounds were primarily cis-�,�'-dimethylstilbene for the higher melting stereoisomer, and trans-�,�'-dimethylstilbene for the lower melting isomer.The crystal-structure determination of the title compound, which is the higher melting isomer, enabled the determination that the reactions involved inversion at each of the asymmetric �-C atoms, but no crystallographic details were given in the above paper.Continuing interest in the stereochemistry of such reactions (Du ¨fert, 2023;Paquette, 2001) prompted this publication to give details of the structure analysis of the title compound, C 16 H 17 BrO 2 S.
The structure of the molecule, with displacement ellipsoids, is shown in Fig. 1, where it is evident that the stereochemistries of the two �-C atoms to the sulfone group are RR.As the sample was present as a racemic mixture, there are equal numbers of molecules in the crystal with the SS configuration -these configurations are referred to as erythro in the 1970 publication (Bordwell et al., 1970).While the phenyl group C11-C16 is trans to the S1-C1 bond in the molecule, phenyl group C5-C10 is gauche to the S1-C2 bond, with the Br1 atom taking the trans position.The planes of the two phenyl groups are inclined at 49.4 (2) � with one another.
The S O distances of 1.426 (3) and 1.436 (4) A ˚are close to the mean of 1.437 A ˚found for 1142 sulfones with tetrahedral �-C atoms in the Cambridge Structural Database (CSD; Groom et al., 2016).The C1-Br1 bond length in the present structure is 1.976 (5) A ˚, close to the mean of 1.950 (2) A ˚found for 11000 aliphatic C-Br bond lengths in the database.The only other sulfone in the database with a phenyl group on each �-C atom and a bromine atom on at least one of the �-C atoms is entry WAVWOJ (Corfield, 2022).That analysis resulted from a similar collaboration with the Bordwell laboratory.
Table 1 lists four C-H� � �O and C-H� � �Br hydrogen bonds, chosen for contacts with C� � �O and C� � �Br distances close to the sum of the van der Waals radii and with C-H� � �O and C-H� � �Br angles of 140 � or larger.These hydrogen bonds are shown in Fig. 2. The C-H� � �Br and C-H� � �O1 hydrogen bonds link the molecules into sheets parallel to the ab plane, while the C-H� � �O2 hydrogen bonds complete the tri-periodic intermolecular network via hydrogen bonds to molecules related by a screw axis.
Analysis of the Hirshfeld surface of the molecule carried out with CrystalExplorer (Spackman et al., 2021) confirmed that the hydrogen bonds are the most significant intermolecular contacts.The d norm surface shown in Fig. 3 is colored blue for points where closest contacts are greater than the sum of the relevant van der Waals radii, while the red areas correspond to contacts closer than that sum.In the view shown, there are red areas corresponding to intermolecular contacts for all of the four C-H donors and for two of the acceptors.There are also C� � �H contacts of 3.4-3.5A ˚between phenyl rings C5-C10 related by the screw axes, which may be reflected in the red area at the lower right of Fig. 3.There are, however, no C� � �C contacts less than 4.0 A ˚between these screw-related phenyl rings.

Synthesis and crystallization
The diastereomer was obtained by bromination of dl-bis-�-methylbenzyl sulfone with N-bromosuccinimide.Details of similar syntheses by the Bordwell group are given in Carpino et al. (1971).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.The data were collected in 1969 with a linear diffractometer unit.The (4 5 6) reflection was omitted due to a clear typewriter error in the data listing.Frequent system errors were common at that time, so that data collection could take much more time than is usual with today's equipment.This is why the data do not reach the resolution expected in today's work and why almost no symmetry equivalents were collected.No absorption corrections were made when the data was first processed, but the use of XABS2 (Parkin et al., 1995) in our current final refinements led to a smoother final difference map and somewhat lower reliability factors.XABS2 rescales the observed data, using a tensor analysis.In Table 2, the minimum and maximum XABS2 corrections of 0.84 and 1.12 for the transmission coefficients have been multiplied by exp (-�r), with � = 4.754 mm À 1 and r = 0.23 mm.The phenyl groups were refined as rigid hexagons, in order to reduce the number of parameters varied.C-C distances of 1.38 A ˚were chosen to minimize the reliability factors.C-H distances were constrained at 0.98 A ˚for the methine C2 atom, 0.96 A ˚for the methyl groups at C3 and C4, and 0.93 A ˚for the phenyl H atoms, while the H atom displacement parameters were set at 1.2U eq of the parental C atoms.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.At the time when this dataset was collected, mechanical failures were frequent enough that minimum redundancy was sought.This accounts for the low resolution of the data and the lack of many symmetry equivalents.

Figure 2
Figure 2 Projection of the crystal structure down the b axis.Atom colors: Br green, S yellow, O red, C,H black.C-H� � �Br and C-H� � �O hydrogen bonds are shown in green and red, respectively.The reference molecule is bolded, with O1 and O2 labeled.

Figure 3
Figure 3Hirshfeld d norm surface for the title compound.

Figure 1
Figure 1View of the title molecule showing the atomic numbering and displacement ellipsoids at the 50% probability level.

Table 2
Experimental details.