Benzene-1,3,5-triyl tribenzoate

The title compound, C27H18O6, commonly known as phloroglucinol tribenzoate, is a standard unit for the family of benzyl ether dendrimers. The central phloroglucinol residue is close to planar, with out-of-plane distances for the three oxygen atoms of up to 0.095 (3) Å, while the three attached benzoate groups are approximately planar. One benzoate group is twisted [C—C—O—C torsion angle = 98.2 (3)°] from the central plane, with its carbonyl O atom 2.226 (4) Å above that plane, while the other two benzoate groups are twisted in the opposite direction [C—C—O—C torsion angles = 24.7 (2) and 54.8 (2)°], so that their carbonyl O atoms are on the other side of, and closer to the central plane, with distances from the plane of 1.743 (4) and 1.206 (4) Å. One benzoate group is disordered between two conformers, with occupancies of 86.9 (3) and 13.1 (3)%, related by a 143 (1)° rotation about the bond to the central benzene ring. The phenyl groups of the two conformers occupy the same space. The molecule packs in the crystal with two of the three benzoate phenyl rings stacked parallel to symmetry-related counterparts, with perpendicular distances of 3.715 (5) and 3.791 (5) Å. The parallel rings are slipped away from each other, however, with centroid–centroid distances of 4.122 (2) and 4.363 (2) Å, respectively.

The title compound, C 27 H 18 O 6 , commonly known as phloroglucinol tribenzoate, is a standard unit for the family of benzyl ether dendrimers. The central phloroglucinol residue is close to planar, with out-of-plane distances for the three oxygen atoms of up to 0.095 (3) Å , while the three attached benzoate groups are approximately planar. One benzoate group is twisted [C-C-O-C torsion angle = 98.2 (3) ] from the central plane, with its carbonyl O atom 2.226 (4) Å above that plane, while the other two benzoate groups are twisted in the opposite direction [C-C-O-C torsion angles = 24.7 (2) and 54.8 (2) ], so that their carbonyl O atoms are on the other side of, and closer to the central plane, with distances from the plane of 1.743 (4) and 1.206 (4) Å . One benzoate group is disordered between two conformers, with occupancies of 86.9 (3) and 13.1 (3)%, related by a 143 (1) rotation about the bond to the central benzene ring. The phenyl groups of the two conformers occupy the same space. The molecule packs in the crystal with two of the three benzoate phenyl rings stacked parallel to symmetry-related counterparts, with perpendicular distances of 3.715 (5) and 3.791 (5) Å . The parallel rings are slipped away from each other, however, with centroidcentroid distances of 4.122 (2) and 4.363 (2) Å , respectively.

Comment
Dendrimers are macromolecules whose composition and molecular weights are well defined. The present work is part of a systematic study examining how functional groups within a dendrimer family influence the ability to remove small organic pollutants from an aqueous environment (Monaco et al. 2013). The title compound is a model for larger dendrimer systems.
The central phloroglucinol residue is close to planar, with out-of-plane distances for the three oxygen atoms varying up to 0.09 Å. Deviations from planarity for the three benzoate groups are larger, with the carbonyl groups twisting to make their oxygen atoms 0.3-0.4 Å from the planes of the phenyl groups (see Fig.1). The benzoate group (C16-C21,C8,O5) is twisted approximately perpendicular to the central plane, with torsional angle C2-C3-O2-C8 = 98.2 (3)°, forcing its carbonyl oxygen atom 2.226 (4) Å Above the central plane. The other two benzoate groups are twisted less, and in the opposite sense, with torsional angles C6-C1-O1-C7 = -125.2 (2) and C4-C5-O3-C9A = -146.3 (2)°, and carbonyl oxygen atoms on the other side of and closer to the central plane. Similar torsional angles were observed in one of the two similar molecules in Shi and Zhang (2006), and in Sasvari and Parkanyi (1980). Fig. 2 shows the packing of the phloroglucinol tribenzoate molecules in the crystal. There may be some interactions between aromatic rings C10-C15 and C16-C21 and their parallel counterparts related by centers of symmetry at 1/2,1/2,1/2 and 0,0,1/2. The perpendicular distances between the planes of the symmetry related rings are 3.715 (5) Å and 3.791 (5) Å respectively. There are few close contacts between the parallel rings, however, as the rings are slipped from direct opposition by 1.78 and 2.15 Å respectively. Indeed the shortest intermolecular contacts in the crystal occur between hydrogen atoms on parallel rings displaced by one unit cell in the direction of the b axis: H21.. H21 (-x,1 -y,1z) = 2.32 Å and H11.. H11(1 -x,-y,1 -z) = 2.74 Å. The disordered benzoate does not show any interaction between parallel phenyl rings.

Experimental
The synthesis described below was performed under an argon gas atmosphere with oven dried glassware. Reagents were obtained from Aldrich. The reagent 2-(dimethylamino)pyridinium p-toluenesulfonate (DPTS) was synthesized as reported previously (Moore et al., 1990). Solvents and reagents were used without further purification except for the following: dichloromethane was distilled from CaH 2 and phloroglucinol dihydrate was azeotroped 5 times with toluene prior to use.
Eluent solvent ratios are reported in v/v. 1 H NMR spectra were recorded at 300 MHz and 13 C NMR spectra were recorded at 75 MHz on a Bruker AV-300 High Performance Digital NMR Spectrometer. Chemical shifts are reported in parts per million (p.p.m.) and coupling constants are reported in Hertz (Hz). 1 H NMR spectra obtained in CDCl 3 were referenced to 7.26 p.p.m. and 13 C NMR spectra obtained in CDCl 3 were referenced to 77.2 p.p.m.. Mass spectra were obtained from the University of Illinois Mass Spectrometry Center (Micromass Q-Tof Ultra, ESI).

Refinement
Refinements with anisotropic temperature factors for C and O atoms and constrained hydrogen atom parameters converged smoothly to R(F 2 >2σ)=0.0563 for 299 variables.
The difference Fourier synthesis at this point showed two peaks of 0.78 and 0.55 e Å 3 in the vicinity of the ester oxygen O3, with no other peak above 0.21 e Å 3 . We have interpreted these two peaks with a partially disordered structure in which the benzoate group O3-C9A(-O6)-(C22-C27) is rotated 149 (1)° about C5-O3 so that C9B and O6B, alternatives to C9A and O6A, fit on the two peaks. The rotated ring C22B-C27B occupies the same space as the original C22A-C27A ring. The relationship of the disordered rings is illustrated in Fig. 3.
In final refinements modeling this disorder, the bond lengths for O3-C9B and C9B-C27B were constrained, to avoid their refinement to unreasonable values. The disordered phenyl group C22B-C27B was constrained to a rigid hexagon with bond lengths 1.378 Å, a value chosen from results of refinements where this distance was increased incrementally.
Joint anisotropic temperature factors were assigned for corresponding carbon atoms in the disordered phenyl groups.
Atom O6B was allowed to vibrate anisotropically. To reduce the number of parameters varied, the benzoate phenyl groups C10-C15 and C16-C21 were also constrained as rigid hexagons. With these constraints, refinement converged with R(F 2 >2σ)=0.0401 for 295 variables. Occupancy factors for the disordered groups are 86.9 (3)% and 13.1 (3)%. The new final difference Fourier synthesis showed no peaks above 0.16 e Å 3 . Use of further restraints on distances in the disordered benzoate group did not improve the geometry.

Computing details
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software (Enraf-Nonius, 1989); data reduction: data reduction followed procedures in Corfield et al. (1973); data were averaged with a local version of SORTAV (Blessing, 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).   Packing diagram for the phloroglucinol tribenzoate structure, showing how two of the benzoate phenyl groups stack around centers of symmetry at (0,0,1/2) and (1/2,1/2,1/2). The molecule at (x,y,z) is boldly outlined. Ellipsoids are at the 30% level. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.15 e Å −3 Δρ min = −0.16 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0067 (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.