Methyl 3,5-bis(cyclohexylmethoxy)benzoate

In the title compound, C22H32O4, the atoms of the methyl ester group and the alkoxy O atoms are all coplanar with the central aromatic ring, with an r.m.s. deviation of 0.008 Å. Bonds to the methylene and cyclohexyl groups are also very close to this plane, so that the molecule is essentially flat, apart from the cyclohexyl groups. The mean planes through the cyclohexyl groups are tilted by 30.08 (9) and 36.14 (7)° with respect to the central aromatic ring. In the crystal, pairs of molecules linked by C—H⋯O hydrogen bonds form planar units which are stacked along the a axis, with an average interplanar distance of 3.549 (2) Å. Stacking appears to be stabilized by further weak C—H⋯O hydrogen bonds.

We are grateful for the Dean's Office at Fordham University for its generous financial support. We thank Matthew P. Tracey for his assistance with this work. The Q-Tof Ultima mass spectrometer (University of Illinois at Urbana-Champaign) was purchased in part with a grant from the NSF, Division of Biological Infrastructure (DBI-0100085). organic compounds o400 Corfield et al.

Synthesis and crystallization
The reaction was performed under an argon gas atmosphere with oven dried glassware. Reagents were obtained from Aldrich and used without further purification. 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 (ppm) and coupling constants in Hertz (Hz). 1 H NMR spectra obtained in CDCl 3 were referenced to 7.26 ppm and 13 C NMR spectra obtained in CDCl 3 were referenced to 77.2 ppm. Mass spectra were obtained from University of Illinois Mass Spectrometry Center (Micromass Q-TOF Ultra, ESI).

Refinement
Both forms of the 0 1 0 and of the 0 0 1 reflections were partially obscured by the beam stop, and were omitted from the refinements. H atoms were constrained to idealized positions with C-H distances of 0.93Å for the aromatic H atoms, 0.96Å for the methyl H atoms, 0.97Å for the secondary H atoms and 0.98Å for the tertiary H atoms on C10 and C17. The orientation of the methyl group was determined by calculation of electron density in the toroid that should contain the H atoms of the idealized methyl group. The U eq values for all H atoms were fixed at 1.2 times the U iso of their bonded C atoms.

Comment
Dendrimers are macromolecules prepared in a stepwise fashion from monomer units and a core molecule. This work is part of a larger study examining how the the modification of functional groups in the monomer impacts the physical and In the title compound, C 22 H 32 O 4 , the four atoms of the methyl ester group and the two oxygen atoms of the 3,5 alkoxy substituents are all coplanar with the central aromatic ring, with a dihedral angle of the ester group to the ring of only 0.7 (1)°. Bonds to the cyclohexyl groups are also close to this plane, with torsional angles C2-C3-O1-C9 and C3-O1-C9-C10 of 172.88 (15)° and 179.66 (14)° respectively, and C6-C5-O2-C16 and C5-O2-C16-C17 angles of 3.4 (3)° and 175.59 (14)° respectively. The C10-C15 and C17-C22 cyclohexyl groups are oriented respectively away from and towards the methyl ester group on C1 (Fig. 1), and their mean planes are tilted 30.08 (9)° and 36.14 (7)° to the central aromatic ring. A similar extended conformation for the cyclohexylmethoxy substituent in a related compound is found in Yang et al. (2008).
Steric repulsion between methylene hydrogen atoms of the alkoxy groups and ring protons leads to opening of the exterior ring angles to 124.6 (1)° and 24.8 (1)°, and of the bond angles at the ether oxygen atoms to 118.7 (1)° and 117.9 (1)°.
Pairs of molecules are connected by weak C-H··· O hydrogen bonds across the center of symmetry at (1 -x, 1 -y, 1z). (Figs. 2 and 3) The central planes of the symmetry-related molecules are almost coplanar, with a perpendicular distance between them of 0.105 (3)Å. The molecular pairs are stacked along the a axis, with average interplanar spacing of 3.549 (2) Å. (Fig. 4) There are no obvious π-π interactions to explain the short stacking distance. We propose that part of the interplanar interaction arises from the presence of long C-H···O hydrogen bonds between O3 and methylene and cyclohexyl hydrogen atoms H16A and H18A. (See Table 1) Such non-classical hydrogen bonds are frequently invoked in recent publications in this journal, and their impact on reaction stereochemistry is reviewed in Johnston and Cheong (2013).

Figure 1
The molecular structure of the title molecule, with ellipsoids at the 50% level.    Stacking of molecular pairs related by translations along the a axis. The dashed lines represent the proposed long C-H···O hydrogen bonds. This figure is related to Fig. 3 by rotation of 90° about the horizontal axis.  (2) 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.