1-(2,4,6-Triisopropylphenyl)ethanone

The title compound, C17H26O, is a di-ortho-alkyl substituted phenyl ethanone that exhibits a significant twisting of the ketone fragment relative to the aromatic ring [O—C—C—C torsion angle = 89.32 (17)°] due to steric pressure from the ortho-isopropyl groups. One ortho- and the para-isopropyl group exhibit orientational disorder with a refined site occupancy factor of 0.562 (3):0.438 (3).

The title compound, C 17 H 26 O, is a di-ortho-alkyl substituted phenyl ethanone that exhibits a significant twisting of the ketone fragment relative to the aromatic ring [O-C-C-C torsion angle = 89.32 (17) ] due to steric pressure from the ortho-isopropyl groups. One ortho-and the para-isopropyl group exhibit orientational disorder with a refined site occupancy factor of 0.562 (3):0.438 (3).

Comment
We have had a long standing interest in the impact of sterically bulky ortho-alkyl groups on the conformation of ligands containing aryl rings, and in particular, those with ortho-isopropyl substituents (Boeré & Masuda, 2002;Boeré et al., 2008;Giffin et al., 2010a;Giffin, et al., 2010b;Giffin et al., 2011). The steric impact of these ortho-isopropyl groups has proven important in the stabilization of many reactive functional groups. In our continuing interest in these systems we have prepared and studied the title compound which is an intermediate to the related acetylene, 2-ethynyl-1,3,5-triisopropylbenzene (Tani et al., 1963).
This can be attributed to the increased steric pressure of the ortho-isopropyl groups relative to the ortho-methyl groups in the previous two examples.
One ortho-and the para-isopropyl group exhibit two-site disorder with a refined site occupancy factor of 0.562 (3):0.438 (3). A careful look at the packing of the molecule reveals no typical hydrogen bonding and lacks significant intermolecular interactions (Figure 2).

Experimental
The title compound was prepared following literature methods (Delair et al, 1996) and was crystallized as large needles from a hot methanol solution cooled to room temperature.

Refinement
The hydrogen atoms were placed in geometrically idealized positions of 0.98Å (methyl C-H), 0.95Å (aromatic C-H) and 1.00Å (methine C-H) and constrained to ride on the parent atom with U iso (H) = 1.2 U eq (C) for aromatic and tertiary protons as well as U iso (H) = 1.5 U eq (C) for the methyl groups. Two of the three isopropyl groups were modeled with two-site disorder. The isopropyl groups containing atoms C12A, C13A, C14A and C12B, C13B, C14B as well as C15A, C16A, C17A and C15B, C16B, C17B were modeled with a refined site occupancy factor of 0.562 (3):0.438 (3). In order to obtain satisfactory thermal parameters for the disordered part of the molecule DELU commands were used on the atoms C12A, C12B, C13A, C13B, C14A, C14B and C15A, C15B, C16A, C16B, C17A, C17B respectively for each isopropyl group.
Unit-cell parameters were determinedd using a θ range of 2.54 to 27.83° however, in order to obtian a reasonable level of data completeness, θ was limited to 26.00° for refinement.  Fig. 1. The molecular structure of 1-(2,4,6-triisopropylphenyl)ethanone, with atom labels and 50% probability displacement ellipsoids for non-H atoms. Hydrogen atoms have been removed for clarity.