3-Triphenyl­methyl-2,4-penta­nedione

The title compound, C₂₄H₂₂O₂, exists exclusively as the keto tautomer in the crystalline state with a dihedral angle of 66.8 (2)° between the carbonyl groups. Furthermore, steric crowding produces an uncommonly long carbon-carbon bond [1.587 (3) Å] linking the triphenyl­methyl and diketone moieties.

Key indicators

• Single-crystal X-ray study
• T = 290 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.047
• wR factor = 0.148
• Data-to-parameter ratio = 14.2

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Alert level B
PLAT063_ALERT_3_B Crystal Probably too Large for Beam Size .......       1.00 mm

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   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
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S1. Comment

Acetylacetone (2,4-pentanedione) and other β-diketones are molecules in dynamic equilibrium with both tautomers present in measurable concentrations at equilibrium. The keto-enol ratio in these systems is modulated by solvent polarity, hydrogen bonding capacity, and the concentration of dissolved salts (Pocker & Spyridis, 2002; Emsley, 1984). This ratio is also exquisitely sensitive to the size of the substituents on the carbon between the carbonyls, with the keto concentration increasing as the steric bulk rises (Emsley, 1984). In light of our recent investigations into the keto-enol ratio of acetylacetone in highly concentrated nonaqueous salt solutions (Pocker & Spyridis, 2002), we prepared and crystallized 3-triphenyl-2,4-pentanedione, 1.

The title compound exists exclusively in the diketo form with steric crowding producing an uncommonly long C3—C6 bond of 1.587 (3) Å. This is close to the adamantyl-diketone bond length of 1.595 (8) Å observed in 3-methyl-3-(1-adamantyl)-2,4-pentanedione, 2 (Moreno-Manas et al., 1992). The C2—C3 and C3—C4 linkages at 1.544 (3) and 1.531 (3) Å, respectively, are also slightly longer than the 1.50 Å typical for sp²-sp³ carbon-carbon bonds (Wiorkiewicz-Kuczera & Rabczenko, 1986), as are the phenyl-carbon bonds about C6. Steric congestion also produces bond angles about C3 that are unusually large for a sp³ hybridized carbon: C2—C3—C6 is 116.5 (2)° while C4—C3—C6 is 117.23 (19)°.

The main factor determining the conformation of the keto tautomer is the strong repulsion of the localized C═O bond dipoles (Emsley et al., 1986). For both 1 and 2 the C2—C3—C4 angle is between 105–107° while for the keto tautomer of acetylaceone (Lowery et al., 1971) the corresponding angle is 114°, possibly in an effort to minimize the interaction between the carbonyl bond dipoles. For β-diketones possessing large groups about C3 semiempirical MM2 calculations (Moreno-Manas et al., 1991) reveal that the conformations which predominate are those with a dihedral angle between the carbonyls of less than 90°, with their contribution increasing as the bulk of the substituent rises. For 1 only a single conformation is oberved in the crystalline state and it possesses a dihedral angle of 66.8 (2)° between the carbonyls.

Related literature

For related literature, see: Emsley (1984); Emsley et al. (1986); Lowery et al. (1971); Moreno-Manas et al. (1991, 1992); Pocker & Spyridis (2002); Wiorkiewicz-Kuczera & Rabczenko (1986); Zaugg & Schaefer (1965).

S2. Experimental

The title compound was synthesized as outlined in the literature (Zaugg & Schaefer, 1965) and purified by column chromatography over silica gel using 1:1 n-pentane: n-hexane as the mobile phase. Crystals suitable for X-ray analysis were grown by slow evaporation from 1:1 n-pentane: n-hexane at 298 K. The crystals of 1 did not cleave very well and several attempts to break or cut them were unsuccessful. Therefore a larger than standard crystal (1 mm max. dimension) was used for this study. The beam tube that was used was large enough (2 mm i.d.) to ensure that the crystal was completely inside of the X-ray beam during the diffraction experiment.

S3. Refinement

H atoms were placed in calculated positions and allowed to ride during subsequent refinement, with U_iso(H) = 1.2U_eq(C) and C—H distances of 0.93 Å for H atoms attached to the aromatic rings, U_iso(H) = 1.5U_eq(C) and C—H distances of 0.96 Å for the methyl H atoms, and U_iso(H) = 1.2U_eq(C) and a C—H distance of 0.98 Å for the tertiary H atom.

Computing details

Data collection: CAD-4-PC Software (Enraf–Nonius, 1993); cell refinement: CAD-4-PC Software (Enraf–Nonius, 1993); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: publCIF (Westrip, 2007).

Figures

Fig. 1. The molecular structure of 1, with the atom-numbering scheme. Displacement ellipsoids for non-hydrogen atoms are drawn at the 50% probability level. Hydrogen atoms are not shown for clarity.

3-Triphenylmethyl-2,4-pentanedione

Crystal data

C24H22O2	F(000) = 728
Mr = 342.42	Dx = 1.225 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 9.1906 (11) Å	θ = 8.1–13.5°
b = 23.704 (3) Å	µ = 0.08 mm^−1
c = 9.3251 (13) Å	T = 290 K
β = 113.941 (12)°	Plate, colorless
V = 1856.7 (4) Å^3	1.00 × 0.48 × 0.17 mm
Z = 4

Data collection

Enraf–Nonius CAD-4 diffractometer	1775 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.043
Graphite monochromator	θmax = 25.4°, θmin = 2.5°
θ/2θ scans	h = 0→11
Absorption correction: ψ scan (North et al., 1968)	k = 0→28
Tmin = 0.868, Tmax = 0.991	l = −11→10
3594 measured reflections	3 standard reflections every 120 min
3378 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.047	H-atom parameters constrained
wR(F^2) = 0.148	w = 1/[σ^2(Fo^2) + (0.0688P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.99	(Δ/σ)max < 0.001
3378 reflections	Δρmax = 0.19 e Å^−3
238 parameters	Δρmin = −0.16 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.014 (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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.9972 (2)	0.23311 (8)	0.6900 (2)	0.0575 (5)
O2	0.9543 (3)	0.27619 (8)	0.3716 (2)	0.0740 (7)
C1	0.7447 (4)	0.27723 (14)	0.5824 (4)	0.0776 (10)
H1A	0.7873	0.2995	0.6764	0.116*
H1B	0.6527	0.2571	0.5786	0.116*
H1C	0.7152	0.3015	0.4926	0.116*
C2	0.8678 (3)	0.23625 (11)	0.5817 (3)	0.0472 (7)
C3	0.8210 (3)	0.20020 (10)	0.4317 (3)	0.0382 (6)
H3A	0.7051	0.2037	0.3774	0.046*
C4	0.8882 (3)	0.23122 (11)	0.3279 (3)	0.0457 (7)
C5	0.8630 (3)	0.20898 (12)	0.1699 (3)	0.0583 (8)
H5A	0.9423	0.2244	0.1387	0.087*
H5B	0.7591	0.2197	0.0952	0.087*
H5C	0.8714	0.1686	0.1743	0.087*
C6	0.8549 (3)	0.13449 (9)	0.4564 (3)	0.0349 (6)
C7	0.8657 (3)	0.11838 (10)	0.6212 (3)	0.0377 (6)
C8	0.9936 (3)	0.09073 (11)	0.7339 (3)	0.0496 (7)
H8A	1.0816	0.0817	0.7132	0.060*
C9	0.9922 (4)	0.07632 (13)	0.8774 (3)	0.0633 (8)
H9A	1.0796	0.0580	0.9522	0.076*
C10	0.8635 (4)	0.08876 (14)	0.9098 (3)	0.0665 (9)
H10A	0.8632	0.0788	1.0062	0.080*
C11	0.7344 (4)	0.11606 (14)	0.7995 (3)	0.0627 (8)
H11A	0.6468	0.1248	0.8212	0.075*
C12	0.7357 (3)	0.13033 (12)	0.6568 (3)	0.0504 (7)
H12A	0.6475	0.1484	0.5824	0.060*
C13	0.7134 (3)	0.09979 (10)	0.3388 (3)	0.0365 (6)
C14	0.6992 (3)	0.04335 (11)	0.3709 (3)	0.0495 (7)
H14A	0.7752	0.0276	0.4617	0.059*
C15	0.5764 (3)	0.00993 (12)	0.2726 (3)	0.0585 (8)
H15A	0.5708	−0.0278	0.2973	0.070*
C16	0.4627 (3)	0.03230 (13)	0.1384 (3)	0.0591 (8)
H16A	0.3789	0.0100	0.0726	0.071*
C17	0.4733 (3)	0.08740 (12)	0.1020 (3)	0.0556 (8)
H17A	0.3975	0.1025	0.0100	0.067*
C18	0.5965 (3)	0.12122 (11)	0.2015 (3)	0.0445 (6)
H18A	0.6009	0.1589	0.1757	0.053*
C19	1.0120 (3)	0.11948 (10)	0.4404 (3)	0.0361 (6)
C20	1.1484 (3)	0.15112 (11)	0.5224 (3)	0.0483 (7)
H20A	1.1444	0.1802	0.5877	0.058*
C21	1.2892 (3)	0.14001 (12)	0.5082 (4)	0.0568 (8)
H21A	1.3793	0.1613	0.5651	0.068*
C22	1.2977 (3)	0.09809 (12)	0.4113 (3)	0.0548 (7)
H22A	1.3920	0.0915	0.3995	0.066*
C23	1.1649 (3)	0.06562 (11)	0.3315 (3)	0.0493 (7)
H23A	1.1701	0.0365	0.2670	0.059*
C24	1.0237 (3)	0.07625 (10)	0.3468 (3)	0.0421 (6)
H24A	0.9352	0.0538	0.2929	0.051*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0433 (11)	0.0637 (12)	0.0543 (12)	−0.0069 (9)	0.0082 (10)	−0.0163 (9)
O2	0.0818 (15)	0.0550 (13)	0.0785 (15)	−0.0209 (11)	0.0257 (12)	0.0060 (11)
C1	0.0573 (19)	0.078 (2)	0.092 (2)	0.0045 (16)	0.0250 (18)	−0.0377 (19)
C2	0.0375 (15)	0.0458 (15)	0.0561 (17)	−0.0059 (12)	0.0168 (14)	−0.0075 (13)
C3	0.0280 (12)	0.0394 (13)	0.0420 (13)	−0.0005 (10)	0.0088 (11)	−0.0024 (11)
C4	0.0377 (14)	0.0385 (14)	0.0538 (17)	0.0031 (12)	0.0113 (12)	0.0090 (12)
C5	0.0631 (19)	0.0624 (17)	0.0569 (17)	0.0063 (15)	0.0321 (15)	0.0117 (15)
C6	0.0282 (12)	0.0387 (13)	0.0339 (13)	0.0014 (10)	0.0085 (10)	0.0008 (10)
C7	0.0301 (13)	0.0447 (14)	0.0322 (13)	−0.0042 (11)	0.0063 (11)	−0.0024 (11)
C8	0.0403 (15)	0.0570 (17)	0.0422 (15)	0.0008 (13)	0.0071 (12)	0.0028 (13)
C9	0.0616 (19)	0.076 (2)	0.0379 (16)	0.0029 (16)	0.0055 (14)	0.0109 (15)
C10	0.078 (2)	0.085 (2)	0.0332 (16)	−0.0149 (18)	0.0195 (16)	−0.0009 (15)
C11	0.0549 (18)	0.087 (2)	0.0472 (17)	−0.0075 (16)	0.0221 (15)	−0.0045 (16)
C12	0.0375 (14)	0.0686 (19)	0.0419 (16)	−0.0021 (13)	0.0129 (12)	−0.0005 (13)
C13	0.0333 (13)	0.0408 (14)	0.0344 (13)	−0.0011 (10)	0.0126 (11)	−0.0032 (11)
C14	0.0499 (16)	0.0475 (16)	0.0437 (15)	−0.0022 (13)	0.0112 (13)	−0.0008 (13)
C15	0.0632 (19)	0.0460 (16)	0.0615 (18)	−0.0150 (14)	0.0202 (16)	−0.0102 (14)
C16	0.0455 (17)	0.0642 (19)	0.0583 (19)	−0.0119 (14)	0.0114 (15)	−0.0238 (15)
C17	0.0399 (15)	0.0672 (19)	0.0432 (16)	−0.0009 (14)	0.0000 (13)	−0.0110 (14)
C18	0.0380 (14)	0.0473 (15)	0.0418 (14)	0.0004 (11)	0.0096 (12)	−0.0014 (12)
C19	0.0303 (13)	0.0383 (13)	0.0374 (13)	0.0041 (10)	0.0112 (10)	0.0051 (11)
C20	0.0358 (14)	0.0486 (15)	0.0583 (17)	0.0003 (12)	0.0167 (13)	−0.0069 (13)
C21	0.0324 (15)	0.0601 (18)	0.074 (2)	−0.0009 (13)	0.0181 (14)	−0.0084 (16)
C22	0.0381 (15)	0.0669 (19)	0.0624 (19)	0.0089 (13)	0.0235 (14)	0.0030 (15)
C23	0.0503 (17)	0.0562 (17)	0.0440 (15)	0.0122 (13)	0.0219 (13)	−0.0011 (13)
C24	0.0378 (14)	0.0478 (15)	0.0344 (13)	0.0046 (11)	0.0082 (11)	0.0015 (11)

Geometric parameters (Å, º)

O1—C2	1.211 (3)	C11—C12	1.378 (4)
O2—C4	1.212 (3)	C11—H11A	0.9300
C1—C2	1.493 (4)	C12—H12A	0.9300
C1—H1A	0.9600	C13—C14	1.388 (3)
C1—H1B	0.9600	C13—C18	1.391 (3)
C1—H1C	0.9600	C14—C15	1.379 (3)
C2—C3	1.544 (3)	C14—H14A	0.9300
C3—C4	1.531 (3)	C15—C16	1.370 (4)
C3—C6	1.587 (3)	C15—H15A	0.9300
C3—H3A	0.9800	C16—C17	1.363 (4)
C4—C5	1.492 (4)	C16—H16A	0.9300
C5—H5A	0.9600	C17—C18	1.390 (3)
C5—H5B	0.9600	C17—H17A	0.9300
C5—H5C	0.9600	C18—H18A	0.9300
C6—C7	1.547 (3)	C19—C24	1.379 (3)
C6—C19	1.551 (3)	C19—C20	1.393 (3)
C6—C13	1.554 (3)	C20—C21	1.379 (3)
C7—C8	1.383 (3)	C20—H20A	0.9300
C7—C12	1.393 (3)	C21—C22	1.366 (4)
C8—C9	1.386 (4)	C21—H21A	0.9300
C8—H8A	0.9300	C22—C23	1.378 (4)
C9—C10	1.366 (4)	C22—H22A	0.9300
C9—H9A	0.9300	C23—C24	1.385 (3)
C10—C11	1.376 (4)	C23—H23A	0.9300
C10—H10A	0.9300	C24—H24A	0.9300
C2—C1—H1A	109.5	C10—C11—C12	119.7 (3)
C2—C1—H1B	109.5	C10—C11—H11A	120.2
H1A—C1—H1B	109.5	C12—C11—H11A	120.2
C2—C1—H1C	109.5	C11—C12—C7	121.6 (3)
H1A—C1—H1C	109.5	C11—C12—H12A	119.2
H1B—C1—H1C	109.5	C7—C12—H12A	119.2
O1—C2—C1	121.7 (2)	C14—C13—C18	116.5 (2)
O1—C2—C3	122.7 (2)	C14—C13—C6	118.9 (2)
C1—C2—C3	115.6 (2)	C18—C13—C6	124.7 (2)
C4—C3—C2	105.75 (19)	C15—C14—C13	122.2 (3)
C4—C3—C6	117.23 (19)	C15—C14—H14A	118.9
C2—C3—C6	116.5 (2)	C13—C14—H14A	118.9
C4—C3—H3A	105.4	C16—C15—C14	120.0 (3)
C2—C3—H3A	105.4	C16—C15—H15A	120.0
C6—C3—H3A	105.4	C14—C15—H15A	120.0
O2—C4—C5	119.9 (3)	C17—C16—C15	119.5 (3)
O2—C4—C3	119.1 (2)	C17—C16—H16A	120.2
C5—C4—C3	120.9 (2)	C15—C16—H16A	120.2
C4—C5—H5A	109.5	C16—C17—C18	120.5 (3)
C4—C5—H5B	109.5	C16—C17—H17A	119.7
H5A—C5—H5B	109.5	C18—C17—H17A	119.7
C4—C5—H5C	109.5	C17—C18—C13	121.3 (2)
H5A—C5—H5C	109.5	C17—C18—H18A	119.4
H5B—C5—H5C	109.5	C13—C18—H18A	119.4
C7—C6—C19	110.60 (18)	C24—C19—C20	117.6 (2)
C7—C6—C13	105.55 (18)	C24—C19—C6	123.1 (2)
C19—C6—C13	110.85 (18)	C20—C19—C6	119.3 (2)
C7—C6—C3	108.44 (18)	C21—C20—C19	121.0 (3)
C19—C6—C3	110.29 (18)	C21—C20—H20A	119.5
C13—C6—C3	111.00 (17)	C19—C20—H20A	119.5
C8—C7—C12	117.5 (2)	C22—C21—C20	120.7 (3)
C8—C7—C6	124.3 (2)	C22—C21—H21A	119.7
C12—C7—C6	118.1 (2)	C20—C21—H21A	119.7
C7—C8—C9	120.8 (3)	C21—C22—C23	119.2 (3)
C7—C8—H8A	119.6	C21—C22—H22A	120.4
C9—C8—H8A	119.6	C23—C22—H22A	120.4
C10—C9—C8	120.5 (3)	C22—C23—C24	120.3 (3)
C10—C9—H9A	119.7	C22—C23—H23A	119.9
C8—C9—H9A	119.7	C24—C23—H23A	119.9
C9—C10—C11	119.8 (3)	C19—C24—C23	121.2 (2)
C9—C10—H10A	120.1	C19—C24—H24A	119.4
C11—C10—H10A	120.1	C23—C24—H24A	119.4