Cyclo­penta­deca­none

In the crystal structure, the title compound (exaltone), C₁₅H₂₈O, exhibits no disorder, and the 15-membered ring exists in the quinquangular [13353] C₁ symmetry conformation. The crystal exhibits nonmerohedral twinning by twofold rotation about [100], but adjustment of the temperature to 90 K causes the [101] distance to equal the c axial length, allowing the twinning to be treated as pseudo-merohedral. The literature description of the structure as disordered ortho­rhom­bic with halved a-axis length is corrected.

S1. Comment

The conformations of cyclic ketones have been studied in solution by dynamic NMR spectroscopy (e.g. Anet et al., 1973, 1974) and in the solid state by X-ray crystallography (e.g. Groth, 1974, 1975, 1976, 1979). Completely ordered crystals were found for cyclodecanone at 113 K (Groth, 1976) and cycloundecanone at 108 K (Groth, 1974); the conformation in each case was based on a stable conformation of the parent hydrocarbon {[2323] (Pawar et al., 1998) or [335] (Pawar et al., 2006)}.

The ring skeletons for cyclododecanone (Groth, 1979) and cyclotetradecanone (Groth, 1975) matched those of cyclododecane ([3333]; Dunitz & Shearer, 1960) and cyclotetradecane ([3434]; Anet et al., 1972), but the crystals were disordered with respect to placement of the carbonyl groups. Groth (1979) concluded from preliminary studies of cyclotridecanone and cycloheptadecanone that the crystals were disordered, and the structures were not determined. Crystals of cyclopentadecanone [the title compound, (I)] and cyclohexadecanone were reported to be orthorhombic, and cell dimensions were given [incorrectly for compound (I); see below] by Groth (1976). The author concluded that the crystals were disordered, and attempts to solve both structures were unsuccessful.

Attempts to study the conformations of (I) in solution by low-temperature ¹H and ¹³C NMR spectroscopy were inconclusive, and conformational assignments were not made (Cheng, 1973). Cyclopentadecanone phenylsemicarbazone has been reported to have a [3435] conformation in the solid state by X-ray diffraction (van den Hoek et al., 1979), and a [12345] conformation was found for the 2,4-dintrophenylhydrazone of (I) by the same method (Pawar et al., 2007). Strain energies have been calculated using MOLBUILD [Reference for software?] for several conformations of cyclopentadecane, and the [33333] conformation was predicted to be the most stable of those considered (Anet & Rawdah, 1978).

The molecular structure of (I) is shown in Fig. 1. The cyclopentadecane ring exists in the quinquangular [13353] conformation with corner positions at C atoms 3, 4, 7, 10 and 15, as described by the torsion angles in Table 1. The atoms of the C₁₅ ring are coplanar to a mean deviation of 0.382 Å, with a maximum deviation of 0.603 (2) Å for atom C8. The O atom lies 1.646 (2) Å out of this plane, and the ketone plane (O1/C1/C2/C15) forms a dihedral angle of 66.12 (2)° with it.

While the unit cell has monoclinic symmetry, the lattice has a nearly C-centered orthorhombic metric, with the transformation (-1 0 0, 1 0 2, 0 1 0) yielding a cell with dimensions a = 15.663, b = 31.719 and c = 5.553 Å, and α = β = 90 and γ = 90.04°. Groth (1976) reported an orthorhombic cell at 113 K having dimensions 7.814 (4), 15.990 (8) and 5.589 (3) Å, noting that its cell volume (half ours) would yield Z = 2 and require disorder of the molecule. We note that the Groth cell has two of its dimensions near half those of the C-centered cell from our data. Examination of the packing in Fig. 2 suggests how the incorrect description of the unit-cell dimensions came about for this soft weakly-scattering compound. The centroid of the 15-membered ring is very near (3/4, 1/2, 1/2), and thus its equivalent by inversion through the center of the cell is related to it by an approximate translation of a/2, corresponding to the 7.81 Å ce l l dimension of the Groth cell. The vector from the origin to (1/2, 0, 1/2) is nearly orthogonal to our a axis, and corresponds to Groth's 15.99 Å ce l l dimension, half the 31.7 Å axis of the C-centered metric. The molecules related by the a/2 approximate translation would not overlap exactly, so would necessarily be disordered in the smaller cell, as pointed out by Groth (1976).

We noted splitting of spots in the diffraction pattern at nearer ambient temperatures, hinting that crystals of (I) are twinned. The twinning is a twofold rotation about [100], bringing the [101] and [001] vectors into near coincidence. At T = 150 K, these two distances differ by 0.6%, but we found that lowering the temperature to 90 K caused anisotropic shrinkage of the cell, making the [101] distance equal to the c axis and causing the split spots to coalesce (Fronczek & Fox, 2007). Thus, we measured diffraction data at 90 K, and were able to treat the twin as essentially perfectly pseudo-merohedral. Introducing one TWIN and one BASF command into the refinement in SHELXL97 (Sheldrick, 1997) lowered the R value from 0.296 to 0.059.

Related literature

For related literature, see: Anet & Rawdah (1978); Anet et al. (1972, 1973, 1974); Cheng (1973); Dunitz & Shearer (1960); Fronczek & Fox (2007); Giral (1935); Groth (1974, 1975, 1976, 1979); Hoek et al. (1979); Pawar et al. (1998, 2006, 2007); Sheldrick (1997).

S2. Experimental

A commercial sample (Aldrich Chemical Company) of cyclopentadecanone was recrystallized from ethanol [m.p. 336.5 K; literature m.p. 338.5 K (Giral, 1935)]. Purity was determined by a room-temperature ¹³C NMR spectrum.

S3. Refinement

H atoms were placed in calculated positions, guided by difference maps, with C—H bond distances of 0.99 Å and with U_iso = 1.2U_eq(C), and thereafter treated as riding. The structure was refined as a pseudo-merohedral twin with twin law (1 0 0, 0 - 1 0, -1 0 - 1). The twinning was perfect, with the BASF parameter refined to 0.500 (2).

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2 (Bruker, 2006); data reduction: APEX2 (Bruker, 2006); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: XSHELL (Bruker, 2004).

Figures

	Fig. 1. The molecule of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A unit-cell diagram for (I), viewed down the symmetry direction. The bold lines correspond to the cell reported by Groth (1976), and the dotted line, [101], has a length equal to that of the c axis in this twinned structure.

Cyclopentadecanone

Crystal data

C15H28O	F(000) = 504
Mr = 224.37	Dx = 1.080 Mg m^−3
Monoclinic, P21/c	Melting point: 336.5 K
Hall symbol: -P 2ybc	Cu Kα radiation, λ = 1.54178 Å
a = 15.6634 (16) Å	Cell parameters from 1310 reflections
b = 5.5531 (5) Å	θ = 3.1–67.1°
c = 17.6928 (18) Å	µ = 0.48 mm^−1
β = 116.315 (8)°	T = 90 K
V = 1379.4 (3) Å^3	Lath, colourless
Z = 4	0.34 × 0.12 × 0.07 mm

Data collection

Bruker Kappa APEXII CCD area-detector diffractometer	2359 independent reflections
Radiation source: fine-focus sealed tube	2007 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.052
ϕ and ω scans	θmax = 67.6°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	h = −17→17
Tmin = 0.853, Tmax = 0.967	k = −6→2
5210 measured reflections	l = −20→19

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.059	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.164	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.1051P)^2 + 0.0175P] where P = (Fo^2 + 2Fc^2)/3
2359 reflections	(Δ/σ)max < 0.001
146 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

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 > σ(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	0.60985 (18)	−0.1031 (4)	0.49740 (16)	0.0375 (6)
C1	0.5870 (2)	0.1048 (5)	0.4775 (2)	0.0251 (7)
C2	0.6166 (2)	0.3050 (5)	0.54111 (19)	0.0273 (7)
H2A	0.5587	0.3729	0.5421	0.033*
H2B	0.6459	0.4341	0.5219	0.033*
C3	0.6859 (2)	0.2361 (5)	0.63058 (19)	0.0282 (7)
H3A	0.7214	0.0900	0.6292	0.034*
H3B	0.6499	0.1976	0.6630	0.034*
C4	0.7561 (2)	0.4378 (5)	0.67466 (19)	0.0277 (7)
H4A	0.7884	0.4037	0.7359	0.033*
H4B	0.7204	0.5904	0.6666	0.033*
C5	0.8314 (2)	0.4708 (5)	0.64291 (19)	0.0260 (7)
H5A	0.8758	0.3324	0.6618	0.031*
H5B	0.7998	0.4704	0.5805	0.031*
C6	0.8883 (2)	0.7024 (5)	0.67346 (19)	0.0271 (7)
H6A	0.8449	0.8406	0.6486	0.033*
H6B	0.9128	0.7123	0.7354	0.033*
C7	0.9716 (2)	0.7260 (5)	0.65205 (19)	0.0292 (7)
H7A	1.0206	0.6064	0.6858	0.035*
H7B	1.0000	0.8878	0.6699	0.035*
C8	0.9488 (2)	0.6918 (5)	0.55938 (19)	0.0280 (7)
H8A	1.0086	0.7068	0.5536	0.034*
H8B	0.9244	0.5263	0.5422	0.034*
C9	0.8768 (2)	0.8681 (5)	0.49947 (19)	0.0248 (6)
H9A	0.9017	1.0337	0.5155	0.030*
H9B	0.8172	0.8554	0.5056	0.030*
C10	0.8540 (2)	0.8260 (5)	0.40634 (19)	0.0261 (7)
H10A	0.8177	0.9660	0.3729	0.031*
H10B	0.9145	0.8178	0.4016	0.031*
C11	0.7964 (2)	0.5957 (5)	0.36799 (19)	0.0269 (7)
H11A	0.7963	0.5645	0.3129	0.032*
H11B	0.8282	0.4579	0.4055	0.032*
C12	0.6946 (2)	0.6108 (5)	0.3555 (2)	0.0277 (7)
H12A	0.6557	0.6914	0.3010	0.033*
H12B	0.6927	0.7126	0.4007	0.033*
C13	0.6499 (2)	0.3687 (5)	0.35609 (19)	0.0271 (7)
H13A	0.6920	0.2806	0.4080	0.033*
H13B	0.6454	0.2729	0.3073	0.033*
C14	0.5508 (2)	0.3906 (6)	0.35226 (19)	0.0260 (7)
H14A	0.5037	0.4170	0.2930	0.031*
H14B	0.5495	0.5336	0.3852	0.031*
C15	0.5212 (2)	0.1684 (5)	0.3865 (2)	0.0286 (7)
H15A	0.4565	0.1960	0.3815	0.034*
H15B	0.5176	0.0286	0.3505	0.034*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0567 (16)	0.0171 (10)	0.0427 (14)	0.0019 (10)	0.0257 (13)	0.0027 (10)
C1	0.0309 (17)	0.0144 (14)	0.0364 (18)	−0.0027 (11)	0.0207 (14)	−0.0017 (12)
C2	0.0283 (17)	0.0153 (14)	0.0309 (17)	0.0004 (12)	0.0064 (14)	0.0001 (11)
C3	0.0346 (18)	0.0190 (14)	0.0289 (17)	0.0012 (12)	0.0121 (14)	0.0044 (12)
C4	0.0356 (18)	0.0210 (14)	0.0205 (15)	−0.0006 (12)	0.0069 (14)	0.0012 (11)
C5	0.0329 (17)	0.0199 (14)	0.0197 (14)	−0.0007 (12)	0.0067 (14)	−0.0025 (11)
C6	0.0346 (18)	0.0196 (14)	0.0228 (15)	0.0008 (13)	0.0087 (14)	−0.0004 (11)
C7	0.0287 (16)	0.0247 (15)	0.0286 (17)	0.0002 (13)	0.0076 (14)	−0.0013 (12)
C8	0.0328 (17)	0.0202 (14)	0.0306 (17)	0.0014 (12)	0.0137 (14)	0.0018 (11)
C9	0.0278 (16)	0.0168 (12)	0.0279 (16)	0.0000 (11)	0.0104 (14)	0.0021 (11)
C10	0.0258 (16)	0.0223 (14)	0.0283 (17)	−0.0043 (12)	0.0102 (14)	0.0018 (11)
C11	0.0320 (17)	0.0225 (14)	0.0245 (16)	−0.0068 (12)	0.0110 (14)	−0.0044 (12)
C12	0.0279 (16)	0.0205 (13)	0.0283 (16)	−0.0017 (12)	0.0065 (13)	0.0021 (13)
C13	0.0337 (18)	0.0204 (14)	0.0270 (16)	−0.0021 (12)	0.0131 (14)	−0.0002 (12)
C14	0.0299 (17)	0.0203 (13)	0.0229 (15)	−0.0003 (12)	0.0074 (13)	−0.0010 (11)
C15	0.0346 (17)	0.0200 (13)	0.0298 (18)	−0.0067 (12)	0.0130 (14)	−0.0044 (12)

Geometric parameters (Å, º)

O1—C1	1.214 (3)	C8—H8A	0.9900
C1—C2	1.502 (4)	C8—H8B	0.9900
C1—C15	1.519 (4)	C9—C10	1.541 (4)
C2—C3	1.519 (4)	C9—H9A	0.9900
C2—H2A	0.9900	C9—H9B	0.9900
C2—H2B	0.9900	C10—C11	1.538 (4)
C3—C4	1.520 (4)	C10—H10A	0.9900
C3—H3A	0.9900	C10—H10B	0.9900
C3—H3B	0.9900	C11—C12	1.512 (4)
C4—C5	1.526 (5)	C11—H11A	0.9900
C4—H4A	0.9900	C11—H11B	0.9900
C4—H4B	0.9900	C12—C13	1.518 (4)
C5—C6	1.521 (4)	C12—H12A	0.9900
C5—H5A	0.9900	C12—H12B	0.9900
C5—H5B	0.9900	C13—C14	1.528 (4)
C6—C7	1.517 (4)	C13—H13A	0.9900
C6—H6A	0.9900	C13—H13B	0.9900
C6—H6B	0.9900	C14—C15	1.534 (4)
C7—C8	1.527 (4)	C14—H14A	0.9900
C7—H7A	0.9900	C14—H14B	0.9900
C7—H7B	0.9900	C15—H15A	0.9900
C8—C9	1.514 (4)	C15—H15B	0.9900
O1—C1—C2	122.2 (3)	H8A—C8—H8B	107.6
O1—C1—C15	120.2 (3)	C8—C9—C10	113.5 (2)
C2—C1—C15	117.5 (2)	C8—C9—H9A	108.9
C1—C2—C3	115.8 (2)	C10—C9—H9A	108.9
C1—C2—H2A	108.3	C8—C9—H9B	108.9
C3—C2—H2A	108.3	C10—C9—H9B	108.9
C1—C2—H2B	108.3	H9A—C9—H9B	107.7
C3—C2—H2B	108.3	C11—C10—C9	114.3 (2)
H2A—C2—H2B	107.4	C11—C10—H10A	108.7
C2—C3—C4	111.7 (2)	C9—C10—H10A	108.7
C2—C3—H3A	109.3	C11—C10—H10B	108.7
C4—C3—H3A	109.3	C9—C10—H10B	108.7
C2—C3—H3B	109.3	H10A—C10—H10B	107.6
C4—C3—H3B	109.3	C12—C11—C10	113.1 (3)
H3A—C3—H3B	107.9	C12—C11—H11A	109.0
C3—C4—C5	113.6 (3)	C10—C11—H11A	109.0
C3—C4—H4A	108.8	C12—C11—H11B	109.0
C5—C4—H4A	108.8	C10—C11—H11B	109.0
C3—C4—H4B	108.8	H11A—C11—H11B	107.8
C5—C4—H4B	108.8	C11—C12—C13	114.2 (2)
H4A—C4—H4B	107.7	C11—C12—H12A	108.7
C6—C5—C4	113.4 (2)	C13—C12—H12A	108.7
C6—C5—H5A	108.9	C11—C12—H12B	108.7
C4—C5—H5A	108.9	C13—C12—H12B	108.7
C6—C5—H5B	108.9	H12A—C12—H12B	107.6
C4—C5—H5B	108.9	C12—C13—C14	113.0 (2)
H5A—C5—H5B	107.7	C12—C13—H13A	109.0
C7—C6—C5	114.7 (3)	C14—C13—H13A	109.0
C7—C6—H6A	108.6	C12—C13—H13B	109.0
C5—C6—H6A	108.6	C14—C13—H13B	109.0
C7—C6—H6B	108.6	H13A—C13—H13B	107.8
C5—C6—H6B	108.6	C13—C14—C15	113.4 (2)
H6A—C6—H6B	107.6	C13—C14—H14A	108.9
C6—C7—C8	116.1 (3)	C15—C14—H14A	108.9
C6—C7—H7A	108.3	C13—C14—H14B	108.9
C8—C7—H7A	108.3	C15—C14—H14B	108.9
C6—C7—H7B	108.3	H14A—C14—H14B	107.7
C8—C7—H7B	108.3	C1—C15—C14	115.1 (2)
H7A—C7—H7B	107.4	C1—C15—H15A	108.5
C9—C8—C7	114.7 (3)	C14—C15—H15A	108.5
C9—C8—H8A	108.6	C1—C15—H15B	108.5
C7—C8—H8A	108.6	C14—C15—H15B	108.5
C9—C8—H8B	108.6	H15A—C15—H15B	107.5
C7—C8—H8B	108.6
O1—C1—C2—C3	6.5 (4)	C8—C9—C10—C11	70.2 (3)
C15—C1—C2—C3	−177.3 (3)	C9—C10—C11—C12	70.3 (3)
C1—C2—C3—C4	144.6 (3)	C10—C11—C12—C13	−154.0 (3)
C2—C3—C4—C5	−72.9 (3)	C11—C12—C13—C14	174.2 (3)
C3—C4—C5—C6	168.1 (2)	C12—C13—C14—C15	−157.6 (3)
C4—C5—C6—C7	172.8 (3)	O1—C1—C15—C14	−136.1 (3)
C5—C6—C7—C8	52.9 (4)	C2—C1—C15—C14	47.6 (4)
C6—C7—C8—C9	59.9 (4)	C13—C14—C15—C1	58.6 (3)
C7—C8—C9—C10	−178.9 (2)