Ethyl propionate at 185 K

Shallard-Brown, H.A.; Watkin, D.J.; Cowley, A.R.

doi:10.1107/S1600536805005271

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 61| Part 4| April 2005| Pages o1118-o1120

https://doi.org/10.1107/S1600536805005271

Ethyl propionate at 185 K

Howard A. Shallard-Brown,^a ^* David J. Watkin ^a and Andrew R. Cowley ^a

^aChemical Crystallography Laboratory, Chemistry Research Laboratory, Mansfield Road, Oxford University, Oxford OX1 3TA, England
^*Correspondence e-mail: howard.shallard-brown@lmh.ox.ac.uk

(Received 9 February 2005; accepted 16 February 2005; online 25 March 2005)

The title compound, C₅H₁₀O₂, was prepared by a modified zone-refining technique, and has a layered structure with a high degree of disorder within the layers.

Comment

Many of the esters and ketones used in the flavours and fragrances industry are liquid at room temperature; thus, in the past, crystalline derivatives have had to be prepared for X-ray analysis. The examination of this substance is part of a programme to simplify and systematize the study of substances which are liquid at room temperature.

The diffraction pattern could be indexed as tetragonal with a = 9.52 Å and c = 6.89 Å. If some weak and diffuse reflections in layers perpendicular to c were included in the indexing, this doubled the c axis. The diffraction data were processed on the basis of both cells. In both cases, the space group assignment was uncertain. A clear molecular motif could be obtained by direct methods for a range of space groups, though those for the larger cell could not be refined. Eventually, it was decided to discard the weak layers, and work only with the smaller cell. For this cell, space groups P4₂bc (No. 106) and P4₂/mbc (No. 135) gave plausible but disordered solutions. In both cases, the molecules lie at (½, ½, ½), with their molecular mirror plane more or less perpendicular to c. This leads to the molecules lying in sheets perpendicular to c, with an intersheet spacing of 3.45 Å. In space group No. 106, the molecule lies on a twofold rotation axis only, whereas in space group No. 135 it lies on the centre of symmetry at the intersection of a twofold axis and a mirror plane. The structure was refined in both space groups.

Because both types of disorder lead to interpenetration of the molecule with its image, unrestrained geometric parameters were slightly abnormal. Target values for bond lengths and inter-bond angles were taken from the MOGUL database (Bruno et al., 2004 ), together with standard uncertainties. These were used as restraints for refinement in both space groups.

In space group No. 106, the twofold rotation does not require the molecule to be planar, and the deviations of the non-H atoms from their mean plane are C3 0.08 (2), C2 −0.04 (2), C1 −0.15 (2), O1 −0.04 (2), O2 0.08 (2), C4 0.12 (2), C5 −0.07 (2) Å. The relatively large anisotropic displacement parameters were restrained to satisfy the Hirshfeld (1976 ) condition for rigid bonds. This refinement concluded satisfactorily with a conventional R value of 0.053 for 64 parameters and 383 observations. However, we could see no reason why the disordered molecule should not lie on a centre of symmetry, so the refinement was repeated in space group No. 135. The molecule is not required to be planar, even in this space group, but the atoms lie so close to the mirror that disordered displacements from it could not be modelled. In this space group, the anisotropic displacement parameters are less eccentric than in No. 106, and provide no evidence for believing that the non-H atoms do not actually lie on the mirror plane. It is this refinement which is presented for publication, though we suspect that, in reality, the crystal may suffer from stacking faults and possibly twinning.

Figure 1
The title molecular structure, with displacement ellipsoids drawn at the 50% probability level. H atoms are of arbitrary radii. The disorder is not shown.

Figure 2
Packing diagram, showing the overall layered structure, viewed along the b axis, with disorder included.

Figure 3
Diagram showing the twofold disordered molecules within one layer, viewed along the c axis.

Experimental

A 3 mm column of the title material, which is a liquid at room temperature, was sealed in a 0.2 mm Lindemann tube. A single crystal was grown by keeping the compound under a cold nitrogen gas stream at 185 K (not far below its melting point of 198 K) and slowly moving a small liquid zone, created by a micro-heating coil, up and down the sample. Once a suitable approximately single crystal had been obtained, the main data collection was undertaken at this temperature.

Crystal data

C₅H₁₀O₂
M_r = 102.14
Tetragonal, P4₂/mbc
a = 9.5153 (3) Å
c = 6.8933 (2) Å
V = 624.13 (3) Å³
Z = 4
D_x = 1.087 Mg m⁻³
Mo Kα radiation
Cell parameters from 458 reflections
θ = 5–27°
μ = 0.08 mm⁻¹
T = 185 K
Cylinder, colourless
0.50 × 0.1 mm (radius)

Data collection

Nonius KappaCCD diffractometer
ω scans
Absorption correction: multi-scan DENZO/SCALEPACK (Otwinowski & Minor, 1997 ) T_min = 0.98, T_max = 0.98
719 measured reflections
384 independent reflections
383 reflections with I > -3σ(I)
R_int = 0.013
θ_max = 27.5°
h = −12 → 12
k = −12 → 12
l = −8 → 8

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.062
wR(F²) = 0.100
S = 0.90
383 reflections
43 parameters
H-atom parameters constrained
w = 1/[σ²(F²) + 0.04 + 0.17P] where P = [max(F_o²,0) + 2F_c²]/3
(Δ/σ)_max = 0.013
Δρ_max = 0.14 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

O1—C1	1.168 (16)
O2—C1	1.351 (6)
O2—C4	1.483 (13)
C1—C2	1.497 (14)
C2—C3	1.519 (10)
C4—C5	1.481 (10)

C1—O2—C4	107.6 (6)
O2—C1—O1	122.4 (10)
O2—C1—C2	118.7 (8)
O1—C1—C2	119.0 (12)
C1—C2—C3	107.8 (9)
O2—C4—C5	111.6 (10)

H atoms were positioned geometrically after each cycle, with C—H = 1.0 Å and U_iso(H) = 1.2U_eq(C). All atoms are disordered, with occupancy factor 0.5.

Data collection: COLLECT (Nonius, 2001 ); cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO/SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003 ); molecular graphics: CAMERON (Watkin et al., 1996 ); software used to prepare material for publication: CRYSTALS.

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536805005271/cf6408sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536805005271/cf6408Isup2.hkl

Computing details top

Data collection: COLLECT (Nonius, 2001); cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO/SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS.

(I) top

Crystal data top

C₅H₁₀O₂	D_x = 1.087 Mg m⁻³
M_r = 102.14	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P4₂/mbc	Cell parameters from 458 reflections
a = 9.5153 (3) Å	θ = 5–27°
c = 6.8933 (2) Å	µ = 0.08 mm⁻¹
V = 624.13 (3) Å³	T = 185 K
Z = 4	Cylinder, colourless
F(000) = 224	0.50 × 0.20 × 0.20 × 0.1 (radius) mm

Data collection top

Nonius KappaCCD diffractometer	383 reflections with I > −3σ(I)
Graphite monochromator	R_int = 0.013
ω scans	θ_max = 27.5°, θ_min = 5.2°
Absorption correction: multi-scan DENZO/SCALEPACK (Otwinowski & Minor, 1997)	h = −12→12
T_min = 0.98, T_max = 0.98	k = −12→12
719 measured reflections	l = −8→8
384 independent reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.062	H-atom parameters constrained
wR(F²) = 0.100	w = 1/[σ²(F²) + 0.04 + 0.17P] where P = [max(F_o²,0) + 2F_c²]/3
S = 0.90	(Δ/σ)_max = 0.013
383 reflections	Δρ_max = 0.14 e Å⁻³
43 parameters	Δρ_min = −0.17 e Å⁻³
42 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
O1	0.5978 (3)	0.3630 (3)	0.5000	0.0785	0.5000
O2	0.4285 (12)	0.5218 (12)	0.5000	0.0569	0.5000
C1	0.5646 (18)	0.4812 (16)	0.5000	0.0535	0.5000
C2	0.6764 (16)	0.5919 (14)	0.5000	0.0597	0.5000
C3	0.8180 (13)	0.5182 (8)	0.5000	0.0677	0.5000
C4	0.3407 (17)	0.3930 (15)	0.5000	0.0687	0.5000
C5	0.1889 (14)	0.4272 (9)	0.5000	0.0860	0.5000
H21	0.6673	0.6519	0.6184	0.0717*	0.5000
H31	0.8948	0.5900	0.5000	0.0813*	0.5000
H32	0.8262	0.4581	0.6185	0.0813*	0.5000
H41	0.3630	0.3366	0.6184	0.0824*	0.5000
H51	0.1329	0.3382	0.5000	0.1032*	0.5000
H52	0.1656	0.4832	0.6185	0.1032*	0.5000

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.070 (2)	0.0585 (18)	0.107 (2)	0.0162 (15)	0.0000	0.0000
O2	0.054 (2)	0.059 (3)	0.058 (5)	−0.001 (3)	0.0000	0.0000
C1	0.057 (2)	0.050 (3)	0.054 (7)	0.000 (3)	0.0000	0.0000
C2	0.065 (5)	0.050 (3)	0.065 (5)	−0.004 (3)	0.0000	0.0000
C3	0.056 (3)	0.064 (4)	0.084 (3)	−0.007 (3)	0.0000	0.0000
C4	0.059 (4)	0.082 (7)	0.066 (5)	−0.019 (4)	0.0000	0.0000
C5	0.062 (4)	0.097 (7)	0.098 (5)	−0.007 (5)	0.0000	0.0000

Geometric parameters (Å, º) top

O1—C1	1.168 (16)	C3—H31	1.000
O2—C1	1.351 (6)	C3—H32	1.000
O2—C4	1.483 (13)	C4—C5	1.481 (10)
C1—C2	1.497 (14)	C4—H41	1.000
C2—C3	1.519 (10)	C5—H51	1.000
C2—H21	1.000	C5—H52	1.000

C1—O2—C4	107.6 (6)	C2—C3—H32	109.5
O2—C1—O1	122.4 (10)	H31—C3—H32	109.5
O2—C1—C2	118.7 (8)	O2—C4—C5	111.6 (10)
O1—C1—C2	119.0 (12)	O2—C4—H41	108.9
C1—C2—C3	107.8 (9)	C5—C4—H41	108.9
C1—C2—H21	109.9	C4—C5—H51	109.5
C3—C2—H21	109.9	C4—C5—H52	109.5
C2—C3—H31	109.5	H51—C5—H52	109.5

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