The structure of 4′-hydroxyacetophenone, C
8H
8O
2, (1), has been redetermined at 150 K. There are two molecules in the asymmetric unit and the equivalent bond lengths and angles in each molecule are the same. Pairs of independent O—H
O hydrogen-bonded molecules (H
O 1.87 Å) are linked, in turn, by different O—H
O hydrogen bonds (H
O 1.90 Å), through 2
1 screw axes, to form chains in the
c direction.
Supporting information
CCDC reference: 198331
Key indicators
- Single-crystal X-ray study
- T = 150 K
- Mean (C-C) = 0.003 Å
- R factor = 0.034
- wR factor = 0.087
- Data-to-parameter ratio = 7.6
checkCIF results
No syntax errors found
ADDSYM reports no extra symmetry
General Notes
REFLT_03
From the CIF: _diffrn_reflns_theta_max 25.01
From the CIF: _reflns_number_total 1405
Count of symmetry unique reflns 1438
Completeness (_total/calc) 97.71%
TEST3: Check Friedels for noncentro structure
Estimate of Friedel pairs measured 0
Fraction of Friedel pairs measured 0.000
Are heavy atom types Z>Si present no
Please check that the estimate of the number of Friedel pairs is
correct. If it is not, please give the correct count in the
_publ_section_exptl_refinement section of the submitted CIF.
Please provide some preparation or crystallization information.
All H atoms were included in calculated positions, with distances of 0.95 and 0.98 Å for C—H and of 0.84 Å for O—H. In the refinement, H atoms were included in a riding-motion approximation, with Uiso = 1.2Ueq (1.5Ueq for methyl H atoms) of the carrier atom. Owing to a lack of significant amomalous scatterers, the absolute stereochemistry could not be determined and Friedel pairs were merged before refinement cycles. Succesive attempts to crystallize the sample gave crystals that were brittle needles and were difficult to cut. The best crystal possible that was finally selected for data collection gave diffuse diffraction spots, indicating the crystal had a large mosciac spread. As a result of this, a few of the diffraction spots were overlapping and the integration of these spots could not be carried out properly by the processing software. A small portion of the reflections collected were therefore rejected on the basis that they were measured incorrectly. Despite this, the title structure was refined using 97.6% of the possible data, which is adequate to give a precise structure.
Data collection: COLLECT (Nonius, 1997-2001); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997); data reduction: DENZO–SMN; program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
4'-Hydroxyacetophenone
top
Crystal data top
C8H8O2 | F(000) = 576 |
Mr = 136.14 | Dx = 1.314 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 1020 reflections |
a = 6.1886 (4) Å | θ = 2.6–25.0° |
b = 9.0710 (6) Å | µ = 0.09 mm−1 |
c = 24.5261 (15) Å | T = 150 K |
V = 1376.82 (15) Å3 | Needle, colourless |
Z = 8 | 0.40 × 0.30 × 0.25 mm |
Data collection top
Nonius KappaCCD diffractometer | 1284 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.032 |
Graphite monochromator | θmax = 25.0°, θmin = 1.7° |
Detector resolution: 9 pixels mm-1 | h = −7→7 |
ϕ scans and ω scans with κ offsets | k = −10→10 |
3693 measured reflections | l = −29→29 |
1405 independent reflections | |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.034 | H-atom parameters constrained |
wR(F2) = 0.087 | w = 1/[σ2(Fo2) + (0.0428P)2 + 0.1416P] where P = (Fo2 + 2Fc2)/3 |
S = 1.08 | (Δ/σ)max < 0.001 |
1405 reflections | Δρmax = 0.09 e Å−3 |
186 parameters | Δρmin = −0.11 e Å−3 |
0 restraints | Extinction correction: SHELXTL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.037 (11) |
Crystal data top
C8H8O2 | V = 1376.82 (15) Å3 |
Mr = 136.14 | Z = 8 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 6.1886 (4) Å | µ = 0.09 mm−1 |
b = 9.0710 (6) Å | T = 150 K |
c = 24.5261 (15) Å | 0.40 × 0.30 × 0.25 mm |
Data collection top
Nonius KappaCCD diffractometer | 1284 reflections with I > 2σ(I) |
3693 measured reflections | Rint = 0.032 |
1405 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.034 | 0 restraints |
wR(F2) = 0.087 | H-atom parameters constrained |
S = 1.08 | Δρmax = 0.09 e Å−3 |
1405 reflections | Δρmin = −0.11 e Å−3 |
186 parameters | |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | |
O1A | 0.9900 (3) | 0.7943 (2) | 0.22764 (6) | 0.0655 (5) | |
O2A | 0.2191 (2) | 0.85197 (17) | 0.39604 (6) | 0.0533 (4) | |
H2A | 0.2422 | 0.7788 | 0.4162 | 0.080* | |
C1A | 0.6839 (4) | 0.8823 (2) | 0.27513 (8) | 0.0444 (5) | |
C2A | 0.5085 (4) | 0.9759 (2) | 0.27658 (8) | 0.0507 (6) | |
H2AA | 0.4934 | 1.0488 | 0.2490 | 0.061* | |
C3A | 0.3544 (4) | 0.9664 (2) | 0.31707 (9) | 0.0517 (6) | |
H3AA | 0.2346 | 1.0319 | 0.3172 | 0.062* | |
C4A | 0.3756 (3) | 0.8604 (2) | 0.35758 (8) | 0.0440 (5) | |
C5A | 0.5527 (4) | 0.7675 (3) | 0.35731 (8) | 0.0522 (6) | |
H5AA | 0.5696 | 0.6961 | 0.3853 | 0.063* | |
C6A | 0.7045 (4) | 0.7785 (3) | 0.31656 (8) | 0.0532 (6) | |
H6AA | 0.8255 | 0.7140 | 0.3167 | 0.064* | |
C7A | 0.8452 (4) | 0.8859 (2) | 0.23062 (8) | 0.0496 (6) | |
C8A | 0.8244 (5) | 1.0039 (3) | 0.18813 (9) | 0.0643 (7) | |
H8AA | 0.9365 | 0.9904 | 0.1603 | 0.096* | |
H8AB | 0.8416 | 1.1008 | 0.2052 | 0.096* | |
H8AC | 0.6816 | 0.9977 | 0.1710 | 0.096* | |
O1B | 0.2677 (3) | 0.63134 (18) | 0.46931 (6) | 0.0557 (4) | |
O2B | 0.1669 (3) | 0.16396 (19) | 0.65927 (6) | 0.0660 (5) | |
H2B | 0.2716 | 0.1858 | 0.6795 | 0.099* | |
C1B | 0.1267 (3) | 0.4480 (2) | 0.52756 (7) | 0.0413 (5) | |
C2B | −0.0365 (4) | 0.3475 (2) | 0.53879 (8) | 0.0468 (5) | |
H2BA | −0.1612 | 0.3446 | 0.5162 | 0.056* | |
C3B | −0.0199 (4) | 0.2517 (3) | 0.58234 (9) | 0.0522 (6) | |
H3BA | −0.1312 | 0.1821 | 0.5893 | 0.063* | |
C4B | 0.1614 (4) | 0.2577 (2) | 0.61606 (8) | 0.0494 (6) | |
C5B | 0.3267 (4) | 0.3557 (3) | 0.60486 (8) | 0.0490 (5) | |
H5BA | 0.4515 | 0.3582 | 0.6274 | 0.059* | |
C6B | 0.3099 (4) | 0.4497 (2) | 0.56082 (8) | 0.0469 (5) | |
H6BA | 0.4243 | 0.5163 | 0.5530 | 0.056* | |
C7B | 0.1108 (4) | 0.5552 (2) | 0.48232 (8) | 0.0446 (5) | |
C8B | −0.0998 (4) | 0.5725 (3) | 0.45297 (8) | 0.0530 (6) | |
H8BA | −0.0888 | 0.6538 | 0.4268 | 0.079* | |
H8BB | −0.2144 | 0.5939 | 0.4794 | 0.079* | |
H8BC | −0.1340 | 0.4811 | 0.4335 | 0.079* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O1A | 0.0579 (11) | 0.0847 (11) | 0.0540 (9) | 0.0079 (10) | 0.0177 (9) | −0.0033 (9) |
O2A | 0.0437 (8) | 0.0628 (9) | 0.0535 (9) | 0.0044 (9) | 0.0148 (7) | 0.0043 (7) |
C1A | 0.0421 (11) | 0.0538 (11) | 0.0373 (10) | −0.0071 (11) | 0.0021 (9) | −0.0077 (9) |
C2A | 0.0564 (14) | 0.0485 (11) | 0.0473 (11) | −0.0020 (11) | 0.0069 (11) | 0.0024 (10) |
C3A | 0.0481 (13) | 0.0491 (11) | 0.0578 (13) | 0.0064 (11) | 0.0089 (11) | 0.0016 (10) |
C4A | 0.0373 (11) | 0.0547 (11) | 0.0401 (11) | 0.0003 (11) | 0.0045 (9) | −0.0047 (9) |
C5A | 0.0441 (12) | 0.0734 (14) | 0.0392 (11) | 0.0099 (12) | 0.0025 (10) | 0.0074 (10) |
C6A | 0.0405 (12) | 0.0760 (14) | 0.0432 (11) | 0.0154 (13) | 0.0047 (10) | 0.0018 (11) |
C7A | 0.0472 (13) | 0.0595 (12) | 0.0422 (11) | −0.0141 (12) | 0.0061 (10) | −0.0124 (10) |
C8A | 0.0680 (17) | 0.0665 (13) | 0.0584 (14) | −0.0158 (15) | 0.0223 (13) | 0.0018 (11) |
O1B | 0.0473 (9) | 0.0695 (9) | 0.0504 (9) | −0.0048 (9) | 0.0017 (7) | 0.0057 (8) |
O2B | 0.0638 (12) | 0.0788 (11) | 0.0555 (10) | −0.0107 (10) | −0.0226 (8) | 0.0184 (9) |
C1B | 0.0388 (11) | 0.0489 (10) | 0.0363 (10) | 0.0028 (10) | −0.0030 (9) | −0.0083 (9) |
C2B | 0.0415 (12) | 0.0556 (12) | 0.0433 (11) | −0.0025 (11) | −0.0099 (9) | −0.0029 (10) |
C3B | 0.0459 (13) | 0.0603 (13) | 0.0504 (12) | −0.0100 (12) | −0.0122 (11) | 0.0049 (10) |
C4B | 0.0518 (13) | 0.0532 (11) | 0.0432 (11) | 0.0010 (12) | −0.0098 (11) | 0.0004 (10) |
C5B | 0.0416 (11) | 0.0616 (12) | 0.0437 (11) | 0.0013 (12) | −0.0108 (10) | −0.0049 (10) |
C6B | 0.0394 (11) | 0.0553 (11) | 0.0459 (11) | −0.0017 (11) | −0.0037 (10) | −0.0059 (10) |
C7B | 0.0443 (12) | 0.0526 (11) | 0.0370 (10) | 0.0049 (12) | 0.0007 (9) | −0.0071 (9) |
C8B | 0.0496 (13) | 0.0655 (13) | 0.0439 (12) | 0.0006 (12) | −0.0049 (10) | 0.0045 (10) |
Geometric parameters (Å, º) top
O1A—C7A | 1.224 (3) | O1B—C7B | 1.234 (3) |
O2A—C4A | 1.354 (2) | O2B—C4B | 1.359 (3) |
O2A—H2A | 0.840 | O2B—H2B | 0.840 |
C1A—C2A | 1.379 (3) | C1B—C2B | 1.389 (3) |
C1A—C6A | 1.391 (3) | C1B—C6B | 1.397 (3) |
C1A—C7A | 1.479 (3) | C1B—C7B | 1.478 (3) |
C2A—C3A | 1.380 (3) | C2B—C3B | 1.381 (3) |
C2A—H2AA | 0.950 | C2B—H2BA | 0.950 |
C3A—C4A | 1.389 (3) | C3B—C4B | 1.395 (3) |
C3A—H3AA | 0.950 | C3B—H3BA | 0.950 |
C4A—C5A | 1.382 (3) | C4B—C5B | 1.383 (3) |
C5A—C6A | 1.375 (3) | C5B—C6B | 1.380 (3) |
C5A—H5AA | 0.950 | C5B—H5BA | 0.950 |
C6A—H6AA | 0.950 | C6B—H6BA | 0.950 |
C7A—C8A | 1.499 (3) | C7B—C8B | 1.497 (3) |
C8A—H8AA | 0.980 | C8B—H8BA | 0.980 |
C8A—H8AB | 0.980 | C8B—H8BB | 0.980 |
C8A—H8AC | 0.980 | C8B—H8BC | 0.980 |
| | | |
C4A—O2A—H2A | 109.5 | C4B—O2B—H2B | 109.5 |
C2A—C1A—C6A | 118.05 (19) | C2B—C1B—C6B | 118.78 (19) |
C2A—C1A—C7A | 122.4 (2) | C2B—C1B—C7B | 122.16 (19) |
C6A—C1A—C7A | 119.5 (2) | C6B—C1B—C7B | 119.04 (19) |
C1A—C2A—C3A | 121.6 (2) | C3B—C2B—C1B | 120.84 (19) |
C1A—C2A—H2AA | 119.2 | C3B—C2B—H2BA | 119.6 |
C3A—C2A—H2AA | 119.2 | C1B—C2B—H2BA | 119.6 |
C2A—C3A—C4A | 119.5 (2) | C2B—C3B—C4B | 119.6 (2) |
C2A—C3A—H3AA | 120.2 | C2B—C3B—H3BA | 120.2 |
C4A—C3A—H3AA | 120.2 | C4B—C3B—H3BA | 120.2 |
O2A—C4A—C5A | 122.43 (19) | O2B—C4B—C5B | 122.6 (2) |
O2A—C4A—C3A | 118.00 (18) | O2B—C4B—C3B | 117.3 (2) |
C5A—C4A—C3A | 119.57 (19) | C5B—C4B—C3B | 120.16 (19) |
C6A—C5A—C4A | 120.1 (2) | C6B—C5B—C4B | 119.8 (2) |
C6A—C5A—H5AA | 120.0 | C6B—C5B—H5BA | 120.1 |
C4A—C5A—H5AA | 120.0 | C4B—C5B—H5BA | 120.1 |
C5A—C6A—C1A | 121.1 (2) | C5B—C6B—C1B | 120.8 (2) |
C5A—C6A—H6AA | 119.4 | C5B—C6B—H6BA | 119.6 |
C1A—C6A—H6AA | 119.4 | C1B—C6B—H6BA | 119.6 |
O1A—C7A—C1A | 121.5 (2) | O1B—C7B—C1B | 120.64 (19) |
O1A—C7A—C8A | 120.4 (2) | O1B—C7B—C8B | 120.15 (19) |
C1A—C7A—C8A | 118.1 (2) | C1B—C7B—C8B | 119.2 (2) |
C7A—C8A—H8AA | 109.5 | C7B—C8B—H8BA | 109.5 |
C7A—C8A—H8AB | 109.5 | C7B—C8B—H8BB | 109.5 |
H8AA—C8A—H8AB | 109.5 | H8BA—C8B—H8BB | 109.5 |
C7A—C8A—H8AC | 109.5 | C7B—C8B—H8BC | 109.5 |
H8AA—C8A—H8AC | 109.5 | H8BA—C8B—H8BC | 109.5 |
H8AB—C8A—H8AC | 109.5 | H8BB—C8B—H8BC | 109.5 |
| | | |
C6A—C1A—C2A—C3A | −1.2 (3) | C6B—C1B—C2B—C3B | 0.7 (3) |
C7A—C1A—C2A—C3A | 177.0 (2) | C7B—C1B—C2B—C3B | −178.03 (19) |
C1A—C2A—C3A—C4A | 0.1 (3) | C1B—C2B—C3B—C4B | 1.1 (3) |
C2A—C3A—C4A—O2A | −178.6 (2) | C2B—C3B—C4B—O2B | 178.2 (2) |
C2A—C3A—C4A—C5A | 1.1 (3) | C2B—C3B—C4B—C5B | −2.2 (3) |
O2A—C4A—C5A—C6A | 178.5 (2) | O2B—C4B—C5B—C6B | −179.0 (2) |
C3A—C4A—C5A—C6A | −1.3 (3) | C3B—C4B—C5B—C6B | 1.3 (3) |
C4A—C5A—C6A—C1A | 0.1 (4) | C4B—C5B—C6B—C1B | 0.5 (3) |
C2A—C1A—C6A—C5A | 1.1 (3) | C2B—C1B—C6B—C5B | −1.5 (3) |
C7A—C1A—C6A—C5A | −177.2 (2) | C7B—C1B—C6B—C5B | 177.23 (19) |
C2A—C1A—C7A—O1A | −174.0 (2) | C2B—C1B—C7B—O1B | −171.5 (2) |
C6A—C1A—C7A—O1A | 4.1 (3) | C6B—C1B—C7B—O1B | 9.7 (3) |
C2A—C1A—C7A—C8A | 4.8 (3) | C2B—C1B—C7B—C8B | 9.6 (3) |
C6A—C1A—C7A—C8A | −177.0 (2) | C6B—C1B—C7B—C8B | −169.11 (19) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O2A—H2A···O1B | 0.84 | 1.87 | 2.707 (2) | 171 |
O2B—H2B···O1Ai | 0.84 | 1.90 | 2.732 (2) | 172 |
Symmetry code: (i) −x+3/2, −y+1, z+1/2. |
Experimental details
Crystal data |
Chemical formula | C8H8O2 |
Mr | 136.14 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 150 |
a, b, c (Å) | 6.1886 (4), 9.0710 (6), 24.5261 (15) |
V (Å3) | 1376.82 (15) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.40 × 0.30 × 0.25 |
|
Data collection |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3693, 1405, 1284 |
Rint | 0.032 |
(sin θ/λ)max (Å−1) | 0.595 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.034, 0.087, 1.08 |
No. of reflections | 1405 |
No. of parameters | 186 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.09, −0.11 |
Selected geometric parameters (Å, º) topO1A—C7A | 1.224 (3) | O1B—C7B | 1.234 (3) |
O2A—C4A | 1.354 (2) | O2B—C4B | 1.359 (3) |
C1A—C7A | 1.479 (3) | C1B—C7B | 1.478 (3) |
C7A—C8A | 1.499 (3) | C7B—C8B | 1.497 (3) |
| | | |
O1A—C7A—C1A | 121.5 (2) | O1B—C7B—C1B | 120.64 (19) |
O1A—C7A—C8A | 120.4 (2) | O1B—C7B—C8B | 120.15 (19) |
C1A—C7A—C8A | 118.1 (2) | C1B—C7B—C8B | 119.2 (2) |
| | | |
C2A—C1A—C7A—O1A | −174.0 (2) | C2B—C1B—C7B—O1B | −171.5 (2) |
C2A—C1A—C7A—C8A | 4.8 (3) | C2B—C1B—C7B—C8B | 9.6 (3) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O2A—H2A···O1B | 0.84 | 1.87 | 2.707 (2) | 171 |
O2B—H2B···O1Ai | 0.84 | 1.90 | 2.732 (2) | 172 |
Symmetry code: (i) −x+3/2, −y+1, z+1/2. |
Ionization of 4'-hydroxyacetophenone, (1), as an oxygen acid gives an anion, (2), whose negative charge can be delocalized into its acetyl group (see Scheme). This gives the anion an additional basic site, whose protonation provides the enolic species (3).
Enols are weakly acidic substances with pKa = 10–11 (Keeffe & Kresge, 1990), and pKa = 9 may be estimated for the hydroxyl group of (1) using a σ–ρ relationship that correlates acidity constants of phenols (Perrin et al., 1981). Combination of these two values then gives pK = 9 - (10–11) = -(1–2) for the equilibrium constant relating (1) and (3). This suggests that (3), and not (1), is the structure of 4'-hydroxyacetophenone.
In order to determine whether or not this is so, we carried out the present X-ray diffraction analysis. The results show unequivocally that the correct structure is the phenolic one shown as (1), and not the enolic one shown as (3).
This conclusion is unexpected on the basis of the argument involving pKa's made above. That argument, however, failed to take into account the fact that ionization of (3) converts a cyclohexadiene ring into a ring having some benzenoid character. The ionization therefore benefits from a gain in benzenoid resonance energy, and that makes (3) a substantially stronger acid than the estimate made above.
The crystal structure of (1) was originally determined by Vainshtein et al. (1974), using visually estimated intensities, which were recorded on photographic film. We have redetermined the structure of (1) at low temperature with more accurate data collected using a CCD area detector. In (1), as in the earlier structure, the space group is P212121 and there are two independent molecules in the asymmetric unit, but there is an expected contraction in the volume of the unit cell of about 1%. In our low-temperature structure the eqivalent bond lengths and angles in each independent molecule (A and B) are the same within experimental error. The only minor difference between molecules A and B is the extent of the rotation of the acetyl group about the C1—C7 bond, with respect to the phenyl ring. This is reflected in the torsion angles of 4.8 (3)° for C2A—C1A—C7A—C8A and 9.6 (3)° for C2B—C1B—C7B—C8B.
In (1), pairs of independent molecules (A and B) are are linked through one type of –O—H···O═C– hydrogen bond (H···O 1.87 Å) and each hydrogen-bonded pair is linked, in turn, through 21 screw axes to form chains in the a direction via another type of –O—H···O═C– hydrogen bond (H···O 1.90 Å) (see Fig. 2 and Table 2). Since there are two distinct O—H···O hydrogen bonds, the primary graph set (N1) is DD and the secondary graph set (N2) is C22(16) (Bernstein et al., 1995).