organic compounds
Di-n-butyl 4,4′-dihydroxy-3,3′-{[(3aRS,7aRS)-2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]bis(methylene)}dibenzoate
aDepartamento de Química, Universidad Nacional de Colombia, Ciudad Universitaria, Bogotá, Colombia, and bInstitute of Physics ASCR, v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic
*Correspondence e-mail: ariverau@unal.edu.co
The complete molecule of the title compound, C31H42N2O6, is generated by crystallographic twofold symmetry, with one C atom lying on the axis. The dihedral angle between the aromatic rings is 57.03 (6)°. The central heterocyclic ring adopts a half-chair conformation. The molecular conformation is stabilized by two intramolecular O—H⋯N hydrogen bonds with the N atoms of the heterocyclic ring as the acceptors. In the crystal, molecules are linked into chains along the c axis by non-classical C—H⋯O hydrogen bonds.
Related literature
For related structures, see: Rivera et al. (2010, 2011); Giordano et al. (1999); Feng & Grant (2006). For background to this work see: Koll et al. (2001); Filarowski et al. (2004).
Experimental
Crystal data
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Refinement
|
Data collection: CrysAlis PRO (Agilent, 2010); cell CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: JANA2006 (Petříček et al., 2006); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: JANA2006.
Supporting information
10.1107/S1600536811031205/bt5598sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536811031205/bt5598Isup2.hkl
Supporting information file. DOI: 10.1107/S1600536811031205/bt5598Isup3.cml
A solution of (2R,7R,11S,16S)-1,8,10,17-tetraazapentacyclo [8.8.1.18,\17.02,7.011,16] icosane (276 mg, 1.00 mmol) in dioxane (3 ml) and water (4 ml), previously prepared following described procedures, was added dropwise in a dioxane solution (3 ml) containing two equivalents of n-butyl 4-hydroxybenzoate (388 mg, 2.00 mmol) in a two-necked round-bottomed flask. The mixture was refluxed for about 12 h and then the solvent was evaporated under reduced pressure until a sticky residue appeared. The product was purified by
on a silica column, and subjected to with benzene:ethyl acetate (yield 19%, m.p. = 414–416 K). Single crystals of racemic (I) were grown from a chloroform solution by slow evaporation of the solvent at room temperature over a period of about 2 weeks.All hydrogen atoms were discernible in difference Fourier maps and could be refined to reasonable geometry. According to common practice H atoms bonded C atoms were kept in ideal positions with C–H distance 0.96 Å during the
The methyl H atoms were allowed to rotate freely about the adjacent C—C bonds. The hydroxyl H atoms were found in difference Fourier maps and their coordinates were refined freely. All H atoms were refined with displacement coefficients Uiso(H) set to 1.5Ueq(C, O) for methyl and hydroxyl groups and to to 1.2Ueq(C) for the CH– and CH2- groups.Data collection: CrysAlis PRO (Agilent, 2010); cell
CrysAlis PRO (Agilent, 2010); data reduction: CrysAlis PRO (Agilent, 2010); program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: JANA2006 (Petříček et al., 2006); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: JANA2006 (Petříček et al., 2006).Fig. 1. A view of (I) with the numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. | |
Fig. 2. Packing of the molecules of the title compound view along b axis. |
C31H42N2O6 | F(000) = 1160 |
Mr = 538.7 | Dx = 1.260 Mg m−3 |
Monoclinic, C2/c | Cu Kα radiation, λ = 1.5418 Å |
Hall symbol: -C 2yc | Cell parameters from 7161 reflections |
a = 15.4471 (3) Å | θ = 2.9–67.0° |
b = 8.8103 (2) Å | µ = 0.70 mm−1 |
c = 20.9374 (4) Å | T = 120 K |
β = 95.077 (2)° | Prism, colourless |
V = 2838.27 (10) Å3 | 0.38 × 0.28 × 0.20 mm |
Z = 4 |
Agilent Xcalibur diffractometer with an Atlas (Gemini ultra Cu) detector | 2533 independent reflections |
Radiation source: Enhance Ultra (Cu) X-ray Source | 2157 reflections with I > 3σ(I) |
Mirror monochromator | Rint = 0.030 |
Detector resolution: 10.3784 pixels mm-1 | θmax = 67.2°, θmin = 4.2° |
Rotation method data acquisition using ω scans | h = −17→18 |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010) | k = −10→10 |
Tmin = 0.868, Tmax = 1 | l = −24→24 |
13938 measured reflections |
Refinement on F2 | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.036 | Weighting scheme based on measured s.u.'s w = 1/[σ2(I) + 0.0016I2] |
wR(F2) = 0.104 | (Δ/σ)max = 0.009 |
S = 1.73 | Δρmax = 0.20 e Å−3 |
2533 reflections | Δρmin = −0.19 e Å−3 |
181 parameters | Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974) |
0 restraints | Extinction coefficient: 2400 (500) |
81 constraints |
C31H42N2O6 | V = 2838.27 (10) Å3 |
Mr = 538.7 | Z = 4 |
Monoclinic, C2/c | Cu Kα radiation |
a = 15.4471 (3) Å | µ = 0.70 mm−1 |
b = 8.8103 (2) Å | T = 120 K |
c = 20.9374 (4) Å | 0.38 × 0.28 × 0.20 mm |
β = 95.077 (2)° |
Agilent Xcalibur diffractometer with an Atlas (Gemini ultra Cu) detector | 2533 independent reflections |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010) | 2157 reflections with I > 3σ(I) |
Tmin = 0.868, Tmax = 1 | Rint = 0.030 |
13938 measured reflections |
R[F2 > 2σ(F2)] = 0.036 | 0 restraints |
wR(F2) = 0.104 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.73 | Δρmax = 0.20 e Å−3 |
2533 reflections | Δρmin = −0.19 e Å−3 |
181 parameters |
Experimental. CrysAlisPro (Agilent Technologies, 2010) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. |
Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F2 for refinement carried out on F and F2, respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement. The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.16850 (6) | 0.28700 (12) | 0.16508 (5) | 0.0355 (3) | |
O2 | 0.23006 (6) | 0.43687 (10) | 0.09549 (4) | 0.0246 (3) | |
O3 | 0.47351 (6) | −0.13568 (10) | 0.08411 (4) | 0.0251 (3) | |
N1 | 0.45250 (4) | −0.23982 (9) | 0.20231 (3) | 0.0195 (3) | |
C1 | 0.5 | −0.13860 (11) | 0.25 | 0.0198 (5) | |
C2 | 0.45565 (8) | −0.39174 (13) | 0.23189 (6) | 0.0198 (4) | |
C3 | 0.44634 (8) | −0.52666 (14) | 0.18685 (6) | 0.0254 (4) | |
C4 | 0.45780 (9) | −0.67130 (15) | 0.22757 (7) | 0.0299 (4) | |
C5 | 0.36225 (8) | −0.19088 (14) | 0.18416 (6) | 0.0224 (4) | |
C6 | 0.35796 (8) | −0.04774 (14) | 0.14442 (6) | 0.0198 (3) | |
C7 | 0.29735 (8) | 0.06379 (14) | 0.15343 (6) | 0.0207 (4) | |
C8 | 0.28954 (8) | 0.19235 (14) | 0.11452 (6) | 0.0209 (4) | |
C9 | 0.34430 (8) | 0.20849 (15) | 0.06556 (6) | 0.0219 (4) | |
C10 | 0.40580 (8) | 0.09904 (15) | 0.05580 (6) | 0.0226 (4) | |
C11 | 0.41305 (8) | −0.02913 (14) | 0.09496 (6) | 0.0208 (4) | |
C12 | 0.22324 (8) | 0.30676 (15) | 0.12800 (6) | 0.0227 (4) | |
C13 | 0.16944 (8) | 0.55491 (14) | 0.11005 (7) | 0.0258 (4) | |
C14 | 0.17797 (8) | 0.68569 (14) | 0.06461 (6) | 0.0235 (4) | |
C15 | 0.12183 (9) | 0.81927 (15) | 0.08138 (7) | 0.0289 (4) | |
C16 | 0.12224 (10) | 0.94748 (16) | 0.03283 (7) | 0.0347 (4) | |
H1a | 0.540883 | −0.078171 | 0.22915 | 0.0238* | |
H2 | 0.406857 | −0.405328 | 0.256706 | 0.0237* | |
H3a | 0.490696 | −0.522444 | 0.157548 | 0.0305* | |
H3b | 0.389436 | −0.526022 | 0.164321 | 0.0305* | |
H4a | 0.408928 | −0.683029 | 0.252453 | 0.0359* | |
H4b | 0.456989 | −0.758307 | 0.19992 | 0.0359* | |
H5a | 0.332944 | −0.174885 | 0.222158 | 0.0269* | |
H5b | 0.331366 | −0.270607 | 0.16066 | 0.0269* | |
H7 | 0.259748 | 0.052498 | 0.18726 | 0.0249* | |
H9 | 0.339264 | 0.296369 | 0.038382 | 0.0263* | |
H10 | 0.443506 | 0.111227 | 0.022094 | 0.0271* | |
H13a | 0.182864 | 0.588987 | 0.153344 | 0.0309* | |
H13b | 0.111248 | 0.515806 | 0.104655 | 0.0309* | |
H14a | 0.161007 | 0.653244 | 0.021541 | 0.0281* | |
H14b | 0.23765 | 0.717093 | 0.066364 | 0.0281* | |
H15a | 0.063247 | 0.785325 | 0.084261 | 0.0346* | |
H15b | 0.141765 | 0.856808 | 0.123154 | 0.0346* | |
H16a | 0.087619 | 1.030154 | 0.046201 | 0.0521* | |
H16b | 0.180815 | 0.981529 | 0.029994 | 0.0521* | |
H16c | 0.098561 | 0.911715 | −0.00838 | 0.0521* | |
H3 | 0.4785 (11) | −0.193 (2) | 0.1188 (9) | 0.0376* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0375 (6) | 0.0326 (6) | 0.0388 (6) | 0.0083 (4) | 0.0174 (5) | 0.0107 (4) |
O2 | 0.0237 (4) | 0.0207 (5) | 0.0297 (5) | 0.0030 (3) | 0.0044 (4) | 0.0042 (4) |
O3 | 0.0297 (5) | 0.0239 (5) | 0.0220 (5) | 0.0055 (4) | 0.0045 (4) | 0.0015 (4) |
N1 | 0.0209 (5) | 0.0171 (5) | 0.0198 (5) | 0.0000 (4) | −0.0019 (4) | 0.0003 (4) |
C1 | 0.0220 (8) | 0.0160 (8) | 0.0210 (8) | 0 | −0.0007 (7) | 0 |
C2 | 0.0217 (6) | 0.0169 (6) | 0.0204 (6) | −0.0003 (5) | 0.0007 (5) | 0.0012 (5) |
C3 | 0.0275 (6) | 0.0205 (7) | 0.0270 (7) | −0.0003 (5) | −0.0044 (5) | −0.0025 (5) |
C4 | 0.0348 (8) | 0.0188 (7) | 0.0345 (7) | −0.0021 (5) | −0.0062 (6) | −0.0024 (5) |
C5 | 0.0191 (6) | 0.0228 (7) | 0.0246 (6) | −0.0008 (5) | −0.0016 (5) | 0.0045 (5) |
C6 | 0.0197 (6) | 0.0207 (6) | 0.0180 (6) | −0.0040 (4) | −0.0036 (5) | 0.0005 (5) |
C7 | 0.0186 (6) | 0.0238 (7) | 0.0194 (6) | −0.0032 (5) | −0.0001 (5) | 0.0010 (5) |
C8 | 0.0217 (6) | 0.0200 (7) | 0.0202 (6) | −0.0025 (5) | −0.0015 (5) | 0.0007 (5) |
C9 | 0.0266 (6) | 0.0201 (6) | 0.0186 (6) | −0.0030 (5) | −0.0004 (5) | 0.0018 (5) |
C10 | 0.0263 (6) | 0.0239 (7) | 0.0177 (6) | −0.0014 (5) | 0.0030 (5) | 0.0005 (5) |
C11 | 0.0207 (6) | 0.0218 (7) | 0.0193 (6) | −0.0013 (5) | −0.0019 (5) | −0.0031 (5) |
C12 | 0.0236 (6) | 0.0234 (7) | 0.0209 (6) | −0.0013 (5) | −0.0002 (5) | 0.0028 (5) |
C13 | 0.0230 (6) | 0.0229 (7) | 0.0320 (7) | 0.0032 (5) | 0.0055 (5) | 0.0006 (5) |
C14 | 0.0237 (6) | 0.0209 (7) | 0.0251 (7) | −0.0001 (5) | −0.0011 (5) | 0.0003 (5) |
C15 | 0.0264 (7) | 0.0222 (7) | 0.0382 (8) | 0.0002 (5) | 0.0039 (6) | −0.0005 (6) |
C16 | 0.0362 (8) | 0.0239 (7) | 0.0432 (8) | 0.0042 (6) | −0.0019 (6) | 0.0033 (6) |
O1—C12 | 1.2100 (17) | C6—C7 | 1.3816 (17) |
O2—C12 | 1.3421 (15) | C6—C11 | 1.4070 (17) |
O2—C13 | 1.4498 (16) | C7—C8 | 1.3943 (17) |
O3—C11 | 1.3575 (15) | C7—H7 | 0.96 |
O3—H3 | 0.884 (18) | C8—C9 | 1.3928 (18) |
N1—C1 | 1.4836 (9) | C8—C12 | 1.4818 (18) |
N1—C2 | 1.4738 (14) | C9—C10 | 1.3815 (18) |
N1—C5 | 1.4765 (13) | C9—H9 | 0.96 |
C1—H1a | 0.96 | C10—C11 | 1.3941 (17) |
C1—H1ai | 0.96 | C10—H10 | 0.96 |
C2—C2i | 1.5061 (16) | C13—C14 | 1.5074 (18) |
C2—C3 | 1.5163 (17) | C13—H13a | 0.96 |
C2—H2 | 0.96 | C13—H13b | 0.96 |
C3—C4 | 1.5347 (18) | C14—C15 | 1.5213 (18) |
C3—H3a | 0.96 | C14—H14a | 0.96 |
C3—H3b | 0.96 | C14—H14b | 0.96 |
C4—C4i | 1.5381 (19) | C15—C16 | 1.520 (2) |
C4—H4a | 0.96 | C15—H15a | 0.96 |
C4—H4b | 0.96 | C15—H15b | 0.96 |
C5—C6 | 1.5090 (17) | C16—H16a | 0.96 |
C5—H5a | 0.96 | C16—H16b | 0.96 |
C5—H5b | 0.96 | C16—H16c | 0.96 |
C12—O2—C13 | 115.15 (10) | C8—C7—H7 | 119.2486 |
C11—O3—H3 | 105.7 (12) | C7—C8—C9 | 119.09 (11) |
C1—N1—C2 | 105.49 (7) | C7—C8—C12 | 117.83 (11) |
C1—N1—C5 | 113.40 (7) | C9—C8—C12 | 123.08 (11) |
C2—N1—C5 | 111.64 (8) | C8—C9—C10 | 120.53 (11) |
N1—C1—N1i | 106.10 (7) | C8—C9—H9 | 119.7338 |
N1—C1—H1a | 109.4715 | C10—C9—H9 | 119.7345 |
N1—C1—H1ai | 109.4713 | C9—C10—C11 | 119.93 (12) |
N1i—C1—H1a | 109.4713 | C9—C10—H10 | 120.0369 |
N1i—C1—H1ai | 109.4715 | C11—C10—H10 | 120.0376 |
H1a—C1—H1ai | 112.6412 | O3—C11—C6 | 120.83 (11) |
N1—C2—C2i | 101.91 (9) | O3—C11—C10 | 118.84 (11) |
N1—C2—C3 | 116.92 (9) | C6—C11—C10 | 120.33 (11) |
N1—C2—H2 | 110.0241 | O1—C12—O2 | 122.61 (12) |
C2i—C2—C3 | 110.19 (10) | O1—C12—C8 | 123.94 (12) |
C2i—C2—H2 | 116.771 | O2—C12—C8 | 113.44 (11) |
C3—C2—H2 | 101.7125 | O2—C13—C14 | 108.75 (11) |
C2—C3—C4 | 107.78 (10) | O2—C13—H13a | 109.4715 |
C2—C3—H3a | 109.471 | O2—C13—H13b | 109.4713 |
C2—C3—H3b | 109.4714 | C14—C13—H13a | 109.4714 |
C4—C3—H3a | 109.4714 | C14—C13—H13b | 109.4715 |
C4—C3—H3b | 109.472 | H13a—C13—H13b | 110.1822 |
H3a—C3—H3b | 111.1071 | C13—C14—C15 | 111.23 (11) |
C3—C4—C4i | 112.90 (11) | C13—C14—H14a | 109.4707 |
C3—C4—H4a | 109.4707 | C13—C14—H14b | 109.4712 |
C3—C4—H4b | 109.4703 | C15—C14—H14a | 109.4716 |
C4i—C4—H4a | 109.4719 | C15—C14—H14b | 109.4715 |
C4i—C4—H4b | 109.4713 | H14a—C14—H14b | 107.6531 |
H4a—C4—H4b | 105.8086 | C14—C15—C16 | 112.60 (12) |
N1—C5—C6 | 112.36 (10) | C14—C15—H15a | 109.4712 |
N1—C5—H5a | 109.4714 | C14—C15—H15b | 109.4717 |
N1—C5—H5b | 109.4706 | C16—C15—H15a | 109.4711 |
C6—C5—H5a | 109.4712 | C16—C15—H15b | 109.4712 |
C6—C5—H5b | 109.4714 | H15a—C15—H15b | 106.1546 |
H5a—C5—H5b | 106.42 | C15—C16—H16a | 109.4718 |
C5—C6—C7 | 121.09 (11) | C15—C16—H16b | 109.4721 |
C5—C6—C11 | 120.22 (11) | C15—C16—H16c | 109.4718 |
C7—C6—C11 | 118.62 (11) | H16a—C16—H16b | 109.4713 |
C6—C7—C8 | 121.50 (11) | H16a—C16—H16c | 109.4705 |
C6—C7—H7 | 119.2469 | H16b—C16—H16c | 109.4698 |
Symmetry code: (i) −x+1, y, −z+1/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
C5—H5a···O1ii | 0.96 | 2.39 | 3.2393 (16) | 148 |
O3—H3···N1 | 0.884 (18) | 1.873 (18) | 2.6859 (12) | 152.0 (17) |
Symmetry code: (ii) −x+1/2, y−1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C31H42N2O6 |
Mr | 538.7 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 120 |
a, b, c (Å) | 15.4471 (3), 8.8103 (2), 20.9374 (4) |
β (°) | 95.077 (2) |
V (Å3) | 2838.27 (10) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 0.70 |
Crystal size (mm) | 0.38 × 0.28 × 0.20 |
Data collection | |
Diffractometer | Agilent Xcalibur diffractometer with an Atlas (Gemini ultra Cu) detector |
Absorption correction | Multi-scan (CrysAlis PRO; Agilent, 2010) |
Tmin, Tmax | 0.868, 1 |
No. of measured, independent and observed [I > 3σ(I)] reflections | 13938, 2533, 2157 |
Rint | 0.030 |
(sin θ/λ)max (Å−1) | 0.598 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.036, 0.104, 1.73 |
No. of reflections | 2533 |
No. of parameters | 181 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.20, −0.19 |
Computer programs: CrysAlis PRO (Agilent, 2010), SIR2002 (Burla et al., 2003), JANA2006 (Petříček et al., 2006), DIAMOND (Brandenburg & Putz, 2005).
D—H···A | D—H | H···A | D···A | D—H···A |
C5—H5a···O1i | 0.96 | 2.39 | 3.2393 (16) | 147.73 |
O3—H3···N1 | 0.884 (18) | 1.873 (18) | 2.6859 (12) | 152.0 (17) |
Symmetry code: (i) −x+1/2, y−1/2, −z+1/2. |
Acknowledgements
We acknowledge the Dirección de Investigaciones, Sede Bogotá (DIB) de la Universidad Nacional de Colombia, for financial support of this work, as well as the Institutional Research Plan No. AVOZ10100521 of the Institute of Physics and the Praemium Academiae Project of the Academy of Sciences of the Czech Republic. DQ acknowledges the Vicerrectoría Académica de la Universidad Nacional de Colombia for a fellowship.
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Rivera, A., Quiroga, D., Ríos-Motta, J., Dušek, M. & Fejfarová, K. (2011). Acta Cryst. E67, o1542. Web of Science CSD CrossRef IUCr Journals Google Scholar
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Intramolecular hydrogen bonding interactions in Mannich bases lead to distortions in the aromatic rings due the existence of ortho-quinonoid resonance structures (Koll et al. 2001; Filarowski et al. 2004), which are evidenced in the bond and bond angle values. During our studies we have synthesized a series of symmetrical di-Mannich bases, by reaction between (2R,7R,11S,16S)-1,8,10,17-tetraazapentacyclo [8.8.1.18,17.02,7.011,16]icosane and p-halophenols. The intramolecular hydrogen bond interaction is weaker in the Mannich base having p-fluorine substituent [N···O 2.711 (2) Å] (Rivera et al. 2011) whereas in the case of the Mannich base p-chlorine substituted [N··· O 2.652 (2) Å] (Rivera et al. 2010), due to electron-withdrawing effect of chlorine atom. However, the distortion in the aromatic ring in these Mannich bases, leads to a conclusion indicating that the effect of halogen atoms seems to be no meaningful which can be explained on the basis of the presence of conjugative electron-release from lone pairs of halogen atom. To avoid the conjugation effect of halogen to aromatic ring we synthesized the title compound (I) which is a racemic Mannich base with a non-halogen electron withdrawing group in para position. The molecular structure and atom-numbering scheme for (I) are shown in Fig. 1. The X-ray diffraction analysis shows the existence of two intramolecular hydrogen bonding interactions between the hydroxy H atom and the amine groups in the heterocyclic ring (table 1).
The observed C11—O3 bond length [1.358 (2)Å] is in good agreement with the p-chlorophenol derivative (Rivera, et al. 2010) but is shorter by 0.01 Å in comparison with p-fluorophenol derivative (Rivera, et al. 2011). Though, in the title compound the X-ray analysis revealed the existence of distortions of the phenol ring in comparison with the related structures (Rivera et al. 2010, 2011), which was evident from the elongation of the C8—C9 bond length in title compound from [1.381 (2) Å, Rivera et al. 2011] to 1.393 (2) Å.
In comparison with the crystal packing of butylparaben, there are not head-to-tail hydrogen bonding interactions inside the chains that involve the O—H group as donor and the carbonyl O atom as acceptor (Giordano et al. 1999; Feng & Grant, 2006), there are non-classical hydrogen bonds C5—H5a··· O1 (table 1) which link neighboring helps stabilize the packing along c axis (Fig. 2).