Chemical context   {#sec1}
==================

Chalcone (systematic name 1,3-diphenyl-2-propene-1-one) is an aromatic ketone that represents the central core for various derivatives with inter­esting properties, known as chalcones (Kostanecki & Tambor, 1899[@bb23]). For example, chalcones are found in fruits, vegetables, spices, tea or soy, and find applications as pharmaceuticals (Di Carlo *et al.*, 1999[@bb5]). Chalcones are also major inter­mediates in the synthesis of natural products and are widely used in synthetic and pharmaceutical chemistry (Dhar, 1981[@bb4]; Ansari *et al.*, 2005[@bb1]) because they have anti­tumor (Modzelewska *et al.*, 2006[@bb14]), anti­fungal (López *et al.*, 2001[@bb11]), anti-inflammatory (Lee *et al.*, 2006[@bb9]), anti-bacterial (Batovska *et al.*, 2009[@bb3]) or anti­tubercular properties (Lin *et al.*, 2002[@bb10]). In general, chalcones consist of two aromatic rings that are linked by a three-carbon α,β-unsaturated carbonyl system, leading to a completely delocalized π-electron system. Recently, chalcones have also been used in the field of materials science as non-linear optical devices (Raghavendra *et al.*, 2017[@bb15]). As part of our studies in this area, we report herein the synthesis, crystal structure and Hirshfeld surface analysis of a new chalcone.

Structural commentary   {#sec2}
=======================

In the title mol­ecule (Fig. 1[▸](#fig1){ref-type="fig"}), the cyclo­hexa­none ring (C1/C2,C7/C8,C9/C10) has an envelope conformation with the flap atom C9 deviating by 0.280 (3) Å from the least-squares plane through the ring. The cyclo­hexa­none ring is nearly co-planar with the benzene ring (C2--C7) being fused at a dihedral angle of 4.70 (18)°, but is inclined to the other benzene ring (C12--C17) by 74.95 (13)°. Torsion angles involving the methyl­ene group C10=C11 are 83.3 (5)° (C17---C12---C11---C10), 129.8 (4)° (C11---C10---C9---C8) and 27.7 (6)° (O1---C1---C10---C11).

Supra­molecular features   {#sec3}
==========================

The main inter­molecular inter­actions in the crystal structure of the title compound are of type C---H⋯O, C---H⋯π (Table 1[▸](#table1){ref-type="table"}) and π--π. Inter­actions between a methyl group and the carbonyl O atom (C20---H20*C*⋯O1^ii^) as well as between an aromatic H atom and the carbonyl atom (C16---H16⋯O1^i^) lead to (20) and (12) motifs (Fig. 2[▸](#fig2){ref-type="fig"}), linking adjacent mol­ecules parallel to (001) (Table 2[▸](#table2){ref-type="table"}, Fig. 2[▸](#fig2){ref-type="fig"}). A weak C9---H9*A*⋯*Cg*2^iii^ (*Cg*2 is the centroid of the C2--C7 benzene ring) inter­action is also present (Fig. 2[▸](#fig2){ref-type="fig"}), along with weak aromatic π-stacking inter­actions \[*Cg*2⋯*Cg*2(−2 − *x*, −*y*, −1 − *z*) = 3.887 (3) Å\] that consolidate the three-dimensional packing.

Database survey   {#sec4}
=================

A search of the Cambridge Structural Database (CSD, version 5.40, update November 2018; Groom *et al.*, 2016[@bb7]) using (*E*)-2-(4-methyl­benzyl­idene)-3,4-di­hydro­naphthalen-1(2*H*)-one as the main skeleton revealed the presence of four structures containing the chalcone moiety with different substituents that are similar to the title compound: (*E*)-4-\[(1-oxo-3,4-di­hydro­naphthalen-2(1*H*)-yl­idene)meth­yl\]benzo­nitrile (QEVMAI; Baddeley *et al.*, 2017[@bb2]); (*E*)-4-\[(5-meth­oxy-1-oxo-3,4-di­hydro­naphthalen-2(1*H*)-yl­idene)meth­yl\]benzo­nitrile (QEVMEM; Baddeley *et al.*, 2017[@bb2]); (*E*)-4-\[(6-meth­oxy-1-oxo-3,4-di­hydro­naphthalen-2(1*H*)-yl­idene)meth­yl\]benzo­nitrile (QEVMIQ; Baddeley *et al.*, 2017[@bb2]); 1′-(4-bromo­phen­yl)-4′-{4-\[(1-oxo-3,4-di­hydro­naphthalen-2(1*H*)-yl­idene) meth­yl\]phen­yl}-3′′,4′′-di­hydro-1′′*H*,2*H*-di­spiro­(ace­naphthyl­ene-1,2′-pyrrolidine-3′,2′′-naphthalene)-1′′,2-dione (VUZXOE; Saravanan *et al.*, 2010[@bb16]). QEVMAI and VUZXOE both crystallize in space group *P* , while QEVMEM and QEVMIQ crystallize in space group *P*2~1~/*c*. In the structures of QEVMAI, QEVMEM and QEVMIQ, the dihedral angles between the phenyl groups are 45.66 (5), 55.06 (7) and 69.78 (5)°, respectively. In the structure of VUZXOE, the central benzene ring makes a dihedral angle of 42.71 (7)° with the bromo­phenyl ring.

Hirshfeld surface analysis   {#sec5}
============================

A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009[@bb19]) and the associated two-dimensional fingerprint plots (McKinnon *et al.*, 2007[@bb13]) were performed with *CrystalExplorer17* (Turner *et al.*, 2017[@bb22]), using standard surface resolution with the three-dimensional *d* ~norm~ surfaces plotted over a fixed colour scale of −0.0870 (red) to 1.2944 (blue) a.u.. The three-dimensional *d* ~norm~ surface of the title mol­ecule is illustrated in Fig. 3[▸](#fig3){ref-type="fig"} *a* and 4[▸](#fig4){ref-type="fig"}. The pale-red spots symbolize short contacts and negative *d* ~norm~ values on the surface correspond to the C---H⋯O inter­actions described above (Table 1[▸](#table1){ref-type="table"}). The overall two-dimensional fingerprint plot is illustrated in Fig. 5[▸](#fig5){ref-type="fig"} *a*. The Hirshfeld surfaces mapped over *d* ~norm~ are shown for the H⋯H, H⋯C/ C⋯H, H⋯O/O⋯H, C⋯C contacts (McKinnon *et al.*, 2007[@bb13]), and the two-dimensional fingerprint plots are shown in Fig. 5[▸](#fig5){ref-type="fig"} *b* and 5*c*, respectively, associated with their relative contributions to the Hirshfeld surface. The largest contribution to the overall crystal packing is from H⋯H inter­actions (66.0%); H⋯H contacts are shown in the middle region 1.10 Å \< (*d* ~i~ + *d* ~e~) \< 1.18 Å. H⋯C/C⋯H contacts contribute 22.3% to the Hirshfeld surface, resulting in two pairs of characteristic wings in the fingerprint plot. The pair of tips appears at 1.10 Å \< (*d* ~i~ + *d* ~e~) \< 1.65 Å. H⋯O/O⋯H contacts make a 9.3% contribution to the Hirshfeld surface. The contacts are represented by a pair of sharp spikes in the region 1.05 Å \< (*d* ~i~ + *d* ~e~) \< 1.4 Å in the fingerprint plot. The C⋯C contacts are a measure of π--π stacking inter­actions and contribute 2.4% to the Hirshfeld surface. They appear as an arrow-shaped distribution at 1.80 Å \< (*d* ~i~ + *d* ~e~) \< 2.0 Å.

The shape-index map of the title mol­ecule (Fig. 3[▸](#fig3){ref-type="fig"} *b*) was generated in the ranges −1 to 1 Å. The convex blue regions symbolize hydrogen-donor groups and concave red regions symbolize hydrogen-acceptor groups. π--π inter­actions on the shape-index map are indicated by adjacent red and blue triangles. As can be seen in Fig. 3[▸](#fig3){ref-type="fig"} *b*, there are π--π inter­actions present between adjacent mol­ecules in the title complex.

The curvedness map of the title compound (Fig. 3[▸](#fig3){ref-type="fig"} *c*) was generated in the range −4 to 0.4 Å. The large green regions represent a relatively flat (*i.e*. planar) surface area, while the blue regions demonstrate areas of curvature. The presence of π--π stacking inter­actions is also evident as flat regions around the rings on the Hirshfeld surface plotted over curvedness.

Synthesis and crystallization   {#sec6}
===============================

2,4,6-Tri­methyl­benzyl­idene­tetra­lone was prepared according to a literature protocol (Kumar *et al.*, 2017[@bb8]). 10 ml of a NaOH solution (40%~wt~) was slowly added to a mixture of tetra­lone (1 mmol) and 2,4,6-tri­methyl­benzaldehyde (1 mmol) in ethanol (10 ml) at room temperature and stirred overnight. Then ice-cold water was added to the reaction mixture. The resulting precipitate was filtered off and dried *in vacuo*. The compound was purified by crystallization from ethanol, resulting in colourless prismatic crystals.

Yield 85%, m.p. 358 K; IR (ν, cm^−1^): 3060 (C---H, aromatic), 2920 (C---H, aliphatic), 1670 (C=O), 1620 (C=C, aromatic); ^1^H NMR (300 MHz, DMSO-*d* ~6~, δ, ppm): 7.9 (1H, *d*, =C---H), 7.58 (1H, *s*, =C---H), 7.50 (1H, *t*, =C---H), 7.38 (1H,t, =C---H), 7.30 (1H, d, =C---H), 6.82 (2H, s, =C---H), 2.8 (2H, t, ---CH~2~), 2.4 (2H, t, ---CH~2~), 2.2 (3H, s,---CH~3~), 2.02 (6H, s, 2 CH~3~); ^13^C NMR (75 MHz, DMSO-*d* ~6~, δ, ppm): 186.9, 144.5, 138.0, 137.2, 135.9, 135.6, 134.2, 133.5, 132.4, 129.3, 128.6, 128.0, 127.6, 28.9, 27.4, 21.3, 20.5. Analysis calculated for C~20~H~20~O: C, 86.92%; H, 7.29%; O, 5.79%. Found: C, 86.99%; H, 7.35%; O, 5.90%.

Refinement details   {#sec7}
====================

Crystal data, data collection and structure refinement details are summarized in Table 2[▸](#table2){ref-type="table"}. Hydrogen atoms were fixed geometrically and treated as riding, with C---H = 0.97 Å for methyl groups, 0.96 Å for methyl­ene groups, 0.93 Å for aromatic hydrogen atoms and 0.98 Å for methine groups, with *U* ~iso~(H) = 1.2*U* ~eq~(C) or 1.5*U* ~eq~(C-meth­yl).

Supplementary Material
======================

Crystal structure: contains datablock(s) I. DOI: [10.1107/S2056989019006182/wm5495sup1.cif](https://doi.org/10.1107/S2056989019006182/wm5495sup1.cif)

Structure factors: contains datablock(s) I. DOI: [10.1107/S2056989019006182/wm5495Isup3.hkl](https://doi.org/10.1107/S2056989019006182/wm5495Isup3.hkl)

###### 

Click here for additional data file.

Supporting information file. DOI: [10.1107/S2056989019006182/wm5495Isup3.cml](https://doi.org/10.1107/S2056989019006182/wm5495Isup3.cml)

CCDC reference: [1913649](http://scripts.iucr.org/cgi-bin/cr.cgi?rm=csd&csdid=1913649)

Additional supporting information: [crystallographic information](http://scripts.iucr.org/cgi-bin/sendsupfiles?wm5495&file=wm5495sup0.html&mime=text/html); [3D view](http://scripts.iucr.org/cgi-bin/sendcif?wm5495sup1&Qmime=cif); [checkCIF report](http://scripts.iucr.org/cgi-bin/paper?wm5495&checkcif=yes)

Crystal data {#d1e152}
============

  ---------------------- ----------------------------------------
  C~20~H~20~O            *Z* = 2
  *M~r~* = 276.36        *F*(000) = 296
  Triclinic, *P*1        *D*~x~ = 1.154 Mg m^−3^
  *a* = 8.728 (2) Å      Mo *K*α radiation, λ = 0.71073 Å
  *b* = 8.757 (2) Å      Cell parameters from 12610 reflections
  *c* = 12.094 (3) Å     θ = 2.7--30.2°
  α = 77.768 (19)°       µ = 0.07 mm^−1^
  β = 80.822 (19)°       *T* = 293 K
  γ = 61.929 (18)°       Prism, colorless
  *V* = 795.2 (4) Å^3^   0.64 × 0.51 × 0.33 mm
  ---------------------- ----------------------------------------

Data collection {#d1e278}
===============

  ---------------------------------------------------------------- --------------------------------------
  Stoe IPDS 2 diffractometer                                       1102 reflections with *I* \> 2σ(*I*)
  Detector resolution: 6.67 pixels mm^-1^                          *R*~int~ = 0.088
  rotation method scans                                            θ~max~ = 25.0°, θ~min~ = 2.7°
  Absorption correction: integration (X-RED32; Stoe & Cie, 2002)   *h* = −10→10
  *T*~min~ = 0.956, *T*~max~ = 0.982                               *k* = −10→10
  8143 measured reflections                                        *l* = −14→14
  2726 independent reflections                                     
  ---------------------------------------------------------------- --------------------------------------

Refinement {#d1e388}
==========

  ------------------------------------- -----------------------------------------------------------------------------------------------------
  Refinement on *F*^2^                  Hydrogen site location: inferred from neighbouring sites
  Least-squares matrix: full            H-atom parameters constrained
  *R*\[*F*^2^ \> 2σ(*F*^2^)\] = 0.061   *w* = 1/\[σ^2^(*F*~o~^2^) + (0.0601*P*)^2^\] where *P* = (*F*~o~^2^ + 2*F*~c~^2^)/3
  *wR*(*F*^2^) = 0.155                  (Δ/σ)~max~ \< 0.001
  *S* = 0.91                            Δρ~max~ = 0.25 e Å^−3^
  2726 reflections                      Δρ~min~ = −0.14 e Å^−3^
  194 parameters                        Extinction correction: SHELXL2018 (Sheldrick, 2015b), Fc^\*^=kFc\[1+0.001xFc^2^λ^3^/sin(2θ)\]^-1/4^
  0 restraints                          Extinction coefficient: 0.016 (4)
  ------------------------------------- -----------------------------------------------------------------------------------------------------

Special details {#d1e556}
===============

  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^2^) {#d1e575}
==================================================================================================

  ------ ------------- ------------- ------------- -------------------- --
         *x*           *y*           *z*           *U*~iso~\*/*U*~eq~   
  O1     −1.0524 (3)   −0.2385 (4)   −0.7862 (2)   0.0977 (9)           
  C12    −0.4930 (4)   −0.5186 (5)   −0.8354 (3)   0.0635 (9)           
  C2     −1.0387 (4)   −0.2214 (4)   −0.5971 (3)   0.0639 (9)           
  C17    −0.4278 (4)   −0.6907 (5)   −0.8516 (3)   0.0705 (10)          
  C1     −0.9638 (4)   −0.2867 (5)   −0.7056 (3)   0.0715 (10)          
  C10    −0.7746 (4)   −0.4083 (4)   −0.7133 (3)   0.0695 (10)          
  C13    −0.3805 (5)   −0.4437 (5)   −0.8456 (3)   0.0744 (10)          
  C11    −0.6837 (4)   −0.4120 (4)   −0.8119 (3)   0.0736 (11)          
  H11    −0.745928     −0.339613     −0.873942     0.088\*              
  C15    −0.1364 (4)   −0.7151 (5)   −0.8870 (3)   0.0711 (10)          
  C7     −0.9379 (4)   −0.2800 (5)   −0.5040 (3)   0.0743 (10)          
  C16    −0.2502 (5)   −0.7860 (5)   −0.8766 (3)   0.0762 (11)          
  H16    −0.206551     −0.902035     −0.886559     0.091\*              
  C14    −0.2038 (5)   −0.5443 (5)   −0.8704 (3)   0.0798 (11)          
  H14    −0.128920     −0.494447     −0.875919     0.096\*              
  C3     −1.2113 (4)   −0.0905 (5)   −0.5883 (3)   0.0792 (11)          
  H3     −1.280000     −0.051417     −0.649452     0.095\*              
  C9     −0.7027 (5)   −0.5193 (6)   −0.6044 (3)   0.1051 (15)          
  H9A    −0.745452     −0.606334     −0.583241     0.126\*              
  H9B    −0.576855     −0.580756     −0.615353     0.126\*              
  C8     −0.7503 (4)   −0.4167 (5)   −0.5111 (3)   0.0951 (13)          
  H8A    −0.676588     −0.358974     −0.520287     0.114\*              
  H8B    −0.726257     −0.496759     −0.439895     0.114\*              
  C4     −1.2801 (5)   −0.0192 (5)   −0.4895 (4)   0.0909 (13)          
  H4     −1.394381     0.067973      −0.484398     0.109\*              
  C6     −1.0115 (5)   −0.2062 (6)   −0.4058 (3)   0.0942 (13)          
  H6     −0.945571     −0.244732     −0.343260     0.113\*              
  C5     −1.1799 (6)   −0.0771 (6)   −0.4000 (4)   0.0988 (14)          
  H5     −1.226312     −0.028553     −0.333787     0.119\*              
  C20    0.0576 (4)    −0.8225 (6)   −0.9157 (3)   0.1039 (15)          
  H20A   0.094884      −0.940932     −0.877619     0.156\*              
  H20B   0.121224      −0.772547     −0.891430     0.156\*              
  H20C   0.078722      −0.821651     −0.996162     0.156\*              
  C18    −0.5449 (5)   −0.7765 (5)   −0.8436 (4)   0.1077 (15)          
  H18A   −0.589023     −0.792507     −0.766309     0.162\*              
  H18B   −0.479794     −0.888378     −0.868695     0.162\*              
  H18C   −0.640231     −0.703345     −0.890605     0.162\*              
  C19    −0.4477 (5)   −0.2554 (5)   −0.8281 (4)   0.1150 (16)          
  H19A   −0.531484     −0.178397     −0.882365     0.173\*              
  H19B   −0.352349     −0.226633     −0.838182     0.173\*              
  H19C   −0.501571     −0.241994     −0.752796     0.173\*              
  ------ ------------- ------------- ------------- -------------------- --

Atomic displacement parameters (Å^2^) {#d1e1342}
=====================================

  ----- ------------- ----------- ----------- -------------- -------------- --------------
        *U*^11^       *U*^22^     *U*^33^     *U*^12^        *U*^13^        *U*^23^
  O1    0.0782 (16)   0.112 (2)   0.088 (2)   −0.0233 (15)   −0.0269 (14)   −0.0175 (16)
  C12   0.069 (2)     0.057 (2)   0.060 (2)   −0.0271 (19)   −0.0034 (16)   −0.0044 (18)
  C2    0.061 (2)     0.066 (2)   0.066 (2)   −0.0311 (19)   −0.0055 (18)   −0.0045 (19)
  C17   0.079 (2)     0.061 (3)   0.073 (3)   −0.032 (2)     −0.0094 (18)   −0.0086 (19)
  C1    0.073 (2)     0.071 (3)   0.069 (3)   −0.031 (2)     −0.019 (2)     −0.001 (2)
  C10   0.062 (2)     0.070 (3)   0.062 (2)   −0.0218 (19)   −0.0091 (18)   0.0017 (19)
  C13   0.082 (3)     0.058 (3)   0.081 (3)   −0.032 (2)     0.0010 (19)    −0.014 (2)
  C11   0.072 (2)     0.072 (3)   0.072 (3)   −0.029 (2)     −0.0174 (19)   −0.001 (2)
  C15   0.077 (2)     0.070 (3)   0.058 (2)   −0.026 (2)     −0.0030 (18)   −0.012 (2)
  C7    0.071 (2)     0.084 (3)   0.067 (2)   −0.037 (2)     −0.005 (2)     −0.006 (2)
  C16   0.095 (3)     0.059 (3)   0.069 (2)   −0.028 (2)     −0.010 (2)     −0.0122 (19)
  C14   0.082 (3)     0.081 (3)   0.085 (3)   −0.045 (2)     0.0018 (19)    −0.015 (2)
  C3    0.069 (2)     0.077 (3)   0.091 (3)   −0.032 (2)     −0.013 (2)     −0.008 (2)
  C9    0.092 (3)     0.101 (3)   0.079 (3)   −0.013 (2)     −0.015 (2)     0.003 (3)
  C8    0.080 (3)     0.099 (3)   0.081 (3)   −0.018 (2)     −0.024 (2)     −0.003 (3)
  C4    0.076 (3)     0.085 (3)   0.102 (3)   −0.030 (2)     0.008 (3)      −0.022 (3)
  C6    0.095 (3)     0.109 (3)   0.072 (3)   −0.040 (3)     −0.010 (2)     −0.012 (3)
  C5    0.101 (3)     0.107 (4)   0.085 (3)   −0.045 (3)     0.008 (3)      −0.025 (3)
  C20   0.076 (3)     0.113 (4)   0.098 (3)   −0.020 (2)     0.003 (2)      −0.030 (3)
  C18   0.114 (3)     0.093 (3)   0.141 (4)   −0.065 (3)     −0.010 (3)     −0.023 (3)
  C19   0.107 (3)     0.073 (3)   0.172 (5)   −0.044 (2)     0.007 (3)      −0.038 (3)
  ----- ------------- ----------- ----------- -------------- -------------- --------------

Geometric parameters (Å, º) {#d1e1814}
===========================

  ----------------------- ------------ ----------------------- ------------
  O1---C1                 1.218 (4)    C3---C4                 1.383 (5)
  C12---C17               1.384 (4)    C3---H3                 0.9300
  C12---C13               1.393 (4)    C9---C8                 1.477 (5)
  C12---C11               1.491 (4)    C9---H9A                0.9700
  C2---C7                 1.396 (5)    C9---H9B                0.9700
  C2---C3                 1.404 (4)    C8---H8A                0.9700
  C2---C1                 1.473 (4)    C8---H8B                0.9700
  C17---C16               1.390 (4)    C4---C5                 1.359 (5)
  C17---C18               1.510 (5)    C4---H4                 0.9300
  C1---C10                1.486 (4)    C6---C5                 1.371 (5)
  C10---C11               1.319 (4)    C6---H6                 0.9300
  C10---C9                1.490 (5)    C5---H5                 0.9300
  C13---C14               1.389 (4)    C20---H20A              0.9600
  C13---C19               1.519 (5)    C20---H20B              0.9600
  C11---H11               0.9300       C20---H20C              0.9600
  C15---C14               1.373 (5)    C18---H18A              0.9600
  C15---C16               1.377 (5)    C18---H18B              0.9600
  C15---C20               1.524 (4)    C18---H18C              0.9600
  C7---C6                 1.390 (5)    C19---H19A              0.9600
  C7---C8                 1.508 (5)    C19---H19B              0.9600
  C16---H16               0.9300       C19---H19C              0.9600
  C14---H14               0.9300                               
                                                               
  C17---C12---C13         119.7 (3)    C10---C9---H9A          109.0
  C17---C12---C11         120.0 (3)    C8---C9---H9B           109.0
  C13---C12---C11         120.3 (3)    C10---C9---H9B          109.0
  C7---C2---C3            119.0 (3)    H9A---C9---H9B          107.8
  C7---C2---C1            121.2 (3)    C9---C8---C7            114.6 (4)
  C3---C2---C1            119.8 (4)    C9---C8---H8A           108.6
  C12---C17---C16         119.0 (3)    C7---C8---H8A           108.6
  C12---C17---C18         121.7 (3)    C9---C8---H8B           108.6
  C16---C17---C18         119.3 (4)    C7---C8---H8B           108.6
  O1---C1---C2            121.3 (3)    H8A---C8---H8B          107.6
  O1---C1---C10           121.8 (3)    C5---C4---C3            119.6 (4)
  C2---C1---C10           116.9 (4)    C5---C4---H4            120.2
  C11---C10---C1          119.9 (3)    C3---C4---H4            120.2
  C11---C10---C9          125.0 (3)    C5---C6---C7            120.9 (4)
  C1---C10---C9           115.1 (3)    C5---C6---H6            119.6
  C14---C13---C12         119.3 (3)    C7---C6---H6            119.6
  C14---C13---C19         119.7 (4)    C4---C5---C6            121.0 (4)
  C12---C13---C19         121.1 (3)    C4---C5---H5            119.5
  C10---C11---C12         127.7 (3)    C6---C5---H5            119.5
  C10---C11---H11         116.2        C15---C20---H20A        109.5
  C12---C11---H11         116.2        C15---C20---H20B        109.5
  C14---C15---C16         117.6 (3)    H20A---C20---H20B       109.5
  C14---C15---C20         121.2 (4)    C15---C20---H20C        109.5
  C16---C15---C20         121.2 (4)    H20A---C20---H20C       109.5
  C6---C7---C2            118.9 (3)    H20B---C20---H20C       109.5
  C6---C7---C8            120.4 (4)    C17---C18---H18A        109.5
  C2---C7---C8            120.6 (3)    C17---C18---H18B        109.5
  C15---C16---C17         122.4 (4)    H18A---C18---H18B       109.5
  C15---C16---H16         118.8        C17---C18---H18C        109.5
  C17---C16---H16         118.8        H18A---C18---H18C       109.5
  C15---C14---C13         122.0 (4)    H18B---C18---H18C       109.5
  C15---C14---H14         119.0        C13---C19---H19A        109.5
  C13---C14---H14         119.0        C13---C19---H19B        109.5
  C4---C3---C2            120.6 (4)    H19A---C19---H19B       109.5
  C4---C3---H3            119.7        C13---C19---H19C        109.5
  C2---C3---H3            119.7        H19A---C19---H19C       109.5
  C8---C9---C10           112.8 (4)    H19B---C19---H19C       109.5
  C8---C9---H9A           109.0                                
                                                               
  C13---C12---C17---C16   0.7 (5)      C3---C2---C7---C8       −178.2 (3)
  C11---C12---C17---C16   178.2 (3)    C1---C2---C7---C8       −2.0 (5)
  C13---C12---C17---C18   −178.9 (3)   C14---C15---C16---C17   0.8 (5)
  C11---C12---C17---C18   −1.3 (5)     C20---C15---C16---C17   −179.4 (3)
  C7---C2---C1---O1       178.4 (4)    C12---C17---C16---C15   −0.7 (5)
  C3---C2---C1---O1       −5.3 (5)     C18---C17---C16---C15   178.9 (3)
  C7---C2---C1---C10      −3.8 (5)     C16---C15---C14---C13   −1.0 (5)
  C3---C2---C1---C10      172.5 (3)    C20---C15---C14---C13   179.2 (3)
  O1---C1---C10---C11     27.7 (6)     C12---C13---C14---C15   1.0 (5)
  C2---C1---C10---C11     −150.1 (3)   C19---C13---C14---C15   −179.9 (4)
  O1---C1---C10---C9      −152.2 (4)   C7---C2---C3---C4       0.7 (5)
  C2---C1---C10---C9      30.0 (5)     C1---C2---C3---C4       −175.6 (3)
  C17---C12---C13---C14   −0.8 (5)     C11---C10---C9---C8     129.8 (4)
  C11---C12---C13---C14   −178.4 (3)   C1---C10---C9---C8      −50.3 (5)
  C17---C12---C13---C19   −179.9 (4)   C10---C9---C8---C7      43.9 (5)
  C11---C12---C13---C19   2.6 (5)      C6---C7---C8---C9       163.5 (4)
  C1---C10---C11---C12    177.2 (3)    C2---C7---C8---C9       −18.7 (6)
  C9---C10---C11---C12    −2.9 (7)     C2---C3---C4---C5       −0.4 (6)
  C17---C12---C11---C10   83.3 (5)     C2---C7---C6---C5       −0.3 (6)
  C13---C12---C11---C10   −99.2 (5)    C8---C7---C6---C5       177.5 (4)
  C3---C2---C7---C6       −0.4 (5)     C3---C4---C5---C6       −0.3 (7)
  C1---C2---C7---C6       175.9 (3)    C7---C6---C5---C4       0.7 (7)
  ----------------------- ------------ ----------------------- ------------

Hydrogen-bond geometry (Å, º) {#d1e2630}
=============================

*Cg*2 is the centroid of the C2--C7 ring.

  ------------------------- --------- --------- ----------- ---------------
  *D*---H···*A*             *D*---H   H···*A*   *D*···*A*   *D*---H···*A*
  C16---H16···O1^i^         0.93      2.69      3.493 (5)   145
  C20---H20*C*···O1^ii^     0.96      2.60      3.535 (5)   165
  C9---H9*A*···*Cg*2^iii^   0.97      2.90      3.865 (6)   175
  ------------------------- --------- --------- ----------- ---------------

Symmetry codes: (i) *x*+1, *y*−1, *z*; (ii) −*x*−1, −*y*−1, −*z*−2; (iii) −*x*+1, −*y*, −*z*+1.

![The mol­ecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.](e-75-00746-fig1){#fig1}

![A view along the *a* axis of the title structure. Blue dashed lines denote the C---H⋯O hydrogen bonds which form (20) and (12) ring motifs. C---H⋯π inter­actions are shown as green dashes lines.](e-75-00746-fig2){#fig2}

![(*a*) *d~norm~* mapped on Hirshfeld surfaces for visualizing the inter­molecular inter­actions; (*b*) shape-index map and *(c)* curvedness map of the title compound.](e-75-00746-fig3){#fig3}

![*d~norm~* mapped on Hirshfeld surfaces for visualizing the inter­molecular inter­actions.](e-75-00746-fig4){#fig4}

![(*a*) The overall two-dimensional fingerprint plot and (*b*) Hirshfeld surface representations with the function *d* ~norm~ plotted onto the surface for (i) H⋯H, (ii) H⋯C/C⋯H, (iii) H⋯O/O⋯H and (iv) C⋯C inter­actions. (*c*) The two-dimensional fingerprint plots for the title compound, delineated into (i) H⋯H, (ii) H⋯C/ C⋯H, (iii) H⋯O/O⋯H, (iv) C⋯C inter­actions.](e-75-00746-fig5){#fig5}

###### Hydrogen-bond geometry (Å, °)

*Cg*2 is the centroid of the C2--C7 ring.

  *D*---H⋯*A*             *D*---H   H⋯*A*   *D*⋯*A*     *D*---H⋯*A*
  ----------------------- --------- ------- ----------- -------------
  C16---H16⋯O1^i^         0.93      2.69    3.493 (5)   145
  C20---H20*C*⋯O1^ii^     0.96      2.60    3.535 (5)   165
  C9---H9*A*⋯*Cg*2^iii^   0.97      2.90    3.865 (6)   175

Symmetry codes: (i) ; (ii) ; (iii) .

###### Experimental details

  -------------------------------------------------------------------------- --------------------------------------------------
  Crystal data                                                               
  Chemical formula                                                           C~20~H~20~O
  *M* ~r~                                                                    276.36
  Crystal system, space group                                                Triclinic, *P*
  Temperature (K)                                                            293
  *a*, *b*, *c* (Å)                                                          8.728 (2), 8.757 (2), 12.094 (3)
  α, β, γ (°)                                                                77.768 (19), 80.822 (19), 61.929 (18)
  *V* (Å^3^)                                                                 795.2 (4)
  *Z*                                                                        2
  Radiation type                                                             Mo *K*α
  μ (mm^−1^)                                                                 0.07
  Crystal size (mm)                                                          0.64 × 0.51 × 0.33
                                                                             
  Data collection                                                            
  Diffractometer                                                             Stoe IPDS 2
  Absorption correction                                                      Integration (*X-RED32*; Stoe & Cie, 2002[@bb21])
  *T* ~min~, *T* ~max~                                                       0.956, 0.982
  No. of measured, independent and observed \[*I* \> 2σ(*I*)\] reflections   8143, 2726, 1102
  *R* ~int~                                                                  0.088
  (sin θ/λ)~max~ (Å^−1^)                                                     0.595
                                                                             
  Refinement                                                                 
  *R*\[*F* ^2^ \> 2σ(*F* ^2^)\], *wR*(*F* ^2^), *S*                          0.061, 0.155, 0.91
  No. of reflections                                                         2726
  No. of parameters                                                          194
  H-atom treatment                                                           H-atom parameters constrained
  Δρ~max~, Δρ~min~ (e Å^−3^)                                                 0.25, −0.14
  -------------------------------------------------------------------------- --------------------------------------------------

Computer programs: *X-AREA* and *X-RED* (Stoe & Cie, 2002[@bb21]), *SHELXT2017* (Sheldrick, 2015*a* [@bb17]), *SHELXL2018* (Sheldrick, 2015*b* [@bb18]), *Mercury* (Macrae *et al.*, 2008[@bb12]), *WinGX* (Farrugia, 2012[@bb6]), *PLATON* (Spek, 2009[@bb20]) and *publCIF* (Westrip, 2010[@bb24]).
