organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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(E)-4-{[(4-Meth­­oxy­naphthalen-1-yl)methyl­­idene]amino}­phenol

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aLaboratoire d'électrochimie des matériaux moléculaires et des complexes, (LEMMC), Département de génie des procédés, Université Ferhat Abbas, Sétif 19000, Algeria, bDépartement de chimie, Faculté des sciences, Université Ferhat Abbas, Sétif 19000, Algeria, cEcole Normale Supérieure de Constantine-Assia Djebar, Université Constantine 3, 25000, Ali Mendjli, Algeria, dLaboratoire des Produits Naturels d'Origine Végétale et de Synthése Organique, Faculté des Sciences Exactes, Université des Fréres Mentouri-Constantine 1, Algeria, eLaboratoire d'électrochimie, d'ingénierie moléculaire et de catalyse redox, Département de génie des procédés, Faculté de technologie, Universite Ferhat Abbas, Sétif 19000, Algeria, fChemistry Department, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg, Switzerland, and gInstitute of Physics, University of Neuchâtel, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland
*Correspondence e-mail: [email protected], [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 17 August 2026; accepted 18 August 2026; online 28 August 2026)

The title Schiff base compound, C18H15NO2, was synthesized via the condensation reaction of 4-hy­droxy aniline and 4-meth­oxy-1-naphthaldehyde in ethanol. The dihedral angle between the phenol ring and the mean plane of the naphthalene ring system is 75.81 (6)°. In the crystal, the mol­ecules are linked by O—H⋯N and C—H⋯O hydrogen bonds, enclosing R33(18) ring motifs and forming zigzag chains propagating along the c-axis direction. The chains are linked via C—H⋯π inter­actions forming slabs lying parallel to the ac plane.

3D view (loading...)
[Scheme 3D1]
Chemical scheme
[Scheme 1]

Structure description

Schiff bases exhibit a wide range of biological activities (Djabbour et al., 2025View full citation; Villar et al., 2004View full citation). They have applications in the field of water treatment as they have a great capacity for complexation of transition metals (Boudraa et al., 2023View full citation; Kalcher et al., 1995View full citation). Their use as corrosion inhibitors (e.g., Boudraa et al., 2023View full citation) reveal their importance in this field too. Herein, we report on the synthesis and crystal structure of the title compound, C18H15NO2 (I).

The mol­ecular structure of compound (I) is illustrated in Fig. 1[link]. The configuration about the N1=C12 azomethine bond is E. The –C=N– bond length [1.282 (2) Å] is a little longer than the bond lengths observed in related compounds, such as (E)-1-(4-meth­oxy­naphthalen-1-yl)-N-phenyl­methanimine (II) [1.264 (4) Å; Linden et al., 1989View full citation] and (E)-2-{[(4-meth­oxy­naphthalen-1-yl)methyl­ene]amino}-4-methyl­phenol (III) [1.274 (2) Å; Yahiaoui et al., 2023View full citation]. A search of the Cambridge Structural Database (CSD, Version 6.01; last update May 2026; Groom et al., 2016View full citation) for the length of the azomethine bond of structures with the benzyl­ideneaniline substructure gave 1601 hits (Filters: R ≤ 0.05, no disorder, no ions, no polymers, single crystals and organics only). An analysis using Mercury (Macrae et al., 2020View full citation) gave an average value for the –C=N– bond length of 1.277 (15) Å, with a median value of 1.278 Å. Hence, the N1=C12 bond length in (I) is normal.

[Figure 1]
Figure 1
A view of the mol­ecular structure of compound (I). The displacement ellipsoids are drawn at the 50% probability level.

The dihedral angle between the phenol ring (C13–C18) and the mean plane of the naphthalene ring system (C1–C10; r.m.s. deviation 0.013 Å) in (I) is 75.81 (6)°. In compound (II) the corresponding dihedral angle is 64.33 (12)°, while in compound (III) the same dihedral angle is smaller, at 33.41 (4)° probably due to the presence of an intra­molecular O—H⋯N hydrogen bond.

In the crystal of (I), the mol­ecules are linked by O—H⋯N hydrogen bonds to form zigzag chains propagating along the c-axis direction (Fig. 2[link]). The chains are consolidated by C—H⋯O hydrogen bonds, so enclosing R33(18) ring motifs (Fig. 2[link], Table 1[link]). The chains are linked by C—H⋯π inter­actions forming slabs lying parallel to the ac plane (Fig. 3[link], Table 1[link]). The slabs stack along the b-axis direction and there are no significant inter-planar inter­actions present.

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 and Cg2 are the centroids of the naphthalene ring system (C1–C10) and the phenol ring (C13–C18), respectively.

D—H⋯A D—H H⋯A DA D—H⋯A
O2—H1⋯N1i 0.91 (3) 1.97 (3) 2.849 (2) 160 (3)
C11—H11A⋯O2ii 0.97 2.53 3.409 (2) 150
C14—H14⋯Cg2iii 0.94 2.90 3.627 (2) 135
C18—H18⋯Cg1iv 0.94 2.82 3.745 (2) 170
Symmetry codes: (i) Mathematical equation; (ii) Mathematical equation; (iii) Mathematical equation; (iv) Mathematical equation.
[Figure 2]
Figure 2
A partial view along the a-axis of the crystal structure of compound I, illustrating the formation of the zigzag chain via O—H⋯N and C—H⋯O hydrogen bonds and the formation of the R33(18) ring motifs (Table 1[link]). The various hydrogen bonds are shown as cyan dashed lines.
[Figure 3]
Figure 3
A view along the c-axis of the crystal packing of compound I. The C—H⋯π inter­actions are shown as dashed double arrows (see Table 1[link]; naphthalene ring system is pale green and the phenol ring is pale blue).

Synthesis and crystallization

Equimolar amounts of 4-hy­droxy aniline (0.109 g, 0.01 mmol) and 4-meth­oxy naphthaldehyde (0.186 g, 0.01 mmol) were mixed in absolute ethanol (30 ml) and refluxed under stirring for 4 h. After cooling to room temperature, the solvent was allowed to evaporate slowly, yielding yellow needle-like crystals of (I).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link].

Table 2
Experimental details

Crystal data
Chemical formula C18H15NO2
Mr 277.31
Crystal system, space group Orthorhombic, Pbca
Temperature (K) 250
a, b, c (Å) 7.8365 (3), 27.460 (1), 13.0741 (5)
V3) 2813.43 (18)
Z 8
Radiation type Cu Kα
μ (mm−1) 0.69
Crystal size (mm) 0.54 × 0.24 × 0.09
 
Data collection
Diffractometer Stoe Stadivari
Absorption correction Analytical (X-RED32 and LANA; Stoe, 2025View full citation)
Tmin, Tmax 0.682, 0.938
No. of measured, independent and observed [I > 2σ(I)] reflections 17634, 2477, 2243
Rint 0.057
(sin θ/λ)max−1) 0.596
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.131, 1.01
No. of reflections 2477
No. of parameters 195
H-atom treatment H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3) 0.19, −0.25
Computer programs: X-AREA Pilatus3_SV, X-AREA and LANA (Stoe, 2025View full citation), SHELXT2019/3 (Sheldrick, 2015aView full citation), Mercury (Macrae et al., 2020View full citation), SHELXL2019/3 (Sheldrick, 2015bView full citation), PLATON (Spek, 2020View full citation) and publCIF (Westrip, 2010View full citation).

Structural data


Computing details top

(E)-4-{[(4-Methoxynaphthalen-1-yl)methylidene]amino}phenol top
Crystal data top
C18H15NO2Dx = 1.309 Mg m3
Mr = 277.31Cu Kα radiation, λ = 1.54186 Å
Orthorhombic, PbcaCell parameters from 30029 reflections
a = 7.8365 (3) Åθ = 4.7–67.1°
b = 27.460 (1) ŵ = 0.69 mm1
c = 13.0741 (5) ÅT = 250 K
V = 2813.43 (18) Å3Needle, yellow
Z = 80.54 × 0.24 × 0.09 mm
F(000) = 1168
Data collection top
Stoe Stadivari
diffractometer
2477 independent reflections
Radiation source: Primux 100 micro2243 reflections with I > 2σ(I)
Graded multilayer mirror monochromatorRint = 0.057
Detector resolution: 5.81 pixels mm-1θmax = 66.9°, θmin = 4.7°
rotation method, ω scansh = 39
Absorption correction: analytical
(X-Red32 and LANA; Stoe, 2025)
k = 3227
Tmin = 0.682, Tmax = 0.938l = 1415
17634 measured reflections
Refinement top
Refinement on F2Primary atom site location: dual
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.046Hydrogen site location: mixed
wR(F2) = 0.131H atoms treated by a mixture of independent and constrained refinement
S = 1.01 w = 1/[σ2(Fo2) + (0.0836P)2 + 0.6531P]
where P = (Fo2 + 2Fc2)/3
2477 reflections(Δ/σ)max = 0.004
195 parametersΔρmax = 0.19 e Å3
0 restraintsΔρmin = 0.25 e Å3
Special details top

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.

Refinement. The hydroxyl H atom (H1) was located in a difference Fourier map and freely refined. The C-bound hydrogen atoms were placed geometrically (C—H = 0.94–0.97 Å) and allowed to ride on their parent atoms with Uiso(H) = 1.5Ueq(C-methyl) and 1.2Ueq(C) for other H atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.54483 (17)0.42260 (4)0.11052 (8)0.0607 (3)
O20.50176 (18)0.27526 (4)0.74559 (9)0.0631 (4)
H10.535 (4)0.2440 (11)0.759 (2)0.112 (9)*
N10.56304 (15)0.31870 (4)0.33044 (9)0.0431 (3)
C10.57080 (17)0.37828 (5)0.19453 (11)0.0408 (3)
C20.48289 (18)0.35110 (5)0.12373 (11)0.0438 (3)
H20.4293060.3222400.1452780.053*
C30.46995 (19)0.36462 (5)0.02107 (11)0.0456 (3)
H30.4084850.3450580.0250150.055*
C40.54710 (19)0.40648 (5)0.01231 (11)0.0448 (4)
C50.7243 (2)0.47925 (5)0.02372 (13)0.0544 (4)
H50.7170670.4886140.0453050.065*
C60.8157 (2)0.50699 (6)0.09119 (14)0.0611 (5)
H60.8712210.5353000.0682130.073*
C70.8272 (2)0.49353 (5)0.19402 (14)0.0566 (4)
H70.8901710.5128960.2397410.068*
C80.74786 (19)0.45251 (5)0.22859 (12)0.0477 (4)
H80.7567750.4440170.2980370.057*
C90.65200 (17)0.42243 (4)0.16155 (11)0.0404 (3)
C100.64038 (18)0.43649 (4)0.05746 (11)0.0423 (3)
C110.4544 (3)0.39390 (7)0.18289 (14)0.0765 (6)
H11C0.4623240.4089150.2498780.115*
H11B0.3355010.3916720.1627650.115*
H11A0.5035810.3615050.1854460.115*
C120.57358 (18)0.36320 (5)0.30148 (11)0.0433 (3)
H120.5836500.3874300.3519190.052*
C130.55024 (17)0.30924 (5)0.43688 (10)0.0404 (3)
C140.64259 (18)0.27075 (5)0.47837 (11)0.0457 (4)
H140.7122890.2517450.4355860.055*
C150.63350 (19)0.26002 (5)0.58132 (12)0.0461 (4)
H150.7014960.2349780.6085360.055*
C160.52446 (19)0.28599 (5)0.64513 (11)0.0453 (4)
C170.4292 (2)0.32384 (5)0.60349 (11)0.0486 (4)
H170.3538630.3414960.6453870.058*
C180.44399 (19)0.33576 (5)0.50134 (11)0.0448 (3)
H180.3814610.3621450.4749990.054*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0941 (9)0.0422 (6)0.0456 (6)0.0098 (5)0.0054 (5)0.0026 (4)
O20.0974 (9)0.0459 (6)0.0459 (6)0.0143 (6)0.0037 (5)0.0037 (5)
N10.0487 (7)0.0341 (6)0.0465 (7)0.0005 (5)0.0025 (5)0.0007 (5)
C10.0435 (7)0.0305 (6)0.0484 (8)0.0030 (5)0.0021 (5)0.0000 (5)
C20.0469 (7)0.0312 (6)0.0534 (8)0.0015 (6)0.0022 (6)0.0008 (6)
C30.0521 (8)0.0352 (7)0.0496 (8)0.0023 (6)0.0043 (6)0.0032 (6)
C40.0550 (8)0.0337 (7)0.0459 (8)0.0037 (6)0.0005 (6)0.0003 (6)
C50.0684 (10)0.0363 (7)0.0585 (9)0.0048 (7)0.0056 (7)0.0038 (6)
C60.0711 (11)0.0369 (8)0.0752 (11)0.0145 (7)0.0048 (8)0.0013 (7)
C70.0594 (10)0.0381 (7)0.0723 (11)0.0078 (7)0.0045 (7)0.0074 (7)
C80.0522 (8)0.0368 (7)0.0541 (8)0.0003 (6)0.0037 (6)0.0028 (6)
C90.0418 (7)0.0293 (6)0.0501 (8)0.0045 (5)0.0020 (6)0.0018 (5)
C100.0470 (8)0.0300 (6)0.0500 (8)0.0026 (5)0.0034 (6)0.0014 (5)
C110.1276 (18)0.0512 (10)0.0508 (10)0.0136 (10)0.0176 (10)0.0001 (7)
C120.0464 (8)0.0342 (7)0.0493 (8)0.0001 (6)0.0001 (6)0.0012 (6)
C130.0452 (7)0.0315 (6)0.0446 (7)0.0036 (5)0.0014 (5)0.0010 (5)
C140.0477 (8)0.0330 (7)0.0563 (9)0.0034 (5)0.0086 (6)0.0022 (6)
C150.0499 (8)0.0330 (7)0.0553 (8)0.0031 (6)0.0001 (6)0.0070 (6)
C160.0583 (8)0.0339 (7)0.0437 (8)0.0025 (6)0.0039 (6)0.0011 (5)
C170.0601 (9)0.0389 (7)0.0467 (8)0.0083 (6)0.0005 (7)0.0064 (6)
C180.0519 (8)0.0346 (7)0.0480 (8)0.0077 (6)0.0045 (6)0.0010 (6)
Geometric parameters (Å, º) top
O1—C41.3583 (18)C7—C81.364 (2)
O1—C111.421 (2)C7—H70.9400
O2—C161.3578 (18)C8—C91.420 (2)
O2—H10.91 (3)C8—H80.9400
N1—C121.2820 (18)C9—C101.417 (2)
N1—C131.4192 (18)C11—H11C0.9700
C1—C21.374 (2)C11—H11B0.9700
C1—C91.4354 (18)C11—H11A0.9700
C1—C121.4585 (19)C12—H120.9400
C2—C31.396 (2)C13—C181.391 (2)
C2—H20.9400C13—C141.3911 (19)
C3—C41.370 (2)C14—C151.380 (2)
C3—H30.9400C14—H140.9400
C4—C101.430 (2)C15—C161.391 (2)
C5—C61.368 (2)C15—H150.9400
C5—C101.416 (2)C16—C171.391 (2)
C5—H50.9400C17—C181.380 (2)
C6—C71.397 (2)C17—H170.9400
C6—H60.9400C18—H180.9400
C4—O1—C11117.08 (12)C9—C10—C5119.68 (13)
C16—O2—H1110.3 (19)C9—C10—C4119.23 (12)
C12—N1—C13117.95 (12)C5—C10—C4121.08 (14)
C2—C1—C9118.59 (13)O1—C11—H11C109.5
C2—C1—C12119.94 (12)O1—C11—H11B109.5
C9—C1—C12121.41 (12)H11C—C11—H11B109.5
C1—C2—C3122.64 (13)O1—C11—H11A109.5
C1—C2—H2118.7H11C—C11—H11A109.5
C3—C2—H2118.7H11B—C11—H11A109.5
C4—C3—C2119.82 (13)N1—C12—C1123.56 (13)
C4—C3—H3120.1N1—C12—H12118.2
C2—C3—H3120.1C1—C12—H12118.2
O1—C4—C3124.66 (13)C18—C13—C14118.23 (13)
O1—C4—C10114.96 (12)C18—C13—N1122.73 (12)
C3—C4—C10120.38 (13)C14—C13—N1118.99 (12)
C6—C5—C10120.26 (15)C15—C14—C13121.05 (13)
C6—C5—H5119.9C15—C14—H14119.5
C10—C5—H5119.9C13—C14—H14119.5
C5—C6—C7120.45 (14)C14—C15—C16120.49 (13)
C5—C6—H6119.8C14—C15—H15119.8
C7—C6—H6119.8C16—C15—H15119.8
C8—C7—C6120.54 (15)O2—C16—C17118.07 (13)
C8—C7—H7119.7O2—C16—C15123.33 (13)
C6—C7—H7119.7C17—C16—C15118.56 (13)
C7—C8—C9121.15 (15)C18—C17—C16120.74 (13)
C7—C8—H8119.4C18—C17—H17119.6
C9—C8—H8119.4C16—C17—H17119.6
C10—C9—C8117.92 (12)C17—C18—C13120.84 (13)
C10—C9—C1119.34 (12)C17—C18—H18119.6
C8—C9—C1122.72 (13)C13—C18—H18119.6
C9—C1—C2—C30.2 (2)C6—C5—C10—C4178.70 (15)
C12—C1—C2—C3177.47 (13)O1—C4—C10—C9179.24 (12)
C1—C2—C3—C40.1 (2)C3—C4—C10—C90.0 (2)
C11—O1—C4—C30.6 (2)O1—C4—C10—C50.7 (2)
C11—O1—C4—C10179.71 (16)C3—C4—C10—C5178.48 (14)
C2—C3—C4—O1178.93 (13)C13—N1—C12—C1173.88 (12)
C2—C3—C4—C100.2 (2)C2—C1—C12—N129.7 (2)
C10—C5—C6—C70.1 (3)C9—C1—C12—N1153.10 (13)
C5—C6—C7—C80.2 (3)C12—N1—C13—C1843.94 (19)
C6—C7—C8—C90.1 (2)C12—N1—C13—C14138.50 (14)
C7—C8—C9—C100.4 (2)C18—C13—C14—C152.0 (2)
C7—C8—C9—C1178.18 (14)N1—C13—C14—C15179.68 (12)
C2—C1—C9—C100.44 (19)C13—C14—C15—C163.4 (2)
C12—C1—C9—C10177.64 (12)C14—C15—C16—O2175.76 (14)
C2—C1—C9—C8178.98 (13)C14—C15—C16—C171.9 (2)
C12—C1—C9—C83.8 (2)O2—C16—C17—C18178.60 (13)
C8—C9—C10—C50.42 (19)C15—C16—C17—C180.8 (2)
C1—C9—C10—C5178.19 (13)C16—C17—C18—C132.1 (2)
C8—C9—C10—C4178.96 (12)C14—C13—C18—C170.7 (2)
C1—C9—C10—C40.35 (19)N1—C13—C18—C17176.85 (13)
C6—C5—C10—C90.2 (2)
Hydrogen-bond geometry (Å, º) top
Cg1 and Cg2 are the centroids of the naphthalene ring system (C1–C10) and the phenol ring (C13–C18), respectively.
D—H···AD—HH···AD···AD—H···A
O2—H1···N1i0.91 (3)1.97 (3)2.849 (2)160 (3)
C11—H11A···O2ii0.972.533.409 (2)150
C14—H14···Cg2iii0.942.903.627 (2)135
C18—H18···Cg1iv0.942.823.745 (2)170
Symmetry codes: (i) x, y+1/2, z+1/2; (ii) x, y, z1; (iii) x+1/2, y+1/2, z+1; (iv) x1/2, y, z+1/2.
 

Footnotes

Prof. Emerita.

Acknowledgements

The authors are grateful to the University of Setif 1 and to the Algerian DGRSDT (Directorate General for Scientific Research and Technological Development) for supporting this research. HSE is grateful to the University of Neuchâtel for their support over the years.

References

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