N-Methyl-N-phenyl­amino­methyl 2-naphthyl ketone: an X-ray diffraction and density functional theory study

The crystallographically observed mol­ecular structure of the title compound, C₁₉H₁₇NO, and its inverted counterpart are compared with that calculated by density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. The results from both methods suggest that the observed mol­ecular conformation of the title compound is primarily determined by inter­molecular inter­actions in the crystal structure. The periodic organization of the mol­ecules is stabilized by weak C—H...O and C—H...π hydrogen bonds and thus a two-dimensional puckered network consisting of R₄⁴(22) and R₄⁴(38) ring motifs is established. The title molecule has a (+)-antiperiplanar conformation about the C—C bond in the aminoacetone bridge. The pyramidal geometry observed around the vertex N atom is flattened by the presence of bulky phenyl and naphthylethanone fragments.

S1. Comment

Considerable research effort has been devoted to the photoinitiated polymerization of acrylates and methacrylates due to their efficient usage for the rapid production of polymeric materials, in particular coatings and imaging materials, and photoresists for versatile applications (Pappas, 1978; Hageman, 1989; Dietliker, 1991; Fouassier, 1995; Davidson, 1999). Photoinitiators play an important role in UV-curable systems by generating the reactive species, free radicals or ions initiating the polymerization of the multifunctional monomers and oligomers. We have recently synthesized 2-(N-methyl-N-phenylamino)acetonaphthone (MPA), (I), as a photoinitiator for the polymerization of methyl methacrylate (Keskin & Arsu, 2006). Since crystal structures of such materials are rare in the literature, our primary interest has been to understand their structural features in the solid state. To ascertain comprehensively the effects of crystallization on the isolated conformer of MPA, its solid-state structure was established by single-crystal X-ray diffraction analysis and compared with that optimized by density functional theory (DFT) calculation at the B3LYP/6–311++G(d,p) level (GAUSSIAN03W; Frisch et al., 2004).

The molecular structure of MPA is shown in Fig. 1 and selected geometric parameters are listed in Table 1. The aminoacetone bridge [N—C(H₂)—C(═O)—C(Ar)] linking the naphthalene fragment with the phenyl ring is slightly distorted from its regular planar arrangement. The N1—C12—C11—C1 torsion angle is 174.8 (2)°, which shows that the conformation about the C12—C11 bond in the reference molecule is (+)-antiperiplanar. In the optimized geometry, the conformational descriptor around this torsion angle is also (+)-antiperiplanar, with a value of 173.29°. The bulky phenyl and naphthylethanone fragments on atom N1 favour a flattening of the pyramid-like geometry, resulting in the sum of the bond angles around the vertex atom (N1) being 358.2 (3)°. Methyl atom C13 deviates slightly from the plane defined by atoms C12, N1 and C14 by 0.34 (1) Å. In the optimized geometry, the corresponding deviation of the methyl C atom is a little smaller at 0.30 Å. Although the optimized geometric parameters are generally in agreement with those found in the crystal structure (Table 1), there are certain discrepancies between them, in particular the orientation of the naphthalene fragment. The structural discrepancies between the energy-minimized molecule and the crystallographically observed geometries (MPA itself and its inverted counterpart) were analysed quantitatively by the r.m.s. overlays including H atoms (Fig. 2). The r.m.s. fits of the atomic positions of MPA (red) and its inverted counterpart (blue) to their corresponding values in the optimized geometry (green) (Fig. 2a and 2b) are 0.0205 and 0.0698 Å, respectively. The r.m.s. fit of the atomic positions of MPA to those of its inverted counterpart (Fig. 2c) is 0.0596 Å. While the dihedral angle between the phenyl and naphthalene fragments is 81.26 (7)° in MPA itself [-81.26 (7)° in the inverted molecule], this angle is 87.46° in the inverted optimized geometry. It can be inferred from these results that the conformations of MPA in the crystal structure and the free molecule are slightly different. These deformations in the crystalloraphically observed geometries of MPA are probably due to weak intermolecular interactions in the crystal lattice.

According to graph-set notation (Bernstein et al., 1995), the molecules of MPA are linked into one-dimensional polymeric C(8) chains generated by a twofold screw operation parallel to the b axis of the unit cell with the aid of weak C18—H18···O1ⁱ hydrogen bonds [symmetry code: (i) -x, 1/2 + y, 1/2 - z] (Fig. 3, Table 2). On the other hand, there is a noteworthy C—H···π interaction (Fig. 4) in the crystal structure involving the C14–C19 phenyl ring [centroid Cg1] and atom C5 in the naphthalene fragment of a neighbouring molecule, C5—H5···Cg1ⁱⁱ, with H5···Cg1ⁱⁱ = 2.70 Å and C5—H5···Cg1ⁱⁱ = 154° [symmetry code: (ii) 1 + x, 1/2 - y, 1/2 + z]. This interaction forms a one-dimensional supramolecular arrangement running along the [201] direction, as shown in Fig. 4, involving both the reference molecules and their inverted counterparts consecutively.

The interactions mentioned above generate two different supramolecular arrangements. In the first, the acetonaphthone fragments of the molecules at (x, y, z) and (1 - x, - y, 1 - z), together with the phenylamine fragments of the molecules at (- x, y - 1/2, 1/2 - z) and (1 + x, 1/2 - y, 1/2 + z), give rise to the formation of pseudocyclic centrosymmetric R₄⁴(22) synthons having their symmetry centre at (1/2, 0, 1/2), as shown in Fig. 5. Propagation of the first supramolecular arrangement by the space group symmetry operations links the R₄⁴(22) synthon centred at (1/2, 0, 1/2) to the next one centred at (1/2, 1, 1/2), so generating the second supramolecular arrangement as a pseudocyclic centrosymmetric R₄⁴(38) ring having its symmetry centre at (1/2, 1/2, 1/2) (Fig. 5). Thus, a rather complex puckered sheet lying almost parallel to (102) is formed by these supramolecular units.

In order to investigate quantitatively the possible effects of the intermolecular interactions on the aromaticity of the naphthalene fragment, HOMA (harmonic oscillator model of aromaticity) indices (Krygowski, 1993) were calculated for the crystallographic and optimized geometry of MPA. The HOMA index is equal to unity for purely aromatic systems and to zero for nonaromatic systems. The calculated HOMA indices for the naphthalene fragment of the crystallographically observed and the optimized geometry of MPA are 0.849 and 0.811, respectively. On the other hand, the HOMA index for naphthalene is 0.81 (Krygowski, 1993) and this value may vary from 0.810 to 0.854 depending on the experimental quality (Rosokha & Kochi, 2006). It can be stated that the intermolecular interactions have a restricted effect on the covalent topology of the naphthalene fragment, but a remarkable effect on its orientation.

Related literature

For related literature, see: Bernstein et al. (1995); Davidson (1999); Dietliker (1991); Fouassier (1995); Frisch (2004); Hageman (1989); Keskin & Arsu (2006); Krygowski (1993); Pappas (1978); Rosokha & Kochi (2006); Sheldrick (2008); Stephens et al. (1994).

S2. Experimental

The synthesis of MPA and the corresponding spectroscopic data have already been reported by Keskin & Arsu (2006). The crystallographically observed geometry of MPA was choosen as the starting geometry in the optimization procedure. Geometry optimization and vibrational analysis were performed without any constraints on the molecule using the B3LYP hybrid exchange-correlation function (Stephens et al., 1994) with the aid of the 6–311++G(d,p) basis set. All normal frequencies at the optimized geometry are real, showing that the optimization results in a stable minimum. All calculations were carried out using GAUSSIAN03W (Frisch et al., 2004).

S3. Refinement

All H atoms were located in their idealized positions and refined using suitable riding models, with C—H distances in the range 0.93–0.97 Å and with U_iso(H) values of 1.2U_eq(C) or 1.5U_eq(methyl C). Following refinement, the anisotropic displacement parameters of atoms C17 and C18 were restrained to be similar (SIMU instruction in SHELXL97; Sheldrick, 2008)). The crystal sample selected for data collection was nonmerohedrally twinned (twin lattice quasi-crystal, TLQS) by a twofold rotation axis perpendicular to (010) with two reciprocal lattices differently oriented, giving rise to double diffraction spot sets (see Supplementary material) with a twinning ratio of 0.51:0.49. We were aware of the twin character of the crystal samples at the data collection stage, but pure crystals having a single diffraction spot set could not be found. Since the partially overlapped reflections arising from the non-merohedral character of the crystal sample could not be integrated separately, 752 partially overlapped independent reflections could not be measured satisfactorily and they were discarded from the data set. As a result of this, the completeness of the data decreased to slightly over 74%.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA (Stoe & Cie, 2002); data reduction: X-RED (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003)and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and enCIFer (Allen et al., 2004).

Figures

	Fig. 1. The molecule of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Superimpositions of (a) the reference molecule and the optimized geometry, (b) the inverted molecule and the inverted optimized geometry and (c) the reference molecule and its symmetry-related inverse in the crystal structure.
	Fig. 3. The hydrogen-bonded C(8) chain along the b axis of the unit cell. H atoms not involved in the motif shown have been omitted for the sake of clarity. [Symmetry code: (i) -x, 1/2 + y, 1/2 - z.]
	Fig. 4. The formation of the chain along [201] generated by the C—H···π interaction. For the sake of clarity, H atoms not involved in the motif have been omitted. [Symmetry code: (ii) 1 + x, 1/2 - y, 1/2 + z.]
	Fig. 5. Part of the crystal structure of MPA, showing the formation of the R4^4(22) and R4^4(38) ring motifs.

N-Methyl-N-phenylaminomethyl 2-naphthyl ketone

Crystal data

C19H17NO	F(000) = 584
Mr = 275.34	Dx = 1.223 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 22947 reflections
a = 8.6049 (8) Å	θ = 2.2–27.9°
b = 12.6787 (7) Å	µ = 0.08 mm^−1
c = 15.5042 (14) Å	T = 296 K
β = 117.900 (6)°	Prism, colourless
V = 1494.9 (2) Å^3	0.42 × 0.34 × 0.26 mm
Z = 4

Data collection

Stoe IPDSII diffractometer	1219 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.096
Graphite monochromator	θmax = 26.0°, θmin = 2.2°
Detector resolution: 6.67 pixels mm^-1	h = −10→10
ω scans	k = −15→15
22658 measured reflections	l = −19→19
2182 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.054	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.133	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0543P)^2 + 0.0761P] where P = (Fo^2 + 2Fc^2)/3
2182 reflections	(Δ/σ)max < 0.001
190 parameters	Δρmax = 0.12 e Å^−3
6 restraints	Δρmin = −0.12 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.2953 (4)	0.1747 (2)	0.48996 (19)	0.0641 (7)
C2	0.4545 (4)	0.1640 (2)	0.5703 (2)	0.0722 (8)
H2	0.5315	0.2210	0.5901	0.087*
C3	0.5069 (4)	0.0699 (2)	0.6245 (2)	0.0693 (7)
C4	0.6704 (4)	0.0589 (3)	0.7084 (2)	0.0872 (9)
H4	0.7488	0.1151	0.7294	0.105*
C5	0.7149 (5)	−0.0334 (3)	0.7591 (2)	0.0947 (10)
H5	0.8229	−0.0391	0.8150	0.114*
C6	0.6019 (6)	−0.1188 (3)	0.7289 (3)	0.0995 (11)
H6	0.6349	−0.1815	0.7641	0.119*
C7	0.4420 (6)	−0.1118 (2)	0.6474 (3)	0.0951 (10)
H7	0.3664	−0.1695	0.6272	0.114*
C8	0.3919 (4)	−0.0163 (2)	0.5937 (2)	0.0727 (8)
C9	0.2285 (5)	−0.0048 (3)	0.5095 (3)	0.0934 (10)
H9	0.1520	−0.0621	0.4876	0.112*
C10	0.1794 (4)	0.0876 (2)	0.4593 (2)	0.0840 (9)
H10	0.0696	0.0935	0.4048	0.101*
C11	0.2372 (4)	0.2733 (2)	0.4320 (2)	0.0672 (7)
C12	0.3752 (4)	0.3574 (2)	0.4494 (2)	0.0788 (8)
H12A	0.4220	0.3824	0.5161	0.095*
H12B	0.4713	0.3252	0.4428	0.095*
C13	0.3029 (6)	0.4317 (3)	0.2898 (3)	0.1125 (13)
H13A	0.3684	0.3701	0.2908	0.169*
H13B	0.3512	0.4923	0.2738	0.169*
H13C	0.1822	0.4231	0.2418	0.169*
C14	0.2297 (4)	0.5308 (2)	0.40272 (19)	0.0650 (7)
C15	0.2080 (4)	0.5350 (2)	0.4863 (2)	0.0712 (8)
H15	0.2462	0.4789	0.5300	0.085*
C16	0.1312 (4)	0.6207 (3)	0.5049 (2)	0.0812 (8)
H16	0.1197	0.6222	0.5616	0.097*
C17	0.0712 (4)	0.7040 (3)	0.4419 (3)	0.0884 (9)
H17	0.0178	0.7614	0.4547	0.106*
C18	0.0916 (4)	0.7010 (2)	0.3594 (3)	0.0897 (10)
H18	0.0526	0.7576	0.3163	0.108*
C19	0.1684 (4)	0.6162 (2)	0.3388 (2)	0.0757 (8)
H19	0.1795	0.6159	0.2820	0.091*
N1	0.3132 (3)	0.4465 (2)	0.38518 (19)	0.0801 (7)
O1	0.0851 (3)	0.28683 (16)	0.37084 (15)	0.0855 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0618 (17)	0.0701 (17)	0.0638 (16)	−0.0026 (13)	0.0322 (14)	−0.0030 (13)
C2	0.0667 (18)	0.0778 (19)	0.0773 (18)	−0.0051 (14)	0.0380 (16)	0.0011 (15)
C3	0.0708 (19)	0.081 (2)	0.0659 (17)	0.0021 (15)	0.0398 (15)	−0.0037 (15)
C4	0.071 (2)	0.107 (3)	0.081 (2)	0.0085 (18)	0.0343 (17)	0.0102 (19)
C5	0.098 (2)	0.104 (3)	0.086 (2)	0.029 (2)	0.047 (2)	0.011 (2)
C6	0.137 (3)	0.085 (2)	0.084 (2)	0.034 (2)	0.057 (2)	0.0069 (19)
C7	0.124 (3)	0.072 (2)	0.095 (2)	0.0069 (19)	0.055 (2)	−0.0092 (18)
C8	0.085 (2)	0.0703 (19)	0.0682 (18)	0.0062 (16)	0.0408 (17)	−0.0066 (15)
C9	0.099 (3)	0.071 (2)	0.098 (3)	−0.0166 (18)	0.035 (2)	−0.0107 (18)
C10	0.0771 (19)	0.079 (2)	0.082 (2)	−0.0102 (16)	0.0248 (17)	−0.0091 (17)
C11	0.0659 (17)	0.0770 (19)	0.0637 (16)	0.0015 (14)	0.0346 (15)	−0.0051 (14)
C12	0.0734 (18)	0.0727 (19)	0.101 (2)	0.0019 (15)	0.0498 (18)	0.0052 (17)
C13	0.169 (4)	0.098 (3)	0.112 (3)	−0.012 (3)	0.100 (3)	−0.008 (2)
C14	0.0623 (16)	0.0707 (18)	0.0615 (16)	−0.0132 (13)	0.0286 (14)	−0.0012 (13)
C15	0.0728 (19)	0.0731 (19)	0.0686 (18)	−0.0052 (14)	0.0338 (16)	0.0038 (14)
C16	0.088 (2)	0.078 (2)	0.081 (2)	−0.0143 (16)	0.0427 (18)	−0.0106 (17)
C17	0.086 (2)	0.069 (2)	0.109 (3)	−0.0121 (16)	0.045 (2)	−0.0146 (18)
C18	0.083 (2)	0.065 (2)	0.103 (3)	−0.0102 (17)	0.029 (2)	0.0156 (17)
C19	0.0797 (19)	0.077 (2)	0.0669 (18)	−0.0136 (16)	0.0315 (15)	0.0055 (15)
N1	0.0951 (19)	0.0799 (17)	0.0816 (17)	0.0019 (14)	0.0550 (15)	0.0074 (13)
O1	0.0712 (13)	0.0944 (15)	0.0796 (13)	−0.0008 (11)	0.0259 (12)	−0.0038 (11)

Geometric parameters (Å, º)

C1—C2	1.360 (4)	C11—C12	1.524 (4)
C1—C10	1.412 (4)	C12—N1	1.433 (4)
C1—C11	1.483 (4)	C12—H12A	0.9700
C2—C3	1.406 (4)	C12—H12B	0.9700
C2—H2	0.9300	C13—N1	1.451 (4)
C3—C8	1.400 (4)	C13—H13A	0.9600
C3—C4	1.407 (4)	C13—H13B	0.9600
C4—C5	1.361 (5)	C13—H13C	0.9600
C4—H4	0.9300	C14—N1	1.384 (4)
C5—C6	1.382 (5)	C14—C15	1.394 (4)
C5—H5	0.9300	C14—C19	1.394 (4)
C6—C7	1.368 (5)	C15—C16	1.372 (4)
C6—H6	0.9300	C15—H15	0.9300
C7—C8	1.417 (4)	C16—C17	1.364 (4)
C7—H7	0.9300	C16—H16	0.9300
C8—C9	1.409 (4)	C17—C18	1.371 (4)
C9—C10	1.361 (4)	C17—H17	0.9300
C9—H9	0.9300	C18—C19	1.375 (5)
C10—H10	0.9300	C18—H18	0.9300
C11—O1	1.216 (3)	C19—H19	0.9300
C2—C1—C10	118.7 (3)	N1—C12—C11	115.0 (2)
C2—C1—C11	123.2 (3)	N1—C12—H12A	108.5
C10—C1—C11	118.0 (3)	C11—C12—H12A	108.5
C1—C2—C3	122.4 (3)	N1—C12—H12B	108.5
C1—C2—H2	118.8	C11—C12—H12B	108.5
C3—C2—H2	118.8	H12A—C12—H12B	107.5
C8—C3—C2	118.7 (3)	N1—C13—H13A	109.5
C8—C3—C4	118.6 (3)	N1—C13—H13B	109.5
C2—C3—C4	122.7 (3)	H13A—C13—H13B	109.5
C5—C4—C3	120.6 (3)	N1—C13—H13C	109.5
C5—C4—H4	119.7	H13A—C13—H13C	109.5
C3—C4—H4	119.7	H13B—C13—H13C	109.5
C4—C5—C6	121.0 (4)	N1—C14—C15	121.3 (3)
C4—C5—H5	119.5	N1—C14—C19	121.3 (3)
C6—C5—H5	119.5	C15—C14—C19	117.4 (3)
C7—C6—C5	120.4 (3)	C16—C15—C14	120.9 (3)
C7—C6—H6	119.8	C16—C15—H15	119.6
C5—C6—H6	119.8	C14—C15—H15	119.6
C6—C7—C8	119.7 (3)	C17—C16—C15	121.4 (3)
C6—C7—H7	120.1	C17—C16—H16	119.3
C8—C7—H7	120.1	C15—C16—H16	119.3
C3—C8—C9	118.4 (3)	C16—C17—C18	118.4 (3)
C3—C8—C7	119.7 (3)	C16—C17—H17	120.8
C9—C8—C7	121.9 (3)	C18—C17—H17	120.8
C10—C9—C8	121.8 (3)	C17—C18—C19	121.6 (3)
C10—C9—H9	119.1	C17—C18—H18	119.2
C8—C9—H9	119.1	C19—C18—H18	119.2
C9—C10—C1	120.0 (3)	C18—C19—C14	120.4 (3)
C9—C10—H10	120.0	C18—C19—H19	119.8
C1—C10—H10	120.0	C14—C19—H19	119.8
O1—C11—C1	121.7 (3)	C14—N1—C12	122.0 (2)
O1—C11—C12	120.3 (3)	C14—N1—C13	120.6 (3)
C1—C11—C12	118.0 (3)	C12—N1—C13	115.6 (3)
C10—C1—C2—C3	−0.8 (5)	C2—C1—C11—O1	−167.6 (3)
C11—C1—C2—C3	179.8 (2)	C10—C1—C11—O1	13.0 (4)
C1—C2—C3—C8	0.9 (4)	C2—C1—C11—C12	13.8 (4)
C1—C2—C3—C4	−179.1 (3)	C10—C1—C11—C12	−165.7 (3)
C8—C3—C4—C5	−0.7 (5)	O1—C11—C12—N1	−3.9 (4)
C2—C3—C4—C5	179.4 (3)	C1—C11—C12—N1	174.8 (2)
C3—C4—C5—C6	0.9 (5)	N1—C14—C15—C16	177.5 (3)
C4—C5—C6—C7	−0.5 (5)	C19—C14—C15—C16	−0.8 (4)
C5—C6—C7—C8	0.0 (6)	C14—C15—C16—C17	0.9 (4)
C2—C3—C8—C9	0.1 (4)	C15—C16—C17—C18	−0.9 (5)
C4—C3—C8—C9	−179.9 (3)	C16—C17—C18—C19	0.8 (5)
C2—C3—C8—C7	−179.9 (3)	C17—C18—C19—C14	−0.7 (5)
C4—C3—C8—C7	0.2 (4)	N1—C14—C19—C18	−177.6 (3)
C6—C7—C8—C3	0.2 (5)	C15—C14—C19—C18	0.6 (4)
C6—C7—C8—C9	−179.8 (4)	C15—C14—N1—C12	2.6 (4)
C3—C8—C9—C10	−1.3 (5)	C19—C14—N1—C12	−179.2 (3)
C7—C8—C9—C10	178.7 (3)	C15—C14—N1—C13	167.0 (3)
C8—C9—C10—C1	1.5 (5)	C19—C14—N1—C13	−14.9 (4)
C2—C1—C10—C9	−0.5 (5)	C11—C12—N1—C14	83.9 (3)
C11—C1—C10—C9	179.0 (3)	C11—C12—N1—C13	−81.2 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C18—H18···O1^i	0.93	2.60	3.341 (4)	137

Symmetry code: (i) −x, y+1/2, −z+1/2.