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In the title compound, C10H11N, the mol­ecules assemble as pseudo-dimers through π–π inter­actions, each dimer being rotated by about 90° with respect to its neighbours. The relative positioning of the dimers and C—H...π inter­actions give, when seen along a, a supramolecular zigzag arrangement. The compound contains a planar pyrroline ring and, as a whole, its mol­ecular conformation is also planar, which represents the first example of a totally planar 2-substituted 1-pyrroline and the simplest ever reported by X-ray diffraction.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108011360/hj3072sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108011360/hj3072Isup2.hkl
Contains datablock I

CCDC reference: 692659

Comment top

Pyrrole and its derivatives, (II), are widely known five-membered heterocyclic compounds. Due to their broad range of applications in areas such as natural products, bioactive molecules, pharmaceuticals, anion-binding systems etc., many efforts have been made to develop new synthetic routes for this type of compound (Rao & Jothilingam, 2001; Braun et al., 2001; Hewton et al., 2002; Sessler et al., 2005).

2-Substituted 1-pyrrolines, (III), also called 3,4-dihydro-2H-pyrroles, are important compounds as well, since they can exhibit strong flavouring and odorant properties, such as a cooked-rice flavour (Harrison & Dake, 2005; Fuganti et al., 2007), besides antiviral (Moriarty et al., 2006) or antifungal activity (Verniest et al., 2005). They can also be found as structural motifs in bioactive molecules, such as alkaloids (Usubillaga et al., 1982), or can be used as optically active tryptophan analogues (van Esseveldt et al., 2003). Recently, our group reported the aromatization of 2-phenyl-1-pyrroline to 2-phenylpyrrole using activated carbon as the dehydrogenation agent under mild reaction conditions (Carabineiro et al., 2006). In this context, the preparation of 2-phenyl-1-pyrroline was carried out using an adapted synthetic procedure of that previously reported in the literature (Craig et al., 1931). In this work, we report the crystal structure of the title compound, 5-phenyl-3,4-dihydro-2H-pyrrole (or 2-phenyl-1-pyrroline), (I), which, to the best of our knowledge, is the first example of a wholly planar monosubstituted 1-pyrroline being determined by single-crystal X-ray diffraction. The molecular structure of this compound is shown in Fig. 1.

The geometry and conformation of pyrroline rings has been a subject of great interest. Theoretical calculations and experimental measurements on unsubstituted 1-pyrroline by microwave and IR spectroscopy have shown that the ring deviates only slightly from planarity (Boggs & Kim, 1985; Edwards et al., 1985). But, generally in the solid state, the pyrroline ring exists in an envelope conformation, with one C atom deviating from the mean plane of the remaining four atoms of the heterocycle (Steel et al., 1992). [The previous two sentences appear to contradict each other - can they be rephrased?] Nevertheless, 2-phenyl-1-pyrroline, (I), despite having a phenyl substituent at the iminic position (C1), shows a planar conformation, where the highest deviation is shown by atom C3 which is only 0.0258 (6) Å away from the average plane of the pyrroline ring. The geometry of the entire structure is also nearly planar, since the angle between the plane that contains the pyrroline ring and that of the phenyl substituent is only 3.34 (10)°.

The sum of the internal angles of the heterocycle is 539.83 (9)°, a value that is very close to that of a regular planar pentagon (540°). The iminic bond is 1.2771 (12) Å and all the other bonds in the heterocycle have lengths that correspond to typical values of single C—C and C—N bonds (Allen et al., 1987). Consequently, the internal angles of the heterocyclic ring are much lower than those defined by the corresponding sp2 N and C atoms and sp3 C atoms, which is consistent with a considerable amount of ring strain and also with a certain extent of conjugation of the CN group with the phenyl ring.

A great variety of geometries and conformations is found in different derivatives of the 1-pyrroline, which seem to depend on the positions and relative orientations of the substituents. The second scheme shows some examples of the simplest 2-substituted-1-pyrrolines found in the Cambridge Structural Database (CSD, Version?; Allen, 2002) with refcodes DETROJ (Reference?), VEDNEY (Reference?) and WIKHUT (Reference?). A brief analysis of some of the structural parameters of these compounds (such as the sum of the internal angles, the deviation from planarity, torsion angles and the angle between the plane that contains the pyrroline ring and that of the 2-substituent) allows their comparison with the title compound, (I). For DETROJ, VEDNEY and WIKHUT, the sums of the internal angles are 537.36, 539.52 and 536.02 (molecules 1 and 2) and 539.32°, respectively. For all structures, atom C3 deviates the most from the average plane of the pyrroline, by 0.086 Å in DETROJ, 0.042 Å in VEDNEY (molecule 1), 0.123 Å in VEDNEY (molecule 2) and 0.049 Å in WIKHUT. For DETROJ and VEDNEY, the geometry of the entire structure is not planar, since the angles between the planes of the pyrroline and of its 2-substituent are 21.38 and 11.51 (molecule 1) or 24.91° (molecule 2), respectively. In fact, WIKHUT has a truly perpendicular geometry, with an angle between the planes of 89.62°. The difference in geometry is further enhanced by comparing the corresponding torsion angles, presented in Table 1. A comparison of these structures with that of (I) leads readily to the conclusion that the present 2-phenyl-1-pyrroline is the first example of a totally planar 2-substituted-1-pyrroline and the simplest ever reported by X-ray diffraction.

No classical hydrogen-bond synthons are found in the molecule of (I), but it is possible to observe the existence of weak intermolecular C—H···N and C—H···π interactions that explain the packing found in the crystal structure. Each pyrroline shows four short contacts with four different neighbouring molecules: two bonds of the type C2—H2B···N1 [C2···N1 = 3.594 (1) Å, H2B···N1 = 2.630 (1) Å and C2—H2B···N1 = 172.33 (6)°; symmetry operation: (i) 1 - x, y + 1/2, -z + 3/2] and two of the type C7—H7···π C10 [C7···π C10 = 3.678 (1) Å, H7···π C10 = 2.892 (1) Å, C7—H7···π C10 = 143.12 (6)°; symmetry operation: (ii) x, 1/2 - y, z + 1/2]. These interactions enable the formation of pseudo-dimers exhibiting ππ interactions [π C1···π C1 = 3.636 (1) Å; symmetry operation: (iii) 1 - x,-y,2 - z], as shown in Fig. 2, where the corresponding molecules are antiparallel to each other.

Due to the supramolecular interactions described above, the crystal packing shows a zigzag arrangement when viewed along a, as depicted in Fig. 3.

Experimental top

Diethyl ether, xylene and bromobenzene were pre-dried over activated 4 Å molecular sieves and then distilled from sodium and kept under an atmosphere of dinitrogen.

The synthetic procedure followed for the synthesis of 2-phenyl-1-pyrroline was that previously used in our group (Carabineiro et al., 2006), which was adapted from the literature (Craig et al., 1931). After trap-to-trap vacuum distillation, colourless crystals of (I) were grown from a mixture of xylene and pyrroline [Ratio?] at 273 K.

Refinement top

All H atoms were inserted in idealized positions and were allowed to refine as riding on their parent C atoms, with C—H distances of 0.93 and 0.97 Å for aromatic and methylene H atoms, respectively, and with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SMART (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: enCIFer (Allen et al., 2004).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity.
[Figure 2] Fig. 2. A view of the pseudo-dimers observed in the crystal structure of (I), rotated relative to each other by about 90°. Dashed lines represent C—H···N, C—H···π and ππ interactions (blue, red and orange, respectively, in the online version of the journal).
[Figure 3] Fig. 3. The packing of the crystal structure of (I), viewed along the a axis.
5-Phenyl-3,4-dihydro-2H-pyrrole top
Crystal data top
C10H11NDx = 1.226 Mg m3
Mr = 145.20Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PbcaCell parameters from 7142 reflections
a = 18.326 (3) Åθ = 3.0–29.6°
b = 10.3875 (14) ŵ = 0.07 mm1
c = 8.2618 (12) ÅT = 150 K
V = 1572.8 (4) Å3Prism, colourless
Z = 80.37 × 0.30 × 0.30 mm
F(000) = 624
Data collection top
Bruker SMART CCD area-detector
diffractometer
2247 independent reflections
Radiation source: fine-focus sealed tube1856 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.051
ϕ and ω scansθmax = 29.8°, θmin = 3.0°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 2425
Tmin = 0.883, Tmax = 0.979k = 1414
46880 measured reflectionsl = 1111
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.042Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.120H-atom parameters constrained
S = 1.08 w = 1/[σ2(Fo2) + (0.0633P)2 + 0.2688P]
where P = (Fo2 + 2Fc2)/3
2247 reflections(Δ/σ)max = 0.001
100 parametersΔρmax = 0.29 e Å3
0 restraintsΔρmin = 0.19 e Å3
Crystal data top
C10H11NV = 1572.8 (4) Å3
Mr = 145.20Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 18.326 (3) ŵ = 0.07 mm1
b = 10.3875 (14) ÅT = 150 K
c = 8.2618 (12) Å0.37 × 0.30 × 0.30 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer
2247 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
1856 reflections with I > 2σ(I)
Tmin = 0.883, Tmax = 0.979Rint = 0.051
46880 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0420 restraints
wR(F2) = 0.120H-atom parameters constrained
S = 1.08Δρmax = 0.29 e Å3
2247 reflectionsΔρmin = 0.19 e Å3
100 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
xyzUiso*/Ueq
N10.49752 (5)0.01918 (8)0.72581 (10)0.0314 (2)
C10.47813 (5)0.10372 (8)0.82948 (10)0.0252 (2)
C20.53789 (5)0.19141 (9)0.88919 (13)0.0322 (2)
H2A0.54640.17971.00410.039*
H2B0.52620.28100.86850.039*
C30.60380 (6)0.14823 (10)0.78991 (13)0.0346 (2)
H3A0.64380.12300.86000.041*
H3B0.62030.21660.71880.041*
C40.57575 (6)0.03262 (10)0.69171 (13)0.0345 (2)
H4A0.58350.04700.57700.041*
H4B0.60150.04500.72300.041*
C50.40191 (5)0.11271 (8)0.88635 (10)0.0256 (2)
C60.38010 (6)0.20932 (10)0.99241 (12)0.0326 (2)
H60.41400.26911.02940.039*
C70.30796 (6)0.21716 (11)1.04356 (13)0.0393 (3)
H70.29390.28211.11440.047*
C80.25722 (6)0.12898 (11)0.98960 (12)0.0380 (3)
H80.20900.13451.02390.046*
C90.27826 (6)0.03192 (10)0.88393 (13)0.0366 (2)
H90.24410.02770.84760.044*
C100.34989 (5)0.02395 (9)0.83276 (12)0.0309 (2)
H100.36370.04120.76180.037*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0330 (4)0.0286 (4)0.0325 (4)0.0008 (3)0.0015 (3)0.0028 (3)
C10.0292 (4)0.0210 (4)0.0254 (4)0.0010 (3)0.0072 (3)0.0039 (3)
C20.0317 (5)0.0264 (4)0.0387 (5)0.0026 (3)0.0082 (4)0.0024 (4)
C30.0308 (5)0.0363 (5)0.0366 (5)0.0027 (4)0.0062 (4)0.0053 (4)
C40.0332 (5)0.0315 (5)0.0389 (5)0.0032 (4)0.0001 (4)0.0020 (4)
C50.0303 (4)0.0227 (4)0.0237 (4)0.0007 (3)0.0062 (3)0.0034 (3)
C60.0354 (5)0.0319 (5)0.0305 (5)0.0009 (4)0.0049 (4)0.0042 (4)
C70.0406 (6)0.0451 (6)0.0320 (5)0.0047 (4)0.0004 (4)0.0064 (4)
C80.0324 (5)0.0489 (6)0.0327 (5)0.0009 (4)0.0008 (4)0.0061 (4)
C90.0335 (5)0.0368 (5)0.0394 (5)0.0074 (4)0.0050 (4)0.0053 (4)
C100.0337 (5)0.0263 (4)0.0328 (5)0.0026 (4)0.0055 (4)0.0004 (3)
Geometric parameters (Å, º) top
N1—C11.2771 (12)C5—C61.3909 (14)
N1—C41.4678 (13)C5—C101.3982 (13)
C1—C51.4767 (13)C6—C71.3905 (15)
C1—C21.5076 (12)C6—H60.9300
C2—C31.5275 (15)C7—C81.3792 (16)
C2—H2A0.9700C7—H70.9300
C2—H2B0.9700C8—C91.3883 (15)
C3—C41.5378 (15)C8—H80.9300
C3—H3A0.9700C9—C101.3816 (15)
C3—H3B0.9700C9—H90.9300
C4—H4A0.9700C10—H100.9300
C4—H4B0.9700
C1—N1—C4109.58 (8)C3—C4—H4B110.2
N1—C1—C5121.34 (8)H4A—C4—H4B108.5
N1—C1—C2115.65 (9)C6—C5—C10118.64 (9)
C5—C1—C2123.01 (8)C6—C5—C1121.19 (8)
C1—C2—C3102.79 (8)C10—C5—C1120.17 (8)
C1—C2—H2A111.2C7—C6—C5120.46 (9)
C3—C2—H2A111.2C7—C6—H6119.8
C1—C2—H2B111.2C5—C6—H6119.8
C3—C2—H2B111.2C8—C7—C6120.25 (10)
H2A—C2—H2B109.1C8—C7—H7119.9
C2—C3—C4104.37 (8)C6—C7—H7119.9
C2—C3—H3A110.9C7—C8—C9119.90 (10)
C4—C3—H3A110.9C7—C8—H8120.1
C2—C3—H3B110.9C9—C8—H8120.1
C4—C3—H3B110.9C10—C9—C8119.98 (10)
H3A—C3—H3B108.9C10—C9—H9120.0
N1—C4—C3107.43 (8)C8—C9—H9120.0
N1—C4—H4A110.2C9—C10—C5120.77 (9)
C3—C4—H4A110.2C9—C10—H10119.6
N1—C4—H4B110.2C5—C10—H10119.6
C4—N1—C1—C5179.92 (8)C2—C1—C5—C10176.52 (8)
C4—N1—C1—C20.48 (11)C10—C5—C6—C70.08 (14)
N1—C1—C2—C33.01 (11)C1—C5—C6—C7179.37 (9)
C5—C1—C2—C3177.40 (8)C5—C6—C7—C80.04 (16)
C1—C2—C3—C43.99 (10)C6—C7—C8—C90.07 (16)
C1—N1—C4—C32.30 (11)C7—C8—C9—C100.13 (16)
C2—C3—C4—N13.98 (10)C8—C9—C10—C50.09 (15)
N1—C1—C5—C6176.40 (9)C6—C5—C10—C90.02 (14)
C2—C1—C5—C64.03 (13)C1—C5—C10—C9179.44 (8)
N1—C1—C5—C103.04 (13)

Experimental details

Crystal data
Chemical formulaC10H11N
Mr145.20
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)150
a, b, c (Å)18.326 (3), 10.3875 (14), 8.2618 (12)
V3)1572.8 (4)
Z8
Radiation typeMo Kα
µ (mm1)0.07
Crystal size (mm)0.37 × 0.30 × 0.30
Data collection
DiffractometerBruker SMART CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.883, 0.979
No. of measured, independent and
observed [I > 2σ(I)] reflections
46880, 2247, 1856
Rint0.051
(sin θ/λ)max1)0.698
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.042, 0.120, 1.08
No. of reflections2247
No. of parameters100
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.29, 0.19

Computer programs: SMART (Bruker, 1997), SAINT (Bruker, 1997), SIR2004 (Burla et al., 2005), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006), enCIFer (Allen et al., 2004).

Torsion angles in the four compared compounds (°) top
Torsion angleCompound (I)DETROJVEDNEY (1)VEDNEY (2)WIKHUT
N1-C1-C5-C6-176.40 (9)175.89-168.29-153.65-93.33
C2-C1-C5-C10-176.52 (8)-162.19170.63-152.11-91.63
N1-C1-C5-C103.05 (13)-0.6810.4624.5784.51
C2-C1-C5-C64.03 (13)14.3810.6129.6790.82
The nomenclature used for the torsion angles is that of compound (I). All the torsion angles are the corresponding ones.
 

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