Structure and conformation of meso-2,4-di(N-carbazolyl)pentane

Article abstract of DOI:10.1016/j.molstruc.2014.07.052

The stereochemistry of the title compound is established as meso. The carbazole groups have no parallel planar close contacts (π-type interactions), which differs from the packing found previously for terminal 1,n-di(N-carbazolyl)alkanes. Bond distances,

Full text of DOI:10.1016/j.molstruc.2014.07.052

Journal of Molecular Structure 1076 (2014) 183–187
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structure and conformation of meso-2,4-di(N-carbazolyl)pentane
Aditya Agrahari a, Patrick Wagers b, Steven M. Schildcrout c, Wiley J. Youngs b, John Masnovi a,
⇑
a Department of Chemistry, Cleveland State University, Cleveland, OH 44115, USA
b Department of Chemistry, University of Akron, Akron, OH 44325, USA
c Department of Chemistry, Youngstown State University, Youngstown, OH 44555, USA
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
ꢀ
The stereochemistry of the title
compound is established as meso.
The carbazole groups have no parallel
planar close contacts (
interactions).
p-type
ꢀ
The nitrogens puckering due to
packing forces as found in related
structures.
ꢀ
ꢀ
Bond distances and angles agree with
density functional calculations.
The molecular asymmetry for
placement of the two carbazoles is
intrinsic.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 May 2014
Received in revised form 17 July 2014
Accepted 19 July 2014
Available online 27 July 2014
The stereochemistry of the title compound is established as meso. The carbazole groups have no parallel
planar close contacts ( -type interactions), which differs from the packing found previously for terminal
p
1,n-di(N-carbazolyl)alkanes. Bond distances, bond angles, and torsion angles are compared with those
calculated for the isolated molecule using M06-2X density functional theory, which is designed to model
intramolecular dispersion effects. The results indicate that dispersion effects have a significant influence
on the molecular conformation, although packing effects likely determine the magnitude of the puckering
about one of the nitrogens (N1) and give a crystal conformation closer to a theoretical local minimum
than to the global minimum potential energy, which are calculated to differ by only 6.7 kJ/mol at 298 K.
Ó 2014 Elsevier B.V. All rights reserved.
Keywords:
Carbazole
Dimer
Anti/gauche conformation
Introduction
(excimers) of anthracene [6] although a nonparallel planar interac-
tion more akin to the orientation of the two anthryl groups in di(9-
Large planar aromatic molecules such as anthracenes and carb-
azoles tend to pack in parallel planar face-to-face or ‘T-shaped’
face-to-edge interactions in the solid state [1–4] as well as in the
gas phase [5]. The optimum geometry for interaction in solution
often contains a face-to-face orientation of the aromatic rings in
anthryl)methane also has been proposed [7].
Intramolecular associations of aryl groups in diarylalkanes
should be entropically less unfavorable than those which occur
intermolecularly, but the connecting linkage can also restrict the
geometries possible for interaction. In particular, aryl groups sepa-
rated by three saturated carbons are optimally situated to achieve
parallel planar interactions (Fig. 1a, n = 3), and 1,3-diarylalkanes
have been used to model the behavior of pendant aryl groups in
organic polymers such as poly(vinylcarbazole) (Fig. 1b) and
poly(vinylanthracene). These polymers become photochemical
semiconductors in the presence of electron accepting dopants
order to maximize
p overlap, as found for the excited state dimers
⇑
Corresponding author. Tel.: +1 (216) 687 2469.
E-mail addresses: aditya.agrahari@gmail.com (A. Agrahari), pow1@zips.uakron.
edu (P. Wagers), smschildcrout@ysu.edu (S.M. Schildcrout), youngs@uakron.edu
(W.J. Youngs), j.masnovi@csuohio.edu (J. Masnovi).
http://dx.doi.org/10.1016/j.molstruc.2014.07.052
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

184
A. Agrahari et al. / Journal of Molecular Structure 1076 (2014) 183–187
2 n
a
c
b
Fig. 1. Chemical structure of (a) 1,n-di(N-carbazolyl)alkanes, (b) poly(N-vinyl)carbazole, and (c) meso-2,4-di(N-carbazolyl)pentane.
[8,9]. Since the tacticity of the polymer will affect the interactions
which can occur between the carbazoles units, and hence the con-
ductive properties, we prepared meso-2,4-di(N-carbazolyl)pentane
(Fig. 1c) in order to determine the conformation and close contacts
involving the carbazolyl groups. The meso compound as well as the
racemate are optically inactive in solution and cannot be distin-
guished in this regard. Therefore we performed a structure deter-
mination in order to verify the stereochemistry of this isomer.
Density-functional-theoretical computations also were performed
to assess the relative importance of intramolecular versus intermo-
lecular influences on the orientation of the groups.
reflections from three different orientations. The data was inte-
grated using SAINT [12]. An empirical absorption correction and
other corrections were applied to the data using SADABS [13].
Structure solution, refinement, and modeling were accomplished
by using the Bruker SHELXTL package [13]. The structure was deter-
mined by full-matrix least-squares refinement of F2 and the selec-
tion of the appropriate atoms from the generated difference map.
Hydrogen atom positions were calculated and Uiso(H) values were
fixed according to a riding model. Crystallographic and refinement
information can be found in Table 1. The calculated crystal density
(1218 kg/m3) is close to that found for the 1,5-di(N-carbazolyl)pen-
tane isomer (calculated 1210 kg/m3, measured 1210 kg/m3).
Theoretical computations were performed using Gaussian soft-
ware [14] through the Ohio Supercomputing Center (Columbus
OH, www.osc.edu) with Zhao and Truhlar’s hybrid meta
exchange–correlation functional, M06-2X [15–17]. This method is
Experimental
A crystal of the known title compound suitable for X-ray analysis
was prepared as follows. 2,4-Pentanediol (Aldrich, 4 g, 0.038 mol) in
15 mL of dry pyridine was added to tosyl chloride (Aldrich, 15.25 g,
0.077 mol) also in 15 mL of dry pyridine. After 15 h, 19 mL of conc.
HCl in 1 mL of distilled water was added. The solution was extracted
twice with 100 mL of CHCl3. The organic layer was extracted with
50 mL of distilled water and with saturated NaHCO3 solution. The
organic layer was evaporated under vacuum to afford 11.46 g
(72.4%) of a mixture of 2,4-ditosyloxypentanes, mp 90–96 °C (meso
135.5–136 °C, rac 91–92 °C) [10]. Crystals grown from the mixture
of 2,4-ditosyloxypentanes using CH2Cl2/hexane mixed solvent sys-
tem contained both diastereomers and were disordered. The mix-
ture of 2,4-ditosyloxypentanes (5.0 g, 0.012 mol) was dissolved in
15 mL of dry DMSO and added dropwise to KH (1.46 g, 0.036 mol)
and carbazole (4.055 g, 0.024 mol) in 15 mL of dry DMSO under
argon. After one day at room temperature, water was added to
destroy the excess hydride. The reaction was extracted twice with
100 mL of CHCl3 and twice with 50 mL of water. Evaporation of
the combined organic extracts afforded an oil which was purified
by column chromatography eluting with 30% CH2Cl2/hexane to
yield 420 mg (8.5%) of meso-2,4-di(N-carbazolyl)pentane, mp
194–196 °C (184 °C from ethanol [11]).
parameterized for nonmetallic systems with noncovalent
p–p
interactions and should better model intramolecular dispersion
Table 1
Cyrstallographic information for C29H26N2.
Space group
a (Å)
b (Å)
Pca21
18.5946(9)
13.7581(6)
8.5774(4)
2194.32(18)
4
c (Å)
Volume (Å3)
Z
Reflections used
Crystal description
Crystal size (mm)
Density (kg/m3)
Mu
4854
Colorless plate
0.25 ꢁ 0.17 ꢁ 0.05
1218
0.071
R equivalents
0.0232
R
(I)/net(I)
0.0251
Total number of reflections
Number of reflections (gt)
Threshold expression
Flack absorbance
Number of reflections used
Number of parameters
R (all)
R (gt)
wR
wR (gt)
S (all)
3115
2899
>2r(I)
ꢂ1(3)
3115
282
A single crystal of C29H26N2 grown from CHCl3/C2H5OH was
coated in paraffin oil, mounted on a CryoLoop™, and placed on
the goniometer head under a stream of nitrogen cooled to 100 K.
The data was collected on a Bruker APEX II Duo CCD system
equipped with a Mo ImuS micro-focus source (k = 0.71073 Å) and
graphite monochromator. The unit cell was determined by using
0.0367
0.0330
0.0846
0.0820
1.082
0.001
Shift/su (max)

A. Agrahari et al. / Journal of Molecular Structure 1076 (2014) 183–187
185
effects than other more general density-functional approaches. The
modest basis set 6-31+G(d) avoids excessive computation times for
an asymmetric system of the present size and flexibility and was
used for all reported computations. The experimental orthogonal-
ized atomic coordinates for a single molecule were used as the ini-
tial guess for the theoretical optimization to a local minimum. The
global minimum was obtained from successive two-dihedral MM2
plots of the torsion angles about the four bridge bonds. This was
followed by scans of torsion angles at 30° intervals around the
MM2 minima using M06-2X with all bond lengths frozen. Finally
the two most stable geometries from these scans were fully opti-
mized by M06-2X, which gave the same final result. The theoretical
geometries are compared with that observed for the crystal.
tent. Thus both experiment and theory show a pyramidalization
or pucker at each N atom, as is seen in torsion angles CX–CY–
N1–C26 and CZ–CW–N2–C28. The pucker at N2 is essentially the
same for experiment and for the theoretical local minimum. At
N1 these experimental torsion angles are about 7° and 4° farther
from planarity than those at the theoretical local and global min-
ima respectively. This difference at N1 is in line with those
reported for other carbazole-containing structures [18–25] and
involves very little energy expenditure, as discussed below. Since
theoretical results are for a gaseous molecule and since the
observed geometry is so similar to that calculated at the local min-
imum, with the possible exception of the N1 pucker, packing
effects seem not to be responsible for the intramolecular geometry
in the crystal. However, packing effects are responsible for which
of the two theoretical geometries, the local or the global minimum,
that the crystal adopts, as considered below.
Results
Four of the carbons (C26–C29) in the alkyl chain are nearly
coplanar, as is each of the carbazolyl groups, each of which is
rotated about 100° from the C26–C29 plane in the crystal. The con-
formation of the N1 carbazolyl unit is found to be close to anti from
the alkyl chain whereas the N2 carbazolyl group is nearly gauche as
revealed by the corresponding torsion angles involving the alkyl
chain and the two carbazolyl groups. Thus the torsion angle N1–
C26–C27–C28 is 160.49(16)° versus N2–C28–C27–C26 at
ꢂ50.7(2)°, which differ substantially from one another but are
close to the values for the optimized local-minimum gas structure.
Comparing the global minimum with the crystal, the latter torsion
angle is consistent, but the former is about 80° less, at a gauche
position. This smaller N1–C26–C27–C28 angle at the theoretical
global minimum reflects a closer approach between the carbazole
groups in a near-parallel planar, face-to-face arrangement, with a
nonbonded N1–N2 distance of 3.07 Å, compared to 4.17 Å at the
An ORTEP of the title compound showing the atom labeling
scheme and a packing diagram are shown in Fig. 2. The structure
establishes the stereochemistry for the compound as meso,
although no internal plane of symmetry exists in the conformation
adopted in the crystal or calculated by theory. We performed cal-
culations on the structure in order to determine the configuration
and conformational preferences in the absence of crystallographic
packing forces. A local potential-energy minimum with bonding
parameters (Table 2) resembling those of the crystal was found
as well as a global minimum at 15 kJ/mol less potential energy.
Vibrational analysis showed that both theoretical geometries are
at true potential-energy minima. Bond lengths as well as bond
angles calculated using the M06-2X theory are in good agreement
with the experimental results. The torsion angles at the local min-
imum show no deviation more than 11° and all signs are consis-
Fig. 2. ORTEP of meso-2,4-di(N-carbazolyl)pentane showing the carbon labeling scheme with hydrogens omitted (top left) and hydrogens included (top right), and stereo
view of the packing (bottom). The hydrogen labels are assigned to be consistent with their designated carbons.

186
A. Agrahari et al. / Journal of Molecular Structure 1076 (2014) 183–187
Table 2
Torsion angles for C29H26N2 and C16H17N (CzBu) involving the alkyl chain.
Torsion angles
Observed (°)a
Calc loc (°)b
Calc glb (°)c
C11–C12–N1–C26
C7–C12–N1–C26
C6–C1–N1–C26
9.9(3)
ꢂ169.62(17)
170.01(16)
ꢂ9.8(3)
2.4
ꢂ177.0
177.1
ꢂ2.4
6.2
ꢂ173.7
174.0
ꢂ6.7
C2–C1–N1–C26
C12–N1–C26–C27
C12–N1–C26–C25
C1–N1–C26–C25
C1–N1–C26–C27
N1–C26–C27–C28
C25–C26–C27–C28
70.2(2)
68.2
56.9
ꢂ58.7(2)
136.38(18)
ꢂ94.7(2)
160.49(16)
ꢂ71.2(2)
ꢂ60.5
124.9
ꢂ106.3
163.7
ꢂ68.2
ꢂ70.2
114.7
ꢂ118.2
81.0
ꢂ152.8
Torsion angles
Observed (°)a
Calc loc (°)b
Calc glb (°)c
Calc (°) for CzBud
C14–C13–N2–C28
C18–C13–N2–C28
C19–C24–N2–C28
C23–C24–N2–C28
C29–C28–N2–C13
C29–C28–N2–C24
C27–C28–N2–C13
C27–C28–N2–C24
N2–C28–C27–C26
C26–C27–C28–C29
14.3(3)
ꢂ166.81(17)
166.32(17)
ꢂ14.4(3)
15.5
ꢂ165.2
164.4
ꢂ15.0
ꢂ120.7
76.7
0.5
ꢂ178.8
178.9
ꢂ0.9
5.2
ꢂ175.0
174.8
ꢂ5.0
ꢂ125.4(2)
71.4(2)
ꢂ112.9
66.9
ꢂ119.2
67.8
108.5(2)
112.6
119.4
ꢂ60.7
ꢂ54.0
178.7
112.7
ꢂ60.4
ꢂ50.8
ꢂ178.1
ꢂ54.7(3)
ꢂ49.9
ꢂ46.2
ꢂ172.6
ꢂ50.7(2)
ꢂ175.98(17)
a
b
c
Crystallographic determination (atom labels correspond to average of chemically equivalent positions).
Calculated using RM06-2X/6-31+G(d) for the gas-phase title molecule optimized to a local minimum obtained from the observed geometry (E = ꢂ1229.82036 au).
Calculated using RM06-2X/6-31+G(d) for the gas-phase title molecule optimized to the global minimum (E = ꢂ1229.82628 au).
Corresponding values calculated using RM06-2X/6-31+G(d) for optimized gaseous 2-(N-carbazolyl)butane.
d
Fig. 3. Close intermolecular contacts found in 1,3-di(N-carbazolyl)propane, form I (P21/n) (a) nearly perpendicular to carbazolyl rings A and B, (b) perpendicular to rings B0
and B0, and (c) perpendicular to rings A0 and A0; in 1,3-di(N-carbazolyl)propane, form II (P21/c), (d) perpendicular to the primed rings and (e) perpendicular to the unprimed
rings; and in meso-2,4-di(N-carbazolyl)pentane showing, (f) the interaction between a carbazolyl ring and the alkyl chain and (g) a ‘T’ type interaction between carbazole
rings. Rings farther behind are shaded darker, and hydrogens have been omitted for clarity.

A. Agrahari et al. / Journal of Molecular Structure 1076 (2014) 183–187
187
local minimum and 4.140(2) Å in the crystal. Therefore, the pre-
ferred intrinsic geometry (in isolation) would be similar to that
as occurs in intramolecular excimers [11,26–28] and dimer radical
ions [23,28–31]. Consistent with the closer association of carbazole
groups and more restrictive torsional vibrations at the global min-
imum is its theoretical entropy, which is 33 J/(mol K) less than at
the local minimum.
It is generally expected that the largest groups, in this case the
carbazolyl substituents, should prefer an anti relationship. Since
only one of these groups adopts an anti conformation in the crystal
whereas the other is gauche, calculations were performed to deter-
mine also whether this preference might be due to intramolecular
interactions or to intermolecular crystallographic packing forces.
The good agreement between the theoretical local-minimum and
observed torsion angles implies that the molecular asymmetry is
intrinsic and not only a crystallographic packing effect, although
packing effects seem to favor the theoretical local-minimum rather
than the global-minimum conformation despite the latter having a
standard free energy 6.7 kJ/mol lower. Therefore, packing effects
would have to be sufficiently large to compensate for the differ-
ence in free energy between the two conformations.
To model an isolated half of the title molecule, theoretical opti-
mization was done also for 2-(N-carbazolyl)butane, C16H17N. Con-
sidering the corresponding torsion angles involving the alkyl chain
(see CzBu in the lower part of Table 2), this optimized gaseous mol-
ecule is found to resemble the N2 half of the crystalline title com-
pound much more closely than its N1 half. Because these
calculations pertain to isolated molecules, the alkyl-chain distor-
tion of the N1 half is attributed mainly to weak intramolecular
effects rather than crystal-packing interactions, at least to the
extent that the geometry of the crystal resembles that calculated
for the title compound within the accuracy of M06-2X theory.
Intermolecular interactions between carbazolyl groups in the
solid typically involve anti-parallel planar associations as shown
in Fig. 3 for three crystallographically different molecules of the
structurally related compound 1,3-di(N-carbazolyl)propane
(Fig. 3a–e) [21,22]. Anti-parallel planar associations also are
observed with different numbers of methylene units intervening
between the carbazolyl groups as in 1,2-di(N-carbazolyl)ethane,
ence. However, packing effects should be responsible for the intra-
molecular geometry which resembles that at the theoretical local,
rather than global, potential energy minimum.
Acknowledgments
We thank the Graduate College and Chemistry Department at
Cleveland State University for support, the Ohio Supercomputing
Center for a grant of computer time, and the National Science
Foundation (CHE-0840446) for funds used to purchase the Bruker
APEX II Duo X-ray diffractometer used in this research.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2014.
07.052.
References
[1] J.E. Kim, J.H. Kim, W. Sim, J.Y. Lee, Acta Cryst. E 69 (2013) o828.
[2] G.B. McGaughey, M. Gagné, A.K. Rappé, J. Biol. Chem. 273 (1998) 15458–
15463.
[3] T. Narasimhamurthy, J.C.N. Benny, K. Pandiarajan, R.S. Rathore, Acta Cryst. C 59
(2003) o620–o621.
[4] I.R. Pottie, C.V.K. Sharma, K. Vaughan, M.J. Zaworotko, J. Chem. Crystallogr. 28
(1998) 5–10.
[5] J.M. Steed, T.A. Dixon, W. Klemperer, J. Chem. Phys. 70 (1979) 4940–4946.
[6] E.A. Chandross, J. Ferguson, J. Chem. Phys. 45 (1966) 397–398.
[7] V. Langer, J. Sieler, H.D. Becker, Z. Kristallogr. 199 (1992) 307–309.
[8] P. Bertoncello, A. Notargiacomo, C. Nicolini, Polymer 45 (2004) 1659–1664.
[9] G. Kaune, P. Mueller-Buschbaum, Phys. Status Solidi RRL 4 (2010) 52–54.
[10] E.L. Eliel, O. Hutchins, J. Am. Chem. Soc. 91 (1969) 2703–2715.
[11] F. Evers, K. Kobs, R. Memming, D.R. Terrell, J. Am. Chem. Soc. 105 (1983) 5988–
5995.
[12] Bruker, SMART (Version 5.625), SAINT (Version 6.22) and SHELXTL (Version
6.10), 1997.
[13] G.M. Sheldrick, SHELX-97, University of Göttingen, Germany, 1997.
[14] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R.
Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken,
C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R.
Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B.
Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision C.01,
Gaussian Inc., Wallingford, CT, 2010.
[15] Y. Zhao, D.G. Truhlar, Theor. Chem. Acc. 120 (2008) 215–241.
[16] D.S. Huh, S.J. Choe, J. Porphyrins Phthalocyanines 14 (2010) 592–604.
[17] S.J. Choe, Bull. Korean Chem. Soc. 33 (2012) 2861–2866.
[18] B.R. Kaafarani, A.O. El-Ballouli, R. Trattnig, A. Fonari, S. Sax, B. Wex, C. Risko,
R.S. Khnayzer, S. Barlow, D. Patra, T.V. Timofeeva, E.J.W. List, J.-L. Brédas, S.R.
Marder, J. Mater. Chem. C 1 (2013) 1638–1650.
1,4-di(N-carbazolyl)butane,
and
1,5-di(N-carbazolyl)pentane
[21,25], and in 1,1-di(N-carbazolyl)methane parallel planar inter-
actions are found [23]. This indicates a general preference for pla-
nar interactions between terminal carbazolyl groups in the solid
state. However, in meso-2,4-di(N-carbazolyl)pentane, the carbazol-
yl groups pack near the methylene chain (Fig. 3f), with neighboring
groups interacting in ‘T-shaped’ associations (Fig. 3g). Apparently
in this case, the terminal methyl groups prevent the aromatic
groups from associating through their
p systems.
[19] M. Arslan, E. Asker, R.B. Krafcik, J. Masnovi, R.J. Baker, Acta Cryst. E 62 (2006)
o4055–o4057.
[20] M.-S. Liao, Y. Lu, V.D. Parker, S. Scheiner, J. Phys. Chem. A 107 (2003) 8939–
8948.
Conclusion
[21] G.J. Haderski, Z. Chen, R.B. Krafcik, J. Masnovi, R.J. Baker, R.L.R. Towns, J. Phys.
Chem. B 104 (2000) 2242–2250.
[22] R.J. Baker, Z. Chen, R.B. Krafcik, J. Masnovi, Acta Cryst. C 47 (1991) 2167–2170.
[23] J. Masnovi, R.B. Krafcik, R.J. Baker, R.L.R. Towns, J. Phys. Chem. 94 (1990) 2010–
2013.
[24] D. Lee, S.C. Wallwork, Acta Cryst. B 34 (1978) 3604–3608.
[25] Z. Chen, Ph.D. dissertation, Cleveland State University, 1993.
[26] J. Vandendriessche, P. Palmans, S. Toppet, N. Boens, F.C. De Schryver, H.
Masuhara, J. Am. Chem. Soc. 106 (1984) 8057–8064.
[27] H. Masuhara, J. Mol. Struct. 126 (1985) 145–158.
[28] H. Masuhara, N. Tamai, N. Mataga, F.C. De Schryver, J. Vandendriessche, J. Am.
Chem. Soc. 105 (1983) 7256–7262.
[29] T. Fushimi, H. Ohkita, S. Ito, M. Yamamoto, Macromolecules 35 (2002) 9523–
9528.
[30] S. Komamine, M. Fujitsuka, O. Ito, A. Itaya, J. Photochem. Photobiol. 135 (2000)
111–117.
The stereochemistry of the sole isomer of 2,4-di(N-carbazol-
yl)pentane prepared according to the procedure reported previ-
ously is established to be meso. The magnitude of puckering
about the nitrogen atoms is in line with that reported for other car-
bazole-containing structures and likely results more from crystal-
lographic packing forces than from intramolecular interactions
for N1, consistent with the calculation of a low energy barrier for
partial pyramidalization. Theoretical M06-2X treatment for the
gaseous molecule shows a local potential-energy minimum in
good agreement with the observed torsion angles for the anti,
gauche geometry for placement of the two carbazolyl groups. This
implies that the molecular asymmetry, present at both the theoret-
ical local and global potential-energy minima, is not only a crystal-
packing effect, with dispersion forces having a significant influ-
[31] Y. Tsujii, A. Tsuchida, M. Yamamoto, T. Momose, T. Shida, J. Phys. Chem. 95
(1991) 8635–8640.