Molecular modeling and experimental studies on structure and NMR parameters of 9-benzyl-3,6-diiodo-9H-carbazole

Article abstract of DOI:10.1007/s11224-014-0554-8

Abstract A combined experimental and theoretical study has been performed on 9-benzyl-3,6-diiodo-9H-carbazole. Experimental X-ray (100.0 K) and room-temperature ¹³C nuclear magnetic resonance (NMR) studies were supported by advanced density fun

Full text of DOI:10.1007/s11224-014-0554-8

Struct Chem
DOI 10.1007/s11224-014-0554-8
ORIGINAL RESEARCH
Molecular modeling and experimental studies on structure
and NMR parameters of 9-benzyl-3,6-diiodo-9H-carbazole
•
Klaudia Radula-Janik Teobald Kupka
•
•
•
Krzysztof Ejsmont Zdzisław Daszkiewicz
Stephan P. A. Sauer
Received: 9 December 2014 / Accepted: 16 December 2014
Ó The Author(s) 2015. This article is published with open access at Springerlink.com
Abstract A combined experimental and theoretical study
has been performed on 9-benzyl-3,6-diiodo-9H-carbazole.
Experimental X-ray (100.0 K) and room-temperature 13C
nuclear magnetic resonance (NMR) studies were supported
by advanced density functional theory calculations. The
non-relativistic structure optimization was performed and
the 13C nuclear magnetic shieldings were predicted at the
relativistic level of theory using the zeroth-order regular
approximation. The changes in the benzene and pyrrole
rings compared to the unsubstituted carbazole or the parent
molecules were discussed in terms of aromaticity changes
using the harmonic oscillator model of aromaticity and the
nucleus independent chemical shift indexes. Theoretical
relativistic calculations of chemical shifts of carbons C3
and C6, directly bonded to iodine atoms, produced a rea-
sonable agreement with experiment (initial deviation from
experiment of 41.57 dropped to 5.6 ppm). A good linear
correlation between experimental and theoretically pre-
dicted structural and NMR parameters was observed.
Graphical Abstract
Keywords 9-Benzyl-3,6-diiodo-9H-carbazole ꢀ X-ray
structure ꢀ 13C NMR spectra ꢀ ZORA ꢀ GIAO NMR
calculations ꢀ HOMA ꢀ NICS
Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s11224-014-0554-8) contains supplementary
material, which is available to authorized users.
Carbazole and its derivatives have been of special interest
because of their unique photoconductive [1] and optical
properties [2]. Polymers containing carbazole moiety are
very promising new materials [3] and are widely used in
electronics and photonics [4–7]. Due to their interesting
properties, the chemistry of carbazole derivatives has been
studied at length [8–10]. One of the most common carba-
zole derivatives applied in electrophotographic [8] is poly
(N-vinylcarbazole). The 3,6- and 2,7-substituted carbazole
K. Radula-Janik ꢀ T. Kupka (&) ꢀ K. Ejsmont ꢀ Z. Daszkiewicz
Faculty of Chemistry, Opole University, 48, Oleska Street,
45-052 Opole, Poland
e-mail: teobaldk@gmail.com
S. P. A. Sauer (&)
Department of Chemistry, University of Copenhagen,
Universitetsparken 5, 2100 Copenhagen, Denmark
e-mail: sauer@kiku.dk
123

Struct Chem
derivatives are currently among the most widely studied
materials [11–15]. It is known that the presence of heavy
atoms (Cl and Br) decreases the relative quantum yield of
fluorescence and increases phosphorescence in the carba-
zole derivatives [16]. Bonesi [17] observed the same effect
in carbazole modified by Cl and Br at positions 3 and 3, 6
in a solid matrix. Finally, in a work of Safoula [18] an
increase in conductivity by molecular doping with iodine
was observed.
showed a clear divergence between the structural, elec-
tronic, and magnetic measures, so it is important to use
different aromaticity indexes to quantify this property. The
HOMA is a structurally based measure of aromaticity. It
was defined by Kruszewski and Krygowski [49, 50] as
X
a
n
2
HOMA ¼ 1 ꢁ
ðRopt ꢁ RiÞ ;
ð1Þ
i¼1
n
where n is the number of included bonds with bond lengths
Ri, and a is an empirical constant chosen in such a way that
HOMA = 0 for a model non aromatic system, and
HOMA = 1 for a system with all bonds equal to an optimal
value Ropt, assumed to be achieved for fully aromatic sys-
tems. The HOMA index has been found to be among the
most effective structural indicators of aromaticity. Another
way to show the aromaticity of a compound is the widely
employed nucleus independent chemical shift (NICS),
which was defined by Schleyer et al. [51] as the negative
value of the absolute shielding computed at the ring center,
or at some other interesting geometrical point of the system.
In common use, there are three variants: NICS(0) calculated
Experimental nuclear magnetic resonance (NMR) stud-
ies are widely used to characterize the geometrical and
electronic structure of isolated compounds, their solute–
solute and solute–solvent interactions in solution. Nowa-
days, the assignment of experimental spectra is often
supported by molecular modeling of the relevant NMR
parameters [19–21], as it is possible to predict satisfactory
chemical shifts for several different nuclei including 13C,
17O, 15N, and 19F [19, 22–25] using density functional
theory (DFT) calculations in combination with gauge
including atomic orbitals (GIAOs [26, 27]) and employing
the Becke three-parameter, Lee–Yang–Parr (B3LYP [27,
28]) or the hybrid half-and-half (BHandHLYP) exchange
correlation functionals [29]. Several NMR reports on the
simplest carbazoles are available [30–33]. However, sys-
tematic studies of the correlation between the molecular
structure of carbazoles and their NMR parameters are
lacking in the literature. The presence of a fairly heavy
nucleus (here iodine) in a molecule affects the NMR
properties of the neighboring light atom (close in space or
directly connected H, C, N atoms). This effect was
˚
at the ring plane, NICS(1) calculated 1 A above the plane,
and its zz-tensor component, NICS(1)zz, where the z-axis is
a normal to the plane. Rings with large negative NICS
values are considered to be aromatic and the more negative
the NICS value is the more aromatic the rings are.
Keeping in mind the above facts, we aimed to synthesize
and characterize a very specific carbazole derivative con-
taining two iodo-substituents. Its crystal structure and
NMR spectra are not yet described in the literature. This
paper presents thus the first report on crystal structure of
9-benzyl-3,6-diiodo-9H-carbazole and its 13C NMR
parameters in CDCl3 solution. We compare the experi-
mental low temperature X-ray (100.0 K) and room-tem-
perature NMR data with the DFT-calculated geometry of a
single molecule in the gas phase and its carbon shifts cal-
culated using standard non-relativistic and the relativistic
ZORA approach. The changes in aromaticity in 9-benzyl-
3,6-diiodo-9H-carbazole compared to free carbazole, ben-
zene, and pyrrole are also discussed via the structural
HOMA and magnetic NICS measures.
¨
described by Pyykko et al. [34] as the heavy-atom-on-light-
atom (HALA) effect. Ziegler, Autschbach and Arc-
isauskaite [35–41] reported on several relativistic calcula-
tions of NMR shieldings. In the work of Pecul et al. [42]
the importance of inclusion of the HALA effect on 13C
shielding constants in organomercury compounds and
halogen derivatives was discussed. They observed large
spin–orbit (SO) contributions to the HALA effects in the
halogen substituted compounds, which were well repro-
duced using zeroth-order regular approximation with SO
coupling (SO ZORA [43–45]) while these effects could not
be recovered using relativistic effective core potentials
´
(ECP [46]) on the halogen atoms. The study of Wodynski
Experimental
and Pecul [47] described the influence of heavy atom on
the spin–spin coupling constants between two light nuclei
in organometallic compounds and halogen derivatives.
Another main factor related to the structural and elec-
tronic parameters of carbazoles and resulting in their dif-
ferent chemical properties is aromaticity. This chemical
property can be analyzed in several ways: via structurally
(harmonic oscillator model of aromaticity), electronically
(PDI—para-delocalization index), and magnetically
(NICS) based indices. The work of Poater et al. [48]
Synthesis
3,6-Diiodo-9H-carbazole was obtained according to the
procedure described by Chuang et al. [52]. A solution
containing 16.7 g (0.1 mol) of 9H-carbazole, 21.6 g
(0.13 mol) of KI, 21.4 g (0.1 mol) of KIO3, 150 cm3 of
acetic acid, and 15 cm3 of water was heated for 48 h on a
water bath at 80 °C. After cooling to the room temperature,
123

Struct Chem
Theoretical calculations
the precipitate was filtered off and washed with water,
saturated Na2CO3 solution, and methanol. The crude
product was crystallized from toluene. The yield was 25 g
of 3,6-diiodo-9H-carbazole (mp = 206–207 °C; Ed.
60 %).
The geometric parameters of the isolated molecule were
obtained from an unconstrained optimization using the
B3LYP density functional [27, 28, 56] and a flexible
6-311++G(3df,2pd) basis set for C, N and H, and the
smaller 6-311G** basis set for iodine. The subsequent
vibrational analysis at the same level of theory showed no
imaginary frequencies indicating a true energy minimum.
These traditional non-relativistic calculations were carried
out using Gaussian 09 [57]. In the subsequent steps, the
non-relativistic geometry has been used both for typical
non-relativistic shielding calculations with the BHandH-
LYP half-and-half hybrid functional [29] and for the rela-
tivistic shielding calculations employing the zeroth-order
regular approximation Hamiltonian, including the SO
coupling term (SO ZORA) [58]. For consistence, all NMR
parameters were obtained with Amsterdam density func-
tional (ADF) program [59]. In this case, we employed the
DZP-, TZ2P-, and QZ4P STO-type basis sets. However, we
are aware that slightly better agreement between theoretical
and experimental NMR parameters could be obtained using
optimized structures at the same level of theory [60].
Theoretical chemical shifts (in ppm) were referenced to
benzene calculated at the same level of theory.
The preparation of 9-benzyl-3,6-diiodo-9H-carbazole is
shown in Scheme 1.
To the intensively stirred solution of 2 g (4.77 mmol) of
3,6-diiodo-9H-carbazole in DMSO (30 ml) and tetrabu-
tylammonium iodide (0.2 g), 50 % aqueous KOH solution
(2 ml) was added and treated dropwise with 1.9 cm3
(16 mmol) of benzyl bromide in DMSO (10 ml). After two
hours the mixture was poured into water (100 ml). The
precipitate was dissolved in methylene chloride (30 ml)
and dried with anhydrous MgSO4. After evaporation of the
solvent, the residue (2.35 g) was crystallized from 20 cm3
of acetone. The yield was 2.2 g of 9-benzyl-3,6-diiodo-9H-
carbazole (mp = 175–176 °C; Ed. 90.5 %).
The crystals suitable for X-ray analysis of 9-benzyl-3,6-
diiodo-9H-carbazole were obtained by slow evaporation of
a saturated solution in chloroform.
Characterization
The single crystals of 9-benzyl-3,6-diiodo-9H-carbazole
were used for data collection at 100.0(1) K on a four-circle
Oxford Diffraction Xcalibur diffractometer equipped with
a two-dimensional area CCD detector with the graphite
The HOMA and NICS indexes of aromaticity were
calculated in Gaussian 09 at the same level as the geometry
optimization.
˚
monochromatised MoKa radiation (k = 0.71073 A) and
the x-scan technique. Integration of the intensities and
correction for Lorenz and polarization effects were per-
formed using the CrysAlis RED software [53]. Crystal
structures were solved by direct methods and refined by a
full-matrix least-squares method on F2 using the SHELXL-
97 program [54]. Complete crystallographic details are
available as a supplementary material, and have been
deposited at the Cambridge Crystallographic Data Centre
(CCDC 990604) CCDC [55]. Any request to the CCDC for
this material should quote the full literature citation. The
room-temperature 13C NMR spectra in CDCl3 solution
were measured using Bruker Ultrashield 400 MHz NMR
spectrometer operating at 100.663 MHz for carbon nuclei
at ambient temperature and referenced to tetramethylsilane
(TMS) as internal standard.
Results and discussion
Crystal structure
The molecular structure of 9-benzyl-3,6-diiodo-9H-carba-
zole, the atomic numbering and ring labeling schemes are
presented in Fig. 1. The packing arrangement in the crystal
state is presented in Fig. 2. The molecular structure of
9-benzyl-3,6-diiodo-9H-carbazole consists of two units: the
carbazole unit containing atoms C1–C9A and the benzyl
unit containing atoms C10–C16.
The crystal data measured at 100 K and refinement
parameters are summarized in Table 1. The interatomic dis-
tances between iodine atoms in neighboring molecules are
given in Table 2 and selected bond lengths in Table 3. For
brevity, all experimental bond distances, bond angles, and
torsion angles within this compound are given in Tables S1,
S2, and S3 in the Supplementary Material. The value of
iodine–iodine distance coincides well with their van der Waals
I
I
I
I
PhCH2Br
DMSO
N
H
N
˚
radius proposed by Bondi (1.98 A [61]) or Bastanov (2.1 A
˚
CH2Ph
˚
[62, 63]). Thus, the intermolecular IꢀꢀꢀI contact of 3.9558(3) A
419.00 g/mol
508.93 g/mol
in the crystal structure of the title compound is about twice the
iodine van der Waals radius (see Table 2; Fig. 2).
Scheme 1 Synthesis of 9-benzyl-3,6-diiodo-9H-carbazole
123

Struct Chem
apparent from Table S1. Therefore, we will limit the dis-
cussion of theoretical bond lengths to C–C, C–N, and C–I
only (see Table 3). All measured bond lengths and angles
are within normal ranges and fairly similar to distances
reported earlier for 9-benzyl-9H-carbazole X-ray structure
[65] (see Table 3). For better illustration of the quality of
predictions in the gas phase, we compared in Fig. 3 the
theoretical (non-relativistic) bond lengths with experi-
mental values obtained from X-ray measurement at low
temperature. A good agreement between theoretical and
experimental interatomic distances of 9-benzyl-3,6-diiodo-
9H-carbazole is apparent from a perfect linear correlation
between theory and experiment (y = 1.0415x–0.0535,
R2 = 0.9998), see Fig. 3).
The structural parameters obtained at the ZORA
(B3LYP/DZP/TZP level of theory) are of similar accuracy
to the results of the non-relativistic calculations, but they
are more time-consuming and we will not consider them in
future studies. The differences between theoretical and
experimental C–C and C–N bond lengths are in the range
Fig. 1 The molecular structure of 9-benzyl-3,6-diiodo-9H-carbazole,
showing the atom numbering scheme and the ring labeling.
Displacement ellipsoids are drawn at the 50 % probability level
˚
of 0.013–0.001 A. For the C–I bond the difference is
˚
higher (in the range of 0.03–0.04 A). All geometric data for
the studied carbazole derivative correlate also well with the
corresponding values found in the crystal structure of the
It is well known that X-ray crystallography determines
accurately bond lengths between non-hydrogen atoms and
significantly underestimates C–H bonds [64]. This is also
non-halogenated
Table 3).
9-benzyl-9H-carbazole
[65]
(see
Fig. 2 A packing diagram for
9-benzyl-3,6-diiodo-9H-
carbazole
123

Struct Chem
Table 1 Crystallographic data for 9-benzyl-3,6-diiodo-9H-carbazole at 100 K
9-Benzyl-3,6-diiodo-9H-carbazole
Chemical formula
Mr
C19 H13 I2 N
509.10
Cell setting, space group
Temperature (K)
Monoclinic, P21/n
100.0 (1)
˚
a, b, c (A)
4.20240 (10), 18.8796 (3), 20.3862 (3)
b (o)
92.8680 (10)
3
V (A )
˚
1615.41 (5)
Z
4
Dx (mg m-3
Radiation type
l (mm-1
)
2.093
MoKa
)
3.889
Crystal size (mm)
0.30 9 0.28 9 0.26
No. of measured, independent, and observed reflections
9726/2806/2707
Rint
0.0146
-1
)
˚
(sinh/k)max (A
0.595
R [F2 [ 2r(F2)], wR (F2), S
No. of reflections
0.0186, 0.0405, 1.303
2,806
No. of parameters
No. of restrains
200
0
H-atom treatment
Weighting scheme
H atoms treated by a mixture of independent and considered refinement
w = 1/[r2(Fo2) + (0.0131P)2 + 1.9288P] where P = (Fo2 + 2F2c)/3
0.393, -0.379
-3
]
˚
Dqmax, Dqmin [e A
˚
earlier results for halogen-substituted carbon atoms [15, 35,
42]. The other carbons, however, do practically not feel the
presence of the heavy halogen atoms.
Table 2 Experimental iodine–iodine distance (in A) for 9-benzyl-
3,6-diiodo-9H-carbazole in the solid state at 100 K
D–IꢀꢀꢀA
d(D–I)
d(IꢀꢀꢀA)
C(3)–I(1)ꢀꢀꢀI(1)i
Symmetry transformations used to generate equivalent atoms:
i = 1-x, 2-y, -z
2.103
3.9558(3)
HOMA and NICS indexes
The calculated HOMA and NICS values are gathered in
Table 5. HOMA indexes were calculated from Equation (1)
˚
using a = 257.7 and Ropt (CC) = 1.388 A [66] and bond
13C NMR chemical shift
lengths from B3LYP/6-311++G(3df,2pd) optimized geom-
etries. For comparison, the corresponding HOMA values for
benzene and pyrrole, calculated at the same level of theory
are 0.998 and 0.772. The most aromatic ring within the
studied molecule is the benzyl unit (D): HOMA = 0.996.
The two benzene rings of the carbazole moiety (A and C) are
very similar (0.960 and 0.962). The aromaticity of these
rings is higher than in the parent unsubstituted carbazole
molecule (HOMA = 0.919). The least aromatic is the pyr-
rolic unit (ring B). In comparison to the parent pyrrole, the
five-membered ring B is significantly less aromatic (0.446)
than in the pyrrole molecule (0.772) or in the unsubstituted
carbazole (0.679).
All experimental and calculated 13C chemical shifts of the
studied carbazole are collected in Table 4. It is apparent
that a very significant HALA effect of about -42 ppm is
only present for the C3 and C6 carbons directly bond to
iodine atoms.
Thus, the non-relativistic calculations of C3 and C6
chemical shifts lead to significant errors with a root mean
square deviation (RMS) of 12.85 ppm (for SO ZORA
calculations RMS = 3.34 ppm, see Table 4 and Fig. 4). It
is also apparent from Fig. 4 that the spin–orbit effects
played a major role in the calculations of chemical shifts of
carbon atoms directly attached to the halogen atom (here
iodine). The observed HALA effects are very close to
Apart from HOMA, in Table 5 are also gathered the
results for the three variants of the NICS parameter,
123

Struct Chem
Table 3 Comparison of
selected geometric data for
9-benzyl-3,6-diiodo-9H-
Bond
X-ray
NR DFT
ZORA DFT
9-Benzyl-9H-carbazole (X-ray) [65]
I(1)–C(3)
2.103(3)
2.097(3)
1.384(4)
1.391(4)
1.401(4)
1.376(4)
1.397(4)
1.414(4)
1.444(4)
1.397(4)
1.413(4)
1.378(4)
1.402(4)
1.385(4)
1.393(4)
1.387(3)
1.388(3)
1.458(3)
1.512(4)
1.390(4)
1.392(4)
1.390(4)
1.385(4)
1.386(4)
1.388(4)
2.135
2.135
1.391
1.395
1.403
1.389
1.398
1.417
1.447
1.398
1.418
1.389
1.403
1.391
1.396
1.390
1.389
1.451
1.523
1.395
1.399
1.395
1.393
1.395
1.393
0.012
2.135
2.135
1.387
1.389
1.398
1.383
1.394
1.411
1.443
1.413
1.413
1.383
1.397
1.387
1.389
1.383
1.383
1.443
1.517
1.390
1.394
1.390
1.388
1.387
1.390
0.012
–
˚
carbazole (A) and 9-benzyl-9H-
I(2)–C(6)
–
˚
carbazole (A) obtained from
X-ray measurements at 100 K
and calculated via non-
relativistic (NR) B3LYP/6-
311++G(3df,2pd)/6-311G**
and relativistic ZORA/DZP/
TZP geometry optimizations
C(1)–C(2)
1.383(5)
1.04(3)
1.396(4)
1.380(5)
1.395(4)
1.410(4)
1.442(4)
1.398(4)
1.401(4)
1.372(4)
1.401(4)
1.377(4)
1.398(4)
1.391(4)
1.381(4)
1.458(4)
1.509(4)
1.393(4)
1.384(4)
1.386(4)
1.379(5)
1.379(5)
1.387(4)
0.073
C(1)–C(9A)
C(2)–C(3)
C(3)–C(4)
C(4)–C(4A)
C(4A)–C(9A)
C(4A)–C(5A)
C(5A)–C(5)
C(5A)–C(8A)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(8A)
C(8A)–N(9)
N(9)–C(9A)
N(9)–C(10)
C(10)–C(11)
C(11)–C(12)
C(11)–C(16)
C(12)–C(13)
C(13)–C(14)
C(14)–C(15)
C(15)–C(16)
RMS
RMS values are marked using
bold font
benzene, calculated at B3LYP/6-311++G(3df,2pd) level of
theory (-7.81, -10.21, and -29.88). The calculated NICS
indexes prove (confirm) the aromaticity of all rings in the
studied compound (see Table 5; Fig. 5).
Interestingly, examining the above results it is evident
that the most sensitive marker of aromaticity is NICS(1)zz.
Following the theory, that the more negative the NICS
value the more aromatic the ring is, it is apparent from
Fig. 5 that NICS(0) calculated for pyrrole, 9H-carbazole,
and 9-benzyl-3,6-diiodo-9H-carbazole predicts more aro-
matic rings than for benzene. The other two variants
NICS(1) and NICS(1)zz, however, show a different pattern.
Based on NICS(1)zz only the pyrrole ring is more aromatic
than benzene in complete contrast to the HOMA index.
Also the zz-component of NICS(1) indicates that the
addition of the benzyl ring and the two iodine atoms sig-
nificantly affects the aromaticity of carbazole. In compar-
ison to pristine carbazole, the aromaticity of the benzene
rings (A and C) of 9-benzyl-3,6-diiodo-9H-carbazole are
slightly different. This could reflect the effect of specific
twisting of benzyl ring to one of the benzene ring of car-
bazole moiety.
Fig. 3 Linear correlation between theoretical (predicted at B3LYP/6-
311++G(3df,2pd) level, and 6-311G** for iodine atom) and exper-
imental bond lengths for 9-benzyl-3,6-diiodo-9H-carbazole
collected for the studied carbazole derivative and for sev-
eral related compounds. For a direct reference of aroma-
ticity, we show the corresponding NICS values for
123

Struct Chem
Table 4 Comparison of
Theoretical calculations
Experimental data
experimental and theoretically
calculated 13C NMR chemical
shifts (in ppm) at BHandHLYP/
DZP level of theory using scalar
ZORA, spin–orbit ZORA, and
non-relativistic approaches
Atom numbering
NR
SR ZORA
SO ZORA
C1, 8
112.35
137.64
123.80
131.64
127.21
144.32
47.89
112.18
137.1
112.48
137.94
87.83
111.08
134.70
82.23
C2, 7
C3, 6
C4, 5
127.89
131.07
127.12
144.17
47.98
132.34
127.38
143.89
47.94
129.33
127.74
139.62
46.56
C4A, 5A
C8A, 9A
C10
C11
140.74
128.40
130.43
128.81
12.85
140.82
128.38
130.57
128.77
14.04
140.78
128.37
130.40
128.75
3.34
136.10
124.05
128.88
126.18
Both the carbon shieldings
experiencing HALA effect and
RMS values are marked using
bold font
C12, 16
C13, 15
C14
SR ZORA scalar ZORA, NR
non-relativistic
RMS
Conclusions
A combined experimental and theoretical study has been
performed on 9-benzyl-3,6-diiodo-9H-carbazole. For the
first time its crystal structure was determined at 100 K and
the room-temperature 13C NMR spectrum in CDCl3 solu-
tion was measured. The B3LYP/6-311++G(3df,2pd) cal-
culated gas-phase geometry was close (not identical) to the
X-ray measured structure in the solid state. The observed
IꢀꢀꢀI contact distances in the crystal structure were
˚
3.9558(3) A and no H-bonding was observed.
It was essential to employ the relativistic SO ZORA
approach in the chemical shift calculations to reproduce the
experimental chemical shift of carbons C3 and C6 (a very
large HALA effect of -42 ppm was calculated). Finally, we
observed a good linear correlation between experimental
and theoretically predicted structural and NMR parameters.
The aromaticity of individual rings was determined by
calculations of structural (HOMA) and magnetic (NICS)
Fig. 4 Deviation of theoretically calculated non-relativistic (NR) and
relativistic (scalar ZORA and spin–orbit ZORA) 13C chemical shifts
(Dd in ppm) from experimental data measured for 9-benzyl-3,6-
diiodo-9H-carbazole in CDCl3 solution at room temperature
Table 5 Comparison of
HOMA and selected NICS
Compound
Ring
HOMA
NICS(0)
NICS (1)
NICS (1)zz
values for individual rings in
9-benzyl-3,6-diiodo-9H-
carbazole with benzene, pyrrole,
and 9H-carbazole
9-Benzyl-3,6-diiodo-9H-carbazole
A
B
C
D
A
B
C
A
B
C
0.962
0.446
0.960
0.996
0.919
0.679
0.919
–
-9.93
-9.18
-8.40
-7.96
-12.95
-10.24
-12.95
-9.18
-8.80
-9.18
-13.47
-7.81
-9.45
-7.66
-8.65
-9.55
–
-26.68
-21.62
-24.22
-21.97
–
9H-Carbazolea
9H-Carbazole
–
–
–
–
-10.48
-8.47
-10.48
-10.26
-10.21
-1.46
-1.20
-1.46
-32.10
-29.88
–
–
For the labeling of the rings see
Fig. 1
Pyrrole
0.772
0.998
Benzene
a
Values taken from Ref. [48]
123

Struct Chem
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scholarship under a project financed out of the European Social Fund.
Teobald Kupka, Zdzisław Daszkiewicz, Krzysztof Ejsmont and
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and software in the Supercomputing and Networking Center ACK
CYFRONET AGH in Krakow (Grant No. MNiSW/SGI3700/
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Center in Wrocław are also acknowledged. Stephan P.A. Sauer
acknowledges support from DCSC and the Lundbeck foundation.
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