Isomer specific synthesis using the Suzuki-coupling. Polychlorinated terphenyls as standards for environmental analysis

Article abstract of DOI:10.1016/S0045-6535(02)00647-1

Defined polychlorinated terphenyl (PCT) single congeners as reference standards are the prerequisite for the development of analytical methods for their determination and quantification in the environment. The selective synthesis of PCTs for environmental

Full text of DOI:10.1016/S0045-6535(02)00647-1

Chemosphere 50 (2003) 1151–1156
www.elsevier.com/locate/chemosphere
Isomer specific synthesis using the Suzuki-coupling.
Polychlorinated terphenyls as standards
for environmental analysis
a,
a
a
a
M. Bahadir *, A. Pieper , R. Vogt , H. Wichmann ,
b
J. Grunenberg , H. Hopf
b
a
Institute of Ecological Chemistry and Waste Analysis, TU Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany
b
Institute of Organic Chemistry, TU Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany
Received 25 April 2002; received in revised form 23 September 2002; accepted 2 October 2002
Abstract
Defined polychlorinated terphenyl (PCT) single congeners as reference standards are the prerequisite for the de-
velopment of analytical methods for their determination and quantification in the environment. The selective synthesis
of PCTs for environmental analytical purposes by application of the Suzuki-coupling reaction is described. Under easily
modified standard reaction conditions of this coupling process the PCTs can be obtained by reaction of benzeneboronic
acids with dibromobenzenes mostly in good yields, as described by the synthesis of following PCT congeners: p-PCT
(3,300,5,500-tetrachloro-, 2,200,4,400-tetrachloro-, 20,3,300,5,500-pentachloro-); m-PCT (3,300,5,500-tetrachloro-) and o-PCT
(3,300,5,500-tetrachloro-). The terphenyl congeners were characterized by NMR (1H, 13C)- and FT-IR-spectroscopy.
Their purity was checked by GC/MS analysis. The experimental and quantum-chemically calculated FT-IR-spectra
were compared and it was shown, that the determination of the chlorine substitution pattern in the terphenyl congeners
by their typical absorption spectra is possible.
Ó 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Polychlorinated terphenyls; PCT; Suzuki-coupling; Regioselective synthesis; Environmental analysis; Single congeners;
Reference standards
1. Introduction
patterns of PCT were similar to those of PCBs due to
similar chemical and physical properties of both sub-
stance groups, such as high chemical stability, high heat
capacity, excellent dielectric properties, etc., why they
were, for instance, used in transformers. But in con-
trast to the PCBs they were predominantly applied in so-
called open systems for coatings, as insulating paints
for wires and flame retarding paintings (Birn and Jung,
1993). From the former application fields as well as
from landfills PCTs are emitted into the environment
as low volatile, persistent, and bioaccumulating sub-
stances.
Starting from 1955 about 60,000 tons of polychlori-
nated terphenyls (PCT) were manufactured in different
countries, whereas production was largely stopped at the
beginning of the 1980s. The total production quantity
was 15–20 times lower than that of the PCBs, which
does not diminish, however, their environmental toxi-
cological relevance (de Boer, 2000). The application
* Corresponding author. Tel.: +49-531-391-5960; fax: +49-
531-391-5799.
E-mail address: m.bahadir@tu-bs.de (M. Bahadir).
Analytical investigation of PCTs in environmental
samples has so far hardly been performed, due to the
0045-6535/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved.
PII: S0045-6535(02)00647-1

1152
M. Bahadir et al. / Chemosphere 50 (2003) 1151–1156
huge number of congeners compared with the PCBs
(max. 209). The introduction of a third phenyl-ring in
ortho-, meta- or para-position leads to different terphe-
nyl basic structures with different planes of symmetry.
The resulting numerous substitution patterns for chlo-
rine atoms cause a large variety of isomers within each
series. The more than 8.500 possible PCT-congeners
(Remberg et al., 1998) could not be separated by com-
mon gas chromatographic techniques so far. Further-
more, excepting a few special cases, pure reference
standards are not available, which are, of course, nec-
essary for the development of suitable analytical meth-
ods. Because of the lacking analytical approaches the
toxicological and ecotoxicological behavior of PCT
congeners has only been examined to a small extent, and
just a few data are available for these substances.
Therefore, published data in the literature on the oc-
currence of PCT must be dealt with utmost care due to
the large variation of analytical procedures and calcu-
lation methods used (Gallagher et al., 1993; Wester et al.,
1996; Fernandez et al., 1998). Concerning their toxicity
similar properties as dioxins can be expected, particu-
larly for coplanar congeners.
further improve the analytical approaches for purposes
of environmental monitoring, and to investigate the
(eco)toxicological behavior of the PCTs. The procedure
should be suitable to generate a broad substitution
pattern in just a few reaction steps.
Some suitable reactions to attach C–C bonds to
aromatics, are the Ullmann reaction (Fanta, 1974), the
Cadogan reaction (Cadogan et al., 1962). These proto-
cols have already been used for the synthesis of indi-
vidual PCB congeners. However, they have substantial
disadvantages since in many cases only low to moderate
yields are obtained and numerous by-products are
formed. For the synthesis of specific PCT congeners
according to these transformations an even less fa-
vourable situation can be expected.
More recent route to construct aryl systems is pro-
vided by the Suzuki-coupling, where a palladium-cata-
lyzed cross-coupling reaction of substituted aromatics is
used (starting material 1: benzeneboronic acid, starting
material 2: halogen aromatic). This reaction (Miyaura
et al., 1981) has already been applied successfully for the
synthesis of various PCBs (Lehmler and Robertson,
2001), yielding PCBs in good yields with only few by-
products.
Besides the technical mixtures of different degree of
chlorination only 14 specific PCT congeners are com-
mercially available as single standards. These are cong-
eners with a low degree of chlorination (1–5 chlorine
atoms) and the three perchlorinated isomers, respec-
tively (4-chloro-o-terphenyl, 4-chloro-p-terphenyl, 2,
4-dichloro-p-terphenyl, 2,5-dichloro-o-terphenyl, 2,5-
dichloro-m-terphenyl, 2,5-dichloro-p-terphenyl, 2,400,5-
trichloro-p-terphenyl, 2,4,6-trichloro-p-terphenyl, 2,3,
5,6-tetrachloro-p-terphenyl, 2,4,400,6-tetrachloro-p-ter-
phenyl, 2,3,4,5,6-pentachloro-p-terphenyl, tetradeca-
chloro-o-terphenyl, tetradecachloro-m-terphenyl, and
tetradecachloro-p-terphenyl).
Chittim et al. (1977) synthesized 22 PCT-congeners
by diazotization of a biphenyl amine, which reacted in a
further step with a chlorobenzene to the terphenyl. A
disadvantage of this procedure is, in fact, that a large
excess of chlorobenzene has to be applied. Still, product
mixtures are obtained in case of unsymmetrical chloro-
benzenes. Furthermore, the possible variety of substi-
tution patterns is comparably small, as they essentially
depend on the chlorobenzene utilized. Direct chlorina-
tion of the unsubstituted terphenyl basic structures (o-,
m-, p-terphenyl, C18H14) as starting materials is less
suitable, because specific positions are chlorinated
preferentially due to the regioselectivity, but again not
with sufficient selectivity. Numerous substitution pat-
terns cannot be realized by this route. Additionally, the
separation of the various product mixtures into indi-
vidual congeners will be most difficult.
It was the aim of the investigation presented here
to transfer this principle from PCB to PCT synthesis
and to study the isomer specific syntheses of tetra-
and pentachlorinated terphenyls by the Suzuki-coupling
of different chlorinated benzeneboronic acids with
dibromobenzenes and dibromochlorobenzenes. The raw
and recrystallized products should be characterized by
chromatographic and the usual spectroscopic methods
(GC/MS, 1H and 13C NMR, and FT-IR analysis) to
explore whether this strategy is applicable for the syn-
thesis of a wide variety of specific PCT congeners.
Therefore, it was of special interest to examine whether
and to what extent steric and electronic features of the
substrates influence the reaction process.
2. Materials and methods
The chemicals used were 2,4-dichlorobenzeneboronic
acid, 3,5-dichlorobenzeneboronic acid, 1,2-dibromo-
benzene, 1,3-dibromobenzene, 1,4-dibromobenzene, 1,
4-dibromo-2-chlorobenzene and tetrakistriphenyl phos-
phine-palladium(0), all of them commercially available
with a purity of 97–98% (Lancaster Synthesis GmbH,
Acros Organics). Solvents were purchased from com-
mercial sources in p.a. quality (Merck AG).
All PCT congeners synthesized were characterized by
FT-IR and NMR (1H and 13C) and GC/MS analysis.
FT-IR-spectra (gas phase) were recorded on a Hewlett–
Packard GC 6890/FT-IR 5965 A, equipped with a HP-5,
30 m  0:32 mm column, film thickness 0.25 lm. Tem-
The primary goal of PCT synthesis is, therefore, to
synthesize well defined single isomers with regioselective
methods in acceptable yields, in order to develop, and to

M. Bahadir et al. / Chemosphere 50 (2003) 1151–1156
1153
perature program was 80 °C (2 min)–10 °C/min–300 °C
(20 min).
The quantum chemical simulation of the IR-spectra
3. Results and discussion
The selective formation of carbon–carbon bonds by
Suzuki-coupling is based on the presence of good leav-
ing groups in the starting materials (boric acid, bromine,
or iodine). This palladium-catalyzed cross-coupling re-
action tolerates a broad range of other functionalities in
the aromatic compounds compared with conventional
methods. If necessary, the reaction conditions can be
adopted specifically according to the substrates applied.
Afurther advantage of this method is that low toxic and
safe starting materials can be used for the syntheses.
The results of preliminary experiments carried out
are most encouraging. The described syntheses of the
polychlorinated terphenyls succeeded in an one-step re-
action in good yields. The chlorine substitution pattern
of the congeners obtained was determined by the choice
of the starting materials, whereby different chlorinated
benzeneboronic acids and halogenated aromatic com-
pounds could be combined like building blocks in an
construction system to the corresponding terphenyls.
In the reaction of 3,5-dichlorobenzeneboronic acid
with different dibromobenzene isomers effects of the
substitution pattern were studied. 1,3-dibromobenzene
and 1,4-dibromobenzene as starting materials led to the
corresponding m- and p-terphenyls in good yields.
In case of 1,2-dibromobenzene the corresponding o-
terphenyl was formed in poor yield only. It could even
not be isolated from the raw mixture. Under the stan-
dard reaction conditions of the Suzuki-coupling the re-
action led predominantly to an intermediate, which was
identified as 20-bromo-3,5-dichlorobiphenyl. The reason
for this incomplete coupling is likely the steric hindrance
of the second bromine atom in the ortho-position, the
replacement of which is difficult; this reaction step pre-
sumably occurs very slowly. In further experiments we
will vary the reaction conditions to increase the yield of
the o-terphenyl product.
were performed with the B3LYP/6-31G* implementa-
tion of Gaussian 98 program (Becke, 1993).
NMR-spectra were obtained on a Bruker AM 400 at
400.1 MHz (1H) and at 100.6 MHz (13C) resp., using
CDCl3 as solvent and TMS as internal standard. The
purity after recrystallization was >98% as determined as
relative peak area in GC/MS chromatogram. GC/MS
analyses was performed on a Shimadzu GC 17A/MS QP
5050 equipped with a DB 5 MS column, 25 m  0:25
mm, film thickness 0.25 lm in full scan mode. Tem-
perature program was 80 °C (2 min)–10 °C/min–300 °C
(20 min). HRMS-measurements were carried out on
MAT95, Thermofinniganmat, with a resolution of 10 000
(10%-valley-definition). The melting points were deter-
mined on a MEL-TEMP II apparatus and are uncor-
rected.
2.1. Common procedure for the synthesis of PCT
To a solution of 2.5 mmol dibromobenzene or di-
bromochlorobenzene, resp., and 180 mg of Pd(PPh3)4 (ꢀ3
mol%) in toluene (25 ml), 5 ml aqueous sodium car-
bonate (2 M) was added. Asolution of dichloroben-
zeneboronic acid (5 mmol) in 20 ml of ethanol was
added slowly under nitrogen atmosphere. This reaction
mixture was stirred at 80 °C for 20 h. To destroy unre-
acted boronic acid 1 ml of hydrogen peroxide (30%) was
added slowly after cooling to room temperature, and the
reaction mixture was stirred for additional 3 h. After
addition 10 ml of NaOH (1 M aq.) the reaction mixture
was extracted 5–6 times with each 50 ml of dichloro-
methane. In the case of 3,300,5,500-tetrachloro-p-terphenyl
each 100 ml of solvent were used 5–6 times, because of
the lower solubility of this substance. The organic phase
was washed three times with 20 ml of water and dried
over sodium sulfate. Then the solvent was removed
under reduced pressure, whereby the raw product pre-
cipitated as a solid. Purities of raw products were 75–
85%. The terphenyls were recrystallized from acetone/
cyclohexane. The purities of recrystallized terphenyls
were 97.8–99.6% (Table 1).
In case of ortho-substituted chlorinated starting ma-
terials (one chlorine atom in the benzeneboronic acid or
one in the bromobenzene) no negative effects caused by
steric hindrance were observed. The reaction worked
well without any problems. In the cross-coupling of 3,5-
dichlorobenzeneboronic acid with 1,4-dibromo-2-chloro-
benzene the terphenyl congener was obtained in good
Table 1
Educts and raw yields of syntheses performed
Benzeneboronic acid
Halogenated benzene
PCT congener
Raw yield (g/% Th.)
3,5-dichloro-
2,4-dichloro-
3,5-dichloro-
3,5-dichloro-
3,5-dichloro-
1,4-dibromo-
1,4-dibromo-
3,300,5,500-tetrachloro-p-terphenyl
2,200,4,400-tetrachloro-p-terphenyl
20,3,300,5,500-pentachloro-p-terphenyl
3,300,5,500-tetrachloro-m-terphenyl
3,300,5,500-tetrachloro-o-terphenyl
0:85=90
1:0=101
1,4-dibromo-2-chloro-
1,3-dibromo-
1,2-dibromo-
1:12=80
1:07=94
Not isolated

1154
M. Bahadir et al. / Chemosphere 50 (2003) 1151–1156
Fig. 1. Theoretically (B3LYP) calculated IR-spectrum (wave number in cmÀ1) of 3,300,5,500-tetrachloro-p-terphenyl (upper trace),
compared with experimental gas phase spectrum (lower trace).
yield also. In the combination of 2,4-dichlorobenzene-
boronic acid with 1,4-dibromobenzene the results were
almost identical.
loss of chlorine atoms. The four tetrachlorinated cong-
eners synthesized showed a very similar fragmentation.
The chlorine substitution pattern of the synthesized
terphenyl congeners could be proven by NMR and
FT-IR-spectroscopy. The high agreement between the
theoretically calculated and experimental IR-spectra
(Figs. 1 and 2) enables the identification of individual
congeners in product mixtures after gas chromato-
graphic separation by pattern recognition. Detailed as-
pects on the agreement of both IR-spectra will published
in a subsequent paper. The automatically identification
of terphenyls by a spectrum library of single reference
standards seems to be likely possible in the near future.
The by-products occurring in small quantities
showed a similar distribution pattern in all transforma-
tions. In most cases these compounds could be identified
by GC/MS analysis. Their formation can be easily un-
derstood. Predominantly there are self-coupling prod-
ucts (biphenyl derivatives) and triphenylphosphine oxide
(oxidation product of the catalyst) as the major impu-
rity. The formation of further biphenyl derivatives and
PCT congeners in very low concentration was observed.
These products are explained by partial loss of chlorine
substituents and their replacement by hydrogen in the
following reaction step. Rearrangements due to migra-
tion of chlorine atoms under the reaction conditions
appear to be insignificant.
4. Conclusions
The terphenyl congeners synthesized are colorless
powders or needles after purification. The highly sym-
metrical structured 3,300,5,500-tetrachloro-p-terphenyl is,
as expected, poorly soluble in organic solvents compared
with the other terphenyl congeners. The raw product
could easily be purified by washing off the impurities
with diethyl ether.
It could be shown that the Suzuki-coupling repre-
sents a suitable procedure for the selective synthesis of
defined PCT congeners. By selection of suitable starting
materials the isomeric o-, m- and p-terphenyls with a
great variety in degree of chlorination and substitution
pattern should be available in preparative yields. In a
series of experiments started already we will synthesize
further PCT congeners, describe their characteristic
features, and their fate and behavior in different envi-
ronmental compartments. The combination of experi-
mentally and quantum-chemically calculated IR-spectra
of reference standards synthesized is a powerful tool to
identify PCT congeners in different mixtures.
The solubility of the compounds increased with the
disturbance of the symmetric structure. The introduc-
tion of just a further chlorine atom into the 20-position in
20,3,300,5,500-pentachloro-p-terphenyl has a great influ-
ence on the solubility.
In the mass spectra of the chlorinated terphenyls the
molecule ion is the signal of highest intensity (base
peak), other typical fragment ions indicate the stepwise
Although dealing with the PCT family is a most
complex matter due to the huge number of congeners, in

M. Bahadir et al. / Chemosphere 50 (2003) 1151–1156
1155
Fig. 2. Theoretically (B3LYP) calculated IR-spectrum (wave number in cmÀ1) of 2,200,4,400-tetrachloro-p-terphenyl (upper trace),
compared with experimental gas phase spectrum (lower trace).
contrast to the analogous PCBs, we expect a renaissance
in PCT research once defined congeners as reference
standards become available.
A.2. 2,200,4,400-Tetrachloro-p-terphenyl
m.p.: 146–148 °C.
HRMS: calculated 365.9538; found: 365.9529.
GC/MS: Rt 21.84 min; m=z ¼ 368 [Mþ þ 2, 100%],
296 [Mþ À 2 Cl].
Appendix A
FTIR cmÀ1 (gas phase): 3041, 1897, 1743, 1587, 1549,
1513, 1465, 1375, 1141, 1103, 1006, 866, 813, 728, 563.
NMR-spectra:
Spectroscopic data of the PCT congeners synthe-
sized.
1
H
2
H
A.1. 3,300,5,500-Tetrachloro-p-terphenyl
Cl
5
8
4
6
7
7
3
1
2
m.p.: 227 °C.
Cl
Cl
HRMS: calculated 365.9538; found: 365.9531.
GC/MS: Rt 23.24 min; m=z ¼ 368 [Mþ þ 2, 100%],
296 [Mþ À 2 Cl].
H
H
H
Cl
34
34
2
FTIR cmÀ1 (gas phase): 3047, 2323, 1758, 1584, 1570,
1518, 1426, 1386, 1285, 1118, 1072, 872, 800, 681, 594.
NMR-spectra:
1H-NMR (400 MHz, in CDCl3): H-1: d ¼ 7:52 (ps-t,
2 H); H-2: d ¼ 7:49 (s, 4 H); H-3/H-4: d ¼ 7:33 (m, 4 H).
13C-NMR (100 MHz, in CDCl3): C-1: d ¼ 138:46; C-
2: d ¼ 137:82; C-3: d ¼ 133:90; C-4: d ¼ 133:20; C-5:
d ¼ 132:12; C-6: d ¼ 129:83; C-7: d ¼ 129:17; C-8:
d ¼ 127:25.
2
1
Cl
H
H
Cl
3
3
6
6
4
4
3
H
5
1
2
A.3. 20,3,300,5,500-Pentachloro-p-terphenyl
Cl
H
H
Cl
2
1
m.p.: 175 °C.
1H-NMR (400 MHz, in CDCl3): H-1: d ¼ 7:63 (s, 4
H); H-2: d ¼ 7:50 (d, J ¼ 1:84 Hz, 4 H); H-3: d ¼ 7:37
(t, J ¼ 1:84 Hz, 2 H).
HRMS: calculated 399.9147; found: 399.9131.
GC/MS: Rt 23.54 min; m=z ¼ 402 [Mþ þ 2, 100%],
330 [Mþ À 2 Cl].
13C-NMR (100 MHz, in CDCl3): C-1: d ¼ 143:24; C-
2: d ¼ 138:58; C-3: d ¼ 135:43; C-4: d ¼ 127:69; C-5:
d ¼ 127:50; C-6: d ¼ 125:56.
FTIR cmÀ1 (gas phase): 1582, 1569, 1499, 1422,
1377, 1288, 1251, 1118, 1097, 1073, 860, 801, 713, 686,
627.

1156
NMR-spectra:
M. Bahadir et al. / Chemosphere 50 (2003) 1151–1156
d ¼ 127:56; C-6: d ¼ 127:14; C-7: d ¼ 125:85; C-8:
d ¼ 125:75.
(The assignment of C4/C7 and C5/C6 can possibly be
7
1
3
Cl
H Cl
H
H
Cl
exchanged.)
6
6
12
12
7
8
9
14
14
5
5
11
2
4
3
1
10
4
5
H
H
References
13
Cl
H
H
H
H
Cl
7
6
2
3
Becke, A.D., 1993. Density-functional thermo chemistry.
III. The role of exact exchange. J. Chem. Phys. 98, 5648–
5652.
1H-NMR (400 MHz, in CDCl3): H-1: d ¼ 7:66 (d,
J ¼ 1:82 Hz, 1 H); H-2: d ¼ 7:495 (dd, J1 ¼ 8:00 Hz,
J2 ¼ 1:85 Hz, 1 H); H-3: d ¼ 7:47 (d, J ¼ 1:83 Hz, 2 H);
H-4: d ¼ 7:41 (t, J ¼ 1:88 Hz, 1 H); H-5: d ¼ 7:395 (t,
J ¼ 1:82 Hz, 1 H); H-6: d ¼ 7:39 (d, J ¼ 8:00 Hz, 1 H);
H-7: d ¼ 7:36 (d, J ¼ 1:86 Hz, 2 H).
€
Birn, H., Jung, G., 1993. Abfallbeseitigungsrecht fur die
betriebliche Praxis. Teil 18, Kap. 5: Polychlorierte Biphenyle
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13C-NMR (100 MHz, in CDCl3): C-1: d ¼ 141:94; C-
2: d ¼ 141:32; C-3: d ¼ 139:37; C-4: d ¼ 137:77; C-5:
d ¼ 135:61; C-6: d ¼ 134:73; C-7: d ¼ 133:05; C-8: d ¼
131:66; C-9: d ¼ 128:69; C-10: d ¼ 128:13; C-11: d ¼
128:07; C-12: d ¼ 127:98; C-13: d ¼ 125:70; C-14:
d ¼ 125:63.
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A.4. 3,300,5,500-Tetrachloro-m-terphenyl
ꢀ
ꢀ
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terphenyls in marine samples. Chemosphere 36, 2941–2948.
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D.A., 1993. Accumulation of polychlorinated terphenyls in
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26, 302–312.
m.p.: 205–207 °C.
HRMS: calculated 365.9538; found: 365.9530.
GC/MS: Rt 22.45 min; m=z ¼ 368 [Mþ þ 2, 100%],
296 [Mþ À 2 Cl].
FTIR cmÀ1 (gas phase): 3067, 2315, 1581, 1565, 1420,
1378, 1251, 1118, 1081, 998, 892, 858, 794, 688, 643.
NMR-spectra:
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rinated biphenyls (PCBs) using the Suzuki-coupling. Che-
mosphere 45, 137–143.
2
H
Miyaura, N., Yanagi, T., Suzuki, A., 1981. The palladium-
catalyzed cross-coupling reaction of phenylboronic acid
with haloarenes in the presence of bases. Synth. Comm. 11,
513–519.
2
2
4
3
H
H
5
2
H
8
Cl
Cl
3
6
1
8
7
Remberg, G., Sandra, P., Nyiry, W., Winker, N., Nikiforov, A.,
1998. Calculation of the polychlorinated terphenyl congener
distribution and gas chromatographic retention behaviour
of selected single standards on four stationary liquid phases.
Fresenius J. Anal. Chem. 362, 404–408.
H
1
4
3
H
H
3
Cl
Cl
1H-NMR (400 MHz, in CDCl3): H-1: d ¼ 7:66 (m, 1
H); H-2: d ¼ 7:56 (m, 3 H); H-3: d ¼ 7:50 (d, J ¼ 1:86
Hz, 4 H); H-4: d ¼ 7:38 (t, J ¼ 1:85 Hz, 2 H).
Wester, P.G., de Boer, J., Brinkman, U.A.Th., 1996. Determi-
nation of polychlorinated terphenyls in aquatic biota and
sediment with gas chromatography/mass spectrometry using
negative chemical ionization. Environ. Sci. Technol. 30,
473–480.
13C-NMR (100 MHz, in CDCl3): C-1: d ¼ 143:63; C-
2: d ¼ 139:50; C-3: d ¼ 135:43; C-4: d ¼ 129:77; C-5: