Meso-Multi(iodophenyl) porphyrins: Synthesis, isolation, and identification

Article abstract of DOI:10.1016/j.tetlet.2011.07.041

We report on a simple method for identification of a series of six meso-substituted porphyrins by ¹H NMR spectroscopy. The meso-substituted porphyrins are synthesized by a simple mixed-aldehyde condensation approach [3,5-di-tert-butylstyrylbenzaldehyde (A) and 4-iodobenzaldehyde (B)] to give the two parent porphyrins (A₄, B ₄) and four hybrid porphyrins (A₃B, cis-A ₂B₂, trans-A₂B₂, AB₃) which are isolated and characterized.

Full text of DOI:10.1016/j.tetlet.2011.07.041

Tetrahedron Letters 52 (2011) 4795–4798
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
meso-Multi(iodophenyl) porphyrins: synthesis, isolation, and identification
Preecha Moonsin, Kanokkorn Sirithip, Siriporn Jungsuttiwong, Tinnagon Keawin, Taweesak Sudyoadsuk,
⇑
Vinich Promarak
Center for Organic Electronic and Alternative Energy, Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University,
Warinchumrap, Ubon Ratchathani 34190, Thailand
a r t i c l e i n f o
a b s t r a c t
We report on a simple method for identification of a series of six meso-substituted porphyrins by 1H NMR
spectroscopy. The meso-substituted porphyrins are synthesized by a simple mixed-aldehyde condensa-
tion approach [3,5-di-tert-butylstyrylbenzaldehyde (A) and 4-iodobenzaldehyde (B)] to give the two par-
ent porphyrins (A4, B4) and four hybrid porphyrins (A3B, cis-A2B2, trans-A2B2, AB3) which are isolated and
characterized.
Article history:
Received 11 April 2011
Revised 29 June 2011
Accepted 11 July 2011
Available online 30 July 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Porphyrin
meso-Substituted porphyrin
Iodophenyl porphyrin
Mixed-aldehyde condensation
Multiporphyrin array
Multiporphyrin arrays have been the topic of interesting re-
search because they are very useful in understanding the process
of photosynthesis. A variety of covalently and non-covalently
linked porphyrin arrays have been synthesized and their excited
state properties are well documented in the literature.1 Porphyrin
arrays with meso aryl linkers exhibited essentially unchanged visi-
ble absorption spectra indicating limited excitonic interactions.2
The weak electronic coupling and the efficient energy transfer
properties of these arrays make them well suited for modeling pho-
tosynthetic processes in biological systems.3 These meso aryl linked
dyads have been constructed by employing metal-catalyzed cou-
pling reactions. The meso-mono, -di (cis, trans), -tri and -tetrahal-
ophenyl substituted porphyrins are crucial building blocks and
provide versatile handles for incorporation into a variety of molec-
ular architectures leading to new classes of organic materials for
energy funnels,4 molecular wires,5 photovoltaic cells,6 and organic
light-emitting diodes (OLEDs).7 Various methods including a binary
mixed aldehyde condensation of two different aldehydes8 and Mac-
Donald 2 + 2 condensation of a dipyrromethane and an aldehyde9
have been used for the synthesis of these porphyrins. However, a
major limitation concerns the ability to obtain these porphyrins
as all approaches are statistical in nature and usually require chro-
matographic separation of multiple porphyrin products. In particu-
lar, chromatographic separation of cis- and trans-disubstituted
porphyrins bearing two of each of the substituents is often difficult.
To our knowledge, clear separation and identification of the mixed
porphyrins obtained from these syntheses have not yet been re-
ported. In this Letter, we report on the isolation, using common
flash column chromatography, and a simple identification proce-
dure, using 1H NMR spectroscopy, of mixed meso-iodophenyl
porphyrins formed via a mixed-aldehyde condensation approach.
These porphyrins might be useful as versatile building blocks for
creating both covalently meso-linked linear and three-dimensional
multiporphyrin arrays as red light-emitters for OLEDs.
In our investigation, porphyrins bearing two different types of
meso-substituents, 4-iodophenyl and 3,5-di-tert-butylstyrylphe-
nyl, were synthesized via mixed-aldehyde condensation of pyrrole
and the two corresponding aldehydes. This approach is simple and
widely used for the preparation of a variety of meso-substituted
porphyrins. A slightly modified Alder–Longo method was em-
ployed.10 This involved preheating a mixture of 3,5-di-tert-butyl-
styrylbenzaldehyde11 (aldehyde A) and 4-iodobenzaldehyde
(aldehyde B) in a 1:1 ratio followed by addition of zinc acetate
dihydrate in propionic acid and pyrrole (2 equiv), and further heat-
ing at reflux for 3 h (Scheme 1). The porphyrins were isolated by
first removing the propionic acid by distillation followed by col-
umn chromatography. In principle, the reaction of pyrrole with
two aldehydes affords a set of six porphyrins. The six porphyrins
expected to spot (TLC) from our synthesis include the two parent
porphyrins (A4, B4) and the four hybrid porphyrins (A3B, cis-A2B2,
trans-A2B2, AB3). In our case, six purple spots were observed on
thin layer chromatography (TLC) (hexane-CH2Cl2, 3:1) with Rf
values of 0.75, 0.71, 0.62, 0.58, 0.48 and 0.25. The expected ratio
of porphyrins in a mixed-aldehyde condensation is given by the
binomial distribution. With a 1:1 ratio of aldehydes, and assuming
⇑
Corresponding author. Tel.: +66 45 353400x4484; fax: +66 45 288379.
E-mail addresses: pvinich@ubu.ac.th, pvinich@gmail.com (V. Promarak).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.07.041

4796
P. Moonsin et al. / Tetrahedron Letters 52 (2011) 4795–4798
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
I
t-Bu
t-Bu
+
1 equiv.
1 equiv.
CHO
CHO
A =
propionic acid,
Zn(OAc)2.2H2O, heat
2 equiv.
N
N
H
A
t-Bu
N
B =
I
B
Zn
B
N
N
A
A
A
Zn
B
B
3
A
N
N
N
N
N
N
N
N
N
N
N
N
trans-A2B2-porphyrin
A
A
Zn
A
Zn
B
B
B
B
Zn
B
A
N
N
N
N
N
N
N
N
A
A
B
A
Zn
B
A4-porphyrin
A3B-porphyrin
AB3-porphyrin
B4-porphyrin
1
2
5
6
B
4
cis-A2B2-porphyrin
Scheme 1. Synthesis of mixed meso-substituted porphyrins.
C2
C2
D4
D4
D2
C2
H1
A
H1
A
H2
A
H1
A
H1
A
H2
H3
H2
H1
B
H1
H3
H2
H3
B
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
A
A
B
Zn
A
Zn
B
Zn
B
A
Zn
B
Zn
B
B
Zn
B
N
H4
H1
A
A
A
B
B
B
H1
A4-porphyrin
trans-A2B2-porphyrin
A3B-porphyrin
cis-A2B2-porphyrin
AB3-porphyrin
B4-porphyrin
1 singlet (H-1)
1 singlet (H-1)
1 singlet (H-1)
1 AA'BB' (H-1,H-2)
2 singlet (H-1,H-4)
1 AA'BB' (H-2,H-3)
1 singlet (H-1)
1 AA'BB' (H-2,H-3)
1 AA'BB' (H-2,H-3)
Figure 1. Symmetry groups and expected 1H NMR patterns of the b-pyrrolic protons of each meso-substituted porphyrin.
H-1
H-1
H-1
H-1
H-2
H-4
H-1
H-1
H-2
H-3
H-3
H-2
H-2
H-3
1 (A4)
2 (A3B)
3 (trans-A2B2)
4 (cis-A2B2)
5 (AB3)
6 (B4)
Figure 2. 1H NMR patterns of the b-pyrrolic protons of porphyrins 1–6.
equal reactivity of the two aldehydes at all stages of the porphyrin-
forming reaction, the distribution is as follows: A4, 6.25%; A3B, 25%;
cis-A2B2, 25%; trans-A2B2, 12.5%; AB3, 25% and B4, 6.25%.12 How-
ever, the ratio giving the highest isolated yield of certain meso-
substituted porphyrins depends on, firstly the ratio of the mixed
aldehydes and the actual reactivities of the two aldehydes, as well

P. Moonsin et al. / Tetrahedron Letters 52 (2011) 4795–4798
4797
as the ease of separation from the mixture of porphyrins. For
example, the fraction of A3B-porphyrin was maximized by reaction
of a 3:1 ratio of aldehydes A and B, and higher ratios shifted the
distribution toward the A4-porphyrin and the amount of A3B-por-
phyrin declined.12
(J = 5.3 Hz) ppm. The fourth eluted porphyrin, the cis-isomer of
[5,10-bis(40-iodophenyl)-15,20-bis(300,500-bis(3000,5000-di-tert-butylsty-
ryl)phenyl)porphyrinato]zinc(II) (4, cis-A2B2) showed the 1H NMR
signals for the b-pyrrolic protons as two singlets at 8.99 and
9.16 ppm and well-separated AA0BB0 type resonances at 9.00 and
9.14 ppm (J = 5.0 Hz). The fifth eluted porphyrin was [5,10,15-
tris(40-iodophenyl)-20-(300,500-bis(3000,5000-di-tert-butylstyryl)phenyl)p
orphyrinato]zinc(II) (5, AB3), with the 1H NMR signals of the b-pyrro-
lic protons appearing as a singlet at 8.98 ppm and well-separated
AA0BB0 type resonances at 8.99 and 9.12 ppm (J = 5.0 Hz). The final
eluted porphyrin, identified as [5,10,15,20-tetrakis(40-iodo-
phenyl)porphyrinato]zinc(II) (6, B4), exhibited 1H NMR signals for
the b-pyrrolic protons as a singlet at 8.90 ppm.
The chemical structures of these porphyrins identified were
strongly supported by MALDI-TOF mass spectrometry which
showed isotopic distributions for each of the molecular ions corre-
sponding to their molecular weights.13 The isolated yields of the
six porphyrins were: 1 (1.5%), 2 (3%), 3 (4%), 4 (2.5%), 5 (2%) and
6 (1%).
In conclusion, we have demonstrated the synthesis of mixed
meso-substituted porphyrins formed by a mixed-aldehyde conden-
sation approach and their isolation using common flash column
chromatography. The six isolated porphyrins were identified by
analysis of the 1H NMR patterns of their b-pyrrolic protons com-
bined with their relative polarity. This work provides a simple
method for identification of meso-substituted porphyrins. Work
is underway in our laboratory to utilize these porphyrin building
blocks for creating both covalently meso-linked linear and three-
dimensional multiporphyrin arrays.
Separation of the mixture of porphyrins is invariably accom-
plished via chromatography. The ease of separation of the porphy-
rins hinges on the following factors: the differences in polarity of
the two types of meso-substituents, and the extent of facial hin-
drance imparted by the meso-substituents. The latter could play
a key role for the separation of our mixed porphyrins by modulat-
ing the interaction of the porphyrin macrocycle with the chro-
matographic medium. Furthermore, addition of zinc acetate
dihydrate to the reaction assisted porphyrin ring formation by che-
lation, and simplified separation of the mixed porphyrins by form-
ing the corresponding Zn-porphyrins. From our study, it was found
that chelation of the porphyrins with zinc(II) improved the separa-
tion of these porphyrins by column chromatography.13 This is due
to the higher polarity of the zinc porphyrins compared with the
free-base derivatives which results in larger Rf differences for the
zinc porphyrin mixtures compared with those for the free-base
porphyrin mixtures. The six porphyrins were isolated by perform-
ing a series of flash column chromatographic purifications over sil-
ica gel eluting with a mixture of hexane and CH2Cl2.
Identification of their structures was accomplished using a com-
bination of analysis of the 1H NMR signal pattern of the b-pyrrolic
protons and the relative polarities of the porphyrins. As the number
of 3,5-di-tert-butylstyrylphenyl substituents on the meso-positions
of the porphyrin macrocycle increased, the porphyrin becomes
more lipophilic, and thus under our chromatographic separation
conditions the elution sequence of the porphyrins was as follows:
A4 >A3B >cis-A2B2 and trans-A2B2 >AB3 >B4. The 1H NMR signal pat-
tern of the b-pyrrolic protons of each of these meso-substituted por-
phyrins was characteristic and depended on the symmetry
elements possessed by the molecules. Figure 1 shows the symmetry
type of each porphyrin and the expected 1H NMR patterns of the b-
pyrrolic protons. The A4- and B4-porphyrins have D4 symmetry and
all eight b-pyrrolic protons (H-1) are chemically equivalent, and
hence a singlet peak (H-1) is expected. A3B- and AB3-porphyrins
have C2 symmetry with the C2 axis crossing through the 5-(A), 15-
(B) substituents. This leads to the formation of three unequivalent
b-pyrrolic protons (H-1, H-2, H-3), and hence one singlet (H-1)
and AA0BB0 (H-2, H-3) type peaks are expected. The trans- and cis-
A2B2-porphyrins are geometrical isomers but have different sym-
metries, D2 and C2 point groups, respectively. The trans isomer pos-
sesses two C2 axes crossing through the 5,15-bis(B) and the 10,20-
bis(A) substituents leading to the formation of two unequivalent
b-pyrrolic protons (H-1, H-2), and hence AA0BB0 (H-1, H-2) type
peaks are expected. The cis isomer possesses one C2 axis bisecting
through the two opposite pyrrole rings leading to the formation of
four unequivalent b-pyrrolic protons (H-1, H-2, H-3, H-4), and
hence two singlet (H-1, H-4) and AA0BB0 (H-2, H-3) type peaks are
expected.
Acknowledgments
This work was supported by a grant from the program, Strategic
Scholarships for Frontier Research Network for Research Groups
(CHE-RES-RG50) from the Office of the Higher Education Commis-
sion, Thailand. We acknowledge the scholarship support from the
Center for Innovation in Chemistry (PERCH-CIC).
References and notes
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Accordingly, the eluted porphyrins were isolated and identified.14
The 1H NMR patterns of the b-pyrrolic protons are shown in Figure 2.
The first eluted porphyrin was identified as [5,15,10,20-tetrakis(30,50-
bis(300,500-di-tert-butylstyryl)phenyl)porphyrinato]zinc(II) (1, A4) and
showed the b-pyrrolic protons as a singlet at 9.17 ppm. The second
eluted porphyrin, [5-(40-iodophenyl)-10,15,20-tris(300,500-bis(3000,5000-
di-tert-butylstyryl)phenyl)porphyrinato]zinc(II) (2, A3B) exhibited
the b-pyrrolic protons as a singlet at 9.16 ppm and well-separated
AA0BB0 type resonances at 9.02 and 9.14 ppm (J = 4.7 Hz). The third
eluted porphyrin was identified as the trans-isomer of [5,15-bis(40-
iodophenyl)-10,20-bis(300,500-bis(3000,5000-di-tert-butylstyryl)phenyl)po
rphyrinato]zinc(II) (3, trans-A2B2) exhibiting the b-pyrrolic protons as
well-separated AA0BB0 type peaks at 9.01 (J = 5.0 Hz) and 9.14

4798
P. Moonsin et al. / Tetrahedron Letters 52 (2011) 4795–4798
ˇ
´
9. (a) Harmjanz, M.; Bozidarevic, I.; Scott, M. J. Org. Lett. 2001, 3, 2281; (b)
Wallace, D. M.; Leung, S. H.; Senge, M. O.; Smith, K. M. J. Org. Chem. 1993, 58,
7245; (c) Robinson, A. E.; Buldain, G. Y. J. Heterocycl. Chem. 1995, 32, 1567.
10. Alder, A. D.; Longo, F. R.; Shergalis, W. J. Am. Chem. Soc. 1964, 86, 3145.
11. Promarak, V.; Pankwaung, A. J. Ubon Rajathanee University 2005, 7, 69.
12. Staley, S. W.; Eliasson, B.; Kearney, P. C.; Scheriman, I. C.; Lindsey, J. S. In
Molecular Electronic Devices; Carter, F. L., Siatkowski, R. E., Wohtjen, H., Eds.,
third ed; Elsevier: North Holland, 1988; p 543.
2961, 1594, 1362, 999, 796 and 705; UV-Vis (CH2Cl2) kmax/nm (log
e/
dm3 molꢂ1 cmꢂ1
)
299 (5.25), 406sh (4.84), 427 (5.92), 485sh (3.39), 513
(3.67), 550 (4.52) and 588 (3.77); 1H NMR (300 MHz, CDCl3) d/ppm 1.37 (72H,
s), 7.39 (4H, t, J = 1.5 Hz), 7.44–7.48 (16H, m), 8.01 (4H, d, J = 8.5 Hz), 8.12 (4H,
d, J = 8.5 Hz), 8.15 (2H, t), 8.33 (4H, d, J = 1.4 Hz), and 9.01 and 9.14 (8H, AA0BB0,
J = 5.0 Hz and J = 5.3 Hz); 13C NMR (75 MHz, CDCl3) d/ppm 31.48, 34.89, 93.99,
119.88, 121.00, 121.23, 122.33, 124.07, 127.78, 130.96, 131.68, 131.95, 132.50,
135.80, 136.08, 136.23, 136.45, 142.32, 143.29, 150.04, 150.39 and 151.12; m/z
(MALDI) 1786.90 (M+, 100%); C108H114I2N4Zn requires 1786.60 (M+).
13. Promarak, V. D. Phil. Thesis, University of Oxford, England, 2001.
14.
A
mixture of 3,5-di-tert-butylstyrylbenzaldehyde (2.5 g, 4.67 mmol), 4-
Compound 4: purple solid (52 mg, 2.5%), mp. >300 °C; FT-IR (KBr)
2961, 1593, 1392, 1001, 797 and 706; UV-Vis (CH2Cl2) kmax/nm (log
dm3 molꢂ1 cmꢂ1
311 (5.25), 406sh (5.02), 426 (6.02), 483sh (3.43), 513
m
max/cmꢂ1
iodobenzaldehyde (1.08 g, 4.67 mmol) and Zn(OAc)2ꢀ2H2O (1.53 g,
7.00 mmol) in propionic acid (50 ml) was heated at 100 °C for 10 min.
Pyrrole (0.39 ml, 9.34 mmol) was added and the mixture heated at reflux
(open to the air) for 3 h. The solvent was removed by distillation to give a black
residue which was dissolved in CH2Cl2 (200 ml), and washed with H2O
(3 ꢁ 100 ml), dilute NaHCO3 (2 ꢁ 100 ml) and brine (100 ml), then dried over
anhydrous Na2SO4, filtered and evaporated to dryness. The residue was
purified by silica gel column chromatography eluting with a gradient mixture
of CH2Cl2:hexane. Six porphyrins were isolated. Compound 1: purple solid
e/
)
(3.69), 550 (4.58) and 588 (3.83); 1H NMR (300 MHz, CDCl3) d/ppm 1.36 (72H,
s), 7.38 (4H, t, J = 1.5 Hz), 7.40–7.47 (16H, m), 8.00 (4H, d, J = 8.1 Hz), 8.12 (4H,
d, J = 8.1 Hz), 8.14 (2H, s), 8.34 (4H, d, J = 1.5 Hz), 8.99 (2H, s), 9.00 and 9.14
(4H, AA0BB0, J = 5 Hz), and 9.16 (2H, s); 13C NMR (75 MHz, CDCl3) d/ppm 31.47,
34.82, 94.01, 119.98, 120.95, 121.23, 122.33, 124.07, 127.78, 131.00, 131.68,
131.95, 132.50, 135.80, 136.18, 136.33, 136.45, 142.32, 143.30, 150.14, 150.39
and 151.13; m/z (MALDI) 1786.78 (M+, 100%); C108H114I2N4Zn requires 1786.64
(M+).
(40 mg, 1.5%), mp. >300 °C; FT-IR (KBr)
706; UV-Vis (CH2Cl2) kmax/nm (log
m
max/cmꢂ1 2962, 1594, 1362, 960, and
/dm3 molꢂ1 cmꢂ1
312 (5.36), 410sh
e
)
Compound 5: purple solid (35 mg, 2%), mp. >300 °C; FT-IR (KBr)
m
max/cmꢂ1
(4.78), 431 (5.91), 480sh (3.38), 515 (3.63), 552 (4.47) and 589 (3.68); 1H
NMR (300 MHz, CDCl3) d/ppm 1.34 (144H, s), 7.36 (8H, t, J = 1.5 Hz), 7.38–7.47
(32H, m), 8.13 (4H, s,), 8.36 (8H, d, J = 1.4 Hz), and 9.17 (8H, s); 13C NMR
(75 MHz, CDCl3) d/ppm 31.47, 34.72, 119.98, 120.96, 121.43, 122.33, 124.07,
131.10, 131.68, 132.05, 132.50, 135.82, 136.19, 142.32, 150.14, 150.40 and
151.15; m/z (MALDI) 2392.35 (MH+, 100%); C172H204N4Zn requires 2392.55
(M+).
2961, 1593, 1479, 1206, 999 and 796; UV-Vis (CH2Cl2) kmax/nm (log e/
dm3 molꢂ1 cmꢂ1
) 310 (4.87), 403sh (4.80), 424 (5.86), 483sh (3.17), 513
(3.54), 550 (4.42) and 588 (3.67); 1H NMR (300 MHz, CDCl3) d/ppm 1.36 (36H,
s), 7.38 (2H, t, J = 1.5 Hz), 7.40–7.47 (8H, m), 7.96–8.13 (12H, m), 8.15 (1H, s),
8.13 (2H, d, J = 1.6 Hz), 8.98 (4H, s), and 8.99 and 9.12 (4H, AA0BB0, J = 5 Hz); 13C
NMR (75 MHz, CDCl3) d/ppm 31.48, 34.89, 94.02, 119.98, 120.95, 121.23,
122.33, 124.07, 127.98, 131.00, 131.68, 132.05, 132.50, 135.80, 136.28, 136.36,
142.32, 143.30, 149.97, 150.40 and 151.11; m/z (MALDI), 1484.19 (M+, 100%);
Compound 2: purple solid (73 mg, 3%), mp. >300 °C; FT-IR (KBr)
2962, 1594, 1362, 1002 and 960; UV-Vis (CH2Cl2) kmax/nm (log
m
max/cmꢂ1
e/
C
76H69I3N4Zn requires 1484.20 (M+).
Compound 6: purple solid (14 mg, 1%), mp. >300 °C; FT-IR (KBr)
2960, 1591, 1479, 999, 796 and 720; UV-Vis (CH2Cl2) kmax/nm (log
dm3 molꢂ1 cmꢂ1) 313 (5.30), 408sh (4.79), 429 (5.86), 505 (4.16), 551 (4.44),
589 (3.72) and 632 (2.89); 1H NMR (300 MHz, CDCl3) d/ppm 1.35 (108H, s),
7.36 (6H, t, J = 1.5 Hz), 7.42 (24H, s), 8.02 and 8.12 (4H, AA0BB0, J = 8.4 Hz), 8.14
(3H, s), 8.34 (6H, d, J = 1.2 Hz), 9.02 and 9.14 (4H, AA0BB0, J = 4.7 Hz), and 9.16
(4H, s); 13C NMR (75 MHz, CDCl3) d/ppm 31.45, 34.79, 93.79, 119.92, 121.15,
121.23, 122.33, 123.97, 127.78, 131.16, 131.68, 132.00, 132.50, 135.80, 135.98,
136.23, 136.45, 142.35, 143.19, 150.14, 150.36 and 151.11; m/z (MALDI)
2090.00 (MH+, 100%); C140H159IN4Zn requires 2089.10 (M+).
m
max/cmꢂ1
e
/
dm3 molꢂ1 cmꢂ1
) 401sh (4.91), 422 (6.09), 483sh (3.41), 512 (3.73), 549
(4.60) and 588 (3.91); 1H NMR (300 MHz, CDCl3) d/ppm 7.92 (8H, d, J = 8.1 Hz),
8.07 (8H, d, J = 8.1 Hz), and 8.90 (8H, s); 13C NMR (75 MHz, CDCl3) d/ppm 94.01,
115.32, 118.02, 127.98, 128.11, 130.45, 132.07, 135.78, 136.03, 137.91, 142.02
and 149.95; m/z (MALDI), 1179.82 (M+, 100%); C44H24I4N4Zn requires 1179.75
(M+).
Compound 3: purple solid (83 mg, 4%), mp. >300 °C; FT-IR (KBr)
m
max/cmꢂ1