Changing the number of π-electrons in a molecule should alter its aromaticity and antiaromaticity – if the Hückel rule holds! Iron, Cohen and Rybtchinski¹ look at an interesting polycyclic aromatic perylene diimide 1 and its dianion and evaluate the aromaticity and reactivity of these species, using both experiment and computation.

The M06-2x/6-31++G** geometries of 1 and its dianion 1^2- are shown in Figure 1. 1 can be thought of as two naphthalenyl groups joined together by single bond (their distance is 1.479 Å). In the dianion, the bond distance between the two naphthyl groups (making the central 6-member ring) is shorter, 1.425 Å. In addition the C-C(O) bond of the imide ring shortens from 1.485 to 1.441 Å in going from the neutral to the dianion, with the C=O bond also lengthening, from 1.214 to 1.243 Å. These geometric changes suggest the formation of an aromatic central six-member ring, and perhaps some aromaticity in the diimide rings, too.

1

12-

Figure 1. M06-2x optimized structures of 1 and 1^2-.

The changes are reflected in the NICS(1) values. In 1, the NICS values for each ring of the naphthyl group is -9.31, as expected for an aromatic 6-member ring. The diimide has a NICS value of -0.01, indicating a non-aromatic ring, and the central ring has a NICS value of +1.78, suggesting some slight antiaromatic character. Significant changes come about with the reduction to the dianion. The central ring now has a NICS value of -9.10, indicating an aromatic ring. The naphthyl rings have NICS values of -3.94 and the diimide ring has a value of -4.53.

So, the dianion 1^2- species appears to be more aromatic than the neutral 1. This is reflected in its chemistry. The dianion of pegylated 1 is actually stable in water, though it is readily oxidized by air. Its stability in water is understood in terms of the computed reaction energy with water, which is quite positive due to that aromatic stabilization of 1^2-. This is compared with the computed negative free energies for the reaction of other dianions with water, such as the anthracenyl, and perylenyl dianions.

References

1) Iron, M. A.; Cohen, R.; Rybtchinski, B., "On the Unexpected Stability of the Dianion of Perylene Diimide in Water – A Computational Study," J. Phys. Chem. A, 2011, 115, 2047-2056, DOI: 10.1021/jp1107284

InChIs

1: InChI=1/C24H10N2O4/c27-21-13-5-1-9-10-2-6-15-20-16(24(30)26-23(15)29)8-4-12(18(10)20)11-3-7-14(22(28)25-21)19(13)17(9)11/h1-8H,(H,25,27,28)(H,26,29,30)/f/h25-26H
InChIKey=KJOLVZJFMDVPGB-SPEPDGBUCZ

Henry Rzepa brought this interesting paper to my attention via his blog post. I have a few comments too.

Isobe and co-workers prepared the interesting polycyclic aromatic compound 1, which they represent with the picture given below.¹ The molecule is non-planar due to the clash of the interior hydrogens. If you stare at this picture long enough you might decide that something looks amiss. If you start at the lower left phenyl ring of the top segment and move counterclockwise you would move upwards, out of the plane of the page. Then you cross into the lower half and continue the counter clockwise motion, again you climb upwards out of the page. And then you cross back over to the top half and your back where you started – but you’ve been climbing uphill all the time! This might remind you of the famous Escher drawing Ascending and Descending.

So, what’s the catch? Well, the molecule does exist and its crystal structure shows the key. The molecule is in fact of D₂ symmetry, so the upper and lower halves of the molecule are twisted in and out of the plane. B3LYP/6-31G(d,p) computations on the parent compound 2 indicate the D₂ symmetry of the ground state (see Figure 1). (Don’t forget to click on the structure to be able to manipulate the structure!) This is a chiral species. Racemization occurs through a barrier of 10.1 kcal mol^-1 (3) which connects to the meso structure 4, Passing then through the mirror image of 3 completes the process, joining to the mirror image of 2.

2

3

4

I think the title is a bit misleading here – the molecular expression is misleading as its drawn in 1, but the full 3D structure shows no such illusion; the molecule is in fact not a Penrose Stair. But 1 certainly possesses a structure of interesting shape and topology!

References

(1) Nakanishi, W.; Matsuno, T.; Ichikawa, J.; Isobe, H., "Illusory Molecular Expression of “Penrose Stairs” by an Aromatic Hydrocarbon," Angew. Chem. Int. Ed., 2011, ASAP, DOI: 10.1002/anie.201102210

InChIs

1: InChI=1/C52H52/c1-5-9-13-37-25-41-26-38(14-10-6-2)44-22-19-35-30-48(44)51(41)47-29-33(17-21-43(37)47)34-18-23-45-39(15-11-7-3)27-42-28-40(16-12-8-4)46-24-20-36(35)32-50(46)52(42)49(45)31-34/h17-32H,5-16H2,1-4H3
InChIKey=UNDWIIYPHJODRS-UHFFFAOYAO

2: InChI=1/C36H20/c1-9-25-10-2-22-6-15-29-18-32(22)35(25)31-17-27(13-5-21(1)31)28-14-7-23-3-11-26-12-4-24-8-16-30(29)20-34(24)36(26)33(23)19-28/h1-20H
InChIKey=KBDMNQAUFRTSJI-UHFFFAOYAA

Lash has synthesized the simplified component of a porphyrin 1, which lacks two of the pyrrole rings.¹ This compound should act as a modified [18]annulene, and the NMR and x-ray structure support that notion. The NMR shows a multiplet at -2.52 ppm for the internal protons and the external protons show up at 9.88 and 9.96 ppm. The x-ray structure exhibits a nearly planar structure, with the C-C distances around the macrocycle varying from 1.379 to 1.418 Å. Interestingly, the UV-vis of 1shows a Soret-band at 401 nm, indicative of porphyrin-like behavior.

It is a simple thing to do some computations on a model of 1, and so I have computed (at B3LYP/6-311+G(d,p)) the structure and NMR of 2, shown in Figure 1. This compound is strictly planar. The C-C distances about the macrocycle vary from 1.386 to 1.415 Å, in excellent agreement with the experiment and indicating little bond alternation. The NICS values at the center of the macrocycle and 1 Å above this point are -12.6 and -11.9 ppm, supporting the aromatic [18]annulene structure. Further, the chemical shifts of the interior and exterior protons are computed to be -7.6 (interior) and 11.4 ppm (exterior) – in fair agreement with experiment. Nonetheless, simple computations provide support for the notion that this compound, and related porphyrins have a dominant [18]annulene character.

2

Figure 1. B3LYP/6-311+G(d,p) optimized structure of 2.

References

(1) Lash, T. D.; Jones, S. A.; Ferrence, G. M., "Synthesis and Characterization of Tetraphenyl-21,23-dideazaporphyrin: The Best Evidence Yet That Porphyrins Really Are the [18]Annulenes of Nature," J. Am. Chem. Soc., 2010, 132, 12786-12787, DOI: 10.1021/ja105146a

InChIs

1: InChI=1/C44H32N2/c1-2-18-30-38-42(34-23-11-6-12-24-34)44(36-27-15-8-16-28-36)40(46-38)32-20-4-3-19-3
1-39-43(35-25-13-7-14-26-35)41(37(45-39)29-17-1)33-21-9-5-10-22-33/h1-32H/b2-1-,4-3-,17-1+,18-2+,19-3+,20-4+,29-17+,30-18+,31-19+,32-20+,37-29-,38-30-,39-31-,40-32-
InChIKey=SOKXIWMGPPRDDE-VZLTUNCZBQ

2: InChI=1/C20H16N2/c1-2-6-10-18-15-16-20(22-18)12-8-4-3-7-11-19-14-13-17(21-19)9-5-1/h1-16H/b2-1-,4-3-,5-1+,6-2+,7-3+,8-4+,9-5+,10-6+,11-7+,12-8+,17-9-,18-10-,19-11-,20-12-
InChIKey=IWCJELFJBPNKQF-ICIIEBMOBH

The search for ever more intriguing aromatic/antiaromatic species continues on – Haley has recently prepared the TIPS-protected indeno[1,2-b]fluorene 1. ¹ The crystal structure was determined and analogue with the tri-iso-propylsilyl groups replaced with hydrogens (2) has been computed at B3LYP/6-31G(d,p). This optimized structure is shown in Figure 1. The core system has 20 π-electrons – suggesting perhaps an antiaromatic system.

1

2

Figure 1. B3LYP/6-31G(d,p) optimized geometry of 2.

The x-ray structure and computed structure are in close agreement in terms of distances. The terminal phenyl rings exhibit very little alternation. The C₁-C₂ and C₂-C₃ distances are long (1.444 and 1.457 Å, respectively) while the C₁-C_3A and C­2-C₄ distances are short (1.379 and 1.396 Å, respectively.) This suggests a para-xylylene type structure for the central six-member ring. The NICS values of the terminal 6-member ring, the 5-member ring and the central 6-member ring are computed to be -7.12 (a reasonable phenyl value), 1.84, and 0.02. So the middle three rings possess no aromatic or antiaromatic character. Haley describes this structure as “a fully conjugated 20-π-electron hydrocarbon with fused s-trans 1,3-diene linkages across the top and bottom portions of the carbon skeleton”.

References

(1) Chase, D. T.; Rose, B. D.; McClintock, S. P.; Zakharov, L. N.; Haley, M. M., "Indeno[1,2-b]fluorenes: Fully Conjugated Antiaromatic Analogues of Acenes," Angew. Chem. Int. Ed., 2011, 50, 1127-1130, DOI: 10.1002/anie.201006312

InChIs

1: InChI=1/C64H92Si4/c1-41(2)65(42(3)4,43(5)6)37-33-57-53-29-25-27-31-55(53)61-60(36-40-68(50(19)20,51(21)22)52(23)24)64-58(34-38-66(44(7)8,45(9)10)46(11)12)54-30-26-28-32-56(54)62(64)59(63(57)61)35-39-67(47(13)14,48(15)16)49(17)18/h25-32,41-52H,1-24H3
InChIKey=JIXLLIXVMPJPEE-UHFFFAOYAI

2: InChI=1/C28H12/c1-5-17-21-13-9-11-15-23(21)27-20(8-4)26-18(6-2)22-14-10-12-16-24(22)28(26)19(7-3)25(17)27/h1-4,9-16H
InChIKey=DOQPHDKEGVECBF-UHFFFAOYAY

1,2-Azaborine appears to be aromatic (see my previous post). Can the extent of aromatic character be measured? Well, obviously the first thing one must decide is just which “aromaticity metric” to choose. Dixon and Liu have now measured the aromatic resonance stablilization energy (ASE) through computations and heats of hydrogenation.¹

One can set up to hydrogenation comparisons. First, obtain the hydrogenation of 1,2-azaborine itself. They used the t-butyl analog 1, so the hydrogenation is given in Reaction 1.

Then as comparison, one can perform two separate hydrogenations, looking at the double bond adjacent to the nitrogen (Reaction 2) and the double bond adjacent to the boron (Reaction 3).

The heat of hydrogenation of Reaction 1 is -30 ± 1 kcal mol^-1 (-30.1 at G3(MP2). The heats of hydrogenations of reactions 2 and 3 are -22.7 ± 0.5 kcal mol^-1 (-23.8) and -23.9 ± 0.7 (-24.7), respectively. The difference between the sum of reactions 2 and 3 and Reaction 1 is the ASE: 16.6 kcal mol^-1 (18.4 at G3(MP2)). This can be compared to the ASE of benzene determined in the analogous way to be 32.4 kcal mol^-1. Therefore, 1,2-azoborine is aromatic, but appreciably less so than benzene, which is consistent with the NICS computations (see the post).

References

(1) Campbell, P. G.; Abbey, E. R.; Neiner, D.; Grant, D. J.; Dixon, D. A.; Liu, S.-Y., "Resonance Stabilization Energy of 1,2-Azaborines: A Quantitative Experimental Study by Reaction Calorimetry," J. Am. Chem. Soc., 2010, 132, 18048-18050, DOI: 10.1021/ja109596m

How is the aromaticity of benzene affected by nitrogen substitution? Are pyridine and pyrimidine more or less aromatic than benzene? This question has been addressed many times, and Schleyer adds to this discussion with a B3LYP/6-311+G** study of the entire series of azines.¹ Analysis of the aromaticity is based on a two metrics: NICS(0)_πzz and extra cyclic resonance energy (ECRE). The NICS(0) _πzz value is now the ring current measurement advocated by Schleyer as it only includes the π orbitals and uses the tensor component perpendicular to the ring. ECRE is obtained by comparing block-localized energies of the azine to appropriate acyclic references.

Interestingly, both metrics give the same result, namely, that the aromaticity of benzene and all of the azines 1-6 are essentially equally aromatic.

References

(1) Wang, Y.; Wu, J. I. C.; Li, Q.; Schleyer, P. v. R., "Aromaticity and Relative Stabilities of Azines," Org. Lett., 2010, 12, 4824-4827, DOI: 10.1021/ol102012d

InChIs

1: InChI=1/C5H5N/c1-2-4-6-5-3-1/h1-5H
InChIKey=JUJWROOIHBZHMG-UHFFFAOYAY

2a: InChI=1/C4H4N2/c1-2-4-6-5-3-1/h1-4H
InChIKey=PBMFSQRYOILNGV-UHFFFAOYAA

2b: InChI=1/C4H4N2/c1-2-5-4-6-3-1/h1-4H
InChIKey=CZPWVGJYEJSRLH-UHFFFAOYAT

2c: InChI=1/C4H4N2/c1-2-6-4-3-5-1/h1-4H
InChIKey=KYQCOXFCLRTKLS-UHFFFAOYAV

3a: InChI=1/C3H3N3/c1-2-4-6-5-3-1/h1-3H
InChIKey=JYEUMXHLPRZUAT-UHFFFAOYAF

3b: InChI=1/C3H3N3/c1-2-5-6-3-4-1/h1-3H
InChIKey=FYADHXFMURLYQI-UHFFFAOYAY

3c: InChI=1/C3H3N3/c1-4-2-6-3-5-1/h1-3H
InChIKey=JIHQDMXYYFUGFV-UHFFFAOYAG

4a: InChI=1/C2H2N4/c1-2-4-6-5-3-1/h1-2H
InChIKey=DPOPAJRDYZGTIR-UHFFFAOYAI

4b: InChI=1/C2H2N4/c1-3-2-5-6-4-1/h1-2H
InChIKey=ZFXBERJDEUDDMX-UHFFFAOYAH

4c: InChI=1/C2H2N4/c1-3-5-2-6-4-1/h1-2H
InChIKey=HTJMXYRLEDBSLT-UHFFFAOYAH

5: InChI=1/CHN5/c1-2-4-6-5-3-1/h1H
InChIKey=ALAGDBVXZZADSN-UHFFFAOYAQ

6: InChI=1/N6/c1-2-4-6-5-3-1
InChIKey=YRBKSJIXFZPPGF-UHFFFAOYAK

Earlier this year, Barboiu made the astonishing claim of the x-ray characterization of 1,3-dimethylcyclobutadiene, brought about by the photolysis of 4,6-dimethyl-α-pyrone encapsulated in a guanidinium-sulfonate-calixarene crystal (Reaction 1).¹ I had not blogged on this paper because Henry Rzepa did a quite thorough analysis of it in this blog post. Now, a couple of rebuttals have appeared and it is time to examine this study.

Alabugin calls in question whether the reaction has in fact proceeded beyond 2.² They note that in the x-ray crystal structure, the distance between a carbon of the purported cyclobutadiene ring and the carbon of CO₂ is only 1.50 and 1.61 Å. Barboiu called this a “strong van der Waals contact”, but this is a distance much more attributable to a covalent bond. In fact, the shorter distance is in fact shorter than some of the other C-C distances in the structure that Barboiu calls covalent! Perhaps more bizarre is that the putative CO₂ fragment is highly bent: 119.9&;deg;, a value inconsistent with CO₂ but perfectly ordinary for an sp² carbon.  In fact, B3LYP/6-31G** computations suggest that bending CO₂ this much costs about 75 kcal mol^-1 – and tack on another 7 kcal mol^-1 to make the two C-O distances unequal (as found in the x-ray structure!). Thus, Alabugin suggests that only 2 has been formed, and notes that the cleavage to 3 would likely require light of much higher energy that that used in the Barboiu experiment.

Scheschkewitz argues that the x-ray data can be better interpreted as suggesting only the Dewar β-lactone 2 is present, though in its two enantiomeric forms.³ There is no evidence, he suggests of any cyclobutadiene component at all.

It should be noted that Barboiu stands⁴ by his original work and original assignment, claiming that these types of x-ray experiments are quite difficult and large error bars in atom positions are inherent to the study.

Henry Rzepa has blogged again on this controversy and has a paper coming out on this soon. I shall update when it appears. Henry notes in one of the comments to his blog that a TD-DFT computations does show that the Dewar β-lactone 2 is transparent from 320-500nm.

References

(1) Legrand, Y.-M.; van der Lee, A.; Barboiu, M., "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix," Science 2010, 329, 299-302, DOI: 10.1126/science.1188002.

(2) Alabugin, I. V.; Gold, B.; Shatruk, M.; Kovnir, K., "Comment on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," Science, 330, 1047, DOI: 10.1126/science.1196188.

(3) Scheschkewitz, D., "Comment on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," Science 2010, 330, 1047, DOI: 10.1126/science.1195752.

(4) Legrand, Y.-M.; van der Lee, A.; Barboiu, M., "Response to Comments on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," Science, 330, 1047, DOI: 10.1126/science.1195846.

InChIs

1: InChI=1/C7H8O2/c1-5-3-6(2)9-7(8)4-5/h3-4H,1-2H3
InChIKey=IXYLIUKQQQXXON-UHFFFAOYA

2: InChI=1/C7H8O2/c1-4-3-7(2)5(4)6(8)9-7/h3,5H,1-2H3
InChIKey=GLYAMHMFKKLRAL-UHFFFAOYAT

3: InChI=1/C6H8/c1-5-3-6(2)4-5/h3-4H,1-2H3
InChIKey=ADQGKIKNUMJFSL-UHFFFAOYAU

I recently finished reading a book on the application of information theory to “reality”: Decoding Reality by Vlatko Vedral. It’s for the layman (me!) and I was wondering what applications have information theory made in chemistry. Well, just by accident I happened upon a paper by Noorizadeh which proposes an information-based metric to evaluate aromaticity!¹ (I know what you’re thinking – we need another aromaticity metric like we need another hole in the head.) I don’t want to suggest that this metric, which he calls “Shannon aromaticity” after the inventor of information theory, will substitute for previous ones (like aromatic stabilization energy or NICS). But the application here is interesting.

Shannon defined entropy in the information sense as

Where p_i is the probability of occurrence i. This can be converted into a quantum analogue as

Noorizadeh suggests evaluating the electron density at the bond critical points of an aromatic ring and then summing the values of S at each of these ring critical points. An ideal aromatic ring would have S_max= ln (N) where N is the number of bonds in the ring. So, the Shannon aromaticity (SA) is then defined as the difference between the maximum value (ln (N)) and the sum over the ring critical points. A small value would indicate an aromatic ring, and a large value would indicate an antiaromatic ring.

The paper shows a strong correlation exists between the new SA metric and the warhorses ASE and NICS and HOMA for a variety of aromatic, antiaromatic and non-aromatic systems. This new metric is easy to compute and perhaps offers a new way to be thinking about a very old concept: aromaticity.

References

(1) Noorizadeh, S.; Shakerzadeh, E., "Shannon entropy as a new measure of aromaticity, Shannon aromaticity," Phys. Chem. Chem. Phys., 2010, 12, 4742-4749, DOI: 10.1039/b916509f.

Since Heilbronner¹ proposed the Möbius annulene in 1964, organic chemists have been fascinated with this structure and many have tried to synthesize an example. I have written many blog posts (1, 2, 3, 4, 5) related to computed Möbius compounds. Now, Herges and Grimme and co-workers have looked at cationic Möbius annulenes.

For the [9]annulene cation,² a variety of DFT methods, along with SCS-MP2 and CCSSD(T) computations suggest that the lowest energy Hückel (1h) and Möbius (1m) structures, shown in Figure 1, are very close in energy. In fact, the best estimate (CCSD(T)/CBS) is that they differ by only 0.04 kcal mol^-1. Laser flash photolysis of 9-chlorobicyclo[6.1.0]nona-2,4,6-triene suggest however that only the Hückel structure is formed, and that its short lifetime is due to rapid electrocyclic ring closure.

In a follow-up study, Herges has examined the larger annulene cations, specifically [13]-, [17]- and [21]-annulenes. ³ The Möbius form of [13]-annulene cation (2m) is predicted to be 11.0 kcal mol^-1 lower in energy that the Hückel (2h) form at B3LYP/6-311+G**. The structures of these two cations are shown in Figure 1. The Möbius cation 2m is likely aromatic, having NICS(0)= -8.95. Electrocyclic ring closure of 2m requires passing through a barrier of at least 20 kcal mol^-1, suggesting that 2m is a realistic target for preparation and characterization.

1h	1m
2h	2m

Figure 1. Optimized structures of 1 (CCSD(T)/cc-pVTZ)² and 2 (B3LYP/6-311+G**)³.

The energy difference between the Möbius and Hückel structures of the larger annulenes is very dependent on computational method, but in all cases the difference is small. Thus, Herges concludes that [13]-annulene cation should be the sole target of synthetic effort toward identification of a Möbius annulene. Experimental studies are eagerly awaited!

References

(1) Heilbronner, E., “Huckel molecular orbitals of Mobius-type conformations of annulenes,” Tetrahedron Lett., 1964, 5, 1923-1928, DOI: 10.1016/S0040-4039(01)89474-0.

2) Bucher, G.; Grimme, S.; Huenerbein, R.; Auer, A. A.; Mucke, E.; Köhler, F.; Siegwarth, J.; Herges, R., "Is the [9]Annulene Cation a Möbius Annulene?," Angew. Chem. Int. Ed., 2009, 48, 9971-9974, DOI: http://dx.doi.org/10.1002/anie.200900886

(3) Mucke, E.-K.; Kohler, F.; Herges, R., "The [13]Annulene Cation Is a Stable Mobius Annulene Cation," Org. Lett., 2010, 12, 1708–1711, DOI: 10.1021/ol1002384

InChIs

1: InChI=1/C9H9/c1-2-4-6-8-9-7-5-3-1/h1-9H/q+1/b2-1-,5-3-,6-4-,9-7-
InChIKey=LIUDWUIEJKKGNI-BWYSQNKRBF

2: InChI=1/C13H13/c1-2-4-6-8-10-12-13-11-9-7-5-3-1/h1-13H/q+1/b2-1-,5-3-,6-4-,9-7-,10-8-,13-11-
InChIKey=FUBPZYTZTJGXKZ-OGBOFXOGBR

How would you characterized the benzotrithiophene 1? Is it planar? How about when methyl groups are attached (2)? Are these compounds aromatic? A joint computational/experimental study by Wu and Baldridge has tackled these questions.¹

It turns out that both of these compounds are non-planar and have C₂ symmetry. Now, 1 is very nearly planar. But 2 is decidedly non-planar. The MO6-2X/DZ(2d,p) structures are shown in Figure 1. The central 6-member ring has long bonds and expresses some bond alternation: the C-C distance for the bond between the thiophene rings is 1.469 Å and that of the bond shared by the two rings is 1.451 Å The exocyclic bonds are short, 1.375 Å. This appears to be [6]-radialene-like. NICS computations confirm this notion. The NICS(0) value for the central ring of 1 and 2 is -1.6, significantly less negative than the value in benzene of -7.2. The NICS_zz values also reflect non-aromatic character of the central ring. The central ring is non-aromatic.

1

2

Figure 1. MO6-2X/DZ(2d,p) structures of 1 and 2.¹

References

(1) Wu, T.-T.; Tai, C.-C.; Lin, W.-C.; Baldridge, K. K., "1,3,4,6,7,9-Hexamethylbenzo[1,2-c:3,4-c:5,6-c]trithiophene: a twisted heteroarene," Org. Biomol. Chem., 2009, 7, 2748-2755, DOI: 10.1039/b902517k.

InChIs

1: InChI=1/C12H6S3/c1-7-8(2-13-1)10-4-15-6-12(10)11-5-14-3-9(7)11/h1-6H
InChIKey=INZUTJPYADZZEL-UHFFFAOYAI

2: InChI=1/C18H18S3/c1-7-13-14(8(2)19-7)16-10(4)21-12(6)18(16)17-11(5)20-9(3)15(13)17/h1-6H3
InChIKey=WYVKJYPLPAEMLN-UHFFFAOYAA