A pentacoordinate carbon

Schaefer &Schleyer Steven Bachrach 25 Aug 2014 No Comments

Trying to get carbon to bond in unnatural ways seems to be a passion for many organic chemists! Schleyer has been interested in unusual carbon structures for decades and he and Schaefer now report a molecule with a pentacoordinate carbon bound to five other carbon atoms. Their proposed target is pentamethylmethane cation C(CH3)5+ 1.1 The optimized geometry of 1, which has C3h symmetry, at MP2/cc-pVTZ is shown in Figure 1. The bonds from the central carbon to the equatorial carbon are a rather long 1.612 Å, but the bonds to the axial carbon are even longer, namely 1.736 Å. Bader analysis shows five bond critical points, each connecting the central carbon to one of the methyl carbons. Wiberg bond index and MO analysis suggests that the central carbon is tetravalent, with a 2-electron-3-center bond involving the central and axial carbons.




Figure 1. MP2/cc-pVTZ optimized geometries of 1 and dissociation transition states.

So while 1 is a local energy minimum, it sits in a very shallow well. One computed dissociation path, which passes through TS1 (Figure 1) on its way to 2-methyl-butyl cation and methane has a barrier of only 1.65 kcal mol-1 (CCSD(T)/CBS + ZPE). A second dissociation pathway goes through TS2 to t-butyl cation and ethane with a barrier of only 1.34 kcal mol-1. Worse still is that the free energy estimates suggest “spontaneous dissociation … through both pathways”.

Undoubtedly, this will not be the last word on trying to torture a poor carbon atom.


(1) McKee, W. C.; Agarwal, J.; Schaefer, H. F.; Schleyer, P. v. R. "Covalent Hypercoordination: Can Carbon Bind Five Methyl Ligands?," Angew. Chem. Int. Ed. 2014, 53, 7875-7878, DOI: 10.1002/anie.201403314.


1: InChI=1S/C6H15/c1-6(2,3,4)5/h1-5H3/q+1

Torqoselectivity in forming a Cis,Trans-Cyclooctadienone

Houk Steven Bachrach 11 Aug 2014 No Comments

Houk’s theory of torquoselectivity is a great achievement of computational chemistry, as told in Chapter 4.6 of the second edition of my book. Houk, in a collaboration with Krenske and Hsung, now report on an application of torquoselectivity in the formation of a cis-trans-cyclooctadienone intermediate.1

The proposed reaction is shown in Scheme 1, where the bicyclic compound undergoes a conrotatory ring opening in just one orientation to form the E,E-cyclooctadienone, which can then ring close to product.

Scheme 1.

Houk ran M06-2x//6-311+G(d,p)//B3LYP/6-31G(d) computations on the model system 1, passing over the two torquodistinctive transition states TSEE and TSZZ, and on to produce the two cyclooctadienones 2EE and 2ZZ, respectively. As seen in Figure 1, the barrier through TSEE is favored by 9.8 kcal mol-1, and leads to the much more favorable cycloocatadienone 2EE.







Figure 1. B3LYP/6-31G(d) optimized structures and relative free energies (kcal mol-1) at M06-2x//6-311+G(d,p)//B3LYP/6-31G(d).

Ring closure taking TSEE to product goes through TS2 (Figure 1), with a very high barrier, 47.5 kcal mol-1 above reactant, suggesting that this path is not likely to occur. Instead, they propose that 2EE is first protonated (2EEH+) and then cyclizes through TS2H+ (Figure 2). This barrier is only 6.2 kcal mol-1, some 44 kcal mol-1 lower than the neutral process through TS2.



Figure 2. B3LYP/6-31G(d) optimized structures


(1) Wang, X.-N.; Krenske, E. H.; Johnston, R. C.; Houk, K. N.; Hsung, R. P. "Torquoselective Ring Opening of Fused Cyclobutenamides: Evidence for a Cis,Trans-Cyclooctadienone Intermediate," J. Am. Chem. Soc. 2014, 136, 9802-9805, DOI: 10.1021/ja502252t.

Splitting CO2 with a two-coordinate boron cation

Uncategorized Steven Bachrach 04 Aug 2014 1 Comment

This paper is a bit afield from the usual material I cover but this is an interesting reaction. Shoji and coworkers have prepared the two-coordinate boron species 1,1 and confirmed its geometry by an x-ray crystal structure. What I find interesting is its reaction with CO2, which gives 2 and organoboranes that are not identified, though presumably derived from 3.

M06-2x/6-311+G(d,p) computations support a hypothetical mechanism whereby first a complex between 1 and CO2 is formed (CP1), that is 4.4 kcal mol-1 above isolated reactants. Then passing through TS1, which is 4.2 kcal mol-1 above CP1, an intermediate is formed (INT), which is almost 6 kcal mol-1 below starting materials. A second transition state is then traversed (about 1 kcal mol-1 below starting materials), to form an exit complex between 2 and 3, which can then separate to the final products with an overall exothermicity of 10.6 kcal mol-1. The structures of these critical points are shown in Figure 1.







Figure 1. M06-2x/6-311+G(d,p) optimized structures. Relative energy in kcal mol-1.


(1) Shoji, Y.; Tanaka, N.; Mikami, K.; Uchiyama, M.; Fukushima, T. "A two-coordinate boron cation featuring C–B+–C bonding," Nat. Chem. 2014, 6, 498-503, DOI: 10.1038/nchem.1948.


1: InChI=1S/C18H22B/c1-11-7-13(3)17(14(4)8-11)19-18-15(5)9-12(2)10-16(18)6/h7-10H,1-6H3/q+1

2: InChI=1S/C10H11O/c1-7-4-8(2)10(6-11)9(3)5-7/h4-5H,1-3H3/q+1

3: InChI=1S/C9H11BO/c1-6-4-7(2)9(10-11)8(3)5-6/h4-5H,1-3H3

New policy regarding articles I will blog

E-publishing Steven Bachrach 28 Jul 2014 6 Comments

I was all set to write a review of an interesting study of bowtiene 1: its rearrangement to other C10H6 isomers and its dimerization. But as I was gathering my information, I wanted to prepare the images of the optimized geometries, and so I went to get the supplementary materials.

The author has a section on the supplementary materials that indicates it contains Cartesian coordinates – just what I need. (This section ends with the curious line “This material is available for free of charge via the internet at http://pubs.acs.org.”; it’s curious because the article is in a journal not published by ACS. I’ll leave for speculation just what happened here, but clearly the copy-editing done by the Canadian Journal of Chemistry is not quite up to snuff!)

So, I went to the website and clicked on the link for the supplementary material and was then told that I did not have access to this material and that either I had to become a subscriber or I had to purchase access to the article. (I should point out here that I received this article through interlibrary loan.) This is the first time that I have run into a paywall to get supporting materials! I know I am probably lucky that it took 7 years before running into this problem. But that makes this situation so frustrating – just why is the Canadian Journal of Chemistry placing supplementary material behind a paywall, especially when so few other publishers are doing this?

Well, until I get the supplementary materials, I will not write a post about this article.

New policy: I will not blog about an article unless (a) there is information on the 3-D structure of the molecules, typically in supporting materials, and (b) this information is available for free. This requirement should really be the minimum for publishing computational chemistry results. Now, I would also hope that the coordinates are readily reusable – see Henry Rzepa’s post about recent problems he’s run into!

Fused aromatic ring effect on electrocyclization reactions

Aromaticity &electrocyclization Steven Bachrach 22 Jul 2014 1 Comment

Aromaticity and orbital symmetry rules, though seemingly of ancient origin, remain areas of active interest. This paper by Fukazawa, et al combine both issues.1 The multiple-step electrocyclization of 1 gives 2 in a reaction that takes 9 days at 80 °C. What would be the effect of diminishing the aromatic character of the fused rings of 1? Would the reaction be faster or slower?

Before discussing the experimental results, let’s examine the B3LYP/6-31G(d) results for the reaction of 1’, 3 and 5. (Note that a slightly smaller pendant substituent is used in the computations than in the experiment.) The optimized geometries of the critical points along the reaction pathway for the cyclization of 3 are shown in Figure 1.






Figure 1. B3LYP/6-31G(d) optimized geometries and relative energies (kcal mol-1) for the critical points along the reaction 34.
Remember that all structures on my blog can be viewed interactively by clicking on the image of the molecule.

For 1’, the first barrier (for the 8π cyclization) has a barrier of about 23 kcal mol-1, but the second step (the 4π cyclization) has an even larger barrier of 28 kcal mol-1. However, reducing the aromaticity of one of the fused rings (compound 3) leads to lower barriers of 18 and 13 kcal mol-1. For the cyclization of 5, only a single transition state was found – no intermediate and no second TS – with a barrier of 12 kcal mol-1. Thus, removing these external aromatic rings reduces the barrier of the reaction, and that is exactly what is found experimentally!


(1) Fukazawa, A.; Oshima, H.; Shimizu, S.; Kobayashi, N.; Yamaguchi, S. "Dearomatization-Induced Transannular Cyclization: Synthesis of Electron-Accepting Thiophene-S,S-Dioxide-Fused Biphenylene," J. Am. Chem. Soc. 2014, 136, 8738-8745, DOI: 10.1021/ja503499n.


1: InChI=1S/C44H64S4Si4/c1-41(2,3)49(13,14)37-25-29-30-26-38(50(15,16)42(4,5)6)46-34(30)23-24-36-32(28-40(48-36)52(19,20)44(10,11)12)31-27-39(51(17,18)43(7,8)9)47-35(31)22-21-33(29)45-37/h25-28H,1-20H3/b30-29-,32-31-


2: InChI=1S/C44H64S4Si4/c1-41(2,3)49(13,14)29-21-25-26-22-30(50(15,16)42(4,5)6)46-38(26)34-33(37(25)45-29)35-36(34)40-28(24-32(48-40)52(19,20)44(10,11)12)27-23-31(47-39(27)35)51(17,18)43(7,8)9/h21-24H,1-20H3

2’: InChI=1S/C32H40S4Si4/c1-37(2,3)21-13-17-18-14-22(38(4,5)6)34-30(18)26-25(29(17)33-21)27-28(26)32-20(16-24(36-32)40(10,11)12)19-15-23(35-31(19)27)39(7,8)9/h13-16H,1-12H3

3: InChI=1S/C32H40O2S4Si4/c1-39(2,3)29-17-21-22-18-30(40(4,5)6)37-27(22)15-16-28-24(20-32(38(28,33)34)42(10,11)12)23-19-31(41(7,8)9)36-26(23)14-13-25(21)35-29/h17-20H,1-12H3/b22-21-,24-23-

4: InChI=1S/C32H40O2S4Si4/c1-39(2,3)21-13-17-18-14-22(40(4,5)6)36-30(18)26-25(29(17)35-21)27-28(26)32-20(16-24(38(32,33)34)42(10,11)12)19-15-23(37-31(19)27)41(7,8)9/h13-16H,1-12H3

5: InChI=1S/C32H40O8S4Si4/c1-45(2,3)29-17-21-22-18-30(46(4,5)6)42(35,36)26(22)15-16-28-24(20-32(44(28,39)40)48(10,11)12)23-19-31(47(7,8)9)43(37,38)27(23)14-13-25(21)41(29,33)34/h17-20H,1-12H3/b22-21-,24-23-

6: InChI=1S/C32H40O8S4Si4/c1-45(2,3)21-13-17-18-14-22(46(4,5)6)42(35,36)30(18)26-25(29(17)41(21,33)34)27-28(26)32-20(16-24(44(32,39)40)48(10,11)12)19-15-23(47(7,8)9)43(37,38)31(19)27/h13-16H,1-12H3


Aromaticity Steven Bachrach 09 Jul 2014 No Comments

Macrocycles composed of aromatic subunits, like polycycloparaphenylenes, are of interest as components of nanotubes and for possible interesting optical properties. Tremendous advances have occurred over the past decade in preparing these rings ; see for examples these posts. Yamago now reports on the synthesis, optical properties and structure of [4]cyclo-2,7-pyrenylene 1, made by joining four pyrene units together.1

B3LYP/6-31G(d) optimization of the structure of 1 reveals a D2 geometry (Figure 1). This structure shows a very distorted pyrene unit. The strain energy of 1 is estimated as 392 kJ mol-1 (though how this was arrived at is not mentioned!), which is much larger than the strain energy of [8]-cycloparaphenylene.

Figure 1. B3LYP/6-31G(d) optimized structure of 1
This is another molecule to be sure to click on and rotate using JMol.

The nature of the HOMO and LUMO of 1 is very different than that of linear tetra-2,7-pyrene. The degenerate HOMOs and degenerate LUMOs of the linear compound have a node at the 2 and 7 positions and are localized to the terminal and central pyrene units, respectively. The HOMO and LUMO of 1 are fully delocalized. The implications of this are seen in the spectroscopy and electrochemistry of 1.


(1) Iwamoto, T.; Kayahara, E.; Yasuda, N.; Suzuki, T.; Yamago, S. "Synthesis, Characterization, and Properties of [4]Cyclo-2,7-pyrenylene: Effects of Cyclic Structure on the Electronic Properties of Pyrene Oligomers," Angew. Chem. Int. Ed. 2014, 53, 6430-6434, DOI: http://dx.doi.org/10.1002/anie.201403624.


1: InChI=1S/C64H32/c1-2-34-18-50-20-36-4-3-35-19-49(17-33(1)57(35)58(34)36)51-21-37-5-7-41-25-53(26-42-8-6-38(22-51)59(37)61(41)42)55-29-45-13-15-47-31-56(32-48-16-14-46(30-55)63(45)64(47)48)54-27-43-11-9-39-23-52(50)24-40-10-12-44(28-54)62(43)60(39)40/h1-32H/b51-49-,52-50-,55-53-,56-54-

Structure of Citrinalin B

NMR Steven Bachrach 24 Jun 2014 3 Comments

Here is another nice example of the partnership between experiment and computation in ascertaining molecular structure. The Sarpong, Tantillo, Andersen, Berlinck, and Miller groups collaborated on the synthesis, characterization and biosynthesis of some metabolites from Penniculium strains.1 I will focus here on just the structural identification component of this paper; the synthesis and the biosynthesis are very interesting too!

Cyclopiamine A 1 and cyclopiamine B 2 interconvert through an intermediate that allows for the epimerization at carbon bearing the nitro group.2



Citrinalin A 3 might also seem to undergo the same type of ring opening-ring closing reaction to produce citrinalin B. However, the original proposed structure3 of citrinalin B 4 implies an epimerization at a different carbon (at the ring fusion to the terminal 5 member ring). These authors suggested that perhaps the proper structure of citrinalin B is 5, which differs from citrinalin A only at the carbon bearing the nitro group, analogous to the relationship between 1 and 2.




The low energy conformations of both 4 and 5 (actually the trifluoroacetic acid salts) were optimized at B3LYP/6-31+G(d,p) and the chemical shifts for both 1H and 13C were computed, Boltzmann-weighted and scaled, and then compared with the NMR spectra of authentic citrinalin B. (The lowest energy conformations of 4 and 5 are shown in Figure 1.) The corrected mean absolute deviations for the 1H and 13C chemical shift for the original structure 4 are 0.45 ppm and 2.0 ppm, respectively (with the largest outliers of 2.3 ppm for H and 9.6 ppm for C). These errors are about twice what is observed in comparing the experimental and computed 1H and 13C chemical shifts of 3. The agreement between the computed and experimental values using 5 are much improved, with mean deviations of 0.12 and 1.6ppm, and largest deviations of 0.38 ppm for 1H and 4.4 ppm for 13C. Use of Goodman’s DP4 method indicates a 100% probability that the structure of citrinalin B is 5. This prediction is confirmed by the x-ray structure.



Figure 1. B3LYP/6-31+G(d,p) optimized lowest energy conformers of 4 and 5.


(1) Mercado-Marin, E. V.; Garcia-Reynaga, P.; Romminger, S.; Pimenta, E. F.; Romney, D. K.; Lodewyk, M. W.; Williams, D. E.; Andersen, R. J.; Miller, S. J.; Tantillo, D. J.; Berlinck, R. G. S.; Sarpong, R. "Total synthesis and isolation of citrinalin and cyclopiamine congeners," Nature 2014, 509, 318-324, DOI: 10.1038/nature13273.

(2) Bond, R. F.; Boeyens, J. C. A.; Holzapfel, C. W.; Steyn, P. S. "Cyclopiamines A and B, novel oxindole metabolites of Penicillium cyclopium westling," J. Chem. Soc., Perkin Trans I 1979, 1751-1761, DOI: 10.1039/P19790001751.

(3) Pimenta, E. F.; Vita-Marques, A. M.; Tininis, A.; Seleghim, M. H. R.; Sette, L. D.; Veloso, K.; Ferreira, A. G.; Williams, D. E.; Patrick, B. O.; Dalisay, D. S.; Andersen, R. J.; Berlinck, R. G. S. "Use of Experimental Design for the Optimization of the Production of New Secondary Metabolites by Two Penicillium Species," J. Nat. Prod. 2010, 73, 1821-1832, DOI: 10.1021/np100470h.


1: InChI=1S/C26H33N3O5/c1-23(2)12-17(30)20-18(34-5)9-8-16-21(20)28(23)22(31)26(16)13-25(29(32)33)14-27-10-6-7-15(27)11-19(25)24(26,3)4/h8-9,15,19H,6-7,10-14H2,1-5H3/t15-,19+,25+,26-/m1/s1

2: InChI=1S/C26H33N3O5/c1-23(2)12-17(30)20-18(34-5)9-8-16-21(20)28(23)22(31)26(16)13-25(29(32)33)14-27-10-6-7-15(27)11-19(25)24(26,3)4/h8-9,15,19H,6-7,10-14H2,1-5H3/t15-,19+,25-,26-/m1/s1

3: InChI=1S/C25H31N3O5/c1-22(2)11-16(29)19-17(33-22)8-7-15-20(19)26-21(30)25(15)12-24(28(31)32)13-27-9-5-6-14(27)10-18(24)23(25,3)4/h7-8,14,18H,5-6,9-13H2,1-4H3,(H,26,30)/t14-,18+,24+,25-/m0/s1

4: InChI=1S/C25H31N3O5/c1-22(2)11-16(29)19-17(33-22)8-7-15-20(19)26-21(30)25(15)12-24(28(31)32)13-27-9-5-6-14(27)10-18(24)23(25,3)4/h7-8,14,18H,5-6,9-13H2,1-4H3,(H,26,30)/t14-,18-,24-,25+/m1/s1

5: InChI=1S/C25H31N3O5/c1-22(2)11-16(29)19-17(33-22)8-7-15-20(19)26-21(30)25(15)12-24(28(31)32)13-27-9-5-6-14(27)10-18(24)23(25,3)4/h7-8,14,18H,5-6,9-13H2,1-4H3,(H,26,30)/t14-,18+,24-,25-/m0/s1

Solvent effect on carbene spin state

carbenes Steven Bachrach 18 Jun 2014 No Comments

Carbenes remain an active area of interest for computational chemists, as seen in Chapter 5 of my book. For many carbenes, the triplet is the ground state, and that is true of diphenylcarbene 1. Can solvent play a role in the stability of carbene spin states? Surprisingly, the answer, provided in a recent paper by Sander,1 is yes!

In the gas phase, the singlet-triplet gap of 1 is computed to be 5.62 kcal mol-1 at (U)B3LYP/6-311++G(d,p) (and this reduces to 5.06 at (U)B3LYP+D3/6-311++G(d,p)) with the ground state as a triplet. If a single methanol molecules is allowed to approach 1, then the complex involving the singlet has a short hydrogen bond distance of 1.97 Å but the triplet has a much longer distance of 2.33 Å. These structures are shown in Figure 1. This manifests in a dramatic change in the relative stability, with the singlet complex now 0.26 kcal mol-1 (0.44 with the D3 correction) lower in energy than the triplet.



Figure 1. (U)B3LYP/6-311++G(d,p) optimized geometries of the compelxes of methanol with singlet or triplet 1.

IR spectroscopy of 1 in an argon matrix doped with a small amount of methanol confirms the presence of the singlet carbene, and detailed description of the difference in the reactivities of the singlet and triplet are provided.


(1) Costa, P.; Sander, W. "Hydrogen Bonding Switches the Spin State of Diphenylcarbene from Triplet to Singlet," Angew. Chem. Int. Ed. 2014, 53, 5122-5125, DOI: 10.1002/anie.201400176.


1: InChI=1S/C13H10/c1-3-7-12(8-4-1)11-13-9-5-2-6-10-13/h1-10H

Structure of dihydroxycarbene

carbenes Steven Bachrach 09 Jun 2014 No Comments

Dihdroxycarbene was the subject of a post a few years ago relating to how this carbene does not undergo tunneling,1 while related hydroxycarbene do undergo a tunneling rearrangement.

Now we have a gas-phase microwave determination of the trans,cis isomer of dihydroxycarbene.2 The computed CCSD(T)/cc-pCVQZ structure is shown in Figure 1. What is truly remarkable here is the amazing agreement between the experimental and computed structure – as seen in Table 1.The bond distance are in agreement within 0.001 Å and the bond angles agree within 0.3°! Just further evidence of the quality one can expect from high-level computations. And computing this structure was certainly far easier than the experiments!

Figure 1. CCSD(T)/cc-pCVQZ optimized geometry of dihydroxycarbene.

Table 1. Experimental and computed (CCSD(T)/cc-pCVQZ) geometric parameters of dihydroxycarbene.a

























aDistances in Å and angles in deg.


(1) Schreiner, P. R.; Reisenauer, H. P. "Spectroscopic Identification of Dihydroxycarbene," Angew. Chem. Int. Ed. 2008, 47, 7071-7074, DOI: 10.1002/anie.200802105.

(2) Womack, C. C.; Crabtree, K. N.; McCaslin, L.; Martinez, O.; Field, R. W.; Stanton, J. F.; McCarthy, M. C. "Gas-Phase Structure Determination of Dihydroxycarbene, One of the Smallest Stable Singlet Carbenes," Angew. Chem. Int. Ed. 2014, 53, 4089-4092, DOI: 10.1002/anie.201311082.


Dihydroxycarbene: InChI=1S/CH2O2/c2-1-3/h2-3H

[2,2]paracyclophane – structure resolved

Uncategorized Steven Bachrach 28 May 2014 2 Comments

The structure of [2,2]paracyclophane 1 has been somewhat controversial for some time. Early x-ray structures indicated that the molecule was quite symmetric, D2h with the phenyl rings and the ethyl bridges eclipsed. Subsequent low-T experiments suggested a lower symmetry form D2 with a twist that relieves some of the unfavorable eclipsing interactions in the ethano bridges. High-level computations by Grimme1 and then some by myself2 indicated that the D2 structure is the lowest energy conformation, with however a low barrier through the D2h structure.

The suggestion of the D2 minimum was vehemently criticized by Dodziuk, et al. on the basis of NMR analysis.3

Now, a low temperature x-ray experiment of 1 brings clarity to the situation.4 (The introduction provides a nice summary of the previous 70 year history regarding the structure of 1.) At temperatures below 45 K, 1 is found as a single structure of D2 symmetry (with space group P4n2). The structure is shown in Figure 1. A phase change occurs at about 45 K, and above 60 K the crystal has P42/mnm symmetry. The structure of 1 at the high temperature appears as D2h with somewhat broader thermal motion of the ethano carbons than the phenyl carbons. The low T structure is in excellent accord with the previous theoretical studies, and the phase transition helps bring into accord all of the previous x-ray crystallographic work.

Figure 1. X-ray structure at 15K of 1.


(1) Grimme, S. "On the Importance of Electron Correlation Effects for the π-π Interactions in Cyclophanes," Chemistry Eur. J. 2004, 10, 3423-3429, DOI: 10.1002/chem.200400091.

(2) Bachrach, S. M. "DFT Study of [2.2]-, [3.3]-, and [4.4]Paracyclophanes: Strain Energy, Conformations, and Rotational Barriers," J. Phys. Chem. A 2011, 115, 2396-2401, DOI: 10.1021/jp111523u.

(3) Dodziuk, H.; Szymański, S.; Jaźwiński, J.; Ostrowski, M.; Demissie, T. B.; Ruud, K.; Kuś, P.; Hopf, H.; Lin, S.-T. "Structure and NMR Spectra of Some [2.2]Paracyclophanes. The Dilemma of [2.2]Paracyclophane Symmetry," J. Phys. Chem. A 2011, 115, 10638-10649, DOI: 10.1021/jp205693a.

(4) Wolf, H.; Leusser, D.; R. V. Jørgensen, M.; Herbst-Irmer, R.; Chen, Y.-S.; Scheidt, E.-W.; Scherer, W.; Iversen, B. B.; Stalke, D. "Phase Transition of [2,2]-Paracyclophane – An End to an Apparently Endless Story," Chem. Eur. J. 2014, 20, 7048–7053, DOI: 10.1002/chem.201304972.


1: InChI=1S/C16H16/c1-2-14-4-3-13(1)9-10-15-5-7-16(8-6-15)12-11-14/h1-8H,9-12H2

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