Houk and Doubleday have a nice follow-up study¹ to their previous MD study² of 1,3-dipolar cycloadditions, which I posted on here. They report on the cycloaddition of either acetylene or ethylene to 9 different 1,3-dipoles. Continuing on Houk’s recent thread of looking at distortion energies to attain the TS, they note that a sizable fraction (often over 50%) of the distortion energy is associated with bending the X-Y-Z bond of the dipole, consistent with their earlier work suggesting the importance of this vibration in attaining and crossing the TS. What’s new in this paper is the extensive MD studies, with trajectory studies of all 18 reactions. These revealed again the importance of vibrational energy in this X-Y-Z bending mode in crossing the TS. They also noted the role of translational energy, and the relationship between translational vs. vibrational energy depending on the early/late nature of the TS. Their final point was that the lifetime of any diradical or diradical-like intermediate is so short, less than the time of a bond vibration, so that one can discount any diradical participation. The reaction is concerted.

References

(1) Xu, L.; Doubleday, C. E.; Houk, K. N., "Dynamics of 1,3-Dipolar Cycloadditions: Energy Partitioning of Reactants and Quantitation of Synchronicity," J. Am. Chem. Soc., 2010, ASAP, DOI: /10.1021/ja909372f

(2) Xu, L.; Doubleday, C. E.; Houk, K. N., "Dynamics of 1,3-Dipolar Cycloaddition Reactions of Diazonium Betaines to Acetylene and Ethylene: Bending Vibrations Facilitate Reaction," Angew. Chem. Int. Ed., 2009, 48, 2746-2748, DOI: 10.1002/anie.200805906

The nature of reactions of indolynes is the subject of two recent computational/experimental studies. There are three isomeric indolynes 1a-c which are analogues of the more famous benzyne (which I discuss in significant detail in Chapter 4.4 of my book).

One might anticipate that the indolynes undergo comparable reactions as benzyne, like Diels-Alder reactions and nucleophilic attack. In fact the indolynes do undergo these reactions, with unusual regiospecificity. For example, the reaction of the substituted 6,7-indolyne undergoes regioselective Diels-Alder cycloaddition with substituted furans (Scheme 1), but the reaction with the other indolynes gives no regioselection. ¹ Note that the preferred product is the more sterically congested adduct.

Scheme 1

In the case of nucleophilic addition, the nucleophiles add specifically to C₆ with substituted 6,7-indolynes (Scheme 2), while addition to 4,5-indolynes preferentially gives the C₅-adduct (greater than 3:1) while addition to the 5,6-indolynes preferentially gives the C₅-adduct), but with small selectivity (less than 3:1).²

Scheme 2

The authors of both papers – Chris Cramer studied the Diels-Alder chemistry and Ken Houk studied the nucleophilic reactions – employed DFT computations to examine the activation barriers leading to the two regioisomeric products. So for example, Figure 1 shows the two transition states for the reaction of 2c with 2-iso-propyl furan computed at MO6-2X/6-311+G(2df,p).

ΔG‡ = 9.7

ΔG‡ = 7.6

Figure 1. MO6-21/6-311+G(2df,p) optimized TSs for the reaction of 2-iso-propylfuran with 2c. Activation energy (kcal mol^-1) listed below each structure.¹

The computational results are completely consistent with the experiments. For the Diels-Alder reaction of 2-t-butylfuran with the three indolynes 2a-c, the lower computed TS always corresponds with the experimentally observed major product. The difference in the energy of the TSs leading to the two regioisomers for reaction with 2a and 2b is small (less than 1 kcal mol^-1), consistent with the small selectivity. On the other hand, no barrier could be found for the reaction of 2-t-butylfuran with 2c that leads to the major product. Similar results are also obtained for the nucleophilic addition – in all cases, the experimentally observed major product corresponds with the lower computed activation barrier.

So what accounts for the regioselectivity? Both papers make the same argument, though couched in slightly different terms. Houk argues in terms of distortion energy – the energy needed to distort reactants to their geometries in the TS. As seen in Figure 2, the benzyne fragment of 2a is distorted, with the C-C-C angle at C₄ of 125° and at C₅ of 129°. In the transition states, the angle at the point of nucleophilic attack widens. Since the angle starts out wider at C₅, attack there is preferred, since less distortion is needed to achieve the geometry of the TS.

2a
TS at C4 ΔG‡ = 12.9	TS at C5 ΔG‡ = 9.9

Figure 2. B3LYP/6-31G(d) optimized structures of 2a and the TSs for the reaction of aniline with 2a. Activation energy in kcal mol^-1.²

Cramer argues in terms of the indolyne acting as an electrophile. Increasing substitution at the furan 2-position makes is better at stabilizing incipient positive charge that will build up there during a (very) asymmetric Diels-Alder transition state. This explains the increasing selectivity of the furan with increasing substitution. The indolyne acting as an electrophile means that the attack will lead from the center will lesser charge. In 2c, the C-C-C angle at C₆ is 135.3°, while that at C₇ is 117.2°. This makes C₇ more carbanionic and C₆ more carbocationic; therefore, the first bond made is to C₆, leading to the more sterically congested product. Note that Houk’s argument applies equally well, as C₆ is predistorted to the TS geometry.

References

(1) Garr, A. N.; Luo, D.; Brown, N.; Cramer, C. J.; Buszek, K. R.; VanderVelde, D., "Experimental and Theoretical Investigations into the Unusual Regioselectivity of 4,5-, 5,6-, and 6,7-Indole Aryne Cycloadditions," Org. Lett., 2010, 12, 96-99, DOI: 10.1021/ol902415s

(2) Cheong, P. H. Y.; Paton, R. S.; Bronner, S. M.; Im, G. Y. J.; Garg, N. K.; Houk, K. N., "Indolyne and Aryne Distortions and Nucleophilic Regioselectivites," J. Am. Chem. Soc., 2010, 132, 1267-1269, DOI: 10.1021/ja9098643

InChIs

1a: InChI=1/C8H5N/c1-2-4-8-7(3-1)5-6-9-8/h2,4-6,9H
InChIKey=RNDHGGYOIRREHC-UHFFFAOYAU

1b: InChI=1/C8H5N/c1-2-4-8-7(3-1)5-6-9-8/h3-6,9H
InChIKey=WWZQFJXNXMIWCD-UHFFFAOYAO

1c: InChI=1/C8H5N/c1-2-4-8-7(3-1)5-6-9-8/h1,3,5-6,9H
InChIKey=UHIRLIIPIXHWLT-UHFFFAOYAH

2a: InChI=1/C9H7N/c1-10-7-6-8-4-2-3-5-9(8)10/h3,5-7H,1H3
InChIKey=VTVUPAJGRVFCKI-UHFFFAOYAJ

2b: InChI=1/C9H7N/c1-10-7-6-8-4-2-3-5-9(8)10/h4-7H,1H3
InChIKey=KKPOWDDYMOXTFW-UHFFFAOYAN

2c: InChI=1/C9H7N/c1-10-7-6-8-4-2-3-5-9(8)10/h2,4,6-7H,1H3
InChIKey=MDAHOGWZOBLIEX-UHFFFAOYAZ

Houk has performed a very nice examination of the performance of some density functionals.¹ He takes a quite different approach than what was proposed by Grimme – the “mindless” benchmarking² using random molecules (see this post). Rather, Houk examined a series of simple aldol, Mannich and α-aminoxylation reactions, comparing their reaction energies predicted with DFT against that predicted with CBQ-QB3. The idea here is to benchmark DFT performance for simple reactions of specific interest to organic chemists. These reactions are of notable current interest due their involvement in organocatalytic enantioselective chemistry (see my posts on the aldol, Mannich, and Hajos-Parrish-Eder-Sauer-Wiechert reaction). Examples of the reactions studied (along with their enthalpies at CBS-QB3) are Reaction 1-3.

For the four simple aldol reactions and four simple Mannich reactions, PBE1PBE,
mPW1PW91 and MO6-2X all provided reaction enthalpies with errors of about 2 kcal mol^-1. The much maligned B3LYP functional, along with B3PW91 and B1B95 gave energies with significant larger errors. For the three α-aminoxylation reactions, the errors were better with B3PW91 and B1B95 than with PBE1PBE or MO6-2X. Once again, it appears that one is faced with finding the right functional for the reaction under consideration!

Of particular interest is the decomposition of these reactions into related isogyric, isodesmic
and homdesmic reactions. So for example Reaction 1 can be decomposed into Reactions 4-7 as shown in Scheme 1. (The careful reader might note that these decomposition reactions are isodesmic and homodesmotic and hyperhomodesmotic reactions.) The errors for Reactions 4-7 are typically greater than 4 kcal mol^-1 using B3LYP or B3PW91, and even with MO6-2X the errors are about 2 kcal mol^-1.

Scheme 1.

Houk also points out that Reactions 4, 8 and 9 (Scheme 2) focus on having similar bond changes as in Reactions 1-3. And it’s here that the results are most disappointing. The errors produced by all of the functionals for Reactions 4,8 and 9 are typically greater than 2 kcal mol^-1, and even MO2-6x can be in error by as much as 5 kcal mol^-1. It appears that the reasonable performance of the density functionals for the “real world” aldol and Mannich reactions relies on fortuitous cancellation of errors in the underlying reactions. Houk calls for the development of new functionals designed to deal with fundamental simple bond changing reactions, like the ones in Scheme 2.

Scheme 2

References

(1) Wheeler, S. E.; Moran, A.; Pieniazek, S. N.; Houk, K. N., "Accurate Reaction Enthalpies and Sources of Error in DFT Thermochemistry for Aldol, Mannich, and α-Aminoxylation Reactions," J. Phys. Chem. A 2009, 113, 10376-10384, DOI: 10.1021/jp9058565

(2) Korth, M.; Grimme, S., ""Mindless" DFT Benchmarking," J. Chem. Theory Comput. 2009, 5, 993–1003, DOI: 10.1021/ct800511q

Torquoselectivity rules (discussed in Chapter 3.5 of my book) indicate that 3-phenylcyclobutene will ring-open to give the outward rotated product (Reaction 1). Houk and Tang report a seeming contradiction, namely the ring opening of 1 gives only the inward product 3 (Reaction 2).¹

B3LYP/6-31G* computations on the ring-opening of 4 indicate that the activation barrier for the outward path (leading to 5) is nearly 8 kcal mol^-1 lower than the barrier for the inward path (leading to 6, see Reaction 3). This is consistent with torquoselectivity rules, but what is going on in the experiment?

In the investigation of the isomerization of the outward to inward pathway, they discovered a low-energy pyran intermediate 7. This led to the proposal of the mechanism shown in Reaction 3. The highest barrier is for the electrocyclization that leads to the outward product 5. The subsequent barriers - the closing to the pyran 7 and then the torquoselective ring opening to 6 –  are about than 13 kcal mol^-1 lower in energy than for the first step. The observed product is the thermodynamic sink. And the nice thing about this mechanism is that torquoselection is preserved.

References

(1) Um, J. M.; Xu, H.; Houk, K. N.; Tang, W., "Thermodynamic Control of the Electrocyclic
Ring Opening of Cyclobutenes: C=X Substituents at C-3 Mask the Kinetic Torquoselectivity," J. Am. Chem. Soc. 2009, 131, 6664-6665, DOI: 10.1021/ja9016446.

InChIs

4: InChI=1/C16H16O6/c1-20-13(17)11-9-16(14(18)21-2,15(19)22-3)12(11)10-7-5-4-6-8-10/h4-9,12H,1-3H3
InChIKey=VBOGEHVOAGDMNG-UHFFFAOYAR

5: InChI=1/C16H16O6/c1-20-14(17)12(9-11-7-5-4-6-8-11)10-13(15(18)21-2)16(19)22-3/h4-10H,1-3H3/b12-9-
InChIKey=PZRWKBUUAFMPBC-XFXZXTDPBF

6: InChI=1/C16H16O6/c1-20-14(17)12(9-11-7-5-4-6-8-11)10-13(15(18)21-2)16(19)22-3/h4-10H,1-3H3/b12-9+
InChIKey=PZRWKBUUAFMPBC-FMIVXFBMBS

7: InChI=1/C16H16O6/c1-19-14(17)11-9-12(15(18)20-2)16(21-3)22-13(11)10-7-5-4-6-8-10/h4-9,13H,1-3H3/t13-/m0/s1
InChIKey=QSJZITDSTPMCEM-ZDUSSCGKBG

The importance of dynamics in simple reactions is made yet again in a recent study by Doubleday and Houk in 1,3-dipolar cycloadditions.¹ They looked at the reaction of acetylene or ethylene with either nitrous oxide, diazonioazanide, or methanediazonium. The transition state for these 6 reactions all show a concerted reaction. The transition vector has three major components; (a) symmetric formation/cleavage of the two new σ bonds, (b) bending of the dipolar component, or (c) symmetric bending of the hydrogens of ethylene or acetylene.

Classical trajectories were traced from the transition state back to reactant and forward to product. In the approach of the two fragments, the dipole bend vibrates, but then after the TS, it needs to bend quickly to close the 5-member ring. This means that the bending mode effectively has to “turn a corner” in phase space, and without energy in this mode, the molecules will simple bounce off of each other. Analysis of the reactants indicates significant vibrational excitation of the dipole bending mode.

References

(1) Xu, L.; Doubleday, C. E.; Houk, K. N., "Dynamics of 1,3-Dipolar Cycloaddition Reactions of Diazonium Betaines to Acetylene and Ethylene: Bending Vibrations Facilitate Reaction," Angew. Chem. Int. Ed. 2009, 48, 2746-2748, DOI: 10.1002/anie.200805906

What is the rate determining step in the Hajos-Parrish-Eder-Sauer-Wiechert reaction (reaction 1)? This basic question of the mechanism for the first example of the use of proline as a catalyst remains unanswered, though a recent paper by Meyer and Houk¹ does moves us forward.

Their ¹³C kinetic isotope effect study revealed that only the nucleophilic ketone (the carboyl of the butyl chain) experiences any significant effect, with a value of about 1.03. B3LYP/6-31G(d,p) computations of the three transition states shown below were performed for both the gas phase and solution using IEF-PCM. Calculations of the transition state for the formation of the C-C bond (TS3) predicts no kinetic isotope effect, indicating that it is not the rate limiting step, in conflict with previous² suggestions. The transition states for the formation of the carbinolamine (TS1) and formation of the iminium (TS2) both predict an isotope effect comparable with experiment. TS1 is about 3 kcal mol^-1 higher in energy than TS2. The authors conclude that a step prior to formation of the C-C is the rate limiting step of the Hajos-Parrish-Eder-Sauer-Wiechert reaction, but cannot discern between the two possibilities examined.

References

(1) Zhu, H.; Clemente, F. R.; Houk, K. N.; Meyer, M. P., "Rate Limiting Step Precedes C-C Bond Formation in the Archetypical Proline-Catalyzed Intramolecular Aldol Reaction," J. Am. Chem. Soc., 2009, 131, 1632-1633, DOI: 10.1021/ja806672y.

(2) Clemente, F. R.; Houk, K. N., "Computational Evidence for the Enamine
Mechanism of Intramolecular Aldol Reactions Catalyzed by Proline," Angew. Chem. Int. Ed., 2004, 43, 5766-5768, DOI: 10.1002/anie.200460916.

InChIs

2-methyl-2-(3-oxobutyl)cyclopentane-1,3-dione:
InChI=1/C10H14O3/c1-7(11)5-6-10(2)8(12)3-4-9(10)13/h3-6H2,1-2H3
InChIKey=OZBYSCPBJGAYMQ-UHFFFAOYAW

(3aS,7aS)-3a-hydroxy-7a-methyl-3,4,6,7-tetrahydro-2H-indene-1,5-dione:
InChI=1/C10H14O3/c1-9-4-2-7(11)6-10(9,13)5-3-8(9)12/h13H,2-6H2,1H3/t9-,10+/m1/s1
InChIKey=PUHCDQVSBDIJTM-ZJUUUORDBA

Concern about the use of DFT for general use in organic chemistry remains high; see my previous posts (1, 2, 3). Houk has now examined the reaction enthalpies of ten simple Diels-Alder reactions using a variety of functionals in the search for the root cause of the problem(s).¹

The ten reactions are listed in Scheme 1, and involve cyclic and acyclic dienes and either ethylene or acetylene as the dienophile. Table 1 lists the minimum and maximum deviation of the DFT enthalpies relative to the CBS-QB3 enthalpies (which are in excellent accord with experiment). Clearly, all of the DFT methods perform poorly, with significant errors in these simple reaction energies. The exception is the MO6-2X functional, whose errors are only slightly larger than that found with the SCS-MP2 method. Use of a larger basis set (6-311+G(2df,2p)) reduced errors only a small amount.

Table 1. Maximum, minimum and mean deviation of reaction enthalpies (kcal mol^-1) for the reactions in Scheme 1 using the 6-31+G(d,p) basis set.¹

In order to discern where the problem originates, they next explore the changes that occur in the Diels-Alder reaction: two π bonds are transformed into one σ and one π bond and the conjugation of the diene is lost, leading to (proto)branching in the product. Reactions 1-3 are used to assess the energy consequence of converting a π bond into a σ bond, creating a protobranch, and the loss of conjugation, respectively.

The energies of these reactions were then evaluated with the various functionals. It is only with the conversion of the π bond into a σ bond that they find a significant discrepancy between the DFT estimates and the CBS-QB3 estimate. DFT methods overestimate the energy for the π → σ exchange, by typically around 5 kcal mol^-1, but it can be much worse. Relying on cancellation of errors to save the day for DFT will not work when these types of bond changes are involved. Once again, the user of DFT is severely cautioned!

References

(1) Pieniazek, S. N.; Clemente, F. R.; Houk, K. N., "Sources of Error in DFT Computations of C-C Bond Formation Thermochemistries: π → σ Transformations and Error Cancellation by DFT Methods," Angew. Chem. Int. Ed. 2008, 47, 7746-7749, DOI: 10.1002/anie.200801843

Ken Houk has produced a very nice minireview on bifurcations in organic reactions.¹ This article is a great introduction to a topic that has broad implication for mechanistic concepts. Bifurcations result when a valley-ridge inflection point occurs on or near the intrinsic reaction coordinate. This inflection point allows trajectories to split into neighboring basins (to proceed to different products) without crossing a second transition state. In the examples discussed, the reactant crosses a single transition state and then leads to two different products. This is the so-called “two-step no intermediate” process.

I discuss the implications of these kinds of potential energy surfaces, and other ones of a pathological nature, in the last chapter of my book. Very interesting reaction dynamics often are the result, leading to a mechanistic understanding far from the ordinary!

References

(1) Ess, D. H.; Wheeler, S. E.; Iafe, R. G.; Xu, L.; Çelebi-Ölçüm, N.; Houk, K. N., "Bifurcations on Potential Energy Surfaces of Organic Reactions," Angew. Chem. Int. Ed. 2008, DOI: 10.1002/anie.200800918

An alternative take on the nature of the interaction in π-stacking is offered by Wheeler and Houk.¹ They start by examining the binding between benzene and a series of 24 substituted benzenes. Two representative dimmers are shown in Figure 1, where the substituent is NO₂ or CH₂OH. As was noted in a number of previous studies,^2-6 the binding with any substituted benzene is stronger than the parent benzene dimer. Nonetheless, Wheeler and Houk point out that the binding energy has a reasonable correlation with σ_m. It appears that the benzene dimer itself is the outlier; the binding energy when the substituent is CH₂OH, whose σ_m value is zero, is bound more tightly than the benzene dimer. They conclude that there is a dispersive interaction between any substituent and the other benzene ring.

(a)	(b)
(c)	(d)

Figure 1. MO5-2X/6-31+G(d) optimized geometries of (a) C₆H₆-C₆H₅NO₂, (b) C₆H₆-C₆H₅CH₂OH, (c) C₆H₆-HNO₂, and (d) C₆H₆-HCH₂OH.¹

They next constructed an admittedly very crude model system whereby the substituted benzene C₆H₅X is replaced by HX; the corresponding models are also shown in Figure 1. The binding energies of these model dimmers correlates very well with the real dimmers, with r = 0.91. Rather than involving the interaction of the π-electrons, the origin of the enhanced binding in aromatic dimers involves electrostatic interactions of the substituent with the other aromatic ring – effectively the quadrupole of the unsubstituted ring interacts with the dipoles of the substituent and its ring system. In addition, the inherent dispersive interaction increase the binding.

References

(1) Wheeler, S. E.; Houk, K. N., "Substituent Effects in the Benzene Dimer are Due to Direct Interactions of the Substituents with the Unsubstituted Benzene," J. Am. Chem. Soc., 2008, 130, 10854-10855, DOI: 10.1021/ja802849j.

(2) Sinnokrot, M. O.; Sherrill, C. D., "Unexpected Substituent Effects in Face-to-Face π-Stacking Interactions," J. Phys. Chem. A, 2003, 107, 8377-8379, DOI: 10.1021/jp030880e.

(3) Sinnokrot, M. O.; Sherrill, C. D., "Substituent Effects in π-&pi Interactions: Sandwich and T-Shaped Configurations," J. Am. Chem. Soc., 2004, 126, 7690-7697, DOI: 10.1021/ja049434a.

(4) Sinnokrot, M. O.; Sherrill, C. D., "Highly Accurate Coupled Cluster Potential Energy Curves for the Benzene Dimer: Sandwich, T-Shaped, and Parallel-Displaced Configurations," J. Phys. Chem. A, 2004, 108, 10200-10207, DOI: 10.1021/jp0469517

(5) Lee, E. C.; Kim, D.; Jurecka, P.; Tarakeshwar, P.; Hobza, P.; Kim, K. S., "Understanding of Assembly Phenomena by Aromatic-Aromatic Interactions: Benzene Dimer and the Substituted Systems," J. Phys. Chem. A 2007, 111, 3446-3457, DOI: 10.1021/jp068635t.

(6) Grimme, S.; Antony, J.; Schwabe, T.; Mück-Lichtenfeld, C., "Density functional theory with dispersion corrections for supramolecular structures, aggregates, and complexes of
(bio)organic molecules," Org. Biomol. Chem. 2007, 741-758, DOI: 10.1039/b615319b

Peter Vollhardt and Ken Houk have teamed up on an interesting account of pericyclic reactions of molecules related to starphenylene.¹ This touches on the nature of aromatic compounds and pericyclic reaction mechanisms, topics I take up in a few places in the book.

Compound 1 rearranges at 120 °C to 3, and the presumed pathway is
through 2 – the simultaneous [2+2+2] ring opening through the all-disrotatory path.
However, the computed (B3LYP/6-31G(d) activation energy is 34.6 kcal mol^-1 for this path, much higher than the experimental activation enthalpy, which is 28.9 kcal mol^-1.

The alternative path is to sequential break the cyclobutene rings with the standard conrotatory stereochemistry. This would give 4 and the barrier is 32.5 kcal mol^-1, in better agreement with experiment. From here, there is a bond shift, which traverses a Möbius geometry – as proposed by Karney and Castro (see the book and also this previous post). An electrocylization, followed by a Diels-Alder cycloaddition completes the path to 3. The rate determining step is the first: 1 ↔ 4.

On the other hand, upon heating 5 produces 6. Here the computed barrier for the [2+2+2] reaction (32.6 kcal mol^-1) is in nice agreement with the experimental value (34.1 kcal mol^-1), while the stepwise pathway has a much higher barrier (39.9 kcal mol^-1). They did not locate the polycyclic analogue of 3 (namely, 7) in the reaction of 5. This may be due in part to the fact that the bond shift is accompanied by a loss of aromaticity.

References

(1) Eichberg, M. J. H., K. N.; Lehmann, J.; Leonard, P. W.; Märker, A.; Norton, J. E.; Sawicka, D.; Vollhardt, K. P. C. W., G. D.; Wolff, S., "The Thermal Retro[2+2+2] cycloaddition of Cyclohexane Activated by Triscyclobutenannelation: Concerted All-Disrotatory versus Stepwise Conrotatory Pathways to Fused [12]Annulenes," Angew. Chem. Int. Ed., 2007, 46, 6894-6898, DOI: 10.1002/anie.200702474

InChIs

1: InChI=1/C24H30/c1-2-8-14-13(7-1)19-20(14)22-17-11-5-6-12-18(17)24(22)23-16-10-4-3-9-15(16)21(19)23/h19-24H,1-12H2/t19-,20+,21-,22+,23-,24+

2: InChI=1/C24H30/c1-2-8-20-15-16-22-10-5-6-12-24(22)18-17-23-11-4-3-9-21(23)14-13-19(20)7-1/h13-18H,1-12H2/b14-13-,16-15-,18-17-,19-13-,20-15+,21-14+,22-16+,23-17+,24-18-

3: InChI=1/C24H30/c1-2-8-14-13(7-1)19-21-15-9-3-4-10-16(15)22-20(14)23(19)17-11-5-6-12-18(17)24(21)22/h19-24H,1-12H2

4: InChI=1/C24H30/c1-2-8-20-15-16-22-10-5-6-12-24(22)18-17-23-11-4-3-9-21(23)14-13-19(20)7-1/h13-18H,1-12H2/b14-13+,16-15+,18-17+,19-13-,20-15+,21-14+,22-16-,23-17-,24-18+

5: InChI=1/C24H18/c1-2-8-14-13(7-1)19-20(14)22-17-11-5-6-12-18(17)24(22)23-16-10-4-3-9-15(16)21(19)23/h1-12,19-24H/t19-,20+,21-,22+,23-,24+

6: InChI=1/C24H18/c1-2-8-20-15-16-22-10-5-6-12-24(22)18-17-23-11-4-3-9-21(23)14-13-19(20)7-1/h1-18H/b14-13-,16-15-,18-17-,19-13-,20-15+,21-14+,22-16+,23-17+,24-18-

7: InChI=1/C24H18/c1-2-8-14-13(7-1)19-21-15-9-3-4-10-16(15)22-20(14)23(19)17-11-5-6-12-18(17)24(21)22/h1-12,19-24H