Stereoisomerism, crystal structures, and dynamics of belt-shaped cyclonaphthylenes

Edited by Jerrold Meinwald, Cornell University, Ithaca, NY, and approved May 26, 2016 (received for review April 25, 2016)
June 29, 2016
113 (29) 8109-8114

Significance

Stereoisomerism of molecules shapes an indispensable concept in molecular science. Stereoisomerism becomes complicated in cyclic structures such as saccharides but has now been established to form a fundamental knowledge in chemistry. When dynamic conformations are involved in the stereoisomerism of cyclic structures, there emerges a unique type of isomerism. Such perplexing dynamic stereoisomerism is involved in belt-shaped cyclic arrays of aromatic molecules, known recently as carbon nanohoops, but has scarcely been clarified to date. In this paper, a series of nanohoops with multiple panels of naphthalene has been synthesized. Their stereoisomerism, static structures, and dynamic behaviors have been investigated by using mathematical, crystallographic, and spectroscopic methods to reveal the unique structural chemistry present in segmental sp2-carbon networks of carbon nanotubes.

Abstract

The chemistry of a belt-shaped cyclic array of aromatic panels, a so-called “nanohoop,” has increasingly attracted much interest, partly because it serves as a segmental model of single-wall carbon nanotubes with curved sp2-carbon networks. Although the unique molecular structure of nanohoops is expected to deepen our understanding in curved π-systems, its structural chemistry is still in its infancy despite structural variants rapidly accumulated over the past several years. For instance, structural characteristics that endow the belt shapes with rigidity, an important structural feature relevant to carbon nanotubes, have not been clarified to date. We herein report the synthesis and structures of a series of belt-shaped cyclonaphthylenes. Random synthesis methods using three precursor units with different numbers of naphthylene panels allowed us to prepare 6 congeners consisting of 6 to 11 naphthylene panels, and relationships between the rigidity and the panel numbers, i.e., molecular structures, were investigated. Fundamental yet complicated stereoisomerism in the belt-shaped structures was disclosed by mathematical methods, and dynamics in the panel rotation was revealed by dynamic NMR studies with the aid of theoretical calculations.
The chemistry of hoop-shaped cycloarylenes (nanohoops) is being enriched by increasing variations in the molecular structures (14). The structural diversity in the constitutional arylene panels has gradually increased by starting from cyclo-para-phenylenes (CPP; Fig. 1) with the most primordial panel being benzene (57), and the nanohoop chemistry is deepening our understanding of π-conjugated structures with belt-shaped, curved sp2-carbon networks that mimic single-wall carbon nanotubes (SWNTs) (8).
Fig. 1.
Representative examples of nanohoop molecules.
Composed of arylene panels connected via multiple single-bond linkages, the belt-shaped nanohoop structures pose a fundamental and important question related to the isomerism and persistency of the curved sp2-carbon networks (8). Previously, we synthesized the first, to our knowledge, belt-persistent nanohoops to demonstrate that large arylene panels, such as chrysene and anthanthrene, endowed the nanohoop molecules with belt persistency. The belt-shaped atropisomers of [4]cyclochrysenylenes ([4]CC) (9, 10) and [4]cycloanthanthrenylenes ([4]CA) (11) were separated and identified as discrete molecular entities (Fig. 1), and the atropisomerism uniquely originated from restricted sp2–sp2 rotations due to macrocyclic ring strain (12). However, the experimental relationship between the structure and dynamics of the arylene rotations in the nanohoops remains unclear (1316) and will add novel insight to biaryl atropisomerism with structural and historical importance (1720). We herein report our first attempt to reveal the structure–dynamics relationship in belt-shaped nanohoop molecules via the synthesis of a series of [n]cyclo-amphi-naphthylenes ([n]CaNAP, n = 6–11; Fig. 1) (21). Albeit simple at first glance, the molecular structures were rich in structural chemistry including stereoisomerism, belt-shaped crystal structures, and dynamics of naphthylene rotations. In our previous paper reporting, to our knowledge, the first belt-shaped cyclonaphthylenes (21), we disclosed the dynamic, fluctuating structure of one congener ([8]CaNAP) and demonstrated that the belt-shaped structures could be rigidified by bridging half of the biaryl linkages with methylene moieties. In this paper on a series of congeners, we determined that the arylene rotation depended on the hoop size and was spectroscopically restricted in the smallest congener ([6]CaNAP) at ambient temperature in solution.

Results and Discussion

Synthesis.

We synthesized six congeners of [n]CaNAP where n = 6–11 from two sets of macrocyclization reactions. A similar random synthesis route has been investigated by Yamago and co-workers to synthesize six [n]CPP congeners where n = 8–13 via a combination of double-panel biphenyl and triple-panel terphenyl precursors (22). In this study, we prepared three different precursors including naphthalene 1, binaphthyl 2, and ternaphthyl 3 and examined two different combinations in the Pt-mediated macrocyclization of diborylated precursors (9). A combination of single- and double-panel precursors (1 and 2) afforded three [n]CaNAP congeners where n = 6–8 via Pt-mediated macrocyclization followed by reductive elimination reactions (Scheme 1A). The structural variation was increased in another combination of double- and triple-panel precursors (2 and 3) to afford four [n]CaNAP congeners where n = 8–11 (Scheme 1B). The congeners were chromatographically isolated by using gel permeation chromatography with a polystyrene stationary phase (JAI GEL 1H-40, 2H-40, and 2.5H-40) and high-performance liquid chromatography with a naphthalene-capped silica gel stationary phase (Cosmosil πNAP) (SI Appendix). Three possible congeners with n = 4, 5, and 12 were not obtained, most likely because of severe macrocyclic strain for the smaller congeners and low solubility for the larger one. During the synthesis of large congeners, we indeed observed formation of precipitates.
Scheme 1.
Two methods of random synthesis. (A) Synthesis of [n]CaNAP of n = 6–8. (B) Synthesis of [n]CaNAP of n = 8–11.

Stereoisomerism: Structural Mathematics.

The number of possible stereoisomers of the [n]CaNAP congeners requires mathematical consideration. Due to the C2h point symmetry of amphi-linked naphthylene (21), two facial orientations of the arylene panel exist in the belt-shaped nanohoops (“a face” or “b face” in Fig. 2). Owing to the D2h point symmetry of para-linked phenylene panel, this stereoisomerism is absent in CPP congeners, which, in turn, makes it difficult to spectroscopically study their dynamics. The facial orientations in nanohoops with n panels generally result in 2n adoptable structures, and the number of stereoisomers (diastereomers and enantiomer pairs) must be extracted from these adoptable structures. This problem is common in any nanohoop with isomerism and complicated by increasing numbers of arylene panels. Originally for [8]CaNAP, we manually examined and counted the possible isomeric structures in the 28 adoptable structures but made one mistake in the count (21). Therefore, a versatile, mathematical solution has been developed for nanohoop isomerism, which illustrates the potential difficulty in the synthesis, separation, and identification of corresponding nanohoops that are prepared in the future.
Fig. 2.
Structures of nanohoops and the binary necklace problem in mathematics.
The solution for the numbers of nanohoop isomers was found from the binary necklace problem in the field of mathematics (23). In short, this mathematical solution addresses the number of distinct necklaces with n beads with two different colors (red or blue), which corresponds to the number of nanohoop stereoisomers with n arylene panels with two facial orientations (a or b) (Fig. 2). Therefore, the number of stereoisomers [S(n)] is given by two equations including one equation for n = odd number (Eq. 1) and another equation for n = even number (Eq. 2),
S(n)=12n(k=1n2(n,k)+n×2(n+1)/2),
[1]
S(n)=12n(k=1n2(n,k)+3n×2(n2)/2),
[2]
where (n,k) is the greatest common divisor of n and k.
The diastereomers must account for structural equivalence that emerges due to mirror symmetry and requires another mathematical treatment that considers the symmetry types of the periodic sequences (24, 25). The equations proposed by mathematicians were simplified to be applied to static stereoisomerism of polyols (26). After minor corrections, equations for the numbers of diastereomers [D(n)] are shown in Eqs. 3 and 4 for n = odd number and even number, respectively,
D(n)=14nk=1n2(n,k)+2(n3)/2,
[3]
D(n)=14nk=1n2(n,k)+14nl=12|n/(n,l)n2(n,l)+2(n/2)1,
[4]
where the summation of the second term of the right-hand side of Eq. 4 is taken over all l so that n/(n,l) is even.
The solution for the number of enantiomer pairs [E(n)] was found from the self-dual two-colored necklaces problem (27). The equations for the numbers of E(n) are shown in Eqs. 5 and 6 for n = odd number and even number, respectively,
E(n)=14nk=1n2(n,k)+2(n3)/2,
[5]
E(n)=14nk=1n2(n,k)14nl=12|n/(n,l)n2(n,l)+2(n/2)2,
[6]
where the summation of the second term of the right-hand side of Eq. 6 is taken over all l so that n/(n,l) is even.
The S(n) number is defined as a sum of the number of diastereomers [D(n)] and the number of enantiomer pairs [E(n)]. We may also use
S(n)=D(n)+E(n),
[7]
to elucidate the numbers by using two sets of complicated equations.
With these equations, the numbers of stereoisomers of synthesized [n]CaNAP congeners with n = 6–11 can be determined (Table 1), which indicates the complicated stereoisomerism of nanohoop structures. The breakdown of calculations for each n value is also shown in SI Appendix, and typical numbers for an expanded range of n values can be found in Sloane's On-Line Encyclopedia of Integer Sequences (28) with ID numbers of A000029 for stereoisomers, A000011 for diastereomers, and A007147 for enantiomer pairs.
Table 1.
Numbers of nanohoop stereoisomers with n arylene panels
n67891011
S(n)*1318304678126
D(n)8918234463
E(n)5912233463
*
Number of stereoisomers.
Number of diastereomers.
Number of enantiomer pairs. See SI Appendix for the breakdown.

Structures and Energetics Obtained from Theoretical Calculations.

The molecular structures and energetics of [n]CaNAP were first investigated by using theoretical calculations. Conformational search calculations with a large-scale low-mode method using the Merck molecular force field (MMFF) located a conformer with an identical facial orientation of naphthylene panels (hereafter denoted the an conformer) as the most stable isomers commonly observed for [n]CaNAP with n = 6–11 (29, 30) The helical arrangement of naphthylene panels in the an conformers may be reasonable for the relaxation of the C2h symmetric panels in the belt-shaped structures. More precise energetics were obtained by geometry optimizations using density functional theory (DFT) calculations at the B3LYP/6–31G(d,p) level of theory for [n]CaNAP with n = 6–8. All of the diastereomeric geometries from molecular mechanic calculations were used as the initial geometries, and their structures and energetics are summarized in Fig. 3. The structures in Fig. 3 are designated with developed names for the a(n–m)bm conformers, which is essential for conveying the sequence. As was the case with the force-field calculations, the DFT calculations identified the an conformers as the most stable structure. As another common feature of [n]CaNAP with n = 6–8, a conformer possessing one flipped panel (i.e., a(n–1)b1 conformer) was located as the second most stable structure. A comparison of the theoretical energetics with crystal structures shows that the stable conformers are not necessarily found in crystal structures (vide infra; ref. 21). For instance, two of the most stable structures of [8]CaNAP were absent in the crystal, and the existing a6b2 conformer was theoretically located approximately +2 kcal/mol above the most stable conformer. This observation indicates that crystalline nanohoop structures are affected by packing, and care must be taken during structural discussions based on the crystal structures.
Fig. 3.
Diastereomeric structures and energetics of [n]CaNAP from DFT calculations [B3LYP/6–31G(d,p)]. Chiral isomers with segmental structures of helical SWNTs are labeled with P/M, a chiral isomer with segmental structures of armchair SWNTs is labeled with (+)/(–), and structures found in single crystals are indicated by the labels in red. (A) n = 6. (B) n =7. (C) n = 8.
Next, the theoretical rotational barriers (ΔE) were estimated for a single-panel rotation from the an conformer to the a(n–1)b1 conformer of [n]CaNAP. Based on the nonlinear increase in ΔE values upon reduction in the hoop size, we extended the calculations to include elusive structures with n = 4 and 5. Transition state (TS) structures were obtained using the quadratic synchronous transit (QST3) method (31) by adopting saddle-point structures from scan analyses (12). The TS structures of n = 6–11 and the ΔE values of n = 4–11 are summarized in Fig. 4. The rotational barriers depended on the hoop size with an nonlinear decay toward the larger nanohoops. A theoretical rotational barrier for the rotation of 2,2'-binaphthyl was separately estimated to be +2.74 kcal/mol, and the deviations from this reference value indicated the contributions from macrocyclic ring strain to the rotational barriers of each congener (12).
Fig. 4.
TS structures and rotational barriers from DFT calculations [B3LYP/6–31G(d,p)]. Each TS structures possessed one imaginary frequency. The diameters were obtained as geometrical diameters (11).

Crystal Structures of [n]CaNAP with n = 7.

We obtained a single crystal of [7]CaNAP to reveal the belt-shaped structure in the crystalline solid state, which supplemented our observations of belt-shaped crystal structures of [8]CaNAP (21). Six distinct structures of [7]CaNAP were obtained from two sets of disordered structures in the unit cell of the single crystal grown in a mixture of isopropanol and CH2Cl2 (Fig. 5 and SI Appendix). In the first disordered set, the major structure with 52% occupancy was an a6b1 conformer and the minor structure with 48% occupancy was an a7 conformer. In the second disordered set, four structures consisting of the a6b1, b7, a7, and a1b6 conformers were identified with occupancies of 33%, 25%, 21%, and 21%, respectively. Possessing belt shapes with sp2-carbon networks, the structures can also be designated with SWNT chiral indices (8) as follows: a6b1/a1b6 conformers are (13,8), and a7/b7 conformers are (14,7). The bond-filling and atom-filling indices of the a7/b7 conformers were 100% (8), which indicates that the structure serves as the shortest segmental model of the helical (14,7)-SWNT. Interestingly, the total occupancies of the P and M enantiomers were not identical, and the crystal was in the chiral P21 space group. This observation indicated that optical resolution may have existed in the present crystal even though the data quality precluded a reliable conclusion.
Fig. 5.
Crystal structure of [7]CaNAP. (A) Two structures located in one set of disordered structures. (B) Four structures located in another set of disordered structures.

Solution-Phase Structures: Belt Persistency.

Finally, the solution-phase structures of [n]CaNAP were investigated by variable-temperature (VT) NMR analyses to reveal the experimental dynamics of the nanohoops (32, 33). Note that the present amphi-linked naphthylene panel provided an ideal, simplest structure to realize stereoisomerism required for the dynamic NMR study. The aromatic regions of the 1H NMR spectra of all of the congeners of [n]CaNAP (n = 6–11) in a temperature range of 80 °C to –90 °C are shown in Fig. 6. A singlet resonance was assigned to the protons at the 1-position of the naphthylene panel, and two doublet resonances were assigned to the protons at the 3- and 4-positions. Although the splitting patterns of the resonances did not change upon VT analyses, a careful examination revealed the presence of two transitions that are most typically observed for [7]CaNAP. The resonances of the sharp peaks at a high temperature (80 °C) were broadened upon cooling to approximately –20 °C and sharpened again upon further cooling to approximately –60 °C. This broadening–resharpening behavior is a typical characteristic of the exchange of a dominant species with hidden, unobservable partners of minor populations (34, 35). At a high temperature, the peaks are sharp and originate from one time-averaged structure via rapid exchange, and at low temperature, they are sharp again and originate from one dominant, rigidified species without exchanging with minor species. Therefore, for the nanohoop structures, the sharp peaks at the high temperature indicate the presence of flexible, rapidly fluctuating structures, and the sharp peaks at the low temperature indicate the presence of belt-persistent structures. At an intermediate temperature, the peaks are broad due to slow exchange that proceeds at a rate similar to the NMR time scale.
Fig. 6.
VT NMR spectra of [n]CaNAP in toluene-d8 (aromatic regions).
Due to the importance of the broadening–resharpening behavior for elucidating the structural dynamics, we quantified the peak broadening by measuring the full width at half maximum of the Lorentzian line of one singlet from the 1-position protons (Δ1/2-1; Fig. 7A). One doublet from the 3-position protons was also deconvoluted with the two Lorentzian lines to afford another set of full width at half maximum values (Δ1/2-2; Fig. 7B). Two distinct structures (i.e., the fluctuating structure and the belt-persistent structure) were observed for [n]CaNAP with n = 6, 7, and 8 in the current temperature range, showing two transition in the Δ1/2-values. The simple spectra of the single rigid species at the low temperature also indicated that the observed molecule possessed a high symmetry. This result along with the theoretical results (Fig. 3) suggested the presence of an isomers as the dominant, observable species. For the larger [n]CaNAP congeners with n ≥ 9, fluctuating structures were commonly observed throughout the studied temperature range. To clearly visualize this dynamic behavior, we drew a threshold line for the structural transition at the threefold increase in Δ1/2 from the narrowest peak, and after averaging the threshold temperatures from Δ1/2-1 and Δ1/2-2, we obtained the dynamics diagram shown in Fig. 7C. Most importantly, the belt shape of the smallest congener ([6]CaNAP) was persistent at 20 °C, and the a6 structure possessing a segment of (12,6)-SWNT with 100% bond-filling and atom-filling indices was observed in solution. Although it is important to note that the persistency is present in terms of spectroscopic observations (vide infra; refs. 32, 33), its effect over the characteristics relevant to SWNTs such as fullerene-peapod assembly may be of interest to be explored in the future (36, 37).
Fig. 7.
Broadening–resharpening behaviors of resonances in the VT NMR spectra of [n]CaNAP. Several Δ1/2 values were not obtained due to severe overlaps and are not included. (A) Broadening–resharpening behaviors observed with singlet from the 1-position protons. (B) Broadening–resharpening behaviors observed with doublet from the 3-position protons. (C) Dynamics elucidated based on a threefold broadening threshold.
Then, we derived experimental kinetic parameters for the panel rotation by using two independent methods developed for the analysis of broadening–resharpening behaviors (34, 35). The two methods commonly use the Δ1/2 values of the widest singlet (Δ1/2max) and those of the narrowest singlet (Δ1/2min). The population of the hidden partners (pB) as well as the dominant species (pA) is also estimated by comparing the integrals of the widest peak at high temperature and the narrowest peak at the low temperature. In short, the method developed by Anet and Basus (34) simply uses the Δ1/2 values to derive the rate constant (k) as
k=2π(Δ1/2maxΔ1/2min).
[8]
The method developed by Okazawa and Sorensen (35) affords k via
k=(6.323.90pB)Δ1/2maxΔ1/2min1+pB/2(1pB)2.
[9]
Because these two methods require elucidation of the widest peak, we can apply them to [6]CaNAP and [7]CaNAP, which exhibited two transitions that clarify the locations of the widest peak.
The experimental data for [6]- and [7]CaNAP are summarized in Table 2. It is important to note that the small pB value that is used in the Okazawa and Sorensen method also ensures the pA >> pB condition required for the Anet and Basus method. The rotational barriers from the two different methods (i.e., ΔGAnet and ΔGOkazawa) were consistent with each other, indicating the reliability of these energy values. A barrier of 16 kcal/mol for [6]CaNAP confirmed that the diastereomeric conformers should be observed as distinct entities by NMR spectroscopy at ambient temperature (32, 33). However, this value may also suggest that the isolation of these diastereomers at ambient temperature is not feasible (38). The rotational barrier of the larger congener of [7]CaNAP was decreased by 3 kcal/mol, confirming that the nanohoop structures became more flexible as the hoop size increased. A comparison of the experimental data shown in Table 2 and the theoretical data shown in Fig. 4 indicates that the theoretical DFT calculations afforded reasonable, albeit slightly lower, estimates of the rotational barriers.
Table 2.
Experimental data for the kinetic analyses and resultant rotational barriers
Parameters[6]CaNAP[7]CaNAP
Tmax, °C*50−10
Δ1/2maxΔ1/2min, Hz14.819.5
pB0.100.07
kAnet, s–193.2122.5
kOkazawa, s–182.9113.3
ΔGAnet, kcal/mol16.112.8
ΔGOkazawa, kcal/mol16.112.9
*
Temperature at the widest singlet.
The rate constant (k) was converted to ΔG using the Eyring equation, ΔG = –RT[ln(h/kB)+ln(k/T)], where R is the gas constant, h is the Planck constant, and kB is the Boltzmann constant.

Conclusions

We have synthesized a series of belt-shaped, amphi-linked cyclonaphthylene congeners through a random synthesis method and isolated six hydrocarbon congeners as discrete molecular entities. The belt-shaped structure with C2h panels gave rise to stereoisomerism originating from the facial orientations of the naphthylenes. The stereoisomerism was clarified with the aid of mathematics and revealed the complicated nature of the stereoisomerism of belt-shaped nanohoops. Structures of several stereoisomers with belt shapes were elucidated by crystallographic analyses, and comparison with theoretical energetics indicated that the crystal structure does not necessarily adopt the most stable conformation. The stereoisomerism further allowed us to reveal the presence of fluctuating and rigid structures in solution by VT NMR analyses, and the smallest congener with six naphthylene panels was observed as a rigid belt-shaped species at ambient temperature. Thus, for the present arylene panel of naphthylene, the diameter of 1.26 nm is the spectroscopic threshold that divides fluctuating nanohoops and rigid nanohoops. Another obvious structural factor that controls the structural rigidity is the size of the arylene panels: A chrysenylene nanohoop, (16,0)-[4]CC, with a nearly identical geometrical diameter of 1.27 nm, possessed an extreme rigidity and did not fluctuate for 2 months at 200 °C (10). Dynamics studies with nanohoops possessing various arylene panels are of fundamental interest to reveal the correlations between the hoop/panel size with the rigidity in the future. We hope that the present study may stimulate further studies to deepen our understanding of the unique structural chemistry of nanohoops.

Materials and Methods

Synthesis.

Diborylated precursors (1-3) were prepared by a method reported in the literature (21). Macrocylization with PtCl2(cod) was performed by using an equimolar amount of two diborylated precursors, and subsequent reductive elimination was performed through ligand exchange with PPh3 (9). Structures of isolated compounds were identified by spectroscopic analyses, and the purities were confirmed by HPLC analyses using several stationary phases. Further details of procedures and results are described in SI Appendix.

Crystallographic Analysis.

A single crystal (∼0.13 × 0.04 × 0.02 mm3) suitable for X-ray analysis was obtained by evaporation of isopropanol and dichloromethane solution of [7]CaNAP. A single crystal was mounted on a thin polymer tip with cryoprotectant oil and frozen at –178 °C via flash-cooling. After a laboratory diffractometer failed to afford reliable diffraction data due to the severe disorders of solvent molecules, the diffraction analysis of a single crystal with a synchrotron X-ray source was conducted at –178 °C by using a beamline at the KEK Photon Factory (PF-AR NE3A) using a diffractometer equipped with an Dectris Pilatus 2M-F pixel array detector to afford the final data with a resolution of ∼0.86 Å. Note that this resolution assures the precision of C–C bonds in 0.0206 Å. Further details of data processing are described in SI Appendix.

Theoretical Calculations.

Molecular mechanics calculations were performed by using MacroModel (39), and DFT calculations were performed by using Gaussian 09 (40). Further details of calculations are described in SI Appendix.

NMR Analyses.

Specimens in toluene-d8 were sealed in glass sample tubes (ϕ 5 mm), and VT NMR spectra were recorded on a JEOL JNM-ECS 600II (1H: 600 MHz; 13C: 150 MHz) spectrometer equipped with a temperature controller. Full-range spectra as well as those of synthetic intermediates are included in SI Appendix.

Data Availability

Data deposition: The crystallography, atomic coordinates, and structure factors have been deposited in the Cambridge Structural Database, Cambridge Crystallographic Data Centre, www.ccdc.cam.ac.uk (CSD reference no. 1471735).

Acknowledgments

We thank KEK Photon Factory (2015G097) for the use of the X-ray diffraction instruments. This study was partly supported by Grant-in-Aid for Scientific Research, KAKENHI (24241036, 25102007).

Supporting Information

Appendix (PDF)
Supporting Information

References

1
SE Lewis, Cycloparaphenylenes and related nanohoops. Chem Soc Rev 44, 2221–2304 (2015).
2
Y Segawa, H Ito, K Itami, Structurally uniform and atomically precise carbon nanostructures. Nat Rev Mater 1, 15002 (2016).
3
MR Golder, R Jasti, Syntheses of the smallest carbon nanohoops and the emergence of unique physical phenomena. Acc Chem Res 48, 557–566 (2015).
4
S Yamago, E Kayahara, T Iwamoto, Organoplatinum-mediated synthesis of cyclic π-conjugated molecules: Towards a new era of three-dimensional aromatic compounds. Chem Rec 14, 84–100 (2014).
5
R Jasti, J Bhattacharjee, JB Neaton, CR Bertozzi, Synthesis, characterization, and theory of [9]-, [12]-, and [18]cycloparaphenylene: Carbon nanohoop structures. J Am Chem Soc 130, 17646–17647 (2008).
6
H Takaba, H Omachi, Y Yamamoto, J Bouffard, K Itami, Selective synthesis of [12]cycloparaphenylene. Angew Chem Int Ed Engl 48, 6112–6116 (2009).
7
S Yamago, Y Watanabe, T Iwamoto, Synthesis of [8]cycloparaphenylene from a square-shaped tetranuclear platinum complex. Angew Chem Int Ed Engl 49, 757–759 (2010).
8
T Matsuno, et al., Geometric measures of finite carbon nanotube molecules: A proposal for length index and filling indexes. Pure Appl Chem 86, 489–495 (2014).
9
S Hitosugi, W Nakanishi, T Yamasaki, H Isobe, Bottom-up synthesis of finite models of helical (n,m)-single-wall carbon nanotubes. Nat Commun 2, 492 (2011).
10
S Hitosugi, T Yamasaki, H Isobe, Bottom-up synthesis and thread-in-bead structures of finite (n,0)-zigzag single-wall carbon nanotubes. J Am Chem Soc 134, 12442–12445 (2012).
11
T Matsuno, S Kamata, S Hitosugi, H Isobe, Bottom-up synthesis and structures of π-lengthened tubular macrocycles. Chem Sci (Camb) 4, 3179–3183 (2013).
12
S Hitosugi, W Nakanishi, H Isobe, Atropisomerism in a belt-persistent nanohoop molecule: Rotational restriction forced by macrocyclic ring strain. Chem Asian J 7, 1550–1552 (2012).
13
Y Segawa, H Omachi, K Itami, Theoretical studies on the structures and strain energies of cycloparaphenylenes. Org Lett 12, 2262–2265 (2010).
14
H Omachi, Y Segawa, K Itami, Synthesis and racemization process of chiral carbon nanorings: A step toward the chemical synthesis of chiral carbon nanotubes. Org Lett 13, 2480–2483 (2011).
15
P Sarkar, S Sato, S Kamata, T Matsuno, H Isobe, Synthesis and dynamic structures of a hybrid nanohoop molecule composed of anthanthrenylene and phenylene panels. Chem Lett 44, 1581–1583 (2015).
16
K Ikemoto, et al., Synthesis and structures of π-extended [n]cyclo-para-phenylenes (n= 12, 16, 20) containing n/2 nitrogen atoms. Chem Lett 45, 658–660 (2016).
17
GH Christie, J Kenner, LXXI.—The molecular configurations of polynuclear aromatic compounds. Part I. The resolution of γ-6: 6′-dinitro-and 4: 6: 4′: 6′-tetranitro-diphenic acids into optically active components. J Chem Soc 121, 614–620 (1922).
18
R Adams, HC Yuan, The stereochemistry of diphenyls and analogous compounds. Chem Rev 12, 261–338 (1933).
19
M Oki Topics in Stereochemistry, eds NL Allinger, E Eliel, SH Wilen (John Wiley & Sons, Hoboken, NJ) Vol 14, 1–81 (1983).
20
EL Eliel, SH Willen, Stereochemistry of Organic Compounds (Wiley, New York), Chap 9. (1994).
21
Z Sun, P Sarkar, T Suenaga, S Sato, H Isobe, Belt-shaped ccyclonaphthylenes. Angew Chem Int Ed Engl 54, 12800–12804 (2015).
22
T Iwamoto, Y Watanabe, Y Sakamoto, T Suzuki, S Yamago, Selective and random syntheses of [n]cycloparaphenylenes (n=8-13) and size dependence of their electronic properties. J Am Chem Soc 133, 8354–8361 (2011).
23
JL Fisher Application-Oriented Algebra: An Introduction to Discrete Mathematics (Dun-Donnelley, New York, 1977).
24
EN Gilbert, J Riordan, Symmetry types of periodic sequences. Illinois J Math 5, 657–665 (1961).
25
NJ Fine, Classes of periodic sequences. Illinois J Math 2, 285–302 (1958).
26
A Yajima, How to calculate the number of stereoisomers of inositol homologs. Bull Chem Soc Jpn 87, 1260–1264 (2014).
27
EM Palmer, RW Robinson, Enumeration of self-dual configurations. Pac J Math 110, 203–221 (1984).
28
NJA Sloane, On-Line Encyclopedia of Integer Sequences. Available at https://oeis.org/. Accessed April 25, 2016. (1964).
29
H Isobe, H Tokuyama, M Sawamura, E Nakamura, Synthetic and computational studies on symmetry-defined double cycloaddition of a new tris-annulating reagent to C60. J Org Chem 62, 5034–5041 (1997).
30
W Nakanishi, Y Shimada, H Isobe, Structural fluctuation of disilanyl double-pillared bisheteroarenes. Chem Asian J 8, 1177–1181 (2013).
31
C Peng, HB Schlegel, Combining synchronous transit and quasi-Newton methods to find transition states. Isr J Chem 33, 449–454 (1993).
32
J Sandström Dynamic NMR Spectroscopy (Academic, London, 1982).
33
M Oki Applications of Dynamic NMR Spectroscopy to Organic Chemistry (VCH, Weinheim, Germany, 1985).
34
FAL Anet, VJ Basus, Limiting equations for exchange broadening in two-site NMR systems with very unequal populations. J Magn Reson 32, 339–343 (1978).
35
N Okazawa, TS Sorensen, The line-shape analysis of nuclear magnetic resonance peaks broadened by the presence of a “hidden” exchange partner. Can J Chem 56, 2737–2742 (1978).
36
H Isobe, S Hitosugi, T Yamasaki, R Iizuka, Molecular bearing of finite carbon nanotube and fullerene in ensemble rolling motion. Chem Sci (Camb) 4, 1293–1297 (2013).
37
S Sato, T Yamasaki, H Isobe, Solid-state structures of peapod bearings composed of finite single-wall carbon nanotube and fullerene molecules. Proc Natl Acad Sci USA 111, 8374–8379 (2014).
38
M Oki, Isolation of rotational isomers and developments derived therefrom. Proc Jpn Acad, Ser B, Phys Biol Sci 86, 867–883 (2010).
39
Schrödinger, LLC (2014) MacroModel (Schrödinger, LLC, New York), Version 10.6.
40
MJ Frisch, et al., Gaussian 09 (Gaussian Inc., Wallingford, CT), Revision D.01. (2009).

Information & Authors

Information

Published in

The cover image for PNAS Vol.113; No.29
Proceedings of the National Academy of Sciences
Vol. 113 | No. 29
July 19, 2016
PubMed: 27357686

Classifications

Data Availability

Data deposition: The crystallography, atomic coordinates, and structure factors have been deposited in the Cambridge Structural Database, Cambridge Crystallographic Data Centre, www.ccdc.cam.ac.uk (CSD reference no. 1471735).

Submission history

Published online: June 29, 2016
Published in issue: July 19, 2016

Keywords

  1. stereoisomerism
  2. macrocycles
  3. carbon nanotubes
  4. crystal structures
  5. dynamic structures

Acknowledgments

We thank KEK Photon Factory (2015G097) for the use of the X-ray diffraction instruments. This study was partly supported by Grant-in-Aid for Scientific Research, KAKENHI (24241036, 25102007).

Notes

This article is a PNAS Direct Submission.

Authors

Affiliations

Zhe Sun
Isobe Degenerate π-Integration Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency, Aoba-ku, Sendai 980-8577, Japan;
Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan;
Takuya Suenaga
Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan;
Parantap Sarkar
Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan;
Sota Sato
Isobe Degenerate π-Integration Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency, Aoba-ku, Sendai 980-8577, Japan;
Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan;
Motoko Kotani
Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan;
Mathematical Institute, Tohoku University, Aoba-ku, Sendai 980-8578, Japan;
Isobe Degenerate π-Integration Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency, Aoba-ku, Sendai 980-8577, Japan;
Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan;
Department of Chemistry, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Notes

1
To whom correspondence should be addressed. Email: [email protected].
Author contributions: H.I. designed research, Z.S., T.S., P.S., S.S., and M.K. performed research; Z.S. and S.S. analyzed data; and Z.S. and H.I. wrote the paper.

Competing Interests

The authors declare no conflict of interest.

Metrics & Citations

Metrics

Note: The article usage is presented with a three- to four-day delay and will update daily once available. Due to ths delay, usage data will not appear immediately following publication. Citation information is sourced from Crossref Cited-by service.


Citation statements




Altmetrics

Citations

Export the article citation data by selecting a format from the list below and clicking Export.

Cited by

    Loading...

    View Options

    View options

    PDF format

    Download this article as a PDF file

    DOWNLOAD PDF

    Login options

    Check if you have access through your login credentials or your institution to get full access on this article.

    Personal login Institutional Login

    Recommend to a librarian

    Recommend PNAS to a Librarian

    Purchase options

    Purchase this article to access the full text.

    Single Article Purchase

    Stereoisomerism, crystal structures, and dynamics of belt-shaped cyclonaphthylenes
    Proceedings of the National Academy of Sciences
    • Vol. 113
    • No. 29
    • pp. 7925-E4258

    Figures

    Tables

    Media

    Share

    Share

    Share article link

    Share on social media