Search Results for "nanohoop"

Nanohoop of linked napthlylene groups

Itami continues to design novel macrocycles containing aromatic rings (see this post). This latest paper reports the synthesis of the first nanohoops containing naphthylenes, namely [9]cyclo-1,4-naphthylene 1.1 Since the macrocycle contains an odd number of naphthylene units, the lowest energy conformation is of C2 symmetry with one of the naphthylene rings in the plane of the macrocycle. (See Figure 1 for the B3LYP/6-31G(d) optimized structure). This conformation gives rise to 27 peaks in the proton NMR, and while the value of the computed chemical shifts differ from the experimental ones by about 0.5 to 1 ppm, their relative ordering is in very nice agreement.



Figure 1. B3LYP/6-31G(d) optimized geometries of 1 and the racemization transition state 2.

Itami also notes that 1 is chiral and computed the barrier for racemization of 19.9 kcal mol-1¸ through the transition state 2, also shown in Figure 1. This racemization process is compared with the racemization of 1,1’-binaphthyl.


(1) Yagi, A.; Segawa, Y.; Itami, K., "Synthesis and Properties of [9]Cyclo-1,4-naphthylene: A π-Extended Carbon Nanoring," J. Am. Chem. Soc. 2012, 134, 2962-2965, DOI: 10.1021/ja300001g


1: InChI=1/C90H54/c1-2-20-56-55(19-1)73-37-38-74(56)76-41-42-78(60-24-6-5-23-59(60)76)80-45-46-82(64-28-10-9-27-63(64)80)84-49-50-86(68-32-14-13-31-67(68)84)88-53-54-90(72-36-18-17-35-71(72)88)89-52-51-87(69-33-15-16-34-70(69)89)85-48-47-83(65-29-11-12-30-66(65)85)81-44-43-79(61-25-7-8-26-2(61)81)77-40-39-75(73)57-21-3-4-22-58(57)77/h1-54H/b75-73-,76-74-,79-77-,80-78-,83-81-,84-82-,87-85-,88-86-,90-89-

nanohoops Steven Bachrach 27 Mar 2012 No Comments

Chiral Nanohoops

Single-walled carbon nanotubes (SWNT) can be thought of as built from component macrocycles, often called nanohoops. So, for example, cycloparaphenylenes like 1 can be the thought of as the precursor (at least in principle) of armchair SWNTs. To create chiral SWNTs, Itami1 has suggested that cycloparaphenylene-naphthalene (2) and other acene substituted macrocycles would serve as appropriate precursors.



Itami has synthesized 2 (having 13 phenyl groups and one naphthyl group) and also examined the ring strain energy and racemization energy of a series of these types of compounds at B3LYP/6-31G(d). As might be expected, based on studies of the cycloparaphenylenes themselves,2,3 ring strain energy decreases with increasing size of the macrocycle. So, for example, the macrocycle with one naphthyl group and 5 phenyl rings has a strain energy of 90 kcal mol-1, but the strain is reduced to 40 kcal mol-1 with 13 phenyl rings.

The macrocycle 2 and related structures are chiral, existing in P and M forms. The racemization involves first rotation of the naphthyl group, as shown in Figure 1, with a barrier of about 8 kcal mol-1. The direct product has the opposite stereochemistry but is not in the lowest energy conformation. Rotations of some phenyl groups remains to occur, but these rotations are expected to have a barrier less than that for the rotation of the naphthyl group, based on the previous study of cycloparaphenylenes. Again, the racemization barrier decreases with the size of the macrocycle.




Figure 1. B3LYP/6-31G(d) optimized structures along the racemization pathway of 2.


(1) Omachi, H.; Segawa, Y.; Itami, K., "Synthesis and Racemization Process of Chiral Carbon Nanorings: A Step toward the Chemical Synthesis of Chiral Carbon Nanotubes," Org. Lett., 2011, 13, 2480-2483, DOI: 10.1021/ol200730m

(2) Segawa, Y.; Omachi, H.; Itami, K., "Theoretical Studies on the Structures and Strain Energies of Cycloparaphenylenes," Org. Lett., 2010, 12, 2262-2265, DOI: 10.1021/ol1006168

(3) Bachrach, S. M.; Stuck, D., "DFT Study of Cycloparaphenylenes and Heteroatom-Substituted Nanohoops," J. Org. Chem., 2010, 75, 6595-6604, DOI: 10.1021/jo101371m


2: InChI=1/C88H58/c1-2-60-4-3-59(1)61-5-9-63(10-6-61)65-13-17-67(18-14-65)69-21-25-71(26-22-69)73-29-33-75(34-30-73)77-37-41-79(42-38-77)81-45-49-83(50-46-81)85-53-55-88-58-86(54-56-87(88)57-85)84-51-47-82(48-52-84)80-43-39-78(40-44-80)76-35-31-74(32-36-76)72-27-23-70(24-28-72)68-19-15-66(16-20-68)64-11-7-62(60)8-12-64/h1-58H/b61-59-,62-60-,65-63-,66-64-,69-67-,70-68-,73-71-,74-72-,77-75-,78-76-,81-79-,82-80-,85-83-,86-84+

nanohoops Steven Bachrach 31 May 2011 9 Comments

Planar ring in a nano-Saturn

For the past twelve years, I have avoided posting on any of my own papers, but I will stoop to some shameless promotion to mention my latest paper,1 since it touches on some themes I have discussed in the past.

Back in 2011, Iwamoto, et al. prepared the complex of C60 1 surrounded by [10]cycloparaphenylene 2 to make the Saturn-like system 3.2 Just last year, Yamamoto, et al prepared the Nano-Saturn 5a as the complex of 1 with the macrocycle 4a.3 The principle idea driving their synthesis was to utilize a ring that is flatter than 2. The structures of 3 and 5b (made with the parent macrocycle 4b) are shown in side view in Figure 1, and clearly seen is the achievement of the flatter ring.




Figure 1. Computed structures of 3, 5, and 7.

However, the encompassing ring is not flat, with dihedral angles between the anthrenyl groups of 35°. This twisting is due to the steric interactions of the ortho-ortho’ hydrogens. A few years ago, my undergraduate student David Stück and I suggested that selective substitution of a nitrogen for one of the C-H groups would remove the steric interaction,4 leading to a planar poly-aryl system, such as making twisted biphenyl into the planar 2-(2-pyridyl)-pyridine (Scheme 1)

Scheme 1.

Following this idea leads to four symmetrical nitrogen-substituted analogues of 4b; and I’ll mention just one of them here, 6.

As expected, 6 is perfectly flat. The ring remains flat even when complexed with 1 (as per B3LYP-D3(BJ)/6-31G(d) computations), see the structure of 7 in Figure 1.

I also examined the complex of the flat macrocycle 6 (and its isomers) with a [5,5]-nanotube, 7. The tube bends over to create better dispersion interaction with the ring, which also become somewhat non-planar to accommodate the tube. Though not mentioned in the paper, I like to refer to 7 as Beyoncene, in tribute to All the Single Ladies.

Figure 2. Computed structure of 7.

My sister is a graphic designer and she made this terrific image for this work:


1. Bachrach, S. M., “Planar rings in nano-Saturns and related complexes.” Chem. Commun. 2019, 55, 3650-3653, DOI: 10.1039/C9CC01234F.

2. Iwamoto, T.; Watanabe, Y.; Sadahiro, T.; Haino, T.; Yamago, S., “Size-Selective Encapsulation of C60 by [10]Cycloparaphenylene: Formation of the Shortest Fullerene-Peapod.” Angew. Chem. Int. Ed. 2011, 50, 8342-8344, DOI: 10.1002/anie.201102302

3. Yamamoto, Y.; Tsurumaki, E.; Wakamatsu, K.; Toyota, S., “Nano-Saturn: Experimental Evidence of Complex Formation of an Anthracene Cyclic Ring with C60.” Angew. Chem. Int. Ed. 2018 , 57, 8199-8202, DOI: 10.1002/anie.201804430.

4. Bachrach, S. M.; Stück, D., “DFT Study of Cycloparaphenylenes and Heteroatom-Substituted Nanohoops.” J. Org. Chem. 2010, 75, 6595-6604, DOI: 10.1021/jo101371m


4b: InChI=1S/C84H48/c1-13-61-25-62-15-3-51-33-75(62)43-73(61)31-49(1)50-2-14-63-26-64-16-4-52(34-76(64)44-74(63)32-50)54-6-18-66-28-68-20-8-56(38-80(68)46-78(66)36-54)58-10-22-70-30-72-24-12-60(42-84(72)48-82(70)40-58)59-11-23-71-29-69-21-9-57(39-81(69)47-83(71)41-59)55-7-19-67-27-65-17-5-53(51)35-77(65)45-79(67)37-55/h1-48H

6: InChI=1S/C72H36N12/c1-2-38-14-44-20-45-25-67(73-31-50(45)13-37(1)44)57-9-4-39-15-51-32-74-68(26-46(51)21-61(39)80-57)58-10-5-40-16-52-33-75-69(27-47(52)22-62(40)81-58)59-11-6-41-17-53-34-76-70(28-48(53)23-63(41)82-59)60-12-7-42-18-54-35-77-71(29-49(54)24-64(42)83-60)72-78-36-55-19-43-3-8-56(38)79-65(43)30-66(55)84-72/h1-36H

Aromaticity &host-guest Steven Bachrach 26 Mar 2019 2 Comments


The synthesis of components of nanostructures (like fullerenes and nanotubes) has dramatically matured over the past few years. I have blogged about nanohoops before, and this post presents the recent work of the Itami group in preparing the nanobelt 1.1


The synthesis is accomplished through a series of Wittig reactions with an aryl-aryl coupling to stitch together the final rings. The molecule is characterized by NMR and x-ray crystallography. The authors have also computed the structure of 1 at B3LYP/6-31G(d), shown in Figure 1. The computed C-C distances match up very well with the experimental distances. The strain energy of 1, presumably estimated by Reaction 1,2 is computed to be about 119 kcal mol-1.


Figure 1. B3LYP/6-31G(d) optimized structure of 1.

Rxn 1

NICS(0) values were obtained at B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d); the rings along the middle of the belt have values of -7.44ppm and are indicative of normal aromatic 6-member rings, while the other rings have values of -2.00ppm. This suggests the dominant resonance structure shown below:


1) Povie, G.; Segawa, Y.; Nishihara, T.; Miyauchi, Y.; Itami, K., "Synthesis of a carbon nanobelt." Science 2017, 356, 172-175, DOI: 10.1126/science.aam8158.

2) Segawa, Y.; Yagi, A.; Ito, H.; Itami, K., "A Theoretical Study on the Strain Energy of Carbon Nanobelts." Org. Letters 2016, 18, 1430-1433, DOI: 10.1021/acs.orglett.6b00365.


1: InChI=1S/C48H24/c1-2-26-14-40-28-5-6-31-20-44-32(19-42(31)40)9-10-34-24-48-36(23-46(34)44)12-11-35-21-45-33(22-47(35)48)8-7-30-17-41-29(18-43(30)45)4-3-27-15-37(39(26)16-28)25(1)13-38(27)41/h1-24H

Aromaticity &nanohoops Steven Bachrach 22 May 2017 No Comments

Host-guest complexes

Grimme and coworkers have a featured article on computing host-guest complexes in a recent ChemComm.1 They review the techniques his group has pioneered, particularly dispersion corrections for DFT and ways to treat the thermodynamics in moving from electronic energy to free energy. they briefly review some studies done by other groups. They conclude with a new study of eight different host guest complexes, three of which are shown in Figure 1.




Figure 1. TPSS-D3(BJ)/def2-TZVP optimized structures of 1-3.

These eight host-guest complexes are fairly large systems, and the computational method employed means some fairly long computations. Geometries were optimized at TPSS-D3(BJ)/def2-TZVP, then single point energy determined at PW6B95-D3(BJ)/def2-QZVP. Solvent was included using COSMO-RS. The curcurbituril complex 2 includes a counterion (chloride) along with the guest adamantan-1-aminium. Overall agreement of the computed free energy of binding with the experimental values was very good, except for 3 and the related complex having a larger nanohoop around the fullerene. The error is due to problems in treating the solvent effect, which remains an area of real computational need.

An interesting result uncovered is that the binding energy due to dispersion is greater than the non-dispersion energy for all of these complexes, including the examples that are charged or where hydrogen bonding may be playing a role in the bonding. This points to the absolute necessity of including a dispersion correction when treating a host-guest complex with DFT.

As an aside, you’ll note one of the reasons I was interested in this paper: 3 is closely related to the structure that graces the cover of the second edition of my book.


(1) Antony, J.; Sure, R.; Grimme, S. "Using dispersion-corrected density functional theory to understand supramolecular binding thermodynamics," Chem. Commun. 2015, 51, 1764-1774, DOI: 10.1039/C4CC06722C.

Grimme &host-guest Steven Bachrach 12 May 2015 1 Comment

Fantastic host-guest complex

Check out this an incredibly cool host guest complex: the [10]-cycloparaphenylene ([10]CPP) hoop encapsulating C60!1

(Be sure to click on this image to bring up the 3-D interactive structure – as with all structures in my blog!)

1H and 13C NMR and fluorescence quenching spectrometry clearly indicate that this complex is formed when [10]CPP is mixed with C60 in toluene. In fact, when C60 is mixed with a mixture of nanohoops ranging from 8 to 12 phenyl ring, only the [10]CPP hoop complexes with the fullerene. The experimental binding energy is between 38 and 59 kJ mol-1.

M06-2x/6-31G* computations give the structure shown above. The computed binding energy is 173 kJ mol-1, but the computations do not include solvent. So this overestimation might be somewhat due to the difference in gas phase vs. solution complexation.

(Check out this post for other interesting nanohoops.)


(1) Iwamoto, T.; Watanabe, Y.; Sadahiro, T.; Haino, T.; Yamago, S., "Size-Selective Encapsulation of C60 by [10]Cycloparaphenylene: Formation of the Shortest Fullerene-Peapod," Angew. Chem. Int. Ed., 2011, 50, 8342-8344, DOI: 10.1002/anie.201102302

nanohoops Steven Bachrach 13 Sep 2011 3 Comments