Tuesday, October 14, 2014

Design and synthesis of the first triply twisted Möbius annulene

Schaller, G. R.; Topić, F.; Rissanen, K.; Okamoto, Y.; Shen, J.; Herges, R.  Nat. Chem. 2014, 6, 608-613
Contributed by Steven Bachrach.
Reposted from Computational Organic Chemistry with permission

Herges and co-workers have prepared a triply-twisted Möbius molecule. 1 The key element is recognizing that most of the “twisting” needs to be accomplished through writhe, a twisting that produces figure-8-like crossing, the way an old-school phone cord twists about itself or the way a pretzel is formed. Herges employs three bi-naphthelene subunits to provide the template for the writhe needed. The prepared compound is 1. A clever, relatively straightforword synthesis produces this amazing molecule, along with the single-twisted 2.
The B3LYP/6-31G* optimized geometries of 1 and the single-twisted analogue 2 are shown in Figure 1. Table 1 presents the key topological parameters of 1 and 2, comparing the computed and X-ray crystal structure. The absolute value of the linking number Lk is 3, indicating the three twists, and the reason that this highly twisted molecule can be made is that half of the twist actually results from writhe.

1

2
Figure 1. B3LYP/6-31G* optimized geometries of the two diastereomers if 1. (Be sure to click on these images to launch JMol and interactively manipulate the structures!)
Table 1. Topological parameters of 1a

|Lk|
|Tw|
|Wr|
X-ray, 1
3.0
1.42
1.58
Comp, 1
3.0
1.33
1.67
Comp, 2
1.0
0.37
0.63
aLk is the linking number, Tw is the twist number, and Wr is the writhe number, with the condition that TkWr = Lk.


References

(1) Schaller, G. R.; Topić, F.; Rissanen, K.; Okamoto, Y.; Shen, J.; Herges, R. "Design and synthesis of the first triply twisted Möbius annulene," Nat. Chem. 20146, 608-613, DOI: 10.1038/nchem.1955.


InChIs

1: InChI=1S/C72H36/c1-2-26-56-44-38-50-20-8-14-32-62(50)68(56)70-58(46-40-52-22-10-16-34-64(52)70)28-5-6-30-60-48-42-54-24-12-18-36-66(54)72(60)71-59(47-41-53-23-11-17-35-65(53)71)29-4-3-27-57-45-39-51-21-9-15-33-63(51)69(57)67-55(25-1)43-37-49-19-7-13-31-61(49)67/h7-24,31-48H/b69-67-,70-68-,72-71-
InChIkey=ICOGWBLQQNBWJA-UWFYZODKSA-N




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