72. The name peristylane (p. 51, 295) comes from the Greek word for roof. An [n]-peristylane "has an n-membered base joined by n bonds to alternate atoms of a 2n-membered cycle." Confused? Sure. But pictures help. Shown here are [3]- and [5]-peristylane (two perspectives). Your task is to calculate the energies and geometries of [3]-, [4]-, and [5]-peristylane. Then, use the SSADD command to bring a horizontal five-membered ring close to the five "points" of [5]-peristylane (C15H20); delete five H's from each molecule, join the carbons, and construct the exquisitely symmetrical dodecahedrane (C20H20) for which you should then do the MM calculation.
83. The highly symmetrical "pagodane" (C20H20, A) is another strained molecule. Shown here are several possible synthetic entries to it, including [2 + 2] cycloaddition from dienes B or C and [2 + 2 + 2] reaction from triene D. Also shown is a potential route to B via Diels-Alder dimerization of F followed by intramolecular Diels-Alder reaction of the initially formed E. Do calculations on all six structures, and assess the likelihood of synthetic procedures involving them. Pay particular attention to the "similar-looking" dienes B and C which differ markedly in strain energy; what is the origin of this difference?
[Melder, J.-P.; Prinzbach, H. Chem. Ber. 1991, 124, 1271 and references therein.]
113.
Problems 72, 77, and 78 were concerned with dodecahedrane
(C20H20) and related compounds; Problem 109 was concerned
with the strain introduced by "pyramidalizing" double bonds.
The present question concerns the best (or worst) features of both: you
should do MM calculations on dodecahedrane (shown); on its monodehydro
derivative (i.e., remove two H's at bond a and introduce a double
bond); on the didehdyro compound (double bonds at a and b);
on the tetradehydro and hexadehydro compounds (double bonds at a, b,
c, and d; and at a, b, c, d, e, and f, respectively);
and finally on the completely dehydro derivative having formula C20
(a smaller and very strained analog of buckminsterfullerene C60).
[Weber, K.; Fritz, H.; Prinzbach, H. Tetrahedron Lett. 1992, 33, 619.]
199. This problem
involves compounds similar to those in No. 196.
The interesting cage compound "Golcondane" (C20H24)
has recently been synthesized, more or less according to the route shown
here. (In the actual case, there were carbonyl groups that had to be reduced
at the end of the synthesis.) Do MMX calculations on golcondane, on the
three precursors, and on its decomposition product; discuss the relative
stability of these compounds and identify the source(s) of their strain
energy. [The origin of the name "golcondane" is so obscure that
the interested reader should consult the cited reference.
[Mehta, G.; Reddy, S. H. K. Angew. Chem., Int. Ed. Engl. 1993, 32, 1160.]
203. The beautifully symmetrical dodecahedrane, C20H20, was the subject of calculations in Problems 113, 146, and others cited therein. The present problem is concerned with the effect of halogen substitution (which halogen, how many, and how arranged) on the strain energy of the molecule. Do calculations on the monohalo derivatives (F, Cl, Br), and on the 1,2- and 1,3-dihalo compounds. Compare your computed strain energies with those in the cited article. Also do calculations on other "crowded" derivatives that might appeal to you.
[Wahl, F.; Wörth, J.; Prinzbach, H. Angew. Chem., Int. Ed. Engl. 1993, 32, 1722.]
231. Corannulene,
C20H10, with its fused six- and five-membered rings,
is a partial model for the spherical "buckminsterfullerene" C60.
Do MMX calculations on this molecule; on its penta-CH=CH bridged derivative
C30H10; and on related compounds that interest you.
Comment on their planar or bowl-shaped structures; compare your calculated
bond distances with those in the cited reference.
[Liu, R.; Zhou, X.; Allinger, N. L. J. Phys. Org. Chem.
1994, 7, 551; see also
Kiyobayashi, T.; Nagano, Y.; Sakiyama, M.; Yamamoto, K.; Cheng, P.-C.;
Scott, L. T.
J. Am. Chem. Soc. 1995, 117, 3270.]
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