Abstract:Molekul-Mechanik-oder Kraftfeld-Rechnungen konnen zur Klarung vieler experimenteller Probleme herangezogen werden: Zur Untersuchung der Molekuldynamik (Konformationsanalyse und innere Rotation), zur Suche nach den stabilsten Isomeren von Kohlenwasserstoffen und zur Berechnung von Reaktivitaten einschlieBlich der Solvolyse von Briickenkopf-substituierten Derivaten wurden derartige Rechnungen ebenso angestellt wie zur Aufklarung des Mechanismus vielstufiger Umlagerungen uber Carbokationen und der Struktur von An… Show more
“…Much of the stability of the multilayer D 3 h structure is provided by electron occupying of the 3e‘ MO formed by the overlap in a σ way of π-antibonding MOs of the fragments. The determining role of such type π σ −π σ orbital interaction for stabilization of various polyhedral organic structures built up by parallel superposition of two or more fragment cyclic π-systems has been well established, [ n ]prismanes, , [ n ]asteranes (which may be viewed as [ n ]prismanes sandwiched by a polymethylene pseudocycle), organic molecular crystals, and others. 5 CACAO 29 drawing of the orbital interaction diagram depicting formation of MOs of bi[3]prismane 8a from MOs of the fragments.…”
A series of bi[n]prismanes and tri[n]prismanes (n = 3-6) containing n and 2n, respectively, tetracoordinated carbon centers with nonclassical bisphenoidal (half-planar) configuration has been designed computationally.
“…Much of the stability of the multilayer D 3 h structure is provided by electron occupying of the 3e‘ MO formed by the overlap in a σ way of π-antibonding MOs of the fragments. The determining role of such type π σ −π σ orbital interaction for stabilization of various polyhedral organic structures built up by parallel superposition of two or more fragment cyclic π-systems has been well established, [ n ]prismanes, , [ n ]asteranes (which may be viewed as [ n ]prismanes sandwiched by a polymethylene pseudocycle), organic molecular crystals, and others. 5 CACAO 29 drawing of the orbital interaction diagram depicting formation of MOs of bi[3]prismane 8a from MOs of the fragments.…”
A series of bi[n]prismanes and tri[n]prismanes (n = 3-6) containing n and 2n, respectively, tetracoordinated carbon centers with nonclassical bisphenoidal (half-planar) configuration has been designed computationally.
“…The Platonic hydrocarbons, i.e., the tetrahedrane derivatives, cubane and its many congeners, and the dodecahedranes all fall into this category. Not only cubane and its derivatives − but also the other prismanes, − such as pentaprismane 132 (viz., 2 n 4 + n 5 = 10 + 2 = 12), do as well as does diademane, , (viz., 3 n 3 + n 5 + 0 n 6 = 9 + 3 = 12), to give only a few examples. …”
Section: Cyclopentane Units As “Bending Blocks”mentioning
“…Thus, in this case the thermodynamically most stable isomer 16 is formed upon hydrogenolytic opening of both three-membered rings in 1. This is remarkable, since hydrogenolysis of oligocyclic hydrocarbons with more than one cyclopropane moiety does not necessarily occur with thermodynamic control, as had previously been hypothesized, [25] but may be governed by the mode of adsorption on the catalyst surface. [26] Direct functionalizations of several cage hydrocarbons, especially adamantane (12), with electrophilic (bromination, [27] nitroxylation [28] ) or radical (halogenation, [29] oxygenation [30] ) reagents have been studied.…”
The synthesis of the (CH)12 hydrocarbon [D(3d)]-octahedrane (heptacyclo[6.4.0.0(2,4).0(3,7).0(5,12).0(6,10).0(9,11)]dodecane) 1 and its selective functionalization retaining the hydrocarbon cage is described. The B3LYP/6-311+G* strain energy of 1 is 83.7 kcal mol(-1) (4.7 kcal mol(-1) per C-C bond) which is significantly higher than that of the structurally related (CH)16 [D(4d)]-decahedrane 2 (75.4 kcal mol(-1); 3.1 kcal mol(-1) per C-C bond) and (CH)20 [I(h)]-dodecahedrane 3 (51.5 kcal mol(-1); 1.7 kcal mol(-1) per C-C bond); the heats of formation for 1-3 computed according to homodesmotic equations are 52, 35, and 4 kcal mol(-1). Catalytic hydrogenation of 1 leads to consecutive opening of the two cyclopropane rings to give C2-bisseco-octahedrane (pentacyclo[6.4.0.0(2,6).0(3,11).0(4,9)]dodecane) 16 as the major product. Although 1 is highly strained, its carbon skeleton is kinetically quite stable: Upon heating, 1 does not decompose until above 180 degrees C. The B3LYP/6-31G* barriers for the S(R)2 attack of the tBuO. and Br3C. radicals on a carbon atom of one of the cyclopropane fragments (Delta(298) = 27-28 kcal mol(-1)) are higher than those for hydrogen atom abstraction. The latter barriers are virtually identical for the abstraction from the C1-H and C2-H positions with the tBuO. radical (DeltaG(298) = 17.4 and 17.9 kcal mol(-1), respectively), but significantly different for the reaction at these positions with the Br3C. radical (DeltaG(298) = 18.8 and 21.0 kcal mol(-1)). These computational results agree well with experiments, in which the chlorination of 1 with tert-butyl hypochlorite gave a mixture of 1- and 2-chlorooctahedranes (ratio 3:2). The bromination with carbon tetrabromide under phase-transfer catalytic (PTC) conditions (nBu4NBr/NaOH) selectively gave 1-bromooctahedrane in 43 % isolated yield. For comparison, the PTC bromination was also applied to 2,4-dehydroadamantane yielding 54 % 7-bromo-2,4-dehydroadamantane.
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