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H Prinzbach

Publications and source records attributed to H Prinzbach.

4 recordsLinked to original sources
PubMed2001

Pentagonal dodecahedranes: polyfunctionalization and MS fragmentation.

With the use of four- to eight-fold functionalized dodecahedranes (1-3), opportunities to arrive at highly strained dodecahedranes with two to four pairs of vicinal, eclipsed bromine substituents through front-side substitution and addition reactions have been explored. In standard processes, the interception of beta-OCH(3) radical/cationic intermediates was not problematic (9-12, 37, 50). The interception of beta-CO(2)R radicals was possible for Cl(*) (18) but not for Br(*) (17). The interception of beta-chloro radicals was possible for Cl(*) (27) but not for Br(*) (26), and the interception of beta-Br cations ("bromonium ions") with Br(-) was modest (45) to highly inefficient (24, 26). Two X-ray structural analyses (dimethoxy dibromide 9 and tetramethoxy tetrabromide 53) indicated the structural consequences of the molecular strain introduced by the two (four) vicinal CH(3)O/Br pairs. A systematic analysis of the MS spectra confirms that, in virtually all cases studied, the elimination of the substituents occurs without significant carbon-cage disruption, leading ultimately to multiply unsaturated dodecahedral ions for dodecahedrahexa(C(20)H(8))enes, -hepta(C(20)H(6))enes, and -octa(C(20)H(4))enes.

Journal Article↗
PubMed2000

Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

Journal Article↗