Zur Struktur vicinaler Pentaketone — Röntgenstrukturuntersuchungen und Berechnungen

Abstract

Eine helicale Konformation und damit eine sterisch eher ungünstige Struktur kennzeichnet die Pentaketone 1 und 2. Aus einem einfachen Modell folgt, daß der strukturbestimmende Parameter die Minimierung des Gesamtdipolmoments ist.

The Chemistry of Vicinal Polycarbonyl Compounds

“…A number of MO calculations 173 on vicinal polyketones revealed that there is a flat potential surface with respect to rotation of the CO groups. This picture was confirmed by force field calculations. , However, with the following restrictions: (1) neglect of torsion and van der Waals forces, and (2) assuming that the dipole moment of each CO group is 2.30 D, that the bond distances between adjacent carbon atoms are fixed at 1.54 Å and those between C and O at 1.20 Å as well as bond angles of 120°, the torsion angles between CO groups of vicinal polyketones could be reproduced in contrast to the semiempirical methods discussed above. The minima found on the corresponding hypersurface showed remarkable agreement with experimental data.…”

“…The first synthesis of pentaketones was reported in 1986 by Gleiter and co-workers. , These were open chain compounds 3 with phenyl or tert- butyl end-groups. Starting materials were the bis-diazotriketones 90 prepared from the corresponding 1,3,5-triones by the diazo exchange reaction; the bis-diazodiphenyl compound 90a had been reported many years ago by Regitz and Geelhaar .…”

“…X-ray structures are available for two pentaketones, tert -butylphenyl pentaketone ( 3j ) and diphenyl pentaketone ( 3a ). , Bond distances and torsion angles α 1 −α 4 are summarized in Table , and the molecular structure of 3a is shown in Figure . Comparison of the structures of 3j and 3a shows that, in both, the three central CO groups are arranged approximately cisoid to each other while the outer ones show a transoid conformation.…”