Ph. D. THESIS 2009

1.5.1. Tetramethyl 3,7-dihydroxybicyclo[3.3.1]nona-2,6-diene-
2,4,6,8-tetracarboxylate structure
Two hypothetical structures for the investigated β-ketoester [23] were
theoretically calculated by DFT. One of them has the intramolecular hydrogen
bonds established between the enol hydrogen atom and the carbonyl oxygen
atom of the methoxycarbonyl group (Figure 5b). The second structure has the
intramolecular hydrogen bonds established between the enol hydrogen atom
and the methoxy oxygen atom of the methoxycarbonyl group (Figure 5a).
a b
Figure 5. Two possible conformations of the enol form: a) conf_A; b) conf_B.
The strength of the hydrogen bond shows a steady increase of the stability of βketoester
chelate, which closes a stable six-membered ring through such of
intramolecular weak interactions.
Figure 12. The optimized energetic state transition diagram for both conformations of 1
These two conformations were found to have an energetic barrier of only
0.2204 eV, which suggests a very fast interconversion between each other.
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