ChemInform Abstract: Ion Pairing and Reactivity of Enolate Anions. Part 7. A Spectacular Example of the Importance of Rotational Barriers: The Ionization of Meldrum′s Acid.
Abstract
The free energy of ionization of Meldrum's acid (Ia) is 11.68 kcal/mol more spontaneous than that of its acyclic analogue, dimethyl malonate (VIIIa).
ChemInform Abstract
The free energy of ionization of Meldrum's acid (Ia) is 11.68 kcal/mol more spontaneous than that of its acyclic analogue, dimethyl malonate (VIIIa). This energy difference is thought to be one of the largest stereoelectronic effects in the literature of organic chemistry. By comparing the effects of various structural contributions to the carbon acidity whereby the most dramatic effect results from increasing the size of the bislactone ring system in (II), it is shown that the surprising acidity of (Ia) relative to (VIIIa) and dimedone (III) (X: -CH2-) is the result of restricted rotation of the ester linkage in the bislactone structure.
