Acceptor synthons oxygen

The most straightforward synthesis of the corrin nucleus applied an enam-ine as d -synthon for one pyrrolidine ring bearing the prospective methine bridge as an exocyclic methylene group. Deprotonation of the enamine nitrogen produced the necessary carbanion. As an a -acceptor, an alkylated imidic ester was chosen. This was available by alkylation of a pyrrolidone lactam oxygen with the... 

These rules reflect energetically favored intermolecular recognition and association. Take presently abundant carboxylic acid and pyridine co-crystals as an example, pyridine nitrogen atom is a better proton acceptor than carbonyl oxygen atom, so the heteromeric synthon 4 rather than homomeric synthon 1 (Scheme 3.1) is frequently occurred as a reliable structure motif to direct the assembly. However, exceptions are common and these rules are not guaranteed. They should be taken as guidelines, not as formal rules. 

All four solid forms were structurally characterized, three of them by single crystal XRD and one keto-amino polymorph by high-resolution PXRD. It has been shown that each tautomer had a unique and specific geometry and primary synthons stabilizing its crystal structures. Keto tautomers have a similar geometry to that of X, with the oxygen atoms in cis position. As already discussed, the O-H- - -O synthon between OH(py) and oxo acceptor in keto tautomers... 

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