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Analysis of less common hydrogen bonds involving ester oxygen sp3 atoms as acceptors in crystal structures of small organic molecules

An analysis of hydrogen bonds involving ester oxygen sp3 atoms as acceptors is based on data extracted from the Cambridge Structural Database (Allen, 2002, the version 5.25, November 2003) using ConQuest package for the evaluation of stereochemical and electronic properties of the acceptors. Evidences for the existence of this particular hydrogen bond and its structural function in the crystal packing are presented. Using the cut-off limit on disagreement factors R<5% (for the structures with hydrogen bonds involving an oxygen as a part of a donor group) and R<8.5% (for nitrogen as a part of a donor group) 230 structures out of a total CSD entries of 298100 revealed hydrogen bonds with ester oxygen sp3 atoms as acceptors. The donors of hydrogen atoms are water molecules, hydroxyl groups, primary and secondary amines, and, in a few cases, imino groups. The four modes of the participation of the ester Osp3 oxygen atoms in hydrogen bonding are detected: as a single acceptor, as a double acceptor, as a single acceptor of a hydrogen atom involved in intermolecular bifurcated hydrogen bond, and sharing the acceptor function with the Osp2 in bifurcated hydrogen bond. The role of such direct noncovalent interaction in the crystal packing is demonstrated by a small gallery of selected structures.

hydrogen bonding ; ester Osp3 as a proton acceptor ; Cambridge Structural Database

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