Hydrogen-bonding schemes of galactonic acid hydrazide and its hemihydrate

The crystal structure of L-galactonic acid hemihydrate was determined using data obtained from an imaging plate detector (Stoe IPDS), whereas a conventional scintillation counter was used for the elucidation of the crystal structure of anhydrous D-galactonic acid. The H atom of the terminal hydroxyl group of the water-free sugar participates only in an intramolecular hydrogen bond with the preterminal O atom. This hydrogen bond is part of an antidromic hydrogen-bonding cycle. The hydrogen-bonding scheme of the hemihydrate is very intricate due to the occurrence of two independent molecules and the incorporated water, whose coordination shell can be described by a distorted tetrahedron. One of the hydrogen-bond chains observed in the structure of the hemihydrate is infinite, forming a spiral running in the a direction. The crystal packing of both compounds displays a herringbone arrangement. However, the tilt angle between molecules in different herringbone halves is by far smaller in the structure of the hydrated sugar than in the water-free compound (similar to 60 versus 96 degrees).