The effect of different hydrogen bonding schemes on melting points of two isomeric 2-hydroxy-bornane-3-carboxylic acids

The crystal structures of two isomeric compounds, 2-endo-hydroxybornane-3-e ndo-carboxylic acid and 2-exo-hydroxybornane-3-endo-carboxylic acid, have b een determined by X-ray single crystal analysis. The only difference betwee n these two compounds is the disposition of the 2-hydroxy group with respec t to the bornane skeleton. Both compounds show quite different hydrogen bon ding schemes. In the endo-hydroxy-endo-carboxy isomer there is one intramol ecular and one intermolecular hydrogen bond, which connects molecules into infinite chains, while in the exo-hydroxy-endo-carboxy isomer there are two intermolecular hydrogen bonds that form a more stable architecture of two kinds of chains which interconnect to close rings comprising four molecules . Due to these differences the melting point of 2 is ca. 30 degrees higher than for 1.