Melting-points of themeta- andpara-isomers of anisylpinacolone

Abstract

The generally higher melting‐point of a para‐disubstituted benzene relative to the corresponding meta‐isomer has been ascribed to the fact that, being more symmetrical, it can pack more tightly. Exceptionally, it was observed that whereas m‐anisylpinacolone melts at 58.0 °C, the para‐isomer melts lower at 39.5 °C. In this work we have attempted to understand this apparent anomaly. The crystal structures of both isomers were determined and the packing analysed. Energy calculations of the static structures and molecular dynamics (MD) simulations at temperatures just below the respective melting‐points were performed. The structure analyses indicate that the intermolecular contacts are comparably weak in the two cases, and do not appear to be the direct cause of the melting‐point difference. Thermal motion analysis, packing energies and MD simulations on minicrystals indicate the importance of both enthalpic and entropic factors in the melting behaviour of the two isomers. The higher melting point of the meta‐isomer could originate from both a smaller ΔSf and higher ΔHf relative to the para‐isomer. Copyright © 2000 John Wiley & Sons, Ltd.

Novel tools for visualizing and exploring intermolecular interactions in molecular crystals

“…To our knowledge, the only published applications of the NIPMAT scheme involve a study of the %-acceptor nature of three-membered rings (Allen et al, 1996), comparisons between naphthalene and terephthalic acid (Desiraju, 1997), 2-, 3-and 4-aminophenol (Nangia & Desiraju, 1998, 1,4benzoquinone and¯uoranil (Desiraju, 1996;Desiraju & Steiner, 1999), two isomers of anisylpinacolone (Kuduva et al, 2000), and comparisons within a family of aminophenols (Vangala et al, 2003). By way of example, and for later comparison, the NIPMAT diagrams comparing naphthalene with terephthalic acid are reproduced in Fig.…”

Thermodynamic, energetic, and topological properties of crystal packing of pyrazolo[1,5-a]pyrimidines governed by weak electrostatic intermolecular interactions

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Correlation of melting points of inositols with hydrogen bonding patterns

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