Succinate esters: odd–even effects in melting points. Issue 5 (17th September 2014)

• Record Type: Journal Article
• Authors: Joseph, Sumy; Sathishkumar, Ranganathan
• Is Part Of: Acta crystallographica. Volume 70:Issue 5(2014:Oct.)
• Page Start: 839
• Page End: 846
• Publication Date: 2014-09-17
• DOI: 10.1107/S2052520614013730
• Languages: English
• ISSNs: 2052-5206

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Dialkyl succinates show a pattern of alternating behavior in their melting points, as the number of C atoms in the alkane side chain increases, unlike in the dialkyl oxalates [Joseph <italic>et al.</italic> (2011). <italic>Acta Cryst.</italic> B<bold>67</bold>, 525–534]. Dialkyl succinates with odd numbers of C atoms in the alkyl side chain show higher melting points than the immediately adjacent analogues with even numbers. The crystal structures and their molecular packing have been analyzed for a series of dialkyl succinates with 1−4 C atoms in the alkyl side chain. The energy difference (Δ<italic>E</italic>) between the optimized and observed molecular conformations, density, Kitaigorodskii packing index (KPI) and C—H...O interactions are considered to rationalize this behavior. In contrast to the dialkyl oxalates where a larger number of moderately strong C—H...O interactions were characteristic of oxalates with elevated melting points, here the molecular packing and the density play a major role in raising the melting point. On moving from oxalate to succinate esters the introduction of the C2 spacer adds two activated H atoms to the asymmetric unit, resulting in the formation of stronger C—H...O hydrogen bonds in all succinates. As a result the crystallinity of long‐chain alkyl substituted esters improves enormously in the presence of hydrogen bonds from activated donors.</p> </abstract>