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Succinate esters: odd–even effects in melting points
Author(s) -
Joseph Sumy,
Sathishkumar Ranganathan
Publication year - 2014
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520614013730
Subject(s) - succinates , chemistry , alkyl , crystallinity , melting point , hydrogen bond , oxalate , crystallography , alkane , chain (unit) , stereochemistry , polymer chemistry , hydrocarbon , molecule , organic chemistry , physics , astronomy
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 et al. (2011). Acta Cryst. B 67 , 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 E ) 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.