title: Crystal packing and melting temperatures of small oxalate esters: the role of C-H···O hydrogen bonding.
abstract: The simple dialkyl oxalates are generally liquids at room temperature except for dimethyl and di-tert-butyl oxalate which melt at 327 and 343 K. The crystal structures of diethyl, di-iso-propyl, di-n-butyl, di-tert-butyl and methyl ethyl oxalates were determined. The liquid esters were crystallized using the cryocrystallization technique. A comparison of the intermolecular interactions and packing features in these crystal structures was carried out. The crystal structure of dimethyl oxalate was redetermined at various temperatures. The other compounds were also studied at several temperatures in order to assess the attractive nature of the hydrogen bonds therein. A number of moderate to well defined C-H···O interactions account for the higher melting points of the two solid esters. Additionally, a diminished entropic contribution ΔS(m) in di-tert-butyl oxalate possibly increases the melting point of this compound further.
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India.
authors.forename: Sumy
authors.initials: S
authors.lastname: Joseph
authors.forename: Ranganathan
authors.initials: R
authors.lastname: Sathishkumar
authors.forename: Sudarshan
authors.initials: S
authors.lastname: Mahapatra
authors.forename: Gautam R
authors.initials: GR
authors.lastname: Desiraju