Open Access5‐Butyl‐5‐ethylbarbituric acid: a phase transition at low temperature
Author(s) -
Nichol Gary S.,
Clegg William
Publication year - 2005
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
eISSN - 1600-5759
pISSN - 0108-2701
DOI - 10.1107/s0108270105008486
Subject(s) - phase transition , phase (matter) , chemistry , materials science , thermodynamics , physics , organic chemistry
The room‐temperature crystal structure of 5‐butyl‐5‐ethylbarbituric acid (generally known as butobarbitone), C 10 H 16 N 2 O 3 , was reported in space group C 2/ c [Bideau (1971). C. R. Acad. Sci. Paris Ser. C , 272 , 757–760]. A redetermination at 120 K using synchrotron radiation shows the space group at this temperature to be P 2 1 / n and not C 2/ c . There are two crystallographically independent molecules in the asymmetric unit, but no solvent. Reported issues concerning possible disorder of the molecule are addressed; the butyl substituent of one of the molecules adopts an unusual conformation in being not fully extended. A subsequent re‐collection at room temperature shows that the space group is indeed C 2/ c ( A 2/ a with the axes selected in this report), and so the crystal structure undergoes a phase change upon cooling to 120 K.