Crystal and molecular structure analysis of gamma-hydroxybutyrate (GHB) analogs:trans-4-hydroxycrotonic acid (THCA),trans-4-hydroxy-4-0-chlorophenylcrotonic acid (THCCA), andtrans-4-hydroxy-4-p-nitrophenylcrotonic acid (THNCA)

The crystal structures oftrans-4-hydroxycrotonic acid (THCA), 4-o-chloro-phenyl-THCA (THCCA), and 4-p-nitrophenyl-THCA (THNCA) have been determined by single-crystal X-ray diffraction techniques, and refined by full-matrix least squares. THCA crystallizes in the monoclinic space groupCc witha=7.847(1),b=8.519(1),c=7.685(4) Å,=109.66(2)° andZ=4; THCCA is triclinic, space groupP¯1, witha=7.878(2),b=8.621(1),c=7.653(1) Å,=92.20(1)°,=114.15(2)°, =94.40(2)°, andZ=2; THNCA is orthorhombic, space groupPna2₁, witha=7.488(1),b=19.666(2),c=7.143(3) Å, andZ=4. FinalR-factors are 0.034, 0.045, and 0.031, respectively. The first two compounds present a semiextended conformation. The third structure is extended; however, for this last compound, empirical molecular mechanics calculations show that the semiextended conformation corresponds also to a low-energy state.