Two phases of C~9~H~12~O~4~: why is the structure at 295K so complicated?
Duncan, Laura L.; Patrick, Brian O.; Brock, Carolyn Pratt; Acta Crystallographica, Section B: Structural Science 58 (2002) 502–511; doi:10.1107/S0108768102000630

data_2103118
_publ_section_title
;
 Two phases of C~9~H~12~O~4~: why is the structure at 295K so
 complicated?
;
_journal_coden_ASTM              ASBSDK
_journal_issue                   3
_journal_name_full
;
 Acta Crystallographica, Section B: Structural Science
;
_journal_page_first              502
_journal_page_last               511
_journal_paper_doi               10.1107/S0108768102000630
_journal_volume                  58
_journal_year                    2002
_chemical_formula_moiety         'C9 H12 O4'
_chemical_formula_sum            'C9 H12 O4'
_chemical_formula_weight         184.19
_chemical_melting_point          396.15
_chemical_name_systematic
;
4,4'-dimethyl-2-hydroxy-6-oxo-cyclohexene-1-carboxylic acid
;
_space_group_IT_number           62
_symmetry_cell_setting           orthorhombic
_symmetry_space_group_name_Hall  '-P 2bc 2a'
_symmetry_space_group_name_H-M   'P m n b'
_atom_sites_solution_hydrogens   geom
_audit_creation_method
;
SHELXL-97, macros written locally, and C. P. Brock
;
_cell_angle_alpha                90.
_cell_angle_beta                 90.
_cell_angle_gamma                90.
_cell_formula_units_Z            8
_cell_length_a                   10.471(3)
_cell_length_b                   26.240(9)
_cell_length_c                   6.434(2)
_cell_measurement_reflns_used    23
_cell_measurement_temperature    130(2)
_cell_measurement_theta_max      15.7
_cell_measurement_theta_min      8.6
_cell_volume                     1767.8(10)
_computing_cell_refinement       'CAD4-VAX (ENRAF-Nonius, 1988)'
_computing_data_collection       'CAD4-VAX (ENRAF-Nonius, 1988)'
_computing_molecular_graphics    'SHELXTL PC (Sheldrick, 1990)'
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 1997)'
_computing_structure_solution    'From structure at 295 K'
_diffrn_ambient_temperature      130(2)
_diffrn_measured_fraction_theta_full 1.00
_diffrn_measured_fraction_theta_max 1.00
_diffrn_measurement_device       'ENRAF-Nonius CAD4-VAX diffractometer'
_diffrn_measurement_method       '\w scans'
_diffrn_radiation_monochromator  graphite
_diffrn_radiation_source         'fine-focus sealed tube'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.131
_diffrn_reflns_av_sigmaI/netI    0.108
_diffrn_reflns_limit_h_max       8
_diffrn_reflns_limit_h_min       0
_diffrn_reflns_limit_k_max       20
_diffrn_reflns_limit_k_min       0
_diffrn_reflns_limit_l_max       4
_diffrn_reflns_limit_l_min       -4
_diffrn_reflns_number            960
_diffrn_reflns_theta_full        16.0
_diffrn_reflns_theta_max         16.0
_diffrn_reflns_theta_min         2.5
_diffrn_standards_decay_%        <1.
_diffrn_standards_interval_time  60
_diffrn_standards_number         2
_exptl_absorpt_coefficient_mu    0.109
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            colourless
_exptl_crystal_density_diffrn    1.384
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       Laths
_exptl_crystal_F_000             784
_exptl_crystal_size_max          0.38
_exptl_crystal_size_mid          0.35
_exptl_crystal_size_min          0.10
_refine_diff_density_max         0.42
_refine_diff_density_min         -0.35
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.43
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     20
_refine_ls_number_reflns         465
_refine_ls_number_restraints     8
_refine_ls_restrained_S_all      3.05
_refine_ls_R_factor_all          0.137
_refine_ls_R_factor_gt           0.081
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.06P)^2^] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.199
_refine_ls_wR_factor_ref         0.214
_reflns_number_gt                250
_reflns_number_total             465
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            br0109.cif
_cod_depositor_comments
;
The following automatic conversions were performed:

'_chemical_melting_point' value '123_C' was changed to '396.15' - it
was converted from degrees Celsius(C) to Kelvins(K).

Automatic conversion script
Id: cif_fix_values 1646 2011-03-28 12:23:43Z adriana 
;
_cod_database_code               2103118