Structure of 2',6'-dihydroxy-4,4'-dimethoxychalcone.

1-(2,6-Dihydroxy-4-methoxyphenyl)-3-(4-methoxyphenyl)-2-propen-1-o ne, C17H16O5, Mr = 300.31, orthorhombic, Pbca, a = 27.903 (3), b = 13.958 (2), c = 7.662 (1) A, V = 2984 (1) A3, Z = 8, D chi = 1.337 Mg m-3, lambda(Cu K alpha) = 1.5418 A, mu = 0.729 mm-1, F(000) = 1264, T = 295 K, R = 0.040 for 1702 observed reflections. Two intramolecular hydrogen bonds are observed. The hydroxyl H atom at O(6A) is hydrogen bonded to the C(9) carbonyl group with short distances O(6A)...O(9) = 2.406 (3) and O(9)...H(6A) = 1.38 (3), O(6A)--H(6A) = 1.09 (3) A, the angle O(6A)--H(6A)...O(9) is 153 (4) degrees. The other hydrogen bond is of the C--H...O type with distances C(8)...O(2A) = 2.778 (4), H(8)...O(2A) = 2.09 (3) A and the angle around H(8) is 124 (2) degrees. Conjugation is observed between the aromatic rings and the central enone system. The molecule is not planar, the angle between the planes of the phenyl rings being 13.1 (4) degrees. Intermolecular O--H...O bonds with distances O(6A)...O(2A) = 2.689 (2), H(2A)...O(6A) = 1.86 (4) A and angle O(2A)--H...O(6A) = 176 (4) degrees form endless chains of molecules along b.

Structure of 2-methoxy-6-nonyl-1,4-benzoquinone, C16H24O3, a synthetic contact allergen related to the naturally occurring primin.

C16H24O3, Mr = 264.36, triclinic, P1, alpha = 4.167 (1), b = 9.658 (1), c = 19.093 (1) A, alpha = 89.66 (1), beta = 87.27 (1), gamma = 79.07 (1) degrees, V = 753.65 (1) A3, Z = 2, D chi = 1.165 Mg m-3, lambda(Cu K alpha) = 1.5418 A, mu = 0.595 mm-1, F(000) = 288, T = 295 K, R is 0.047 for 1682 observed unique reflections. The angle between the quinone ring plane and the mean plane defined by the aliphatic nonyl chain atoms is 17.4 (3) degrees. The average Csp3--Csp3 bond distance and corresponding angle of the side chain are 1.522 (3) A and 113.2 (2) degrees. The average dimensions of the quinone ring are C--C 1.485 (3), C = C 1.337 (3), C = O 1.209 (3) A, C--C--C 118.4 (2), C = C--C 120.8 (2), O = C--C 120.8 (2) degrees. Neighboring molecules form dimers across centres of symmetry which are linked by C--H...O hydrogen bonds, with H(3)...O(4i) 2.42 (4), C(3)...O(4i) 3.29 (2) A, and angle C(3)--H(3)...O(4i) 164 (3) degrees. The dimers are held together by van der Waals forces between the nonyl side chains, and by C(16)--H...O(2ii) hydrogen bonds, with H(163)...O(2ii) 2.56 (4), C(16)...O(2ii) 3.357 (3) A, and angle C(16)--H(163)...O(2ii) 140 (3) degrees [(i) -x, 1 -y, -z; (ii) -1 -x, 1-y, -z].

Structure of 6-dodecyl-2-methoxy-1,4-benzoquinone, a new synthetic contact allergen.

C19H30O3, Mr = 306.45, triclinic, P-1, a = 5.453 (1), b = 5.608 (1), c = 30.129 (2) A, alpha = 85.85 (1), beta = 88.66 (1), gamma = 83.02 (1) degree, V = 912.0 (1) A3, Z = 2, Dx = 1.116 Mg m-3, Cu K alpha radiation, lambda = 1.5418 A, mu = 0.548 mm-1, F(000) = 336, T = 296 K, R is 0.040 for 2489 observed unique reflections. The aliphatic side chain is slightly rotated from the quinone ring. The angle between the quinone-ring plane and the mean dodecyl-chain plane is 20.8 (2) degrees. The average Csp3-Csp3 bond lengths and corresponding angles of the side chain are 1.515 (5) A and 113.8 (3) degrees. The average dimensions of the quinone ring are C-C 1.477 (4), C = C 1.337 (4), C = O 1.222 (3) A, C-C-C 118.9 (3), C = C-C 120.6 (3), O = C-C 120.6 (3)degrees. Neighbouring molecules form dimers by C-H...O interactions across centres of symmetry [C(3)...O(3) 3.413 (2) A]. The dimers are linked together via methyl H and carbonyl O along [100] [C(19)...O(3) 3.338 (3) A]; O(3) is a bifurcated acceptor.