Synthesis and X-ray crystallography of cholest-3,5-diene-7-one-oxime

Cholest-3,5-diene-7-one-oxime (C₂₇H₄₃NO) was prepared using a usual synthetic route and its three-dimensional structure was determined by X-ray diffraction methods. The transparent platelike crystals of this compound crystallized in the monoclinic space group P2₁, with unit cell parameters a = 14.302(2) Å, b = 11.475(2) Å, c = 15.919(4) Å, = 106.04(1)°, (Cu K) = 1.5418 Å, Z = 4. The structure was solved by direct methods and refined to an R-value of 0.075 for 4640 observed reflections. Two crystallographically independent molecules were observed in the asymmetric unit cell. The ring A in both the molecules was found to exist in 1,10 half-chair conformation while ring C in chair conformation. The rings B and D in both the molecules adopted different conformations. Three intermolecular interactions of the type C–H O and C–H N were also observed.     

Selinidin: Crystal structure generated by C–H···O, C–H···π and π-π interactions

The title compound, 9,10-dihydro-8,8-dimethyl-2-oxo-2H,8H-benzo[1,2-b:3,4-b']dipyran-9-yl-2-methyl-2-butenoate, C₁₉H₂₀O₅, was isolated from the roots of Selinum vaginatum. The compound crystallizes into monoclinic space group P2 ₁ with unit cell parameters: a = 12.830(2) Å, b = 9.041(1) Å, c = 14.983(1) Å, β = 95.09(1)°, Z = 4. The crystal structure has been determined using direct methods and refined by full-matrix least-squares to a final R value of 0.0529 for 3142 observed reflections. There are two independent molecules, A and B, per asymmetric unit. In both the molecules, the coumarin nucleus is planar. However pronounced differences are observed in the conformation of dihydropyran ring which has a half-chair conformation with an 8β-9α orientation in molecule A and is intermediate between half-chair and sofa in molecule B. Differences also occur in the conformation of the 2-methylbutenoyloxy side chain at C9 due to the different geometry of C–H···π interactions in molecules A and B. Molecules A and B are connected by π–π interactions between their coumarin fragments forming dimers. The dimers interact through C–H···O and C–H···πhydrogen bonds.     

Molecular structure ofrac-(4R*,4aS*,10aS*)-4-nitro-1,2,3,4,4a,9,10,10a-octahydrophenanthren-4a-ol,an unusual by-product of nitration of a crude 9,10-dihydrophenanthrene

A new nitro-octahydrophenanthrenol has been isolated by nitration of a crude 9,10-dihydrophenanthrene, which was identified by nmr and X-ray diffraction analysis. Crystallographic and molecular structure confirmed the compound as therac-(4R^*,4aS^*,10aS^*)-4-Nitro-1,2,3,4,4a,9,10,10a-octahydrophenanthren-4a-ol. The crystal was triclinic, ,a=10.549(3),b=8.530(3),c=7.131(1)Å, =107.07(3), =91.62(3), =96.27(4)°. Cyclohexane and cyclohexene rings aretrans-fused and have chair and half-chair conformations, respectively. The molecules are associated by hydrogen bridge between the hydroxyl oxygen and both nitro oxygens.     

Crystal structure of 3β-acetoxy-pregna-5,16-dien-20-one (16 DPA)

The title compound, 3β-acetoxy-pregna-5,16-dien-20-one, C₂₃H₃₂O₃, has been synthesized by acetylation followed by oxidation of diosgenin and its crystal structure has been solved from single crystal X-ray diffraction data. The compound crystallizes into orthorhombic space group P2₁2₁2₁ with unit cell parameters: a = 6.031(4) ?, b = 12.481(2) ?, c = 27.162(5) ?, Z = 4. The crystal structure has been refined to R = 0.0597 for 1291 observed reflections. Rings A and C of the compound are in chair conformation whereas ring B is in half-chair conformation. Ring D is in envelop conformation. The A/B ring junction is quasi-trans, while ring systems B/C and C/D are trans fused about the C8–C9 and C13–C14 bonds, respectively. The steroid nucleus has a small twist, as shown by the C19–C10⋅C13–C18 pseudo-torsion angle of 9.5°. The crystal packing is determined by a pair of weak C–H⋅O hydrogen bonds in addition to van der Waals interactions.     

争议中的两种“半椅式”结构*——如何讲授环己烷构象翻转过程

环己烷的构象翻转问题是有机化学教学中重要的立体化学内容。虽然诸多中英文教材均指出环己烷构象翻转过程中存在着五碳共平面的半椅式构象,但是这种描述缺乏理论和实验的证据支撑。建议采用四碳共面的结构讲授环己烷构象翻转过程。该四碳共面构象不仅得到理论计算支撑,而且符合势能面的物理化学原理,但遗憾的是目前仅有少量教材使用这一表述。     

Synthesis and Structure Analysis of N-（Dehydroabietyl）maleamic Acid

N-(Dehydroabietyl)maleamic acid was synthesized from dehydroabietylamine and maleic anhydride.Its structure was characterized by IR,1 H-and 13 C-NMR spectra.The stereo structure of the title compound was also unambiguously confirmed by X-ray crystal structure analysis.The white crystal crystallizes in the monoclinic system,space group P2 1 with a=12.075(2),b=10.377(2),c=17.840(4),β=100.31(3) °,V=2199.3(8) 3,R=0.0618 and wR=0.1437.Two crystallographically independent molecules with different conformations co-exist in the unit.In each molecule,the two cyclohexane rings form a trans ring junction with chair and half-chair conformations,respectively.The C=C double bond between two carbonyl groups is in a Z configuration.Intermolecular and intramolecular hydrogen bonds coexist to stabilize the structure.     

Ab initio molecular orbital study of energies and conformers of 3,4-dihydro-1,2-dithiin, 3,6-dihydro-1,2-dithiin, 4H-1,3-dithiin,and 2,3-dihydro-1,4-dithiin

Optimized geometries and energies for 3,4-dihydro-1,2-dithiin ( 1 ), 3,6-dihydro-1,2-dithiin ( 2 ), 4H-1,3-dithiin ( 3 ), and 2,3-dihydro-1,4-dithiin ( 4 ) were calculated using ab initio 6-31G* and MP2/6-31G*//6-31G* methods. At the MP2/6-31G*//6-31G* level, the half-chair conformer of 4 is more stable than those of 1 , 2 , and 3 by 2.5, 3.5, and 3.6 kcal/mol, respectively. The half-chair conformers of 1 , 2 , 3 , and 4 are 2.9, 7.1, 2.0, and 5.6 kcal/mol, respectively, more stable than their boat conformers. The calculated half-chair structures of 1 – 4 are compared with the calculated chair conformer of cyclohexane and the half-chair structures for cyclohexene, 3,4-dihydro-1,2-dioxin ( 5 ), 3,6-dihydro-1,2-dioxin ( 6 ), 4H-1,3-dioxin ( 7 ), and 2,3-dihydro-1,4-dioxin ( 8 ). © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1064–1071, 1998