Vibrational spectra of trans,trans-1,2,3,4-tetrachloro-1,3-butadiene; and the molecular structure of trans,trans-1,2,3,4-tetrachloro-1,3-butadiene and of hexachloro-1,3-butadiene (a reinvestigation) determined by gas-phase electron diffraction

On the Unusual Synclinal Conformations of Hexafluorobutadiene and Structurally Similar Molecules

An explanation is presented for the unusual conformations of some molecules that contain the C═C-C═C core, namely, butadienes, biphenyls, and styrenes. Small substituents often induce a synclinal conformation, which brings the substituents into close proximity, and sometimes, there is no anticlinal minimum at all. This would not be predicted from steric repulsion arguments nor would it be expected that atoms that are nonbonded in a Lewis structure would approach closer than the sum of their van der Waals radii. Atomic energies calculated according to the quantum theory of atoms in molecules (QTAIM) do not show a consistent pattern for these structurally similar molecules, nor are intersubstituent bond paths consistently found, nor favorable diatomic interaction energies calculated using the interacting quantum atoms (IQA) scheme. Instead, the synclinal conformations are found to be driven by the attraction energy of the electron distribution of the carbon atoms and the nuclei of the molecule.

Synthesis of 1,1,4,4-Tetrabromo-2-butenes and Related Compounds via Desilylation−Bromination of Silylated 1,3-Butadiene Derivatives

The combination of zirconocene-mediated coupling of silylated alkynes with a protonation-desilylation or bromination-desilylation process afforded otherwise unavailable butadiene derivatives. When (E,E)-2,3-dialkyl-1,4-bis(trimethylsilyl)-1,3-butadienes were treated with 3 equiv of Br(2) in CH(2)Cl(2), (E)-2,3-dialkyl-1,1,4,4-tetrabromo-2-butenes were obtained in excellent yields with perfect stereoselectivity.

Perthio- and perseleno-1,3-butadienes, -but-1-ene-3-ynes, and -[3]-cumulenes: one-step syntheses from 1,4-dilithio-1,3-butadiyne

[reaction: see text] Treatment of 1,4-dilithio-1,3-butadiyne (1) with dichalcogenides RSSR or RSeSeR affords dithio- and diseleno-1,3-butadiynes (2, 3), perthio- and perseleno-[3]-cumulenes (4, 5), perthio- and perseleno-1,3-butadienes (6, 7), and/or perthio- and perseleno-but-1-ene-3-ynes (8, 9). The products can be controlled by stoichiometry and temperature, by the presence or absence of oxygen, and by choice of the "R" group. By X-ray crystallography, hexa(methylthio)-1,3-butadiene is highly twisted, with a torsion angle [Phi(CCCC)] of 84.7 degrees and an elongated C(2)-C(3) distance of 1.484(3) A.

Conformational aspects of glutathione conjugates of chlorinated alkenes: a computational study

The nephrotoxicity of halogenated alkenes is due to the beta-lyase mediated bioactivation of the hepatic glutathione (GS) conjugate to mutagenic or cytotoxic reactive species in kidney. Experimental evidence obtained for regioisomers and geometric isomers of haloalkene GS conjugates indicates that different isomers may be metabolized and excreted at different rates, follow different metabolic pathways, and exhibit different toxicities. Computational methods were applied in the present work to a conformational study of GS-haloalkene conjugates to determine the relative stabilities of possible regioisomers and geometric isomers of the conjugates. The halogenated alkenes studied were 1,1,2-trichloroethylene (TCE), hexachloro-1,3-butadiene (HCBD), and 1,1,2-trichloro-3,3,3-trifluoro-1-propene (TCTFP). Calculated energies of GS conjugate products were used to approximately infer relative product abundance under synthetic and in vivo conditions. This approach neglects differential solvent effects and enzyme selectivity and assumes a late transition state for GS conjugation and/or some thermodynamic control of the conjugation process. Relative population predictions of GS conjugate isomers, based on computed energies, were in agreement with experimental synthetic and in vivo isomer determinations in the case of TCE, where careful analytical characterization of the isomers was definitive. In the case of HCBD, where analytical determinations were not performed and isomer assignments were based on general reactivity concepts, calculations from the present study supported one GS conjugate isomer assignment and disagreed with the other. Finally, in the case of TCTFP, the calculations predicted that three isomers would have similar populations, whereas only two were detected in the experimental study.