Trans-Tris

Electron deficient species can attack the unshared electron pairs of heteroatoms, to form ylides, such as in the reaction of thietane with bis(methoxycarbonyl)carbene. The S —C ylide rearranges to 2,2-bis(methoxycarbonyl)thiolane (Section 5.14.3.10.1). A"-Ethoxycar-bonylazepine, however, is attacked by dichlorocarbene at the C=C double bonds, with formation of the trans tris-homo compound (Section 5.16.3.7). 

A valuable feature of the Nin/Crn-mediated Nozaki-Takai-Hiyama-Kishi coupling of vinyl iodides and aldehydes is that the stereochemistry of the vinyl iodide partner is reflected in the allylic alcohol coupling product, at least when disubstituted or trans tri-substituted vinyl iodides are employed.68 It is, therefore, imperative that the trans vinyl iodide stereochemistry in 159 be rigorously defined. Of the various ways in which this objective could be achieved, a regioselective syn addition of the Zr-H bond of Schwartz s reagent (Cp2ZrHCl) to the alkyne function in 165, followed by exposure of the resulting vinylzirconium species to iodine, seemed to constitute a distinctly direct solution to this important problem. Alkyne 165 could conceivably be derived in short order from compound 166, the projected product of an asymmetric crotylboration of achiral aldehyde 168. 

TV-Ethoxycarbonylazepine, however, is attacked by dichlorocarbene at the C = C double bonds, with formation of the trans tris-homo compound (CHEC 5.16.3.7). 

Name Cellulose c/s- and trans-tris (4-phenylazophenyl carbamate) (CPAPC)... 

The cis-isomers of the tris(a-amino acid) complexes of cobalt(III) and chromium(III) have larger extinction coefficients for band maxima of d-d transitions than the corresponding trans-isomers (19-24). Although the difference in the coordination environment between the cis- and trans-tris(hydroxamato)chromi-um(III) complexes is less than that in the amino acid complexes, differences in the absorption spectra of the cis- and trans-isomers of Cr(hydroxamate)3 complexes have been found, especially for the extinction coefficients of the high energy transition... 

Figure 3. A perspective drawing of trans-tris(benzohydroxamato) chromium(III) looking down the molecular (pseudo) threefold axis...

Figure 4. A comparison of the octahedral bonding geometries of trans-tris(ben-zohydroxamato)chromium(III) and cis-tris(benzohydroxamato)iron(IH)...

Recently the salts of the cis- and trans-tris(benzohydrox-imato)chromate(III) trianions have been isolated. Their absorption spectra are parallel to those of the neutral species. Figure 5 shows ORTEP plots of these isomers. The corresponding iron complex crystallizes in the cis geometry under the same conditions. 

Figure 5. A perspective drawing of the cis-trisfbenzohydroximato) chromate(III) (5a) and trans-tris(benzohydroximato)-chromate(III) (5b) ions, looking down the threefold and pseudothreefold axes, respectively...

Only small amounts of a cyclotrimer 7, the trans-tris-cr-homobenzene derivative 3,3,6,6,9,9-hexamethyl-e/jffo,exo-tetracyclo[6.1.0.02 4.05,7]nonane, are formed under these conditions. Additionally, two other trimers, 5 and 6, are obtained in low yield. When more basic phosphanes, such as ( -Bu)3 n(i-Pr) P (n = 1,2), are employed, oligomeric mixtures are produced.360 On the other hand, with a bulky phosphane, such as tricyclohexylphosphane [3 mol-% with 2 mol-% of bis(cycloocta-l,5-diene)nickel], 36% of the cyclodimer 4 is obtained after 3 hours at 35°C in benzene as solvent.360 Without phosphane coligands, only benzene-soluble oligomers, presumably containing cyclopropane rings, are formed. 

The tetramers 18 are stereoisomers of 3,3,6,6,9,9,12,12-octamethylpentacyclo-[9.1.0.02 4.05 7.0810)dodecane, as shown by extensive spectroscopic studies. The product distribution is only slightly dependent on the substituents in the 3-position of the cyclopropene ring. With bis(dibenzylideneacetone)palladium as catalyst, about 6% of the hexamethyl-trans-tris-<7-homobenzene 7 is additionally produced. When R1 R2, a large number of isomeric products is formed and a complete analysis of all the tetrameric products has not yet been possible.41... 

C6F906Sb, (R)-Tris(trifluoroacetato)antimony(III), 46B, 707 CsHi,C102Sb, o-Phenylenedioxyant imony (III) chloride, 45B, 777 CgHgOftSb, Antimony(III) pyrogallate monohydrate, 42B, 561 CgHgClsSb, trans,trans,trans-Tri-2-chlorovinyldichlorostibine, 17,... 

C21H1sOgSc, Tris(tropolonato)scandium(III), 40B, 944 C2iHi8CrN30g 2 C3H8O, trans-Tris(benzohydroxamato)chromium(III) propanol solvate, 45B, 1220... 

S.K. Samanta et al. have reported the rheological properties of boron nitride nanotubes (BNNTs) filled gel nanocomposites which indicates that the flow properties of the resulting materials become resistant to applied stress upon incorporation of even a very low wt% of BNNTs. They have prepared gel nanocomposites using a gelator which is made up of all-trans tri-(p-phenylenevinylene) bis (aldoxime) (TPV, 1) which is capable of forming a physical gel in aromatic hydrocarbons such as toluene (Fig. 8a). A transparent solution of 1 (10 mg/mL)... 

The C=C stretching frequency near 1640 cm" in vinyl hydrocarbons is a medium intensity band which becomes inactive in the infrared region in a symmetrical trans- or symmetrical tetrasubstituted double bond compound, both of which have centers of symmetry. Even when the substituents are not exactly alike in trans-md tetrasubstituted olefins, the infrared absorption may be quite weak. These double bond vibrations all appear strongly in the Raman effect, however, where the C=C stretch vibration in all types of ethylenes gives rise to a strong Raman band in the region 1680-1630 cm The trans, tri, and tetra alkyl-substituted ethylenes appear at 1680-1665 cm which are strong in Raman but weak or absent in the infrared. The cis, or... 

The first oxidation in all those porphyrin polymers, found at 1.30, 1.22, 1.29, and 1.17 V, respectively, for cis, trans, tri-, and tetra-substituted derivatives, was assigned to the monoelectronic oxidation of Zn-OEP moiety. Note that those potentials are shifted positively 0.62 to 0.49 V as compared with the +0.68 V measmed for the ZnOEP monomer. Analogously, the cis, trans, tri, and tetrapyridylporphyrin derivatives were, respectively oxidized at 1.48, 1.37, 1.54, and 1.47 V versus SCE. The anodic shift of those potentials can be attributed to the formation of positively charged electron-withdrawing pyridynium spacers connecting the porphyrin rings. 

---