Molecular structures ethyne

Surprisingly, little new research on the prototypal tung-sten-arene complex see Arene Complexes), r] -Ceih)f, has appeared, possibly because of the low-yielding and elaborate experimental procedures required for its synthesis. Photolysis of W(CO)6 in the presence of ethyne leads to the formation of benzene and rf-CdRf) W(CO)3 (101), and the solid-state molecular structure of this complex was... 

Low-temperature trapping experiments of the photolysis products of disilacycloheptene (75), which was prepared by insertion of ethyne into the Si—Si bond of l,l,2,2-tetramethyl-l,2-disilacyclopentane <75JA931>, provided evidence for the trans isomer of (75) <90JA6601>. GC-MS analyses indicated that, as the decay of trans-(75) progressed, a mixture of six dimers of mjz 368 was formed. Only one of the dimeric products was successfully isolated in pure form by preparative GC this dimer was assigned the unsymmetrical c/s,fra 5-fused cyclobutene structure (76) on the basis of NMR data. Trapping experiments of metastable trans-(75) by Diels-Alder cycloadditions with cyclopentadiene and 9,10-dihydro-l l,12-dimethylene-9,10-ethanoanthracene afforded (77) and (78), respectively. The crystal and molecular structures of (78) were determined. 

The term hydrocarbon covers compounds formed from hydrogen and carbon atoms only. In addition to ethane, there are two more hydrocarbons containing of two carbon atoms, C2H4 (ethene) and C2H2 (ethyne). The molecular structures of these compounds are shown in Fig. 14.1. 

Fig. 14.1. Above the molecular structure of ethane side and end views. Below the molecular structures of ethene and ethyne.

Despite the undeniable synthetic value of the benzannulation reaction of aryl and alkenyl Fischer carbene complexes, the details of its mechanism at the molecular level remain to be ascertained. Indeed, although a relatively large number of theoretical studies have been directed to the study of the molecular and electronic structure of Fischer carbene complexes [22], few studies have been devoted to the analysis of the reaction mechanisms of processes involving this kind of complexes [23-30]. The aim of this work is to present a summary of our theoretical research on the reaction mechanism of the Dotz reaction between ethyne and vinyl-substituted hydroxycarbene species to yield p-hydroxyphenol. 

Perhaps the next simplest molecular adsorbates for which quantitative structural information exists are the unsaturated C2 hydrocarbons, notably acetylene (ethyne, HC CH) and ethylene (ethene, H2C=CH2), adsorbed on a number of metal surfaces (especially, Cu, Ni and Pd), and also on Si(100), studied by LEED, SEXAFS, and PhD. In some systems adsorption of ethylene is accompanied by a surface reaction. In particular, on both Pt(lll) [74] and Rh(lll) [75] ethylene is converted to an ethylidyne species, H3C—C—, which bonds to these surfaces through the C atom with the —C axis essentially perpendicular to the surface, in three-fold coordinated hollow sites. In addition, ethylene adsorbed on Ni(l 11) at low temperature dehydrogenates to produce adsorbed acetylene as the surface is warmed towards room temperature this particular system actually provided the first example of the... 

The principle of dick chemistrf presented by Hawker et al. (see Section 2.3.5) offers an efficient and versatile method of functionalisation. For example, it utilises [3+2]-cycloaddition of azide-functionalised reagents with ethyne end groups of a dendrimer precursor to prepare dendrimers with triazole-functionalised end groups. The mild reaction conditions, almost quantitative reaction, and not least the tolerance towards numerous functional groups permit the use of widely differing molecular frameworks (e.g. poly(benzyl ether), POPAM dendrimer structures or hyperbranched polyesters) and different functionalised azides... 

Several molecular orbital calculations have been reported on hydroboration, a more recent one by the group of Houk. According to these calculations, in the reaction between BH3 and ethyne the most favourable transition state has a four-centre structure. The same applies to the transition state of the reaction with propyne here, boron is indeed linked to the terminal carbon. 

There are other alkyne compounds, but they do not have much commercial value, and will not be commonly encountered. A three-carbon compound with one triple bond has prop as a prefix for three carbons and is called propyne, with a molecular formula of C3H4 It is listed in the Condensed Chemical Dictionary as propyne, but you are referred to methylacetylene for information. It is listed as a dangerous fire risk, and it is toxic by inhalation. Propyne is used as a specialty fuel and as a chemical intermediate. A four-carbon alkyne has the prefix but, and the compound is called butyne, with the molecular formula of C4H6. The chemical listing is under the name ethylacetylene, and it is designated as a dangerous fire risk. It is also used as a specialty fuel and as a chemical intermediate. The following shows the structures for ethyne, propyne, and butyne ... 

Fig. 7 Node-strut topology for series of CMPs networks produced by Sonagashira-Hagihara cross-coupling chemistry [19]. The benzene nodes are shown in red. The total number of ethyne plus benzene links per strut increases in increments of one from two (CMP-0) to six (CMP-5) in this series of samples. It should be stressed that these are simple representations of the repeat unit structures for the networks. The actual three-dimensional materials have more complex structures and include both terminal alkyne and halogen end groups (see also molecular simulations, Fig. 9)...

Structures for ethyne based on calculated molecular orbitals and electron density are shown in Fig. 1.31. Circular symmetry exists along the length of a triple bond (Fig. 1.31 ). As a result, there is no restriction of rotation for groups joined by a triple bond (as compared with alkenes), and if rotation would occur, no new compound would form. 

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