Electronic structure acetylene

R. S. Mulliken, /. Chem. Phys., 3, 517 (1935). Electronic Structures of Polyatomic Molecules. IX. Methane, Ethane, Ethylene, Acetylene. 

In Section 2-4, we studied the electronic structure of a triple bond. Let s review this structure, using acetylene as the example. The Lewis structure of acetylene shows three pairs of electrons in the region between the carbon nuclei ... 

Comparison of the electronic structures of acetonitrile and propyne (methylacetylene). In both compounds, the atoms at the ends of the triple bonds are sp hybridized, and the bond angles are 180°. In place of the acetylenic hydrogen atom, the nitrile has a lone pair of electrons in the sp orbital of nitrogen,... 

Alkvnes (acetylenes) are like alkenes in that their electronic structure can he described fairly simply in terms of only o and jr bonding and anti-bonding orbitals, but they are different in that the vertical (it.n )... 

H3NBH3 is isoelectronic with ethane, H2NBH2 is isoelectronic with ethylene, andHNBH is isoelectronic with acetylene. Derive the band structure and the DOS for planar poly- -BHNH- (isoelectronic to polyacetylene) with a single B-N distance and predict its conductivity and stability with respect to a Peierls distortion. Only consider the tt electronic structure. 

Table 1 summarizes the main types of structures that are formed upon adsorption of C2H2 on some of the most extensively studied transition metal surfaces. As Table 1 shows the adsorption mode of acetylene depends on the electronic structure of the surface. For example on (111) surfaces, the p-bridging adsorption mode (II on Fig. 

Figure 4.8-1 Electronic structure and chemical structure of hole and electron polarons (a), hole and electron bipolarons (b), and hole and electron solitons (c). Examples of chemical structures refer to poly(thiophene) and poly(acetylene), respectively.

In the thermal addition reaction a structural change from the butatriene to the acetylene chain structure is observed at n = 6 in the ESR spectra of the short intermediates. Since the ESR is sensitive only to unpaired electrons with S 0 the buta-triene-to-acetylene transformation is observed only in the thermally excited DR... 

In this article it has been shown, that the low temperature photopolymerization reaction of diacetylene crystals is a highly complex reaction with a manifold of different reaction intermediates. Moreover, the diacetylene crystals represent a class of material which play a unique role within the usual polymerization reactions conventionally performed in the fluid phase. The spectroscopic interest of this contribution has been focussed mainly on the electronic properties of the different intermediates, such as butatriene or acetylene chain structure, diradical or carbene electron spin distributions and spin multiplicities. The elementary chemical reactions within all the individual steps of the polymerization reaction have been successfully investigated by the methods of solid state spectroscopy. Moreover we have been able to analyze the physical and chemical primary and secondary processes of the photochemical and thermal polymerization reaction in diacetylene crystals. This success has been largely due to the stability of the intermediates at low temperatures and to the high informational yield of optical and ESR spectroscopy in crystalline systems. 

The electronic structure of alkynes is related to that of alkenes, and the photochemistry of the two classes of compound reflects this similarity. Because the photochemistry of alkenes has received greater attention and has already been described in systematic form - it is not unexpected that the present account should point out the ways in which alkyne photochemistry parallels, or is markedly different from, that of alkenes. There is a considerable difference, however, in the range of compounds which has been studied in each class. Reports of photochemical reactions of alkynes very often refer to mono- or disubstituted acetylenes in which the substituents are alkyl, aryl or alkoxycarbonyl. There have been studies on diyne and enyne systems, but as yet there has emerged nothing in alkyne chemistry to match the wealth of photochemistry reported for dienes and polyenes. This reflects in part the greater tendency of the compounds containing the C=C bond to undergo photopolymerization rather than any other reaction on irradiation. Within this limitation there is a wide variety of reactions open to the excited states of alkynes, and quite a number of the processes have synthetic application or potential. 

---