Complex unsaturated

A Semi-Empirieal Theory of the Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules R. Pariser and R. G. Parr... 

Pariser, R., and Parr, R. G., 1. J. Chem. Phys. 21, 466 II. J. Chew. Phys. 21, 767, "A semi-empirical theory of the electronic spectra and electronic structure of complex unsaturated molecules."... 

Molecular astronomy of carbon molecules is very rich. Of about 120 known interstellar molecules more than three-quarters contain carbon atoms diatomic molecules include CO, CN, C2, CH, CH+, CN+, and CO+ polyatomic include CH2, CH4, C2H2j CH OH, CH3CH2OH, H2CO and HNC large complex unsaturated radicals and polycyclic aromatic hydrocarbons are also detected. These all play a role in the thermochemistry of interstellar clouds. The 2.6-millimeter line of CO diagnoses density and temperature in molecular clouds, as do other molecules. 

Representative examples of these reactions are shown in Table 4. For more details, see recent reviews.8 10 Recently, more complex unsaturated systems were subjected to the tellurium-lithium exchange reaction.137,141 In Scheme 98, some examples of such a process are shown. In all cases, the (Z)-stereochemistry of the starting vinylic telluride was preserved.137... 

Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. I. See also, R. Pariser and R. Parr, J. Chem. Phys., 21, 767 (1953). A Semi-Empirical Theory of the Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. II. J. A. Pople, Trans. Faraday Soc., 49, 1375 (1953). Electron Interactions in Unsaturated Hydrocarbons. J. A. Pople, J. Phys. Chem., 61, 6 (1957). Application of Self-Consistent Molecular Orbital Methods to ti Electrons. 

It should be stressed that in case of the ethynyl-acetylene reaction, a molecular hydrogen loss channel synthesizing the 1,3-butadienyl radical is open as well. Since the reactions of cyano and ethynyl radicals have no entrance barrier, are exoergic, and aU transition states involved are lower than the energy of the separated reactants, these reaction classes are extremely important to form nitriles and complex unsaturated hydrocarbons in low-temperature environments. On the other hand, the corresponding phenyl radical reactions are—due to the presence of an entrance barrier—closed in those environments. However, the elevated temperature in combustion systems helps to overcome these barriers, thus making phenyl radical reactions important pathways to form aromatic molecules in combustion flames. 

Pentacarbonyliron is also capable of producing lactone from epoxides [21]. The reaction of dienemonoepoxide with Fe(CO)5 gives a p-TC-allylcarbonyliron complex. Unsaturated lactone is obtained after treatment of the allyliron intermediate with cerium (Scheme 10.6). 

On the other hand, with saturated complexes, a vacant site must be created if the metal is to take part in oxidative addition reactions. For example, Fe(CO)s is a ds complex and the five-coordination is saturated and stable. In the reaction with Fe(CO)s, one of the carbon monoxide ligands must be liberated to make the complex unsaturated and bring it to an excited state. For this purpose, radiation or heat is necessary as an energy source for the initiation of the reaction using Fe(CO)s ). 

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