Dewar properties compounds

The most notable studies are those of Ingold, on the orienting and activating properties of substituents in the benzene nucleus, and of Dewar on the reactivities of an extensive series of polynuclear aromatic and related compounds ( 5.3.2). The former work was seminal in the foundation of the qualitative electronic theory of the relationship between structure and reactivity, and the latter is the most celebrated example of the more quantitative approaches to the same relationship ( 7.2.3). Both of the series of investigations employed the competitive method, and were not concerned with the kinetics of reaction. 

In his first published paper on the structure of benzene in 1922, Ingold stated his aim to unify aliphatic and aromatic chemistry by studies of ring formation of unsaturated systems. He argued that chemists must accept the Dewar formulation, using a bridged phase of benzene, in order to relate the properties of aromatic compounds to the facts of aliphatic chemistry. 31... 

One hundred and seven years after Faraday s first reported preparation of BHC, Harry Bender of the Great Western Electro-Chemical Company in California, was looking for new uses of chlorine. He added benzene to liquid chlorine in a Dewar flask in the open air and noticed that part of the product which spilled on the ground attracted and killed flies and bees. Thus, although compounds such as p-dichlorobenzene had been used as fumigants since World War I and BHC is said to have been used in smoke screens during that war, Bender s observation made in 1932-3 and referred to only fleetingly in the literature (1), was the first indication that technical BHC had unusual insecticidal properties. 

The partial confusion arising after Dewar s and Chatt s reviews were published, was resolved after Chatt and Duncanson reported in 1953 in the Journal of the Chemical Society the results of infrared spectroscopic studies on a range of olefin platinum(II) complexes [38]. In this highly cited paper they proposed, with particular reference to Dewar s model, that in the olefin platinum(II) complexes the cr-type bond would be formed by overlap of the filled re-orbital of the olefin with a vacant 5d6s6p2 hybrid orbital of the platinum atom, and the re-type bond by overlap of a filled 5d6p hybrid orbital of the metal with the empty antibonding re-orbital of the olefin (Fig. 7.8). In addition, Chatt and Duncanson illustrated how the model could be used to interpret not only the physical properties of the olefin platinum compounds, such as the spectroscopic data and dipole moments, but also their reactivity and their greater stability compared to the olefin silver salts. 

For thermodynamic data, bond distances, and some other properties of Si compounds see M. J. S. Dewar et aL, Organometallics 1986,5, 375. 

Similar results are reported for the perfluorodimethyl compound. The introduction of fluoro-substituents and particularly perfluoroalkyl groups thus imparts a notable increase in the ease of formation and stability of valence bond isomers of aromatic compounds, and the physical properties of those involved in the light-induced interconversion of perfluoro-1,3,5- and -1,2,4-trimethylbenzenes have also been discussed by the Manchester group.14 15 The energetics of the back reaction (i.e. valence-bond isomer to benzenoid compound) have been studied, and it is interesting to note that in the conversion of Dewar acetophenone into acetophenone, the location of the excitation starts off mr -like but ends as... 

The first useful Dewar-type theory was the MINDO/3 (third version of the modified INDO) method, published in 1975. For a sample of compounds containing no elements other than C, H, O, and N, the average absolute errors in MINDO/3 calculated properties are 11 kcal/mol in heats of formation, 0.022 A in bond lengths, 5.6° in bond angles, 0.49 D in dipole moments, and 0.7 eV in ionization energies. The errors in A.H°f 29S are larger than Dewar was aiming for. 

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