Electron diffraction, basis

Here are the results from this job using the two different basis sets. We also include experimental electron diffraction results ... 

An electron-diffraction study of benzene, p-xylene, mesitylene, and hexamethylbenzene has been made recently by Jones, 0 who, on the basis of measurements extending to To = 14, reported the values Ca,. —Caj = 1.50 = = 0.01 A. and Car — Car = 1.40 = = 0.01 A. Jones t0 values are about 1.3% greater than ours, and comparison of them with our calculated values of s.4 leads to... 

It has been reported recently83 that the spectroscopic study of methylacetylene leads to the value 1.462 0.005 A. for the carbon-carbon single-bond distance in this substance. This is 0.08 A. less than the value 1.54 A. which we expect on the basis of the argument that constancy of the single-bond distance should be retained in the presence of an adjacent triple as well as of an adjacent double bond or aromatic nucleus. An electron-diffraction investigation of this substance is under way in these Laboratories. 

On the basis of a number of physico-chemical methods (Mossbauer spectroscopy, electron diffraction, EXAFS) the iron cores of naturally occurring haemosiderins isolated from various iron-loaded animals and man (horse, reindeer, birds and human old age) were consistently shown to have ferrihydrite-like iron cores similar to those of ferritin (Ward et ah, 1992, 2000). In marked contrast, in the tissues of patients with two pathogenic iron-loading syndromes, genetic haemochromatosis and thalassaemia, the haemosiderins isolated had predominantly amorphous ferric oxide and goethite cores, respectively (Dickson etah, 1988 Mann etah, 1988 ... 

The molecular structure of compound 84 in the gaseous phase was analysed by electron diffraction. It has chair conformation with Cs symmetry. The axial methyl groups are twisted outwards to relieve steric repulsion259. The symmetry of gaseous tetraphenyl-germane is debatable on the basis of its electron diffraction spectrum260. Hexamethyl-distannane (MesSnSnMes) has D3 symmetry in the gas phase, as shown by electron diffraction261. 

As a result of these unfavourable interactions, i.e., opposition to bond strain i.e., between the pair of hydrogens shown at the bottom) and also due to bowsprit interaction, the potential energy of the boat form becomes high and this is why the boat conformation is not the preferred one. Hassel in 1947 established by means of electron diffraction studies that cyclohexane exists predominantly in the chair form. This has also been confirmed by electron diffraction studies and results obtained from Raman and I.R. spectra. Calculations made on the basis of entropy show that only about one molecule in a thousand will be in the boat form. 

Stipp and Hochella (1991), on the basis X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED), have shown that CaC03 exposed to water, contains at the surface =C03H and =CaOH functional groups and van Capellen (1991) has proposed a surface complex formation model for carbonates. Similarly, Ronngren et al. (1991) have proposed =SH and =ZnOH functional groups for the surface of hydrous ZnS s). 

Acetyl peroxynitrate (18) and perfluoroacetyl peroxynitrate (19), two important atmospheric oxidation products of hydrocarbons (formation of 18) or chlorofluorocarbon replacements, such as CF3CH3 (formation of 19), preferentially adopt a gauche conformation (C—O—O—N = 84.7° for 18 and 85.8° for 19 electron diffraction). The two peroxides are characterized by comparatively short 0—0 bonds on one side and long 0°—N connectivities (Table 5) on the other. The observed O —N distances may be explained on the basis of an no ct od-n orbital overlap. This type of interaction lowers the 0°—N bond order and could explain the low bond dissociation energies of this connectivity in peroxides 18 and 19 (118 4 klmol for both compounds). It should be noted that this interpretation does not reflect a possible r-type interaction between a lone pair at 0° and virtual orbitals of the nitro group and therefore requires future investigation. 

Electron dilfraction (64TL705) and microwave spectroscopy (65JCP647) of cyclopropanecarboxaldehyde exhibit a twofold barrier for internal rotation, and the two conformers possess almost the same energy content in the gas phase. Ab initio MO calculations (83JST(104)1 IS) in the extended b-BlG basis set predict the s-cis form to be more stable than the s-trans, with the transition state located at 0 a 100°. A twofold barrier was also found (65JCP3043) by electron diffraction for cyclopropyl methyl ketone, with the s-trans isomer destabilized by steric interactions with respect to the aldehyde. 

Since the discovery of Shechtman et al. (1984) that the rapidly quenched Al-14% Mn alloy is quasicrystalline with icosahedral symmetry, there has been intense activity to explore such alloys to find out whether there would be a conceptual revolution in crystallography. Pauling (1985) proposed that the icosahedral symmetry results from multiple twinning of cubic crystals, but many features of these unique alloys, especially their electron diffraction patterns, cannot be understood on the basis of twinning alone. 

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