Chemical arguments

Chemical arguments based on ring closure reactions, etc., were advanced for the existence of 2-methylpyridinc as 297 =... 

The fact that the structure that I formulated for this alloy from chemical arguments with no knowledge about the X-ray diffraction diagram was found later to agree quantitatively with that diagram has convinced me that the structure is correct. I emphasize that I formulated only one structure, and that the X-ray diagram was not involved in any way in its formulation. The probability of chance agreement of the lattice constant to 0,1 A and of adherence to the selection rules for intensities is surely less than 1 in 1,000. 

Other experiments have been reported by Flinn, based on chemical arguments using self-consistent field calculations on various charge states in tin. Lees and Flinn (16) also conclude that AR/R is positive, although they do not give the magnitude for this term. Similar conclusions have been arrived at by Ruby and co-workers who also conclude from chemical evidence that AR is positive. 

Ca2pe205. Geller et al, (15) and Gonser et al. (19) have recently used the Mossbauer effect to study Ga2Fc20r>. This study is an example of how the Mossbauer effect in conjunction with crystal chemical arguments can be used to work out the magnetic structure of a material without using neutron spectroscopy. 

Of hundreds of theoretically possible pathways, the list can be trimmed to four using linear sweep voltammetry (LSV) and chemical arguments [22]. The LSV method is an exceptionally powerful one for analyzing electrochemical processes [24-27]. From LSV studies, it was concluded that a single heterogeneous electron transfer precedes the rate-determining step, cyclization is first order in substrate, and that proton transfer occurs before or in the rate-determining step. The candidates include (a) e-c-P-d-p (radical anion closure). 

This treatment aiming to evaluate thermodynamically the orbital character of the bond in actinide metals, follows closely the general features illustrated above and has a particular value inasmuch as it is accompanied by a fairly comprehensive survey of the chemical and physical properties of actinide metals known at that time. In it, the metallic radius and the crystal structures are taken as valence indicators AH nd Tm as the bonding indicators . The metallic valence, however, is not taken as constant throughout the actinide series, but rather allowed to vary. The particular choices are justified by physical and chemical arguments, which are taken in support of the hypothesis chosen. 

Prior to these two FTIR studies, Nangia and Benson advanced thermo-chemical arguments in favor of an alternative H-atom transfer mechanism to account for then available experimental results [52] ... 

It will be noted in Table 4.1 that the metallic radii along the 5d series are very close to the values for the corresponding atoms in the 4d series. This observation is related to the remarkable chemical similarities between Zr and Hf. The effect of the lanthanide contraction on metallic radii persists to the end of the 5d series, but its chemical consequences become less marked as we pass from left to right. It is important not to make too much of similarities in metallic radii in chemical arguments, however. For example, the triad Mn, Tc and Re all have practically equal metallic radii, but their chemical behaviour shows dramatic differences. The near-equivalence of their metallic radii is less marked when we look at bond lengths in molecules. For example, the M-M distances in (CO)5M—M(CO)5 are respectively 293, 304 and 302 pm for M = Mn, Tc and Re. 

The reader may wonder at this point whether bond energies for coordination compounds can be tabulated and utilised in chemical arguments, in the same way as in Main Group chemistry. The complexity of most coordination/organometallic compounds makes this very difficult, and the ways in which the formation of a coordinate bond affects the bonding within the ligand renders the bond energy concept distinctly dubious. Consider, for example, the relatively simple case of hexacar-bonylchromium(O). For the reaction ... 

In order to underpin these more general descriptive approaches to migration by appropriate physico-chemical arguments, the parameters controlling migration will be presented and discussed in more depth in the following chapter. 

The species (2) or (3), and those from (5) to (7) (all in Fig. 4.53) are supported by both chemical and spectroscopic arguments. It is important to note [91,92] that there are important chemical arguments (exchange reactions) for the presence of multiply-bound species in the presence of hydrogen (or D2), since the presence of H2 suppresses the formation of the multiply bound species so much that they are no longer detected at the temperatures at which vibration spectra are monitored [93]. Species (4) and (5) can be considered as alternatives, both originating from the adsorption of ethene on transition metals. Species (4) is preferred on Pd, (5) on Pt [94], Labelled (C ) isohexanes have been used [95] to show that two mechanisms are operating when, for example, 2-methylpentane is converted into 3-methylpentane [94] (transition state structures are in brackets). 

Fig. 12). Because the vertical and adiabatic ionization potentials may differ by up to 0 5 eV or sometimes more, thermo-chemical arguments must be consistent in their choice of values. 

The application of the group-product function equations to the ligand-field problem is now straightforward and leads to the primitive parameterization in which we omit contributions from the additional term AH(e) these will be discussed in Sect. 5 below. As already implied in Sect. 3 we choose the optimal number of electrons to put in the M set from chemical arguments since the formal oxidation state of the complex can usually be equated with the best (integral) choice for (the d" configuration), and so we can make the partition n = Nj + Nt with 1 < < 9. The functions Pm are then obtained as... 

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