Bond type changes

Coals (the plural is deliberately used because coal has no defined, uniform nature or structure) are fossil sources with low hydrogen content. The structure of coals means only the structural models depicting major bonding types and components relating changes with coal rank. Coal is classified, or ranked, as lignite, subbituminous, bituminous, and anthracite. This is also the order of increased aromaticity and decreased volatile matter. The H C ratio of bituminous coal is about 0.8, whereas anthracite has H C ratios as low as 0.2. 

Add lone pair electrons and assign formal atomic charges in each (do not change bond types). Compare to calculatec charges for formaldehyde BF3 complex. Which structure, if either, is more reasonable ... 

An abrupt change in properties in a series of compounds, as in the melting points or boiling points of halides, is often taken as indicating an abrupt change in bond type. Thus of the fluorides... 

The new curve representing the dependence of carbon-carbon interatomic distance on doublebond character is shown in Fig. 8. As mentioned above, this curve does not differ appreciably from the old one up to 50% double-bond character, and in this region it may be used as before to determine bond type from measured interatomic distances. The change in the curve between 50 and 100% double-bond character enhances its value the new curve can be used to determine bond type in this region also, where the old one was useless because of its small slope. 

In this case, a change in structure occurs. Many metals are elemental in nature and when refined to a pure state have a cubic structure. At some critical temperature (defined by the niunber of metal electrons per atom present emd the type of metallic bonding), a change to a hexagon8d form occurs. 

To simplify comparisons between reactions, we sought to describe entire reactions as a single labeled graph. Just as cause and effect can be considered either as two separate events or as a unified process, changing with time, so a reaction can be perceived as two structures, as shown above, or as a single assembly of nuclei connected by bonds which change with time. The aldol-type reaction just illustrated can be rewritten as follows ... 

Reaction graphs are encoded in the same way as static structures. Bonds which change during the reaction are coded as x y where x is the bond type before the reaction and y is the bond type after the reaction. Thus c-c -c represents the reduction of propene to propane and (c-o -cl-c-c-), cl- i represents the formation of tetrahydrofuran and an iodine atom from 4-iodobutan-l-ol. 

The nickel-based systems include the flowing systems nickel—iron (Ni/Fe), nickel—cadmium (NiCd), nickel—metal hydrides (NiMH), nickel—hydrogen (Ni/ H2), and nickel—zinc (Ni/Zn). All nickel systems are based on the use of a nickel oxide active material (undergoing one valence change from charge to discharge or vice versa). The electrodes can be pocket type, sintered type, fibrous type, foam type, pasted type, or plastic roll-bonded type. All systems use an alkaline electrolyte, KOH. 

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