Formal charge table

A summary of commonly encountered formal charges and the bonding situations in which they occur is given in Table 2.2. Although only a bookkeeping device, formal charges often give clues about chemical reactivity, so it s helpful to be able to identify and calculate them correctly. 

Food, catabolism of, 1126-1128 Formal charge, 40-41 calculation of, 41-42 summary table of, 42 Formaldehyde, dipole moment of, 39 electrostatic potential map of. 167, 704... 

The concept of formal charge has a much wider applicability than this short discussion might imply. In particular, it can be used to predict situations in which conventional Lewis structures, written in accordance with the octet rule, may be incorrect (Table 7.2). 

A formal charge is a charge associated with an atom that does not exhibit the expected number of valence electrons. When calculating the formal charge on an atom, we first need to know the number of valence electrons the atom is supposed to have. We can get this number by inspecting the periodic table, since each column of the periodic table indicates the number of expected valence electrons (valence electrons are the electrons in the valence shell, or the outermost shell of electrons— you probably remember this from high school chemistry). For example, carbon is in Column 4A, and therefore has four valence electrons. Now you know how to determine how many electrons the atom is supposed to have. 

If carbon has a positive formal charge, then it has only three electrons (it is supposed to have four electrons, because carbon is in Column 4A of the periodic table). Since it has only three electrons, it can form only three bonds. That s it. So, a carbon with a positive formal charge will have only three bonds, and you should keep this in mind when counting hydrogen atoms ... 

Table 3.40 displays the calculated 0b charges from natural population analysis (NPA) for all unique B atoms. This table also includes comparison of the NPA charges with corresponding zeroth-order (ZO) estimates given by Lipscomb, which are based essentially on the formal charges for conjectured three-center bond and. s /vx-code assignments for each species (to be discussed below). 

The separation of formal charges in a polar limiting structure like 2b creates a dipole moment of ca. 20 D. Therefore, if such structures were of great importance, quite high dipole moments should be expected for push-pull ethylenes. Data for a reasonable number of mostly symmetrical and rather rigid compounds are known (Table 20). Several high dipole moments are observed, though not in the vicinity of those required for a complete transfer of the double-bond it... 

Lithium Salts Based on Heterocyclic Anions. Lithium salts based on organic anions where the formal charge is delocalized throughout substituted heterocyclic moieties were also reported sporadically, which included, for example, lithium 4,5-dicyano-l,2,3-triazolate ° and lithium bis(trifluoro-borane)imidazolide (Lild). ° The former was developed as a salt to be used for polymer electrolytes such as PEO, and no detailed data with respect to electrochemistry were provided, while the latter, which could be viewed as a Lewis acid—base adduct between LiBp4 and a weak organic base, was intended for lithium ion applications (Table 13). 

There are three kinds of cubane-type cores in this series of complexes (Fig. 24). There are the single cubane-type, Mo3MS4, the double cubane-type, Mo3S4MMS4Mo3, and the sandwich cubane-type, Mo-3S4MS4Mo3. Structural parameters are collected in Table VIII (34, 85-92). Formal charges of the cores are noted after each compound in the table. 

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