Seven valence electrons species

In this chapter, we have studied a list of inter- and intra-row main group (five, six, seven and eight valence electrons species) as well as few transition metal compounds. We attempted to explain their unusual shortness on the basis of their detailed electronic structures. 

Complete active space (CAS) SCF calculations on this species with seven valence electrons showed it to be distorted from tetrahedral (1 ) symmetry. The energy minimum for Cg symmetry in the electronic ground state Ai predicts one very long P-H bond. The geometric parameters were calculated to be r(P-H)=1.438 and 1.877 A and a(H-P-H) = 95.5" [1]. Multireference Cl calculations yielded a relatively high barrier of 83 kJ/mol towards proton loss. The energy of the strongly exothermic deprotonation was found to be -276 kJ/mol [2]. 

Calculated relative positions of various electronic states in the isovalent species C2, BN, CSi and Si (all possessing seven valence electrons). Values in parentheses are... 

Methyl radical has seven valence electrons. The crucial orbital that is stabilized by pyra-midalization, aout, is only singly occupied (Figure 1.8), and the stabilization it provides is to some extent offset by the destabilization of other, doubly occupied orbitals. It is difficult to predict the geometry of this species based on the Walsh diagram, and it is best to say that no obvious preference for planar or pyramidal geometry can be predicted. This, too, is "consistent" with experiment, as simple radicals show only a very weak preference for the planar structure, and simple substitution can produce pyramidal radicals. The net result is that the parent methyl radical, CH3, is planar, but the energy cost for distorting away from planarity is small. 

Hydrogen has one valence electron, and each halogen (F, Cl, Br, 1) has seven valence electrons, so the following species have the indicated formal charges ... 

The splitting of a Cl2 molecule is an initiation step that produces two highly reactive chlorine atoms. A chlorine atom is an example of a reactive intermediate, a short-lived species that is never present in high concentration because it reacts as quickly as it is formed. Each Cl- atom has an odd number of valence electrons (seven), one of which is unpaired. The unpaired electron is called the odd electron or the radical electron. Species with unpaired electrons are called radicals or free radicals. Radicals are electron-deficient because they lack an octet. The odd electron readily combines with an electron in another atom to complete an octet and form a bond. Figure 4-1 shows the Lewis structures of some free radicals. Radicals are often represented by a structure with a single dot representing the unpaired odd electron. 

H20)2 (nta = nitrilotriacetate) with nitric oxide, where a small negative volume of activation suggests that the reaction follows an associative interchange (Ij,) mechanism. It is assumed that such mechanistic changeover reflects the fact that Fe (nta)(Fl20)2 is a six-coordinate complex, whereas it is known that Fe (edta)H20 (edta" = ethylenediaminetetraacetate) is a seven-coordinate. Consequently, the latter species reacts according to an la mechanism as a result of its 20 valence electron character, whereas the six-coordinate nta complex follows an mechanism due to its 18 valence... 

Let us use Scheme 2.7 to illustrate how selective is the Law of Nirvana, by making a molecule from an atom of fluorine (F) and as many H atoms as needed. Since the inner shell electrons do not participate in bonding, we show here and in all examples to follow, only the valence electrons. F resides in family 7A, and hence it has seven electrons in its valence shell, while H has one. Let us suppose we were tempted to think that F utilizes all of its valence electrons to make electron-pair bonds then, as shown in Scheme 2.7a, F will need to surround itself with seven H species, and click, it will form the molecule H7F. Since F has seven electron-pair bonds in this... 

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