Orbitals lone pair

Localized orbitals, see bond orbitals and group orbitals Lone pairs, 9, 39, 42, 49 cyclopropanone, 37 methyl fluoride, 42 pyrazine, 28 water, 42... 

It has been known for some time that the basicities of a heteroatom decrease upon a-silyl substitution [12], For example, alkyl silyl ethers (R3Si-0-R ) are less basic than dialkly ethers. Silylamines are weak bases compared to alkylam-ines. This electron-withdrawing effect of silyl groups has been explained in terms of the interaction between low lying vacant orbitals such as 3d orbitals of silicon or a orbitals with the nonbonding p orbitals (lone pairs) of the heteroatom (Fig. 4). This interaction decreases the HOMO level which in turn lowers the basicity of the heteroatom. Such effect may also cause the increase of the oxidation potentials, but little study has been reported on the electrochemical properties of this type of compounds. 

Although oxidation potentials of aldehydes and ketones are generally very high, silyl substitution at the carbonyl carbon results in a significant decrease in the oxidation potential [16]. The decrease in the oxidation potentials is attributed to the rise of the HOMO level by the interaction of the C Si cr-bond and the nonbonding p orbital (lone pair) of the carbonyl oxygen (Fig. 9). In the case of a-silyl-substituted ethers, the rotation around the C-O bond is free and,... 

Figure 2.IS Types of lone pair electrons, (a) /-orbital (lone pair) (b) n-orbital (nonbonding).

Photoelectron spectroscopy145 has been particularly useful in the conformational analysis of heterocyclic molecules possessing vicinal electron lone pairs, especially in the hexahydropyridazine system.12,145a In such a system the two lone-pair orbitals on nitrogen do not ionize at the same potential because of interactions with each other and with other orbitals. Lone-pair-lone-pair interactions are expected to dominate and are dependent upon the... 

Terms such as a bond, a orbital, n bond, it orbital, lone pair, atomic and molecular orbital, and bonding and antibonding orbital, are all explained in Chapter 4. 

Complexes involving a formal metal-carbon double bond are referred to as either carbene or alkylidene complexes. For simplicity we shall consider the orbitals of singlet methylene, which consist of a filled sp2 orbital ( lone pair ) and an empty and highly electrophilic p orbital (Figure 1.15). 

These summarize topological information about a molecule with atomic properties [39]. A molecular E-state index is expressed as a sum of atomic E-state indices, which are composed of two parts. First is the intrinsic atomic part, and second is perturbation, which depends on its neighborhood (other atoms in the structure). The intrinsic part includes information about the a- and 7r-orbitals, lone pairs, hydrogen atoms attached to heavy atoms, and the principal quantum numbers of valence electrons. The perturbation part is a sum of all other atomic parts modified by fimction, which descends with distance. 

These electrons, according to the particular reaction involved, may come from the or-bond between the third and fourth atoms of the system, when the over-all reaction will be one of elimination or rearrangement, or from a non-bonding orbital (lone-pair) associated with the fourth atom, when the product will be a cyclic derivative such as an epoxide. The generality of this "iSMi -coplanar principle is well illustrated in reactions of steroids (see especially Chapters 3, 5, 6 and 8), and there are very few exceptions. 

Bonding in HCl using MO theory. The correlation diagram shows occupied valence orbitals for H and Cl atoms, resulting MOs from overlap of IsH and Cl orbitals, lone pair nonbonding orbitals and 3py of Cl, and the nonbonding Cl 3s orbital. 

JThe symmetry labels o and n are used to designate molecular orbitals (MOs) that are symmetric and antisymmetric, respectively, with respect to a plane of symmetry of the molecular structure (Section 4.4). Nonbonding o-orbitals (lone pairs) are designated with the label n. 

Following the procedure previously described and briefly reported in the method section, we found (at PWP level) that the Fukui index associated with orbital lone pair of oxygen in sulfine, has the value of 0.04 eV, while those associated with carbon and sulphur, are 0.19 and 0.21 eV, respectively. Speaking in terms of hard-soft theory of Pearson, we can indicate the orbital with the lowest Fukui index as the most reactive in the electrophilic reaction with H" ". 

---