Of unshared electrons

Their polar carbon-oxygen bonds and the presence of unshared electron pairs at oxygen contribute to the ability of ethers to form Lewis acid Lewis base complexes with metal ions... 

Efforts to establish a theoretical explanation of the reactivity of nucleophilic reagents have centered on correlations with intrinsic electron-donor properties which are the fundamental basis of nucleophilicity. According to Edwards and Pearson, in general, such properties include basicity, polarizability, and the presence of unshared electron pairs on the atom adjacent to the nucleophilic atom of the reagent. When only the first two of these properties are operative, Eq. (8), which was proposed by Edwards, has proved successful in... 

The nitrogen atom of each NH3 molecule contributes a pair of unshared electrons to form a covalent bond with the Cu2+ ion. This bond and others like it, where both electrons are contributed by the same atom, are referred to as coordinate covalent bonds. 

Basicity nearly always arises from the presence of unshared electron pairs. Consequently, amines produce an alkaline reaction in aqueous solution by functioning as an electron donor (or Lewis base), withdrawing hydrogen ions from water and leaving an excess of hydroxyl ions in the solution. 

Step 2. Only one bond is broken in this step and no bonds are formed. (The movement of a pair of unshared electrons into the C-C bond, forming a double bond, is not designated by any symbol. In this system, bond multiplicity changes are understood without being specified.) Thus the symbol is D. The broken bond is between a core atom (C) and a nucleofuge (Cl), so the designation is D. ... 

Solubility - The oxidized polymer (VIII) has a greater solubility than the original polymer (VII). It was found to be soluble in acetone, chloroform, benzene, DMF and DMSO. Unlike the polymer (VII), (VIII) was not soluble in formic acid or trifluoroacetic acid that was expected since the pyrrole moiety is less basic than pyrrolidine. In the oxidized polymer, the pair of unshared electrons on the nitrogen atom are contributing to the pyrrole ring aromaticity, therefore, unavailable for protonation as in the case of polymer (VII). A comparison of the solubilities is given in Table I. 

PCI3 — note the lone pair of unshared electrons. 

Which molecule or ion in the following list has the greatest number of unshared electron pairs around the central atom ... 

Many molecules, including ammonia and water, possess one or more pairs of unshared electrons. 

Alcohols act as Bronsted bases as well. It is due to the presence of unshared electron pairs on ojqrgen, which makes them proton acceptors. 

H3O is pyramidal in geometry due to a single pair of unshared electrons. 1 point for correct geometry of the hydronium ion. 

Number of cr Bonds + Number of Unshared Electron Pairs = HON Hybrid State... 

Contribution of Unshared Electron Pairs to the Electric Dipole Moments of Molecules.—In the preceding chapter we discussed the dipole moments of molecules, in relation to the partial ionic character of bonds, without considering the possible contribution of unshared electron pairs. A simple treatment based on hybrid orbitals provides some justification of this procedure. 

There is a pair of unshared electrons in Se(IV) (in the ion [SeBr ] ) occupying the 4s orbital, which is therefore not available for use in forming 4s4pz4d2 bonds. It has been suggested to me by Dr. J. Y. Beach that the role of the s orbital in bond formation is here being... 

Metal ions can act as electron-pair acceptors, reacting with electron donors to form coordination compounds or complexes. The electron donor species, called the ligand, must have at least one pair of unshared electrons with which to form the bond. Chelates are a special class of coordination compound which results from the reaction of the metal ion with a ligand that contains two or more donor groups. 

Figure 16-1 Atomic-orbital description of the carbonyl group. The a bonds to carbon are coplanar, at angles near to 120° the two pairs of unshared electrons on oxygen are shown as occupying orbitals n.

Make an atomic-orbital model of benzenol, showing in detail the orbitals and electrons at the oxygen atom. From your model, would you expect one, or both, pairs of unshared electrons on oxygen to be delocalized over the ring What would be the most favorable orientation of the hydrogen of the hydroxyl group for maximum delocalization of an unshared electron pair ... 

The water molecule is composed of two hydrogen atoms covalently bonded to an oxygen atom with tetrahedral (sp3) electron orbital hybridization. As a result, two lobes of the oxygen sp3 orbital contain pairs of unshared electrons, giving rise to a dipole in the molecule as a whole. The presence of an electric dipole in the water molecule allows it to solvate charged ions because the water dipoles can orient to form energetically favorable electrostatic interactions with charged ions. 

Nucleophiles such as NH2OH and NH2NH2, which have an electronegative atom with one or more pairs of unshared electrons adjacent to the nucleophilic center, tire more reactive than might be expected from the nature of the nucleophilic center, as can be seen from Table 4.5. Suggest a reason for this increased reactivity (this phenomenon is called the a-effect). 

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