The Simple Polar Bond

The value of one half of the anion-cation energy-difference is the polar energy  

It is convenient to define the average of (he cation and anion energy, written as 

Second, if the individual atomic wave functions do not overlap, the probability of 

We can expect the dipole of the bond to be proportional to — = p. The polarity of the bond and the resulting dipole arc central to an understanding of partially covalent solids. 

Another useful concept is the complementary quantity, covalency, defined by 

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Bonding of diatomic molecules in which the constituent atoms are different can be analyzed very directly, and only one or two points need be made. The n slates in heteropolar diatomic bonding are calculated just as the simple polar bond was, In each case only one orbital on each atom is involved. A polarity can be assigned to these bonds, just as it was in Section 1-D. 

N0 H—0< would contribute a dipole moment of 1 3 Debyes. This suggests that the observed dipole moments of H-bonded systems are due both to this and also to electron shifts in the remainder of the two molecules. The example of triphenyl methanol-trimethyl amine referred to in my answer to Dr. Pople shows that about 0 7 D may be due to the simple polar structure. 

At this point we switch from consideration of pairs of hybrid orbitals in each bond to bonding and antibonding combinations in each bond. We do this in the way discussed for a simple polar bond in diatomic molecules (Section 1-D) by writing a general linear combination of the two hybrids. 

Table I shows some results obtained by Bates (1987m. The procedure he followed is straightforward. Having obtained BIN" " ] from A[H, he assumed that the value is independent of the species of ion. He then obtained B " Me] (Me = methyl) from each of A[H3N Me], A[H2N" Me2], and A[Hhr Me3]. The three vines difrer only slightly. Assuming that their mean, T 10.6 kcal mol, is the value in all ions he proceiled in like manner. The five values ofB[N" t](Et = ethyl) are in excellent agrement. Moreover, the increase in going from B[N" Me] through B[N Et] andB[N" nPr] to B[N nBu] (nPr = n-propyl nBu = n-butyl) can reasonably be attributed to an increase in the polarization energy. These and other results support the simple valence bond mo l of polyatomic ions, at least for bonds between atomic ions and functional groups in saturated species.

The underlying principle of the PEOE method is that the electronic polarization within the tr-bond skeleton as measured by the inductive effect is attenuated with each intervening o -bond. The electronic polarization within /r-bond systems as measured by the resonance or mesomeric effect, on the other hand, extends across an entire nr-system without any attenuation. The simple model of an electron in a box expresses this fact. Thus, in calculating the charge distribution in conjugated i -systems an approach different from the PEOE method has to be taken. 

Majeti11 has studied the photochemistry of simple /I-ketosulfoxides, PhCOCH2SOCH3, and found cleavage of the sulfur-carbon bond, especially in polar solvents, and the Norrish Type II process to be the predominant pathways, leading to both 1,2-dibenzoylethane and methyl methanethiolsulfonate by radical dimerization, as well as acetophenone (equation 3). Nozaki and coworkers12 independently revealed similar results and reported in addition a pH-dependent distribution of products. Miyamoto and Nozaki13 have shown the incorporation of protic solvents into methyl styryl sulfoxide, by a polar addition mechanism. 

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