Values for some substituted acetic acids

For more detailed discussions, see L. E. Sutton, in Determination of Organic Structures by Physical Methods, Vol. 1, E. A. Braude and F. C. Nachod (eds.), Academic Press, New York, 1955, Ch. 9 V. I. Minkin, O. A. Osipov, and Y. A. Zhdanov, Dipole Moments in Organic Chemistry, Plenum Press, New York, 1970. 

It is always important to keep in mind the relative aspect of substituent effects. Thus, the effect of the chlorine atoms in the case of dichloroacetic acid is primarily to lower the energy of the dissociated anion. The acid is more highly dissociated than in the unsubstituted case because of this preferential stabilization of the anion. It is the energy difference bet C een the dissociated and undissociated species, not their absolute energies, that determines the extent of ionization. 

Effects that have their origin in bond dipoles are termed inductive effects, and they contribute significantly to many chemical and physical properties of organic molecules. In many instances, however, substituent groups can interact with the remainder of the molecule by other mechanisms as well. The detailed understanding of substituent effects depends on being able to separate these various factors. This problem will be discussed in more detail in Chapter 4. 

Molecular orbital (MO) theory discards the idea that bonding electron pairs are localized between specific atoms in a molecule, and instead pictures electrons as 

In order to make the mathematics tractable, a number of approximations are made. The choice of approximations has produced a variety of molecular orbital methods, the judicious application of which can provide a valuable insight into questions of bonding, structure, and dynamics. The discussion that follows will not be sufficiently detailed for the reader to understand fully how the calculations are performed or the details of the approximations. Instead, the nature of the information obtained will be described, as well as the ways in which organic chemists have applied the results of MO theory in an attempt to understand the structure and reactivity of organic molecules. For more detailed treatments, several excellent sources are available.  

---

Table 1.8. Values for Some Substituted Acetic Acids"...

---