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distribution. This approach has been elegantly developed by Martire et al. (8). In a simplified form, the standard energy can be divided into portions that result from the different types of interaction, e.g.,     In an attempt to explain subtle interactive differences, polar interactions can be divided into weak, moderate and strong interactions that, in the literature, have been, somewhat arbitrarily, given terms such as p/p interactions, dipole/dipole interactions, and hydrogen bonding, e.g.,   Nevertheless, it is important to realize that p/p interactions, dipole/dipole interactions, and hydrogen bonding,  are not different types of interaction but are all polar interactions but of different strength. In fact, many more terms have been introduced to describe subtly different enthalpic and entropic contributions to retention. Again one should remember Einstein's comment on first order effects being simple. However, in fairness, it must be said

it might have with other molecules. For example, water, an extremely polar molecule, has a dipole moment of only 1.76 debyes. Similarly, the dipole moment of methanol, another extremely polar substance, is only 2.9 debyes. Unusually low values of dipole moments for strongly polar substances is often due to internal electric field compensation when more than one dipole is present in the molecule.(e.g., water associates strongly with itself by very strong polar forces or 'hydrogen bonding' . Methanol also associates strongly with itself in a similar manner. Examples of possible associates of water and methanol are shown in figure 5. Figure 7 Possible Self Associates of Water and Methanol Thus, with such associates (should they exist) the electric field from each dipole would oppose that from the other, resulting in a reduction in the net field as measured externally. It follows, bulk properties may not reflect the true value

Polar Forces Polar interactions arise from electrical forces between localized charges resulting from permanent or induced dipoles. They cannot occur in isolation, but must be accompanied by dispersive interactions and under some circumstances may also be combined with ionic interactions. Polar interactions can be very strong and result in molecular associations that approach, in energy, that of a weak chemical bond. Examples of such instances are 'hydrogen bonding' and in particular the association of water with itself. Dipole-Dipole Interactions The interaction energy (UP) between two dipolar molecules is given, to a first approximation, by where (a) is the polarizability of the molecule, (m) is the dipole moment of the molecule, and (r) is the distance between the molecules

into different parts each representing different energy sources that contribute to the equilibrium process. There are two major modes of standard energy distribution; portions of standard energy can be allotted to specific types of molecular interaction that can occur between the solute molecules and the two phases (e.g. energies involved in dispersive interactions, polar interactions and ionic interactions, or subdivisions of these interactive processes such as 'so called' complexation, hydrogen bonding etc.); alternatively, the molecule can be divided into different parts or chemical groups (e.g., methyl groups, methylene groups, phenyl groups etc.) and the interactions of each group allotted a portion of the standard energy. Due to the fact that it is extremely difficult to separate the different interactive processes that take place during distribution, the latter distribution of standard energy (i.e. between different chemical groups or atoms) has provided the more useful

wave numbers helps identify the major groups present in the molecule but gives very little evidence on the size of the molecule or the manner in which the actual groups are joined. It is seen that the vapor and liquid spectra are indeed very similar and can be confidently used to confirm sample identity. It should be noted that the dispersed peak at about 3400 wave numbers, shown in the liquid sample spectrum (which is not present in the vapor spectrum), is probably due to the effect of intra-hydrogen bonding between the OH groups of the n-hexanol and water possibly present in the sample or solvent. Spectra identification and interpretation are best carried out using digitized spectra in conjunction with appropriate comparison or identification software. However, if using analog data, correlation charts can be constructed to help assign specific absorption bands to certain chemical bonds or groups present in an unknown molecule. An example of such a correlation chart, after Stuart (8

force, all of which are electrical in nature. Although it is theoretically possible that magnetic and even gravimetric forces may be also present, they will have no significance compared with those of electrical origin. The three types of molecular interactive force are dispersive, polar and ionic giving rise to dispersive interactions, polar interactions and ionic interactions. Polar forces have been further divided into sub groups ranging from 'strong dipole-dipole interactions' (hydrogen bonding) to 'weak dipole-dipole interactions ((p)-(p) interactions). This type of division is questionably useful as it tends to 'confuse' more than 'explain' when dealing with chromatographic retention. Division into the two groups, dipole-dipole interactions and dipole-induced dipole interactions, however, is appropriate, as it describes two physically different types of polar interaction that is very pertinent to chromatographic retention. However, the arbitrary division of polar