Elements of molecular structure

One of the most fundamental elements of molecular structure is chain length. It serves to fix the hydrocarbon s position on its own subseries curve and thus becomes a factor in determining its physical constants. It also is a major factor in determining the hydrocarbon s rate of combustion and hence its octane number and critical compression ratio. 

An analytical expression for a trajectory in the vicinity of a critical point is given in Section E2.2. While this expression is.necessary for numerical work, a knowledge of the phase portraits given above is all that is required for the definition of the elements of molecular structure which follows. 

It is to be stressed that a bond path is not to be understood as representing a ond . The presence of a bond path linking a pair of nuclei implies that the corresponding atoms are bonded to one another. As demonstrated later, the interaction can be characterized and classified in terms of the properties of the charge density at its associated (3, — 1) critical point. The complete description of the interaction, however, requires the evaluation of operators over the associated interatomic surface. These are the topics of later discussions At this point we continue with the identification of the elements of molecular structure with the topological properties of the remaining stable critical points, (3, + 1) and (3, + 3) critical points. 

The distribution of electrons is another element of molecular structure that is very important for understanding chemical reactivity. It is considerably more difficult to obtain experimental data on electron density, but fortunately, in recent years the rapid development of both structural theory and computational methods has allowed such calculations. We make use of computational electron density data in describing molecular structure, properties, and reactivity. In this chapter, we focus on the minimum energy structure of individual molecules. In Chapter 2, we consider other elements of molecular geometry, including dynamic processes involving conformation, that is, the variation of molecular shape as a result of bond rotation. In Chapter 3, we discuss... 

These qualitative associations of topological features of p with elements of molecular structure can be replaced with a complete theory, one which recovers all of the elements of structure in a manner that is totally independent of any information other than that contained within the charge density The underlying structure of the charge density is brought to the fore in its associated gradient vector field. The boundary condition of a quantum subsystem is also stated in terms of this field... 

The remaining critical points of rank three occur as consequences of particular geometrical arrangements of bond paths and they define the remaining elements of molecular structure—rings and cages. If the bond paths are linked so as to form a ring... 

Figure 2. The geometry shown in Figure 1 is refined for dielectric analysis by fixing a microsphere concentric with the macrosphere and contains the elements of molecular structure.

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