PChem Forebears

From WikidChem

Slide 23 Previously in class, we have discussed composition (what atoms exist in the molecule), constitution (the bonding of the atoms), and configuration (the spatial arrangement of of atoms that cannot be change without breaking bonds). We will next discuss conformation which is the spatial arrangement that can be altered by the rotation around a single bond.

Constitution, configuration, and conformation yield isomers because they are made of the same atoms but in different bonds or spatial arrangements. Only configuration and conformation are stereoisomers because these involve spatial arrangement and not bond sequence.

Configuration is hard to change as the breaking of bonds requires a lot of energy. Rotation around a bond (conformation) is much easier. Not all angles around the bond constitute different isomers, however. Isomers exist at energy minimums and therefore only specific rotations give isomers. (This means that if you have a curve representing all the different temporary structures and their corresponding energies, we don't call every point on this curve an isomer. Rather, we only call those that are local minima isomers-AB)

Slide 24

This slide shows the difference between organic chemists and physical chemists. Organic chemists focused on the molecular structure of compounds while physical chemists focused on energy. (Organic chemistry is more qualitative; physical chemistry is more quantitative -AB )

Slide 25 and 26

There are a number of physical chemists among our chemical ancestors (Ostwald, Noyes, Arrhenius, Lewis) as well as "physical-organic" chemists (Conant and Bartlett). Bringing physical chemistry ideas of energy to bear on organic chemistry led to techniques such as conformational analysis and molecular mechanics modeling.