Mark C Elliott, Kasimir P Gregory, Colan E Hughes, Benjamin D Ward
The stabilization of positive and negative charges by alkyl groups (in particular) in organic compounds is often described as polarizability, but it can also be described as hyperconjugation (and related stereoelectronic effects). To a large extent, how one describes charge stabilization depends on the bonding model used. One can only talk about hyperconjugation in the context of a localized bonding model (hybridization). However, using this bonding model, it is less intuitive to talk about polarization of the whole molecule, which requires full molecular orbitals. It is important in chemical education to be aware of the limitations and intersections of the models we are using. In this work, we show that the polarization of alkyl chains in representative molecules, either by a computationally applied field or by a charge in the molecule, is reflected in changes in hyperconjugative interactions throughout the structure in a logical and predictable manner. This makes a clear and accessible point that hyperconjugation and polarizability are simply two models (at least for charge stabilization) that explain the same phenomenon. In this work, we identify advantages and limitations of each explanation, giving educators examples that can be used in teaching at various levels.