What is the significance of the single covalent bond in a carbon chains 'flexibility'? How is this property involved in the formation of benzene?

A. It is significant in that it leads conformational isomerism whereby atoms in a molecule are arranged in different ways with the preferred conformation being the one that is most stable.

B. It leads to resonance in the benzene structure which gives the benzene molecule its very thermodynamically stabile nature.

Explanation:

The carbon-carbon single bond is formed by the sharing of electrons by two neighboring carbon atoms. The shared electron orbitals overlap end-to-end (sigma) and this enables free rotation about their axis. This free rotation is significant in that it leads to the concept of conformational isomerism in organic molecules.

Conformational isomerism has to do with the different ways atoms of an organic molecule are spatially arranged. Thus, organic compounds will take up conformations which gives them the most thermodynamical stability. These spatial arrangements leads to different properties in organic compounds having similar structures.

B. The structure of the benzene molecule shows alternate double and single carbon-carbon bonds in the 6-carbon ring molecule. Double bonds are electron rich and are thus are very reactive. However, the presence of the alternate single bonds between double bonds stabilizes the benzene molecule by giving its bonds an intermediate property of single and double bonds. This concept is known as resonance and accounts for the thermodynamic stability of benzene.