Which conformational isomer of ETHANE should be LEAST stable?

1 Answer
Jun 10, 2017

Consider the diagram.........

Explanation:

chem.wisc.educhem.wisc.edu

We are looking down the CC vector, i.e. the CC bond of ethane, H3CCH3.......The maximum energy of interaction occurs when the hydrogens are eclipsed, i.e. the situation on TOP of the energy well, i.e. the torsional angle HCCH=0. The minimum energy of interaction occurs when the hydrogens of each methyl group are STAGGERED, i.e. the torsional angle HCCH=60.

This is an example of conformational analysis........and your text will have a lot of examples of this sort of approach, especially with regard to carbocyclic 6-membered rings........

Note that when you try to interpret the relative energies of such conformations there is NOTHING childish or facile in using a model to inform your reasoning, and help you draw the conformation. In my own experience, I have seen a lot of good students FORGO the use of models in exams, and their marks have suffered accordingly.