(a) Draw the two chair conformations of cis-1,3-dimethylcyclohexane and label all the positions as axial or equatorial.
(b) Label the higher-energy conformation and the lower-energy conformation.
(c) The energy difference in these two conformations has been measured to be about 23 kJ (5.4 kcal) per mole. How much of this energy difference is due to the torsional energy of gauche relationships?
(d) How much energy is due to the additional steric strain of the 1,3-diaxial interaction?
Here first we are going to know what is newmann projection model
Newman projection formula :
A Newman projection, useful in alkane stereochemistry, visualizes chemical conformations of a carbon-carbon chemical bond from front to back, with the front carbon represented by a dot and the back carbon as a circle . The front carbon atom is called proximal, while the back atom is called distal. This type of representation is useful for assessing the torsional angle between bonds.
3,3-dimethylhexane about the C3-C4 bond
The most stable conformer for 3,3-dimethylhexane viewed along the C3−C4 bond will have two ethyl groups in anti position and gauche interactions between two methyl groups and one ethyl group.
Start by drawing the bond line notation for the compound
Notice that you have one ethyl group and two methyl groups attached to C3, and two hydrogens and one ethyl group attached to C4.
Start by using a Newman projection template to draw the first staggered projection
Now rotate the front carbon by 120∘ to generate the other two staggered Newman projections .
Projection 2 and Projection 3
Projection 2 and projection 3 will be less stable than projection 1 because in both cases you have gauche interactions between two bulky ethyl groups and a methyl group.
By comparison, projection 1 has the two ethyl groups in anti position, the repulsion between two methyl groups and one ethyl group being a little less unstable than the repulsion the other two staggered conformers have.
Therefore, projection 1 describes the most stable conformer for 3,3-dimethylhexane viewed along the C3−C4 bond.