Question

The Newman projections of 1,1-dichloro-2-bromoethane are shown below. Select the most stable conformation(s).

Answer 1

Concepts and reason

Newman projection is one of the ways of representation for alkanes (saturated hydrocarbons); in this representation, the dot represents the front carbon, the circle represents the back carbon, where substituents are on dot and circle.

Fundamentals

Steric hindrance (crowded by atoms) plays a key role in deciding the stability of these Newman projections; more the steric hindrance, lesser the stability.

Steric hindrance: steric hindrance occurs when large size molecules or groups are closer in the compounds and leads to the unstable structure.

If the steric hindrance increases in the structure then it means stability decreases in that structure.

The given Newman projections are

, , ,

Mainly two groups are shown in this Newman projection, one is halogen group and other one is hydrogen atom.

Halogen group is a more bulky group than the hydrogen atom present in the projection; according to this, the A and C projections are having less steric hindrance than the remaining projections.

Halogen group: chlorine and bromine

The given Newman projections are

, , ,

It is clear that D is less stable due to steric strain present in the projection, and B is also less stable due to the presence of electron pair repulsions, which are surrounded by the halogen atoms. But A) and C) are having almost same energy and stability.

Ans:

The most stable conformation (s)