Question

Draw all possible Newman projections results from the rotation of C3-C4 bond in 2-methylpentane and label all the conformations.

Answer 1

Answer:

See the image Below

Explanation:

Single C-C bonds have free rotation and thus Newman Projections are quite useful for understanding the different 3D conformations of a molecule.

For any Newman Projection you have 2 bonded carbons, one in front of the other, therefore you rotate the bond by rotating the groups that are bonded to the carbons. i. e. in the 2-Methylpentane (viewing the C3-C4 bond) the carbons chosen are the 3rd and the 4th then you look to which are the other groups bonded; 2 H and an isopropyl for the 3rd one, and 2 H and a Methyl for the 4th one.

The different rotations of those groups receive different names:

• Anti Conformation: Main groups of the two Carbons are 180º apart from one another. Making this the most stable conformation of the molecule. (Taking into account steric effects)
• Gauche Conformation: Principal groups are 60º apart from each other. Since are 6 spaces between groups (360º/6)=60º. It is less stable than an Anti conformation due to the same reason.
• Eclipsed Conformation: The less stable conformation since the main groups are confronted.