Question

Use the Newman proyection around the adequate Carbon for represent the more stable conformerer
a) 3-metilpentane around the bond of C2---C3
b) 3,3-dimetilhexane around the bond C3---C4

Answer 1

Recall that these are CONFORMERS, meaning that they can take different positions in order to favor the most stable position.

Analysis will be done on carbns --> C2-C3 respectively

C2 --> front carbon, bonded species --> to H, CH3, CH3

C3 --> back carbon, bonded species --> H, CH3, H

Note that

there are two main types of position; they are either:

- STAGGERED --> will have 60° separation between all groups, therefore, it is much more stable, the groups are the farthest away possible from all

- ECLIPSED --> Half of the Groups are 0° away from each other, the other half is at 120°.. This requires higher energy since it takes more energy to get together at the 0° configuration.

Also...

keep in mind that bulky groups... Bulky groups are those groups which are "larger" considered to other groups

The least bulky group/species is -H atom... since it is small.

Note that there are also energy considerations depending on the type of configuration:

Bulky - Bulky --> most energy

Bulky - nonbulky --> medium energy requirement

nonbulky - nonbulky --> least energy

Now, knowing this....

Number your species from top to bottom as ;

1,2,3,4,5,6

then,

detect the staggered/eclipsed groups and their "strneght"

Most stable conformer:

Must be 3

since CH2CH3 group is 150-180° degree apart of the CH3 CH3 groups and it is STAGGEREDE