1-chloropropane Newman Projection

[Macy Matsukawa 3J]

For the Newman projection when looking at C1-C2 bond for 1-choloropropane why is that for carbon one it is cl, h, h instead of cl,h,ch3?
Also when drawing Newman projections how can one tell where to place your chlorines or methyls for the most stable conformation?

[Kristienne Edrosolan]

Because the name 1-chloropropane suggests that the substituent carbon is on the first Carbon, we know that carbon 1 is bonded to Carbon 2, Cl, H, and H. If carbon one had a methyl group attached to it, then it would not be the first carbon in the parent chain! Personally, the way that helps me understand it the best is drawing out the molecule. Although I can't draw the hydrogen's attached like I would in a normal 2D structure, it still looks something like this: Cl-CH2-CH2-CH3.

Thus, we know that Carbon 1 is only connected to Cl, H, and H. And we also know that Carbon 2 is connected to a H, H, and a CH3.

When drawing your Newman projections, the most stable conformation will be the Anti conformation which has the two largest parts of the molecule opposite from each other on a Newman projection; this is representing that you need to put the largest molecules into where there is the most space, so you put the largest molecules on each Carbon the farthest apart from each other.

So continuing with this problem, Cl would be the largest substituent for Carbon 1, and CH3 would be the largest substituent for Carbon 2, so I would put them opposite from each other on the projection. (ex. one on the top one on the bottom for a 180 degree angle) Hope that helps!