#newman projection

[stephbiostudies]

Afternoon everyone! Back at it with some organic chemistry notes as I review for an upcoming exam. Made my first model of a newman projection. So glad I went home this weekend as our dog, Daisy, keeps following me around! A little off topic of studying but I got a new snoopy, bringing the count up to 9 now. Have a wonderful weekend everyone!

Listening to Cigarette Daydrems by Cage the Elephant

[sciencetylia]

This is a work of art.

[organic-chemistry-notes]

Use of Newman Projections to Show Bond Conformation

In the previous post we discussed how to draw Newman Projections. Here, we will use them to determine bond structure and gauche interactions.

First off, recall how I said that the cluster of Hydrogen bonds on the end of an ethyl group was constantly spinning. For this, it is important to keep in mind that the electrons in an atom's Valence shell surround it like a forcefield, and when bonded in mollecules, they will naturally space themselves as far apart as physically possible.

This is because they don't like those Valence bubbles to overlap, and it takes energy to make them overlap. Far apart spacing = low energy = good thing. That being said, it is not only the atoms bonded to the SAME central atom that try to space themselves apart, but they try to space themselves away from every other atom in the entire mollecule. Why? Because if they are too close to another atom - even if it's on a different part of the mollecule - it takes energy to keep it there.

This is where the Newman Projections come in. If we take our Newman Projection for an ethyl group, we see that it looks like this:

The Hydrogens are all evenly spaced as far apart from one another as they can get. (Note the red "personal space bubbles" that I have drawn around the Hydrogens. They're like 5-year-olds, they don't like when other Hydrogens get inside their "bubble".) Because of this spacing, the energy that the mollecule is using is practically zero. We refer to this as "Staggered Conformation".

What happens if we turn or rotate the top of the mollecule, though? (Because it is difficult to draw overlapping atoms, the lines are simply drawn very close and assumed to be overlapping.)

Here, we have a problem. While all of the top Hydrogens are evenly spaced from one another, and all the bottom Hydrogens are spaced from one another, the top Hydrogens are now overlapping with the bottom ones. This position takes energy to maintain. We call this an "Eclipsed Conformation". Simple enough, right?

Hydrogen's "personal space bubbles" not touching, lines evenly spaced? Staggered Conformation. Hydrogen's "personal space bubbles" overlapping, lines close or overlapping? Eclipsed Conformation.

Now what happens if our mollecule is NOT C2H6? What if it looks a bit more like this:

This follows the same rules, despite the fact that it has a CH3 group bonded to one of the Carbons instead of a Hydrogen. The CH3 is treated the same as if it were a Hydrogen. Where we start running into trouble, however, is when we have more than one CH3 group...

This becomes a problem because each of those CH3 groups has a much larger "personal space bubble" than the Hydrogens, so it takes a lot more energy to keep two CH3 groups overlapped than it does to overlap two Hydrogens or a CH3 and a Hydrogen. How do we specify what position these CH3 groups are in? With the terms "Anti" and "Gauche". Observe the position of the CH3 groups as we rotate the mollecule.

The first picture has the two CH3 groups overlapping with each other. This is Eclipsed (because of the overlap) Gauche (because of the 2 CH3 groups).

The second picture has the two CH3 groups close, but not overlapping. This is Staggered (because they do not overlap) Gauche (because of the 2 CH3 groups).

The third picture has the CH3 groups overlapping with Hydrogens. This is Eclipsed (because of the overlap) Anti (because of the CH3 with Hydrogen).

The fourth picture has the CH3 group on the opposite side of the mollecule. This is Staggered (because they do not overlap) Anti (because the CH3 groups are not near each other).

Easy enough, right?

As a small side-note, there is a glitch with some of the pictures I'm using, where they will show up on the main Tumblr but not the dashboard. If they're not showing, please check them on my page. I will try to get this fixed as soon as possible.