How do i rotate a molecule so the lowest priority substituent is aligned left

[170559]

---

Members don't see this ad.

Kaplan talks about rotating a dash and wedge molecule so line of sight aligns with the lowest priority substituent. I just cannot seem to visualize this😱. Can anyone help with a technique to imagine rotating molecules? Same with trying to translate a dash wedge molecule into a fisher projection.

 

[ManimalJax]

I could also use some help with this one. Plus, I am hoping someone could offer some advice other than buying a stick-and-ball model set. I need to know how to do this mentally.

 

[AZFutureDoc]

This is very tricky stuff even to explain in person with ball and stick models, yet alone on an internet forum. Your best bet is to look at pictures, or little web programs that let you play with molecules, or better yet, a molecule set. In fact, that's really all I can say. Its hard to paint a picture using words on a forum, so your best bet is to either really look at pictures and understand what trigonal pyramidal looks like when you move it or buy a kit and physically do manipulations that the MCAT requires. Sorry for sounding harsh, but there's no one really simple trick. My Ochem professor called this mental gymnastics (applicable during this olympic season) and required us to buy quality model sets.

 

[spyderracing32]

I agree with AZFutureDoc. This really isn't something that can be described on an internet forum. Spatial reasoning like this is something that either comes really easy to you, or it doesn't and it's something you really need to work at.

 

[Phlame217]

This was a quick paint drawing.
First go from 1d to 2d by going from lines to orientation lines

Then make it 3d in your head, the key is remembering the tetrahedral model.
I'd recommend getting a foam ball or a cork or something and using toothpics and make a tetrahedral arrangement.

One this image is solid, mentally label the groups as they are in the 2d and then visually rotate within your mind. It might help to quickly jot down the 2d formation and assign group priorities with numbers instead of labelling all groups and then draw arrows illustrating the movement of all the groups.

The straight arrows are your line of sight (axis of sight)

 

[170559]

This was a quick paint drawing.
First go from 1d to 2d by going from lines to orientation lines

Then make it 3d in your head, the key is remembering the tetrahedral model.
I'd recommend getting a foam ball or a cork or something and using toothpics and make a tetrahedral arrangement.

One this image is solid, mentally label the groups as they are in the 2d and then visually rotate within your mind. It might help to quickly jot down the 2d formation and assign group priorities with numbers instead of labelling all groups and then draw arrows illustrating the movement of all the groups.

The straight arrows are your line of sight (axis of sight)

Thanks so much! The arrow pointing to the line to sight did it for me. So i used my thumbs to point into the page and imagined the 2 groups pointing out. Now when i approach from the side of the arrow i just need to rotate the groups going out of the page. I'm just going to practice it more!

 

[Phlame217]

practice is what it takes, but 3d molecule sets would help you lean much more easily.