[Haaaaaaanh]

I am wondering if the molecular model kit is worth buying and using during a test. I am asking because I am worried that putting the pieces together will waste valuable test time. The reason I am considering a kit is because I am having trouble visualizing the Cahn-Ingold prelog when the hydrogen (lowest priority) atom isn't in the back and I don't know how to put it in the back. Is there any easy tips to remember how to do this on paper? Also is it possible to convert a molecule into a fischer projection easily? Thanks!

[discodermolide]

If the H is not at the back but at the front then work out the configuration using the rules then reverse it.
That is, if you get (S) when the H is at the front, the actual configuration is (R) .

[Dan]

You would be better off practicing R/S assignments in your own time until you consistently get them right without using a model. Then again, I was not allowed models in my exams so I would say that - but I think mental 3D manipulation of chemical structures from a drawing is a very useful skill and can be trained.

[fledarmus]

There are all sorts of tricks like using your hand to represent the lowest priority group and your thumb and first two fingers for the other groups, but it is still easiest to see a model. You don't always need to model the entire molecule, especially to assign R and S configurations. You just need four different groups on a carbon and the ability to line them up with the structure on your paper.

[curiouscat]

Play more Tetris! (the 3D sort especially!) 

[PhDoc]

Best to bring one chiral center, and use it for any of the harder problems. Using a model kit will eat your time.

If you're about to take the stereochemistry exam, be on the lookout for meso compounds and planes of symmetry. Essentially the whole exam is based upon "optical illusion."