Organic Reaction Mechanisms: Memorizing vs. Computing

[thornza]

Hi,

I'm in first year organic chem and we're obviously learning about all the different reaction mechanisms (e.g. elim reactions of alcohols) and I was wondering if the only way to figure out what is going to happen in a particular reaction is to memorize all these different reaction mechanisms and apply accordingly?

Or in later courses do you learn about the general principles behind the reactions so that you are able to "compute" what reaction will take place without having to remember exactly that for e.g. a ketone reacts with a 1 degree amine to give an imine plus water.

Hope this question makes sense?

thanks,

Mark

 

[chemisttree]

A lot of it is memorization so don't skimp on your practice. You can apply some general principles to help jog your memory.

Principle 1. Use the catalyst in the first step. If the catalyst is an acid, apply that proton somewhere where it will produce a meaningful change or intermediate.

Principle 2. Electron rich species usually react at positions which bear a partial positive charge or are electron deficient.

Principle 3. Steric interactions are suprisingly important. For example, in compounds which might undergo Sn2 reactions, elimination reactions can sometimes compete. Steric interactions are usually the deciding factor. Make models! Preferrably space-filling ones.

Principle 4. One of the most useful things you can learn is a table of pKa values. Learing how difficult it is to remove a proton from a particular position can help you avoid some massively emabarrasing hand waving mumbo jumbo (ie. wrong answer). For example, if you treat a compound that has both an alcohol and an amine with a strong base like butyllithium, will you form an alkoxide or an amide(R₂N^-)? ref. http://www.chem.wisc.edu/areas/reich/pkatable/"

Principle 4. Practice, practice, practice. This is where most students make their biggest mistake. Familiarity helps organize your thinking... as opposed to that "deer in the headlights" feeling on test day.

Principle 5. What you think you know is more dangerous than what you don't know.

 

[Wax]

If you understand the mechanisms then it's not so much memorization. Like the guy said above me, the more you practice the better.