I've no idea how to work on synthesis problems

[Theafoni]

Whenever I do these synthesis problems for ochem, I am not sure where to start. For instance, the question may give the starting material and product, I have to show every step of course. The book recommends that you start for the product and work backwards.

Any tips for doing synthesis problems? How you learned them

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[deleted407021]

I was in the same boat all semester long for Ochem II. I still pulled a B, but it was a bit defeating when I could only complete ~45% of the synthesis problems I came into contact with. Sit down with your professor or SI instructor and get them to help you out. There's a method and you just need to know what it is. Don't try to figure it out on your own, because if you learn it wrong it may be hard to get out of that rut.

 

[mehc012]

Look up 'retrosynthetic tree'. That's what you're taught when you start taking upper level synthetics and tackling harder molecules.'

Basically, take the product and think of a few 'steps' backwards you can think of. Then take each of those and do the same. Pretty quickly you'll start to see which path is leading you towards the starting material you want.

If you can't figure out which way to go, go every way until you hit a dead end. It's like solving a maze.

 

[Selladore235]

Most importantly, you have to know your reactions well enough that you're able to identify their products. Specifically, when you're asked to synthesize an unfamiliar molecule, you have to be able to identify certain elements or functional groups of that molecule as characteristics of certain reactions. If you can't see one or two elements in the product, your task is much more difficult. Ultimately, if your knowledge of reactions is spotty, you will struggle.

 

[Doctor Dream]

I know this might be a little obvious but what really works for me is looking at what's changed from the reactants to the products, and then like @Selladore235 said, you have to be able to identify certain elements or functional groups that are characteristic of the reaction. Sometimes it takes a little abstract thinking, but if you know your reactions well you can solve them.

So simple example, say you synthesize a benzene ring with an ethyl substituent from benzene. You know a mechanism directly putting an ethyl group onto the benzene won't work because that would activate other sites on the ring and cause multiple alkylations. You also know a reaction which can put a ketone onto a benzene ring (which wouldn't cause multiple alkylations), and you know another reaction to remove the double bonded oxygen from the ketone, leaving behind just the alkane (ie: your ethyl substituent).

If you know your reactions, all it takes is some critical thinking and creativity and you're golden.

 

[mizzu]

Whenever I do these synthesis problems for ochem, I am not sure where to start. For instance, the question may give the starting material and product, I have to show every step of course. The book recommends that you start for the product and work backwards.

Any tips for doing synthesis problems? How you learned them

I found it helpful to find some key points. Ie- am I extending the chain? Adding an alcohol group? Converting alcohol into acid?

And understand what will make these general changes