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Topic: rememberign rxns  (Read 6645 times)

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Offline aleksxxx

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rememberign rxns
« on: November 07, 2006, 12:16:43 PM »
so we just started into organic rxns.
our instructor suggested flash cards, which i made.

any other suggestions for helping memorize these quickly and efiiciently?

Offline movies

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Re: rememberign rxns
« Reply #1 on: November 07, 2006, 12:43:30 PM »
I think the best way to learn lots of reactions is to learn the mechanisms in great detail.  You'll soon find that many reactions proceed through similar mechanisms and you can use these similarities to learn new reactions quite readily.

Pay particular attention to the behavior of particular functional groups (e.g., electrophilicity of carbonyl groups, resonance structures of nitro groups, etc.)

Offline FeLiXe

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Re: rememberign rxns
« Reply #2 on: November 07, 2006, 03:02:23 PM »
for me it worked to do them one or two at a time. for example I'd read about one reaction riding the subway. I don't think you can go on memorizing organic reactions for hours.
Math and alcohol don't mix, so... please, don't drink and derive!

Offline lavoisier

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Re: rememberign rxns
« Reply #3 on: November 07, 2006, 03:13:00 PM »
I agree with movies.
Another very general way to look at organic reactions is in terms of polarity.

It has been calculated that the vast majority of organic reactions are based on a positive charge / negative charge interactions (exceptions are electrocyclic concerted reaction, like Diels-Alder, many rearrangements...).

If you learn to think of any reagent as a 'synthon', i.e. the formal charged intermediate it is equivalent to, you can see a wider order in the huge number of individual reactions you study.

Examples:

Alkyl iodides R-CH2-I are acceptor (positive) synthons because they are equivalent to R-CH2+.

Sodium alkoxides R'-ONa are donor (negative) synthons because they are equivalent to R'-O-.

These two synthons react to give the ether RCH2OR'.

Amines, thiols and in general all compounds having an available electron pair on a heteroatom are of course donors.

The carbonyl C=O can be regarded as an acceptor because the oxygen polarizes the bond as if it were C+-O-.
But note that a ketone (as a whole) can be both an acceptor (with respect to the carbonyl) and a donor (with respect to the alpha carbon, which can bear a negative charge: the enolate).
In such cases the behaviour depends on what reaction partner you provide and on the reaction conditions. If you add a strong donor (e.g. CN-) you get addition to the carbonyl. If you add a non-nucleophilic base and a strong acceptor (e.g. an aromatic aldehyde) you get addition of the ketone enolate to the acceptor.

The synthon approach is even more powerful in that it helps you with the retrosynthesis of compounds. If you number synthons in terms of distance of the reactive center from the heteroatom which imparts its reactivity, you have a very straightforward system of predicting what reagents you need to generate a specific arrangement of functionalities. E.g., a d2 synthon plus an a1 synthon gives a 1,3-difunctional compound (because 2+1 = 3). An example could be the aldol reaction, where d2 is the ketone enolate, and a1 is an aldehyde or a ketone. The product is a 3-hydroxyaldehyde, which is precisely 1,3-difuctional.
But this is probably too advanced for a beginner.

Having said that, it's clear that the study of organic chemistry requires a lot of time and much exercise, because thermodynamic and kinetic effects must be thorougly understood. The variations and combinations of individual 'pieces' of mechanism are endless.

Offline Ψ×Ψ

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Re: rememberign rxns
« Reply #4 on: November 07, 2006, 09:54:40 PM »
Lavoisier, that sounds exactly like what the prof I had for sophomore organic would say.  Almost intuitive after a while.  It does sound a little rough for a beginner, though...

Offline AWK

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Re: rememberign rxns
« Reply #5 on: November 08, 2006, 04:13:40 AM »
Repetitio est mater studiorum
AWK

Offline lavoisier

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Re: rememberign rxns
« Reply #6 on: November 12, 2006, 12:55:09 PM »
Lavoisier, that sounds exactly like what the prof I had for sophomore organic would say.  Almost intuitive after a while.  It does sound a little rough for a beginner, though...

Yes, I guess it is; not as awkward as your nickname, though ;-)

However, sometimes I wonder if it's wise showing students tons of apparently uncorrelated organic reactions, and waiting/hoping that they find the underlying order. Wouldn't it be better if they had some structure in mind from the beginning? Wouldn't it improve their understanding of the subject?

And I'm also thinking of those students who take general organic chemistry courses, but later choose a different specialistic subject. What will they remember in a few years unless they find that order I was talking about?
It appears that our brain is not very good at remembering single, disconnected pieces of information, but works much better if it can make analogies and connections between them. Therefore...

Offline beheada

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Re: rememberign rxns
« Reply #7 on: November 12, 2006, 04:54:07 PM »
Coming from someone in your exact same position, I had a professor suggest flashcards... 3 of each for each different reaction (reactant variable, product variable, reagent variable). This, however, turned out to be a horrible mistake. The easiest way I've been able to remember them is to make the flashcards with everything on them and then WHAT IT DOES (dehydrohalogenation, markov, syn addition, etc) on the other side. For some reason that seems to click in my brain better.

rayfe

Offline Ψ×Ψ

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Re: rememberign rxns
« Reply #8 on: November 12, 2006, 11:00:42 PM »
Yes, I guess it is; not as awkward as your nickname, though ;-)

Oh, I'm just generally an awkward person... ;)

Offline bnstria

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Re: rememberign rxns
« Reply #9 on: November 13, 2006, 08:28:00 PM »
I guess it depends on where you  learnt organic chemistry but I didn't learn about resonance structures till way after learning the basic organic reactions.  If you are just learning the reactions and haven't even been taught about mechanistic arrows yet then memorisation using flash cards is the best way to go. 

What I guess I am saying is that you should let us know what you have been taught so far so we know how to help you best.  Have you learnt about resonance structure?  Mechanistic arrows? 

When I first learnt the basic reactions like ROH + HX then I used flash cards but if you need to remember mechanisms then an understanding of electrophilicity is a more efficient way of learning.

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