2. Organic chemistry throws a lot of
different reactions at you. Today I want to
quickly talk about how to learn these
reactions without being overwhelmed.
2
3. A Few Basic Things
1. Generalize
2. Analyze
3. Understand
4. Apply
3
4. Generalize
• Focus on the functional groups. The rest of the
molecule can usually be ignored.
• Use "R" liberally to organize each reaction by
functional group. For example, it's more useful
to know that a certain reaction works with
carboxylic acids than with, say,
CH3(CH2)2COOH in particular.
4
5. Analyze
• What bonds form and break? (very important:
don’t miss the hydrogens!) Before you understand
the mechanism, you must be able to see this.
• What functional groups are present in the starting
material and the product?
• Does this reaction have anything in common with
other reactions you’ve learned? Especially pay
attention to the pattern of bonds forming/breaking
here.
5
6. Understand
• Look at the mechanism, if known. What are the
steps? Could you write them out without
looking?
• Do those mechanistic steps have names? (they
usually do! addition, elimination,
protonation/deprotonation, etc)
• Are there any other reactions where you’ve seen
those mechanistic steps?
• Remembering PAPED is a lot easier than
remembering the exact way to draw 12 arrows.
6
7. Examples
1. Conversion of Carboxylic Acids into Esters
2. Hydrolysis of Esters into Carboxylic Acids
3. Conversion of Carboxylic Acids into Amides
4. Hydrolysis of Amides into Carboxylic Acids
5. Formation of Imines from Ketones/Aldehydes and
Amines
6. Hydrolysis of Imines to Ketones/Aldehydes and
Amines
The Six reactions listed might look different, but they actually have
EXACTLY THE SAME MECHANISM. So, if you have learned how
one of them works___ you’ve actually learned them all. Let’s break
it down using the first reaction.
7
8. One should try to come up with a good mnemonic for this. “Piranhas Attack People Every Day”
8
10. APPLY
• Given a starting material and the reagent, could you have predicted
the product?
• Could you predict the reagent or the starting material if given the
other two pieces of information?
• When might this reaction NOT work? [e.g. Grignards don't work on
carboxylic acids because they perform an acid base reaction.]
• Can you think of reaction you could then do with the product of this
reaction? Can you think of a reaction that makes the starting
material? [useful for thinking about synthesis]
Our textbook might cover 200 reactions, but there are definitely not
200 different plots. Our task is to be able to generalize and
recognize the core patterns. (Like described on next Slide)
10
14. The use of MAPS…..!!
At one level of organic synthesis you
can think of functional groups as
being like cities on a map, and
reactions that link them are like
roads.
14
15. A useful technique is to frame reactions
around functional groups - e.g. what reaction
can transform functional group X (say, an
alcohol) to functional group Y (say, an alkene).
Once you know enough reactions you can start
building out little maps. Not all functional
groups can be converted to others in 1 step!
Often 2, 3 or more steps can be required.
15
20. Building Reaction Map for Ketones
If you look at all these reactions – forward and backward – you can link
functional groups to each other through these types of reactions. 20
22. We’re asked to go from an aldehyde to
a tertiary alcohol.
• Go back to the reaction map. Look for the tertiary
alcohol as a product. Then work backwards. How do
you get there? One way is from a ketone, in a Grignard
reaction. Then think backwards from there – how to get
there? One way is to oxidize a secondary alcohol. And
if you trace back secondary alcohols, you can get there
from the aldehyde and a Grignard reaction.
• Once you know what reactions to use, it’s much easier
to design your synthesis. Here, the problem is
identifying what alkyl groups to use in each of the two
Grignard reactions.
22
25. Tips on making flashcards:
1) Use unlined 4" by 6" cards.
2) On the front of card write only the name ("title") of the reaction, e.g.
"Halogenation of Alkane," “Alcohols from Alkyl Halides," etc.
3) On the back of card write out the general reaction.
4) Be as general as possible in designating organic compounds, e.g. RX
rather than CH3Br.
5) Also on the back of card include any other information important to the
reaction that are expected to be known; this may include:
a) Special conditions, e.g. heat, light, etc.
b) Solvents, e.g. DMSO, H2O, etc.
c) Catalysts (if any), e.g. H+ , Pyridine, etc.
d) General reaction type, e.g. substitution, elimination, addition,
oxidation, reduction, etc.
25
26. Tips on studying from Flashcards:
Carry your reaction flashcards with you everywhere and study from
them whenever you get the chance.
Starting with the whole deck (almost 10 cards for phenols in text book),
write out from memory the information on the back of each card, then
check your answer (NO PEEKING!).
If your answer is 100% correct, set that card aside; if your answer is not
100% correct, put that card on the bottom of the deck
Go through the deck as many times as you need to until you can do all
cards 100% correctly; then set aside the deck for a day or two and start
all over from the beginning. Repeat the process as many times as
possible before the Final Exam.
Test your knowledge and understanding of the reactions by doing all
the assigned reaction problems at the end of the chapters; refer to your
cards for help if necessary. Redo the problems as many times as
necessary until you don't have to refer to your flashcards any more.
26
