ORGANIC CONVERSIONSMuhammad Naseem Khan

1

by

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

A Few Basic Things

1. Generalize

2. Analyze

3. Understand

4. Apply

3

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

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

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

Examples1. 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 AminesThe Six reactions listed might look different, but they actually haveEXACTLY THE SAME MECHANISM. So, if you have learned howone of them works___ you’ve actually learned them all. Let’s breakit down using the first reaction.

7

One should try to come up with a good mnemonic for this. “Piranhas Attack People Every Day”

8

9

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

Identifying the Patterns in Carbonyl Reaction Mechanism

11

USEFULL RESOURCES

1. Summary Sheets ("Cheat Sheets")

2. MAPS

3. Flash Cards

12

Summary SheetsThe key points from each chapter are condensed onto single pages.

13

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

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

16

Reaction Map: Reactions of Alkanes, Alkyl Halides, Alkenes, and Alkynes

17

18

How would you build this

Molecule?

19

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

Reaction Map for Secondary Alcohol

21

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

23

Using Flash Cards to Learn

Reactions in Organic Chemistry

24

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

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

Sample of Reaction Flashcards

27

28

Write the starting organic compound

and the reagents on one side:

29

A

B

Write the product(s) on the other side:

30

A

B