Experiment: Dehydration of an Alcohol
Experiment #7 Fall 2014
Dehydration of an alcohol NAME Nick Weinberger
POSTLAB
1. Show the mechanism for the dehydration of -tetralol under conditions employed in the lab. Show all intermediates, and show electron flow with arrows.
2. What general mechanism most likely applies to this reaction (SN2, E2 etc)?
E1
3. Why was acid employed in this reaction?
The acid was used to protonate the leaving group (OH) to form water which is a much better leaving group than OH.
4. What role does the aromatic ring play in both intermediate and product formation?
The aromatic ring is also benzyllic which helps us steer the reaction in the E1 pathway we are trying to achieve. It also forms a very stable carbocation which is essential for an E1 reaction to occur. The ring helps stabilize the carbocation more than just a normal secondary carbocation.
5. You ran 2 “qualitative” tests for unsaturation on your product.
a. Describe what you observed when the Baeyer (KMnO4) test was run on your sample.
After four drops of the product was placed in a small beaker along with ~0.5ml of acetone, three drops of KMnO4 was added. The mixture soon turned into a darkish brown color which concludes a positive for a Baeyer test.
b. Describe what you observed when the Br2 in CH2Cl2 test was run on your sample.
Once again, four drops of the product was used. Only one drop was added at a time to carefully perform the test. It took twelve drops before the orange color disappeared from the solution.
c. What do we mean by “unsaturation” in this context?
Unsaturation in this context means the presence of a double bond between two carbon atoms.
6. Attach your IR spectrum to your report. Compare your product IR with the starting material IR (found on our lab course page—go through Cougarweb, not Bb). What significant peak is (should be) missing in your product IR? In most cases, the peak at ~3030 cm-1 was stronger in product
Dehydration of an alcohol NAME Nick Weinberger
POSTLAB
1. Show the mechanism for the dehydration of -tetralol under conditions employed in the lab. Show all intermediates, and show electron flow with arrows.
2. What general mechanism most likely applies to this reaction (SN2, E2 etc)?
E1
3. Why was acid employed in this reaction?
The acid was used to protonate the leaving group (OH) to form water which is a much better leaving group than OH.
4. What role does the aromatic ring play in both intermediate and product formation?
The aromatic ring is also benzyllic which helps us steer the reaction in the E1 pathway we are trying to achieve. It also forms a very stable carbocation which is essential for an E1 reaction to occur. The ring helps stabilize the carbocation more than just a normal secondary carbocation.
5. You ran 2 “qualitative” tests for unsaturation on your product.
a. Describe what you observed when the Baeyer (KMnO4) test was run on your sample.
After four drops of the product was placed in a small beaker along with ~0.5ml of acetone, three drops of KMnO4 was added. The mixture soon turned into a darkish brown color which concludes a positive for a Baeyer test.
b. Describe what you observed when the Br2 in CH2Cl2 test was run on your sample.
Once again, four drops of the product was used. Only one drop was added at a time to carefully perform the test. It took twelve drops before the orange color disappeared from the solution.
c. What do we mean by “unsaturation” in this context?
Unsaturation in this context means the presence of a double bond between two carbon atoms.
6. Attach your IR spectrum to your report. Compare your product IR with the starting material IR (found on our lab course page—go through Cougarweb, not Bb). What significant peak is (should be) missing in your product IR? In most cases, the peak at ~3030 cm-1 was stronger in product