Rules of the Day

2. Alcohols react with Na° metal to form H2 and alkoxides, which are interesting because they are strong nucleophiles and strong bases.

3. The OH group is not a leaving group, but several reactions involve the conversion of the OH group into a good leaving group, followed by an SN2, E2, E1, or SN1 reaction.

4. 3° and 1° alcohols react with H-X to give haloalkanes via protonation followed by SN1 and SN2 mechanisms, respectively. 2° alcohols give too much rearrangement to be useful. Note the stereochemistry is scrambled for the 3° alcohols (SN1).

5. Alcohols react (dehydrate) with strong acid to give alkenes. 2° and 3° alcohols react via a combination of protonation and an E1 mechanism (carbocation rearrangements possible!) and 1° alcohols react via a combination of protonation and E2. In both cases, remember to make the Zaitzev product when there is a choice.

6. Alcohol dehydration is just the functional reverse of acid-catalyzed alkene hydration. The process is actually an equilibrium, the position of which depends on the reaction conditions.

7. 1° and 2° alcohols react with PBr3 and SOCl2 to give bromo alkanes and chloroalkanes, respectively, via a mechanism involving SN2 attack and thus InVERSiON of stereochemistry. The reagent SOCl2, reacts with alcohols to give chloroalkanes in a mechanism analogous to PBr3.

8. Alcohols react with sulfonyl chlorides (RSO2Cl) such as methanesulfonyl chloride or p-toluenesulfonyl chloride to give alkyl sulfonates that can be isolated.Alkyl sulfonates should be thought of as being similar to bromoalkanes in terms of how they react. The sulfonate anion is a good leaving groups, so this is yet another way to convert the OH group into a good leaving group. (Hint: do not confuse RSO2Clwith SOCl2, THEY ARE DIFFERENT).

9. Note how there is a profound stereochemical difference between the reaction sequence of a chiral secondary alcohol with PBr3 followed by reaction with a nucleophile (a net retention of configuration for the entire process) and the reaction sequence of reaction with a sulfonyl chloride followed by reaction with nucleophile (a net InVERSiON of configuration for the entire process).

10. The mechanism for alcohol oxidations using chromium reagents involves formation of chromic esters, followed by deprotonation and loss of HCrO3. Watch the recorded video for a complete description of this important reaction.

11. For primary alcohols, the initially formed aldehyde reacts with water to give the geminal diol, which reacts again to give a carboxylic acid with H2CrO4. Because the PCC reagent does not have water, the geminal diol does not form and the PCC reaction stops at the aldehyde stage.