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Textbook and Chapters: Brown 6th Ed. (2011), Chapters 10, 11
Keywords: alcohols, epoxides, ethers, organic chemistry
Description: Reactions of Alcohols, Ethers, and Epoxides
Total Problems: 12
Textbook and Chapter: Carey and Giuliano 8th Ed. (2010), Chapter 15
Keywords: alcohols, hydride reduction, oxidation
Description: Goes over how alcohols can be oxidized to form aldehydes/ketones and carboxylic acids, which can be transformed further using Grignard reagents, hydride reagents such as NaBH4, and by performing Fischer esterification. Includes several synthesis problems involving carbonyls and epoxides. Also includes an NMR based problem.
Total Problems: 5
Let's work through an elimination reaction. Draw the structures for each of the species in the three boxes below (protonated thiol, carbocation, and alkene). Also draw curved arrows to show electron movement.
The first step in this reaciton, like many reactions, is an acid-base reaction- when you see an H+ (acid), the first step is usually something getting protonated. This starting material is a thiol (sulfur), but the same thing would happen with an alcohol or ether (oxygen).
When you have a protonated thiol (or alcohol, ether, etc.), you know the reaction isn't finished yet- products are rarely charged. There are two legal moves to get that positive charge off of the protonated thiol. Either the thiol deprotonates, or it takes off as a neutral leaving group. It can't deprontate because that would be going backwards, so your only "legal move" is for the HSCH2CH3 to act as a leaving group (See problem 518).
But then you're left with a carbocation, which is definitely not the final product. How can we get rid of it? (See problem 335 for general ways carbocations react). If the HSCH2CH3 attacked in an SN1 type reaction that would be OK, but it would be going backwards! So the only way to get rid of the carbocation is to do a beta-elminiation (E1).
The alcohol below is protonated and contains an oxygen with a positive charge. Using curved arrows, show the two "legal moves" that result in a neutral oxygen.
Protonation is a common first step in mechanisms. When you have a protonated alcohol, it's likely that either:
Either one is possible. If you're not sure which one happens, remember that when writing out mechanisms, never go backwards- don't draw structures you have drawn before.
