Rules of the Day 2-07-07

Click here for a copy of the mechanism sheet used in lecture today.

1. With some aldehydes and ketones (those without alpha hydrogens [stay tuned to find out what this means]), alkyl lithium reagents react like Grignards. Mechanism A. Carbon-carbon bond forming! However, for this class, you are better off using Grignards for reactions with aldehydes and ketones and alkyl lithium reagents as very strong bases.

3. The anions of terminal alkynes add to aldehydes and ketones to give tetrahedral alkoxide intermediates (can be isolated). These alkoxides are protonated when the chemist opens the flask and adds acid to give alkyne alcohols. Mechanism A. Carbon-carbon bond forming!

4. HCN is in equilibrium with H+ and CN-. CN- reacts with aldehydes and ketones to give a tetrahedral alkoxide intermediate that cannot be isolated becuase it is immediately protonated to give a cyanohydrin product. Mechanism A. Carbon-carbon bond forming! Time Capsule: Cyanohydrins are hydrolyzed in strong H3O+ to give a-hydroxy carboxylic acids.

5. Wittig reactions form C=C bonds from C=O bonds through reaction of the nucleophilic ylide via the famous four-membered ring intermediate (See Pictures of the Day). This is a useful reaction because carbonyl compounds are easily made, and the ylides are made from alkyl halides, also easy to make. Unique mechanism! (See Pictures of the Day) Carbon-carbon bond forming!

6. Alkyl Wittig reagents give predominantly "Z" (cis) alkene products, while Wittig reagents with a carbonyl adjacent to the negative charge give predominantly "E" (trans) products.

Homework: Start working on the fourth homework problem set, due Wed, 2-14-07, BEFORE CLASS. Click here to download the pdf.

Read: Sections 16.7, 16.8 Problems: 16.6-16.8, 16.15, 16.29, 16.30, 16.32, 16.33, 16.38 in the book. You will not turn these in but they are very helpful to PREPARE for the next lecture.