Rules of the Day CH310M/CH318M Fall 2007

11-12-07

Featured Golden Rule of Chemistry: 3. Nature hates unpaired electrons. If a molecule must have an unpaired electron (a.k.a. radical), it is better to have the unpaired electron distributed over as many atoms as possible through resonance, inductive effects, and hyperconjugation.

1. Roadmaps allow you to organize the important information about the reactions we have learned in a form that helps you with synthesis problems. Catch the wave NOW by gettig a posterboard, placing the different functional groups in the pattern recommended and filling in all the reactions we learn. Do this every night from now on. The key to getting synthesis problems correct is learning how to RECOGNIZE where you are on your roadmap!

2. Allyl radicals and cations are stabilized by resonance. Resonance with the adjacent double bond spreads the unpaired electron density (radical) and charge (cation) around.

3. Allylic halogenation uses NBS and light to place a Br atom adjacent to a C=C bond. The mechanism is a free radical chain reaction, involving an allyl radical intermediate. Up to four different sites can be considered for adding the Br atom, the predominant one will be the site that gives the most stable (most highly substituted) C=C in the product.

4. Using a peroxide (ROOR) and light in the presence of HBr and an alkene leads to a free radical chain reaction that leads to non-Markovnikov addition of the HBr. This is a very useful reaction that can make primary alkyl halides from terminal alkenes.

5. Leaving groups can be classified according to leaving group ability, and generally more stable anions are better leaving groups. Thus, the conjugate bases of stronger acids are better leaving groups. Click here to see SN2 movie.

 

HOMEWORK The following readings and problems should be done before the next lecture so you are ready for it.

Read: Sections 9.8-9.9 in the book.

Do the problems in the book (but do not turn them in): 9.8, 9.12-9.14, 9.28, 9.37, 9.38.

Continue working on the Homework 9 (Due Wednesday, Nov. 14)