Rules of the Day CH320M/328M

Featured Golden Rules of Chemistry: Nothing today

1. Anti stereochemistry means that the atoms add to either side of a C=C double bond, syn means they add to the same side, and mixed means they add both syn and anti in the same reaction.

2. Of the intermediates we have seen or will see, only carbocations rearrange, all other intermediates such as the halonium ions do not.

3. Many reaction mechanism intermediates and products are chiral and formed as racemic mixtures. To avoid having to write too many structures, for mechanism questions, you will only need to draw one of the stereoisomers formed as an intermediate or product but you will have to LABEL ALL CHIRAL CENTERS WITH AN ASTERISK (*) AND WRITE "RACEMIC" EVERY PLACE IT IS TRUE.

4. Alkenes react with X2 in the presence of water to give halohydrins. Holonium ion intermediates again so anti adition leading to trans products. Regiochemistry is Markovinikov (OH ends up on more substituted carbon atom) because of extra charge on the more substituted carbon atom of the halonium ion intermediate.

5. Of the intermediates we have seen or will see, only carbocations rearrange, all other intermediates such as the halonium ions do not.

6. When two new chiral centers are produced in an alkene reaction, you need to work through each example on a case-by-case basis just like the Dude says. Make sure you follow the regiochemistry rules to understand which consititutional isomer(s) will predominate (Markovinikov, non-Markavnikov, etc). Then apply the anti, syn, or mixed geometry of addition based on attack from either face of the flat alkene to predict which stereoisomer products are produced. Review the two stereochemistry Lecture sheets (stereochemistry of addition 1 and stereochemistry of addition 2) to help understand this.

7. When trying to predict reaction products, first recognize the chemistry based on the reagents (HBr, H2O/H2SO4, Br2/H2O, etc.), then work out the regiochemistry (which carbon gets what new bond, Markovnikov, etc.) then see if any chiral centers are created. If they chiral centers are formed, focus on the stereochemistry of the reaction (anti, mixed, etc.) to determine which of the possible stereoisomers are made ON A CASE BY CASE BASIS. DO NOT LOOK FOR ONE-SIZE-FITS-ALL SHORT CUTS OR HACKS THAT DO NOT EXIST. CASE BY CASE IS THE ONLY WAY TO GO.

8. For each reaction of an alkene we have covered you need to remember to call a NIRRS:

Nature of the reaction; what is the starting material/product? (i.e. alkene converted to an alcohol)

Intermediate (or "Important transition state" if applicable) of the reaction, the key to the mechanism (carbocation, halonium ion, etc.)

Reagents Learn the exact way to designate the reagents for each reaction

Regiochemistry What is the regiochemistry of addition? (Markovnikov, non-Markovinikov, etc.)

Stereochemistry of addition (anti, syn or mixed)

HOMEWORK:

Read: Sections 6.5 and 6.6 in the eBook.

Take the Daily Quiz 13 before 10 PM tomorrow. Click here to access the quiz. These quizzes are designed to review the important material from today's lecture. Together, they will count as 3% of your final grade.

Start working on the Homework Problem Set 7, due at 10 PM on Tuesday, October 22. Click here to access the Homework Problem Set 7. Note there are Aktiv Learning and Gradescope Questions, and you MUST DO BOTH. Collectively, homeworks count for 10% of your final course grade. The Aktiv Learning homework provides multiple attempts and provides feedback. It is intended to help you prepare for the Gradescope Questions, so we recommend you do the Aktiv Learning questions first.

There is also a 2nd Midterm problem set. You will not turn this in, but it will help you prepare. Click here for the Problems and click here for the Answers.