Click here for a copy of my lecture notes from today's lecture

Click here for a copy of the handout used in class today

Click here for a helpful video that reviews mechanisms for the exam this week

Featured Golden Rules of Chemistry: Nothing today

1. When studying for the exam, remember this material is very different then the first midterm material. You CAN do this. I suggest you follow these steps before looking through old exams: 1) Read each Rule of the Day so you can identify those things you are not familiar with. 2) Binge-watch the lectures recordings, skipping the things you undersrtand and spending time watching the things you do not yet understand (last year's class used this study method and they did great!) 3) Consult the Missed the Wave topics to see if you can get help from those recordings 4) Ask questions at office hours and the Review Session on Tuesday night 5) Start working through the old exams.

Study Tip for Today: Make sure you not only "know" the mechanisms, make sure you understand the role the different reagents play during each step (nucleophile, electrophile, strong acid, etc.)

2. Alkynes with a hydrogen atom attached to one of the sp hybridized atoms are relatively acidic. This is because the anion produced upon deprotonation is on the sp atom, and more s character is stabilizing. Use the wicked strong base NaNH2 to deprotonate a terminal alkyne.

3. Deprotonated alkyne anions react as nucleophiles with primary haloalkanes in a single step in which the carbon-halogen bond is replaced with a carbon-carbon bond (Make a Bond between a nucleophile/electrophile and simultaneously Break a Bond to create stable molecules or ions). Big, mega deal here; We just made our first C-C bond!!! Time capsule: this is an SN2 reaction.

4. The chemistry of alkynes is predictable based on where the electrons are located: In two orthogonal pi bonds. Like alkenes, alkynes have the chemical personality of being a weak nucleophile, weak base.

5. Alkynes react with 2 equivalents of X2 and HX to give vicinal tetrahaloalkanes and dihaloalkanes, respectively. The HX reaction follows Markovnikov regiochemistry with terminal alkynes.

6. Alkynes are prepared from the base (NaNH2) promoted double elimination of a vicinal dihalide. For making an internal alkynes you need two equivalents of NaNH2, but for making terminal alkynes you need to 1. Add 3 equivalents of NaNH2 followed by 2. HCl/H2O to protonate the alkyne product. This provides a way to produce an alkyne from an alkene via the vicinal dihalide produced from an alkene and X2.

7.The enol form of a compound rapidly tautomerizes to the more stable keto form. The keto form is more stable because the C=O pi bond is stronger than the C=C pi bond.

8. Alkynes give enols that rapidly tautomerize to ketones or aldehydes when reacted with 1. BH3 2. H2O2/NaOH. To see a strong preference for the terminal side of an alkyne (non-Markovnikov), use the bulkier (sia)2BH.("borane with antlers")

9. Alkynes add water in the presence HgSO4/H2SO4 to give enols that tautomerize to ketones. For terminal alkynes, the oxygen atom ends up on the internal carbon atom as Markovnikov would predict. You are not responsible for the really long mechanism that involves a mercurinium ion intermediate and eventually loss of Hg2+ to give the enol that tautomerizes to the keto form.

10. Catalytic reduction using H2 takes an alkyne all the way to an alkane when elemental catalyst such as Pd is used. When a kinder/gentler catalyst called Lindlar's catalyst is used, the reaction stops at the alkene stage, stereochemistry of addition is syn, leading to cis products.

11. Flashback Rule of the Day: Trans alkenes are more stable thatn cis alkenes because cis alkenes have some steric strain (non-bonded intereatction strain). In addition, more highly substituted alkenes are more stable than less substituted alkenes (we don't really tell you why, just learn it please.)

12. Chemical reduction using sodium (Na) in liquid ammonia (NH3) gives a trans alkene. The mechanism involves single electron transfers and radical/anion intermediates, resulting from sequential electron and proton transfers, repeated a second time.

HOMEWORK:

Read: Study for the exam on Thursday.

There is no quiz today because it is exam week. These quizzes are designed to review the important material from today's lecture. Together, they will count as 5% of your final grade.

Finish Working on Homework Problem Set 7, due at 10 PM today, October 22.

Click here to go to the Aktive Homework Problem Set 7

Click here to get a copy of the Gradescope Homework Problem Set 7