1. Quiz 1: 1. Naming the following structures. 2. Draw stable conformer for cis-1,3-dimethylcyclohexane. 3. Tell which one is chiral and which one isn’t?

2. Unsaturated Hydrocarbons (Part I)

3.  不饱和烃（烯烃和炔烃）的亲电加成反应；  加成反应 ( 加卤素、卤化氢、水、硫酸、次卤酸、硼氢化、 催化氢化等 ) ，氧化反应，聚合反应，自由基加成反应，不对称 烯烃与极性试剂的加成反应和加成产物的定位； Requirements Reading Chapter: McMurry, Chapter 6, 7 & 8 王彦广， Chapter 4 Homework: McMurry: 6.39, 6.48, 6.49 王彦广：问题 4 － 1

4. Types of addition reactions: Electrophilic addition reaction Nucleophilic addition reaction Cycloaddition reaction

5. Electrophilic addition reaction Characters of  -bonds:  -electrons are delocalized Easily to to be polarized Electron rich system Properties of  -bonds: To electron rich system, it could be attacked by electrophile. Electrophile: electron deficient, such as H +, C + …… To unsaturated bonds, addition reaction would be dominant.

6. Diverse electrophiles: Alkenes react with many electrophiles to give useful products by addition (often through special reagents) –alcohols (add H-OH) –alkanes (add H-H) –halohydrins (add HO-X) –dihalides (add X-X) –halides (add H-X) –diols (add HO-OH) –cyclopropane (add :CH 2 )

7. 1.Electrophilic addition reaction 1.1 Halogenation 1.2 Hydrohalogenation

8.  General equation vicinal dihalide 1.1 Halogenation Alkene is substrate, vicinal dihalide is the product. X 2 is reagent, here is electrophile. 1. Electrophilic addition reaction

9.  Relative reactivity of halogen Normally, bromine in CCl 4 Bromine in carbon tetrachloride is brown, the product is colourless. Therefore, we use this reaction to detect the existence of double bonds (not only double bonds). Fluorine reacts with alkene very rapidly, exothermic reaction. Iodine reacts with alkene very slowly, it is an equilibrating reaction. And the dehalogenation product is favored. Chlorine is similar to bromine.

10.  Relative reactivity of substrates  Ethene is standard.  Alkyl groups are electron donating groups (EDG), enrich  -electron density;  More substituted, more reactive towards electrophile (E); Standard

11.  Vinyl halide is unreactive;  Br donates its electron pair to  -bond due to its p-  conjugate effect;  Br has larger electronegativity, reduces  -electron density;  Conjugate effect versus Inductive effect p-  conjugate effect, +C Inductive effect, -I Electron donating propertyElectron withdrawing property <  As a result, vinyl halide is less reactive than ethene towards halogen.

12.  Other observations of halogenation: 1-bromo-2-chloroethane ?  Reaction goes step by step.  Bromine adds to double first….

13.  Meso one is NOT FOUND.  Reaction is stereoselective reaction.  Stereochemistry of halogenation:

14.  Mechanism of halogenation: More branched, more reactive! 1-Bromo-2-chloroethane forms! Stereoselective reaction! Anti-addition Step 1 Step 2 Step 3 Rate-determing step

15.  Olah showed that bromonium ions are stable in liquid SO 2 with SbF 5 and can be studied directly Evidence for the existence of bromonium: antimony pentafluoride

17. To cyclic system: + Addition is exclusively trans

18.  Addition of bromine to triple bonds: Reaction goes step by step; Initial addition gives trans intermediate; The reaction is used for detection of double or triple bonds.

19. < vinylic carbocation alkyl carbocations  Addition of bromine to enyne:

20. 1.2 Hydrohalogenation  General equation: HI  HBr  HCl  Relative reacticity: Acidity HI is generated from KI and phosphoric acid

21.  Symmetrical substrate:  Asymmetrical substrate: Major productMinor product

22. Major Minor Regiospecific – one product forms where two are possible Addition of HCl to 2-methylpropene Why regiospecific?  Regioselectivity of hydrohalogenation:

23.  Mechanism of HX addition to alkene:  Addition of HBr to 2-Methyl-propene  H-Br transfers proton to C=C  Forms carbocation intermediate  More stable cation forms  Bromide adds to carbocation Step by step Carbocation intermediate

24. Energy Diagram for Electrophilic Addition Rate determining (slowest) step has highest energy transition state

25.  Orientation of Electrophilic Addition: Markovnikov’s Rule In an asymmetrical alkene, HX can add in two different ways, Markovnikov observed in the 19 th century that in the addition of HX to alkene, the H attaches to the carbon with the most H’s and X attaches to the other end This is Markovnikov’s rule Which carbocation is more stable, I or II?

26.  Structure of carbocation: SP 2 hybridized Planar structure 6 electrons Understanding stable carbocation: Inductive effect +  -p hyperconjugation: CF 3 CH 2 + < CH 3 CH 2 + ; CH 3 + < CH 3 CH 2 +

27. (CH 3 ) 3 C + > (CH 3 ) 2 CH + > CH 3 CH 2 + > CH 3 +  Relative stability of carbocation: R 3 C + > R 2 CH + > RCH 2 + > CH 3 + 3º > 2º > 1º > + CH 3 or

28. How to understand?

29.  Rearrangement of carbocation: 1,2-H shift

30.  Rearrangement of carbocation: 1,2-alkyl shift

32.  Reaction goes step by step;  Products obeys Markovnikov rule.  Addition of HX to triple bonds:

33.  Anti-Markovnikov product: Markovnikov product Anti-Markovnikov product A, Epoxy effect B, EWG HI, HCl, no epoxy effect!

34. 1.Electrophilic addition reaction 1.1 Halogenation 1.2 Hydrohalogenation Summary Electron rich system Electrophile Electrophilic addition reaction Halogenation Bromonium intermediate Anti-addition product Stereoselective reaction Hydrohalogenation Markovnikov product Regioselective reaction Carbocation Electron donating group(EDG)/electron withdrawing group(EWG) Rearrangement of carbocation Reaction diagram Substrate/product Intermediate/transition state Acitivation energy/reaction heat Exothermeric reaction/endothermeric reaction