Alkenes CnH2n sp2 hybridized carbons s p p sp2 H H C C H H

Alkenes no rotation at C=C geometric isomers cis- trans- Cl Cl Cl H H

Nomenclature 1. Longest chain with C=C is parent. 2. C numbered from end nearest to C=C. 3. Designate cis- or trans- if necessary. 4. Name substituents. 5. Replace ane with ene ending. 6. If more than one C=C, give smallest numbers and call diene or triene.

Nomenclature octene trans- 2- cis- 2- octene trans- 5-methyl- 1 2 4 6 8 octene 3 5 7 trans- 2- cis- 2- octene trans- 5-methyl- 3-propyl- 1,3- hex ene adi 3 5 1 3-propyl 2 4 6 5-methyl

Alkene - reactions  electrons Lewis Base Lewis Base e- pair donor nucleophile Lewis Acid e- pair acceptor electrophile

Addition Reactions Hrxn = bonds broken - bonds formed Hrxn = + Hrxn = bonds broken - bonds formed Hrxn = (-bond + -bond) - (2 -bonds) < 0 exothermic

Addition of HX C C H3C H Cl C C H3C H H+ + Cl- C C H3C H Cl reaction mechanism Lewis base  electrons nucleophile Lewis acid H+ electrophile

Addition of HX step 1 C H H3C H+ + Cl- H+ formal charge = group # - ½ shared e- - lone pair e- 2o carbocation 1o carbocation

Addition of HX 2o carbocation 1o carbocation Stability of carbocations most stable intermediate Stability of carbocations 3o > 2o > 1o carbocations are e- deficient electrophiles react with nucleophile Lewis acids Lewis base

Addition of HX step 2 major product minor product

Markovnikov’s Rule C with the most H gets the H major product minor product 2-chloropropane 1-chloropropane C with the most H gets the H

Addition of water, H - OH + H2O major product 2-methyl-2-butene minor product

Mechanism of hydration step 1 H+ + H2O catalyst nuclophile  e- electrophile add H+ H+

Mechanism of hydration step 2 .. + H O electrophile nucleophile step 3 oxonium ion + H+ alcohol

Addition of Br2 .. .. bromination Br Br Br-Br Br step 1 Br + Br : step 1 Br .. + + bromonium ion - - .. Br

Addition of Br2 .. “anti” addition stereospecific trans isomer - Br : step 2 “anti” addition stereospecific trans isomer

Addition of H2 hydrogenation C H H-H alkenes  alkanes + alkenes  alkanes heterogeneous catalyst Pt Cl “syn” addition Cl cis isomer H H - stereospecific

. . . . . Polymerization monomer polymer small molecule large molecule built of monomers catalyst . CH2=CH2 . CH2 CH2 . CH2 CH2 . CH2 CH2 . polyethylene ethylene H H –(CH2 – CH – CH2 – CH)– n C6H5 C H5C6 H styrene polystyrene