Slide 1

Slide 2

Alkenes E The double bond consists of a bond and a bond bond from head-on overlap of sp 2 orbitals bond from side-on overlap of p orbitals bond bond Rotating a double bond requires breaking the bond NO FREE ROTATION at room temperature Contain at least one C=C double bond General formula: C n H 2n (like cycloalkanes) Each carbon atom in a C=C double bond is sp 2 hybridized A bond is stronger than a bond. bonds bond

Slide 3

Alkene Nomenclature (Naming) 1.Parent chain = longest chain that includes the double bond(s) 2.The double bonds have priority and must have the lowest number(s) possible 3.The first C atom in the C=C bond indicates the double bonds location (or number in naming) 4.Name, number, & alphabetize substituents as usual 5.Replace ane ending with ene ending Two double bonds: -diene; three double bonds: -triene 6.Put double bond number in front of entire root name (i.e. 2-pentene indicates the double bond starts on carbon 2) 7.Cyclic alkenes: number the atoms in the ring starting with the double bond 2-hexene 3-butyl-2,4-hexadiene

Slide 4

Naming Practice 4-ethyl-3,5-dimethyl-2-heptene 2,4-hexadiene 3,4-dimethyl-1,3-pentadiene 4-isopropyl-3,5-dimethyl- 1,3,5-heptatriene

Slide 5

Cis-trans isomerism in alkenes Substituents will stay on the same or opposite sides of the double bond (no C=C bond rotation) X 2-butene (same side) 2-butene (opposite sides) For cis-trans isomerism, each C in the double bond must have 2 different substituents attached (i.e. a C and a H, etc.) Determining cis or trans: follow the parent chain through the double bond cis-3-methyl-2-heptenecis trans- cis-

Slide 6

Cis/Trans Naming Practice trans-4-ethyl-3,5-dimethyl- 2-heptene trans,trans-2,4-hexadiene 3,4-dimethyl-1,3-pentadiene trans,trans-4-isopropyl-3,5- dimethyl-1,3,5-heptatriene No Cis or Trans Both Hs Both CH 3 s No Cis or Trans Both Hs

Slide 7

Important Common Names Vinyl (branch) Propylene Allyl (branch) Ethylene R R CH 2 HC i.e. polypropylene = milk jugs i.e. polyvinyl chloride = PVC pipe i.e. diallyllysergamide = derivative of LSD i.e. polyethylene = plastic bags

Slide 8

Arranging many double bonds Cumulated C=C double bonds all in a row: C=C=C=C Conjugated Single and double bonds alternate: C=CC=CC=C Isolated >1 single bond between double bonds: C=CCC=CCC=C Lycopene 11 conjugated double bonds 2 isolated double bonds

Slide 9

Reactions of Alkenes Alkanes substitution reactions R-H + A-B R-A + H-B R = residue, a generic alkyl group Alkenes addition reactions + A-B Thermodynamics: H rxn = bonds broken bonds formed = ( bond + bond) ( bond + bond) Exothermic reaction bond is electron-rich

Slide 10

Alkene Addition Reactions + A-B Reaction Hydrohalogenation (addition of H-X, X = halogen) Hydration (addition of H 2 O) Addition of halogens Hydrogenation (addition of H 2 ) A-B H-F, H-Cl, H-Br, H-I H-OH Br-Br, Cl-Cl, F-F H-H

Slide 11

Reactions at the Double Bond bond is electron-rich Acts as a nucleophile Attracts electrophiles to form bonds Electrophile: electron-lover Electron deficient reagent (often + charged cations) seeks e - in reactions Nucleophile: nucleus-lover electron-rich reagent (often charged anions) tries to donate e - to an electrophile in reactions, forming bonds

Slide 12

Markovnikovs Rule Consider the reaction Vladimir Markovnikov Two products are possible Experimentally, only 2-chloropropane is formed + 1-propene 1-chloropropane2-chloropropane Markovnikovs Rule: The alkene carbon with the most H atoms gets the H Hydrohalogenation (H-X), hydration (H 2 O) of alkenes Why? Look at the reaction mechanism to find out... C C

Slide 13

Carbocation Stability Relative carbocation stability: 3 > 2 >> 1 > methyl >>>> 231methyl Most stableLeast stable Why? Electrons can drift into the empty p orbital from C-H bonds on neighboring C atoms to help stabilize Result: The final product comes from the most stable carbocation intermediate

Slide 14

Mechanism of Hydrohalogenation Step 1: Alkene electrons attack H +, forming a carbocation Step 2: Cl - nucleophile forms bond with carbocation or+ carbocation The carbocation formed in step 1 determines the final product

Slide 15

Hydrohalogenation Predict the product of the following hydrohalogenation reaction + HBr OR Markovnikov Product Anti-Markovnikov Product Remember: Markovnikovs rule says that the H (from HBr) will bond to the alkene C with the most Hs

Slide 16

Remember: Markovnikovs rule says that the H (from H 2 O) will bond to the alkene C with the most Hs Hydration Predict the product of the following hydration reaction + H 2 O OR Markovnikov Product Anti-Markovnikov Product

Slide 17

Mechanism of Hydration (R + H 2 O) Step 1: bond attacks electrophilic H + catalyst forming carbocation Step 2: Nucleophilic H 2 O attacks carbocation, forming oxonium ion Step 3: Oxonium ion loses a proton, regenerating H + catalyst Most stable carbocation + Markovnikov product oxonium ion

Slide 18

Mechanism of Halogen Addition (R + X 2 ) Step 1: Br 2 is polarized by electrons, Br + attaches to alkene Step 2:Br + blocks access to one face of the alkene Br - adds to the other face (anti addition) bromonium ion intermediate + trans isomer is the only product

Slide 19

Halogenation + Br 2 The Brs will add to opposite sides of a RING (anti addition) The Brs will be forced into a trans conformation ALWAYS Trans isomer

Slide 20

Mechanism of Hydrogenation (R + H 2 ) Occurs in the presence of a metal catalyst (like Pt) Pt HH + Pt H H Step 1: H 2 adsorbs to catalyst surface Step 2: Both H atoms add to same face of alkene (syn addition) Pt H H cis isomer is the only product

Slide 21

Hydrogenation Occurs in the presence of a metal catalyst (like Pt) + H 2 /Pt Both Hs will add to the same side of a RING (syn addition) If branches are present, they will be forced into a cis conformation cis isomer

Slide 22

Hydrogenation of alkenes vegetable oils + H 2 /Pt unsaturated saturated Contains double bonds Contains NO double bonds

Slide 23

Hydrohalogenation Determine any reactant(s) that could yield the given product of the following hydrohalogenation reaction + HBr trans-3-methyl-2-hexene 3-methyl-1-hexene + HBr Major product using Ms rule Only possible reactant for this product

Slide 24

Hydrohalogenation Determine any reactant(s) that could yield the given product of the following hydrohalogenation reaction + HBr trans-3-methyl-2-hexene trans-3-methyl-3-hexene All three reactants could give this product 2-ethyl-1-pentene

Slide 25

Halogenation Determine any reactant(s) that could yield the given product of the following halogenation reaction trans-3,5-dimethyl-2-heptene Only one possible reactant in this case + Br 2

Slide 26

Alkene Reaction Summary Hydrohalogenation (+ HX) Hydration (+ H 2 O) Halogenation (+ X 2 ) Hydrogenation (H 2 /Pt) Markovnikovs rule Cis/trans with rings

Slide 27

Polymerization of Alkenes Polymer: a large molecule made by linking together small repeat units called monomers Polymerization mechanism: radical chain reaction MonomerPolymer ethene (ethylene) polyethylene propene (propylene) polypropylene

Slide 28

E Alkynes Contain at least one C C triple bond with sp-hybridized C atoms Triple bond: one bond (sp orbitals), two bonds (p orbitals) Naming: triple bond indicated by yne ending Reactivity: same addition reactions as alkenes Use 2 equivalents of addition reagent (i.e. + 2HCl) Use Markovnikovs rule in the same manner ethyne (acetylene) 4-methyl-1-pentyne

Slide 29

Alkyne Naming Practice 3,4-dimethyl-1-pentyne 2-methyl-3-hexyne 3-methyl-1-pentyne 2,5-dimethyl-3-hexyne

Slide 30

Hydrohalogenation of Alkynes Predict the product of the following hydrohalogenation reaction + 2HBr ? Break the reaction into two steps, adding 1 HBr each time to the multiple bond + HBr Final Product 1-pentyne Markovnikovs rule still applies

Slide 31

Hydration of Alkynes Predict the product of the following hydration reaction + 2H 2 O ? Break the reaction into two steps, adding H 2 O each time to the multiple bond + H 2 O Final Product 3,3-dimethyl-1-butyne Markovnikovs rule still applies

Slide 32

Halogenation of Alkynes Predict the product of the following halogenation reaction + 2Br 2 ? Break the reaction into two steps, adding Br 2 each time to the multiple bond + Br 2 Final Product 3,3-dimethyl-1-butyne

Slide 33

Hydrogenation of Alkynes Predict the product of the following hydrogenation reaction + 2H 2 ? This reaction will simply turn the alkyne to an alkene, and then to an alkane + H 2 Final Product 3,3-dimethyl-1-butyne

Slide 34

Alkyne Reaction Practice 1. 2. 3. 4. 5. + 2HCl + 2H 2 O + 2Br 2 + 2H 2 + 2HCl AND