lashcard review: carbocation Alkene reactions:, aq acid. B 3 -T. D, NaD LQ # A Do you know when you need to use wedge/dashed bonds? Generally: LQ # B If a mechanism involves carbocation or radical intermediate only stick bonds. If reaction is stereospecific/selective and MP possesses a configuration use wedge/dashed bonds to show configuration. Last lecture Alkene reactions bjectives Stereospecific This lecture A couple more alkene reactions hirality Model kits for Thursday s lecture!!!! Dr. Kay Sandberg Alkene - zonolysis lysis is a root that can mean to break apart. zone esonance structures of ozone Alkene - zonolysis alkene cleavage reaction Step Step zonolysis + 3 symmetric alkene (tetra-sub) hydrolysis equivalents of a + + + alkene + 3 ozone ozonide ozonide carbonyl compounds Various carbonyl compounds arbonyl compounds aldehyde most oxidized carboxylic acid formaldehyde Alkene - zonolysis Short cut visualization Slice Slide Slap Short cut visualization. 3. heptan-4-one butan--one
Alkene - zonolysis Alkene - zonolysis Trisubstituted alkene. 3, 3. ( 3 ) S or Trisubstituted alkene arboxylic acid. 3.. 3., Zn. 3., Zn aldehyde Alkene - zonolysis 3 Disubstituted alkene 3. 3, 3. ( 3 ) S formaldehyde 3 3 Alkene zonolysis: conditions and results SM alkene (SM=starting material). 3 Various. S( 3 ) (or groups Zn) aldehyde formaldehyde. 3. carboxylic acid formic acid Alkene - zonolysis Practice Draw the skeletal structure of the reactant alkene Alkene - zonolysis 3-ethyl-5-methylhept-3-ene Practice. 3. LQ ) Draw the MP s in the same Marvin window.
3-ethyl-5-methylhept-3-ene Products?. both are s. both are aldehydes 3. both are carboxylic acids 4. one is a & other is aldehyde % % 0% 0% 0% 0%.. 3. 4. 5. 6. 5. one is a & other is carboxylic acid 6. one is an aldehyde & other is carboxylic acid Stereochemistry Stereoisomers Section. (Z)-,-dibromoethene (E)-,-dibromoethene or cis-,-dibromoethene Stereoisomers or trans-,-dibromoethene,-dibromoethene,-dibromocyclopentane cis-,-dibromocyclopentane 4 trans-,-dibromocyclopentane 80 o turns right dashed bond to a left wedge bond & vice versa ydrogenation rotate Section 80 o. Stereoisomers Section. Mirror images that are nonsuperimposable have at least one property that is different. Pd Pd 3 3 5 6 Stereoisomers Section. Mirror images that are nonsuperimposable Section. Mirror images that are superimposable Same molecule 8 3
that are nonsuperimposable Mirror images Section. that are superimposable Same molecule chiral - Greek: cheir - hand Does the mirror image of your left hand remind you of your right hand? hiral Section. Mirror image Superimposable? No otate 80 o chiral 0 Is a shoe chiral? Yes, a shoe & its mirror image differ in the property of foot fittedness. Shoes Is a sock chiral? No, a sock and its mirror image have the same foot fittedness. Socks Which is chiral? Baseball bat and baseball glove (no markings on either) % bromochlorofluoromethane Mirror image Section. chiral? hiral molecule l l. both are chiral. both are achiral 3. only bat is chiral 4. only glove is chiral Is a person chiral? % % %.. 3. 4. 3 Superimposable? No chiral (yes) otate 80 o l 4 4
hiral molecule l l Mirror image Section. l l Mirror image Section. l Superimposable? No hiral l : stereoisomers that are non-superimposable mirror images otate 80 o hiral molecule 5 A shoe is chiral, thus by analogy we could say a pair of shoes would be enantiomers. otate 80 o 6 Molecular chirality achiral molecule Achiral molecule Superimposable? Yes Identical molecules Section. Mirror image otate 80 o Socks are achiral onstitutional Nonsuperimposable mirror images Isomers Isomer flowchart Different Stereoisomers hook up Same hook up order order Different spatial arrangements Diastereomers Not mirror images onformational Same hook up order elated by a rotation anti, gauche eclipsed 8 Isomeric relationship? Stereoisomers Type of Stereoisomer (E)-hex-3-ene (Z)-hex-3-ene. constitutional isomers. enantiomers 3. diastereomers 4. conformational isomers 5. none of these 86% % % % %.. 3. 4. 5. (E)-hex-3-ene (Z)-hex-3-ene Diastereomers 30 5
onstitutional Different hook up order Different physical properties Section. Isomers (same molecular formulas) Isomer properties Stereoisomers Same hook up order Different spatial arrangements Same physical properties except for optical and biological properties Diastereomers Different physical properties 3 If a molecule contains a plane of symmetry Symmetry Section.3 then the molecule is achiral 3 Molecule & its mirror image are superimposable: achiral molecule Section. If a molecule contains a plane of symmetry Symmetry or a center of symmetry l l Section.3 33 l l rotate 80 o,3-dibromo-,4-dichlorocyclobutane then the molecule is achiral 34 If a molecule contains a plane of symmetry Symmetry l l then the molecule is achiral Section.3 A tetrahedral carbon that bears 4 different substituents is referred to as a(n): l * hiral center Section. chirality center chiral carbon atom asymmetric center asymmetric carbon atom stereogenic center stereocenter ne more shortcut: If a molecule has only one chiral carbon, then that molecule is chiral. 35 36 6
88% 6% 4% 0% % 0% 0% 0% 0% 0%.. 3. 4. 5. 6.. 8.. 0. Where is the stereocentric? hiral Where is the stereocentric? hiral molecule.. 3. 3 4. 4 5. 5 6. 6. 8. 8. 0. 0 3 4 0 8 5 6 3 3 0 5 4 3 4 6 8 5 6 0 38 A tetrahedral carbon that bears 4 different Section. substituents is referred to as a stereocentric carbon No point of difference hirality determination Point of difference A B * Plane of symmetry 3 Symetry Section. 3 3 3 Whenever there is only stereocentric in a molecule 3 the molecule is chiral. Achiral - no stereocenter 40 A tetrahedral carbon that bears 4 different Section. substituents is referred to as a stereocentric carbon hiral carbon determination ind the stereocenters in Nootkatone (grapefruit oil). ow many stereocenters? LQ #3 0 3 3 3 4 5 8 6 3.. 3. 3 4. 4 5. 5 6. 6. 8. 8. 0. 0 3 3 3 4 33% % 0% 5 6 0 3 65% 5 0% 0% 8 0% 0% 0% 0% 3 4 4
ow about another alkene? Alkene - Alkene reactions: polymerization 3 B 3 3 B 3 3 3 3 3 Now what can grab the carbocation? That is, what is the nucleophile? 3 3 3 3 polymerization 3 3 3 3 3 3 3 3 3 3 B 3 3 3 b - elimination dimer 3 3 3 3 3 3 3 B b - elimination trimer polymerization polymerization 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 b - elimination tretramer B cationic polymerization LQ 4) Given this alkene, draw the pentamer that would result when the last step is a beta- elimination. polymerization polymerization 8
ree radical ree radical n 00 o 000 atm or peroxides ( ) n- Alkene - ree-radical polymerization Step initiation ne sided arrow hn (or heat) ree radical polymerization oordination polymerization: Ziegler-Natta catalyst (Al-Ti) + omolytic bond cleavage Dissociation of peroxide into alkoxy radicals polymerize + polymerize teflon polystyrene polymerize 3 3 3 Plexiglas And so it keeps on growing 3 ommon materials made from polymers. polymerize polymerize LQ #5 Draw the monomer used to make this polymer (Saran wrap) teflon polystyrene l l l l l l Alkene reactions: stereospecific lashcard review: epoxidation trans-alkene peroxyacetic acid Electronic gain outweighs steric pain Angle strain trans-epoxide
lashcard review: carbocation Alkene reactions: Alkene reactions: stereospecific Syn addition lashcard review: epoxidation peroxyacetic acid Angle strain trans-alkene peroxyacetic acid No! No! No! trans-epoxide You must have Exception: realistic bond angles or alkene configurations you do not need to use wedge/dashed bonds to show configuration. Use only sticks to show alkene configurations. 55 trans-alkene Angle strain & EN atom w/+ trans-epoxide Electronic gain outweighs steric pain Alkene reactions: stereospecific Anti addition Alkene reactions: stereospecific Syn addition lashcard review: anti addition, egioselective Markovnikov alcohol, No rearrangements since no carbocation intermediate. 3 l, cold dark lashcard review: syn addition. B 3 -T., Na. B 3 -T., Na Metal cat. No rearrangements since no carbocation intermediate. egioselective D anti-markovnikov addition D D D D Alkene reactions: via a carbocation intermediate lashcard review: carbocation egioselective Markovnikov addition No stereochemical preference, aq acid Alkene reactions: via a radical intermediate lashcard review: radical egioselective anti-markovnikov addition peroxides No stereochemical preference, aq acid earrangements w/carbocation intermediates peroxides No rearrangements w/radical intermediate 0