ISOMERS. Constitutional isomers (Structural isomers) isomers that differ in their bonding sequence. Stereoisomers
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1 ISMES two distinct molecules with the sme moleculr formul Constitutionl isomers (Structurl isomers) isomers tht differ in their bonding sequence Stereoisomers differ only in how their toms re oriented in spce Distereomers stereoisomers tht re not mirror-imges Enntiomers pir of nonsuperimposble mirror-imge molecules Geometric isomers (Cis-trns isomers) they differ in the geomerty of the groups on double bond or ring ther distereomers (usully molecules with 2 or more chirl centers)! epimers: distereomers tht differ in configurtion t only one of the stereogenic centers! meso compounds: chirl molecules with chirl centers Confirmtionl isomers: re interconvertible by rottions bout single bonds Configurtion: the reltive position of the rrngement of toms in spce 1
2 Constitutionl isomers C 5 10 pent-1-ene pent-2-ene cyclopentene methylcyclobutne C 9 diethyl ether methyl propyl ether butn-1-ol 1 lcohol butn-2-ol 2 lcohol 2-methylpropn-2-ol 3 lcohol 2
3 Conformtions - Butne 3
4 Conformtions Cyclohexne
5 Conformtions Cyclohexne 5
6 Geometric isomers b b b b b b cis (Z) trns (E) no geometric isomers Cl Br 3 C 2 C C 2 F (Z)-2-bromo-1-fluoro- 1-chloroethene 3 C C 2 C 2 (E)--ethyl-3-methylhept-3-ene Difference in rectivity C C het - 2 C C het - 2 mleic cid mp 138 C toxic, irritnt fumric cid mp 287 C essentil metbolite 6
7 Chirl molecules / centrl chirlity CIP rule 1 1 inversion Fischer projection S 3 enntiomers bsolute configurtion 1 chirl rcemistion 2, S resolution S 3 2 plne of symmetry 7
8 Mesurement of opticl ctivity Polrimeter polrizer smple nlyzer Specific rottion α mesured x 100 = [α] x c x l [α] = lc x100 [α]: specific rottion l: 1 dm c: concentrtion (g/100 ml) α m C C C C (2,3)-trtric cid [α] 20 D = +12 (c = 2, 2 ) 8
9 Specific rottion nd bsolute configurtion C C ()-lctic cid "esterifiction" C C ()-methyl lctte [α] D 20 = -3,3 [α] D 20 = +8,2 C=C 2 C C 2 C 2 (S)-3-methylhex-1-ene 2 -Pd/C C 2 - C C 2 C 2 ()-3-methylhexne NBS Br t Bu (S)--tert-butyl-cyclohexene t Bu ()-3-bromo-5-tert-butyl-cyclohexene 9
10 Enntiomeric excess (ee) ee = [] - [S] [] + [S] x 100 = % -%S Determintion of enntiomeric excess chromtogrphic methods (chirl sttionry phse) NM spectroscopy (chirl shift regents) Exmple if = 70%, S = 30%, then ee = 0% The mixture contins: 0% enntiomer, nd 60% rcemic mixture pticl purity (P) P% = [α] mesured [α] mx x
11 pticlly ctive molecules without chirl center C N 2 C 2 N C 2 N tropisomerism C N 2 3 C Cl spirnes Cl 3 C Cl C C C Cl C3 llenes BUT! odd number of cumulted bonds Cl 3 C C C C Cl cis-trns isomerism 3 C Cl C C C C Cl 3 C Cl C C C C Cl 11
12 Molecules with different symmetry elements ) cis-trns isomerism nd stereogenic center 3 C C C C b) hindered rottion nd stereogenic center N Br I 3 C C I 12
13 Stereoisomerism of 1,2-disubstituted cyclohexnes (conformtionl chirlity) chirl derivtives (hve inner mirror plne) 1,1 cis-1,3 cis-1, trns-1, 13
14 chirl derivtives (no plne of symmetry) trns-1,2 cis-1,2 = not only conformers but lso enntiomers trns-1,3 = not only conformers but lso enntiomers chirl molecules, but optillly inctive becuse of the conformtionl equilibrium 1
15 Stereogenic centers (not crbon toms) mines (not resolvble) Δ + = 30 kj/mol N N b c fst inversion c b resolvble molecules b d N + c mmonium ction Et P phosphonic cid ester + S b c sulfonium ction b S sulfoxide 15
16 Different biologicl ctivity of the enntiomers N N Contergne - drug molecule - tertogenic N C 2 C N 2 Amphetmine -stimultory effect -side effects Limonene - lemon smell - ornge smell Crvone - spermint smell - crwy smell 16
17 Two stereogenic centers with different lignds S S 3' 3' S 2' ' ' 2' ' 2' S 3' 3' ' 2' enntiomers enntiomers distereomers Erythrose, threose: C C C C 2 stereoisomers 17
18 n stereogenic center 2 n stereoisomer * * * * * * 3 C C3 * * * C 2 C 2 C 3 C cholic cid 11 stereogenic crbon toms (208 stereoisomers) C 2 C 2 C 18
19 Two stereogenic centers with the sme lignds / meso compounds distereomers meso form opticlly inctive S S = S 2 2 S enntiomers C S C C C S 3 2 = 2 3 trtric cid 3 stereoisomers
20 Concepts in stereochemistry (topism) omotopic = sme Enntiotopic: different; replcement of one or the other of them genertes enntiomers pro S pro D D prochirl C enntiomers 20
21 Distereotopic: different; replcement of one or the other genertes distereomers C D C D C N 2 N 2 N 2 ditereomers Prochirl C Nu Nu Nu: C 1 2 si fce (counterclockwise) re fce (clockwise) 21
22 Exmple t Bu 1. LDA * * t Bu stereoisomers syn distereomers enntiomers t Bu t Bu distereomers distereomers nti distereomers t Bu t Bu enntiomers 22
23 Synthesis of enntiomers 1) Isoltion of chirl compounds nd/or trnsform e.g. morphine, nd morphine derivtives 2) Stereoselective synthesis ) Utiliztion of chirl regent Ph C + Al 3 + Ph C S b) Utiliztion of chirl ctlyst N Ph C + 2 ct. N C Ph S Ph 2 P h PPh 2 23
24 3) pticl resolution of rcemic mixtures chirl regent C C C C enntiomeres (not seprble) enntiomers chirl regent C C distereomers (seprble) C C C C enntiomeric mixture formtion of distereomers neutrliztion seprtion 2
25 Formtion of distereomers with slt formtion ) using one equivlent of resolving gent (+)- C - (+)-Q N 3 + (±)- C + (+)-Q N 2 rcemic mixture resolving gent (-)- C - (+)-Q N 3 + distereomeric slt pir seprtion (e.g. crystlliztion) (+)- C - (+)-Q N 3 + (-)- C - (+)-Q N 3 + neutrliztion neutrliztion (+)- C (-)- C 25
26 Exmple 3 C C N 2 C C C C ()-mndelic cid rcemic mndelic cid ()-phenylethylmine C C (S)-mndelic cid 26
27 b) Using hlf equivlent resolving gent 2 (±)- C + (+)-Q N 2 + N queous solution (+)- C - (+)-Q N 3 + insoluble (-)- CN solution 3 + (+)- C (-)- C 27
28 pticl resolution by extrction 2 (±)- C + (+)-Q N 2 + N CCl 3, 2 queous phse orgnic phse (-)- CN (+)- C - (+)-Q N neutrliztion (-)- C (+)- C 28
29 esolving gents 3 C N N 2 N quinine (S)-(-)-phenylethylmine S 3 (S)-(+)-cmphene-10-sulfonic cid C C C C (,)-trtric cid derivtives pl. =, benzoyl, cethyl C (S)-(+)-mndelic cid 29
30 pticl resolution with derivtiztion (±)-Q + (+)- C esterifiction (+)-Q C (+)- (-)-Q C (+)- seprtion (+)-Q C (+)- (-)-Q C (+)- hydrolysis (+)-Q (-)-Q 30
31 pticl resolution using chromtogrphy S chirl sttionry phse S S S 31
32 Kinetic resolution (±)-A + k 1 k 2 (+)-A (-)-A if k 1 > k 2, then end the rection t certin conversion gives [(+)-A] > [(-)-A] Exmple N 2 (S) C N 2 CBu enzyme (ct.) 6% conversion N 2 () CBu 32
33 Dynmic kinetic resolution k T k rc k rc > k > k S S k S TS Me Me Me Et enzym bse Me Me ()-ibuprofen Me C bse Me Me Me S Et 33
34 SELECTIVITY Chemoselectivity LiAl Et NB Et egioselectivity 2 / + Mrkovonikov rule 3
35 + Br Br thermodynmic control + Br kinetic control 0 C 80 % 20 % 80 C 20 % 80 % 35
36 Stereoselectivity Describes rections tht hve two mechnisticlly cceptble but stereochemiclly different pthwys, so tht the molecule my select the more fvorble (e.g. the fster pthwy - kinetic control; or the more stble product - thermodynmic control). C C fumric cid 2 / enzyme C 2 C C (S)-mlic cid Stereospecific rections Gives specific nd predictble stereochemicl outcomes becuse the mechnism of the rection demnds this. C C Br 2 Br C C Br fumric cid 36
37 Stereospecific rections Substitution S N X Nu: 1 2 Nu inversion Elimintion E2 bse nti-periplnr X nd X ydrogention of lkenes nd lkynes , Pd/C cis ddition Electrophilic ddition to lkenes s cis ddition Electrophilic ddition to lkenes Br Br 2 2 Br trns ddition 37
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