Química Orgânica I 2008/09. w3.ualg.pt\~abrigas QOI 0809 A3 1
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1 Química Orgânica I 2008/09 w3.ualg.pt\~abrigas QOI 0809 A3 1
2 O O O 3 C 3 C O O O C 3 N O C 3 O O O O O O C 3 O w3.ualg.pt\~abrigas QOI 0809 A3 2
3 Adaptado de: Jo Blackburn; 2006, Prentice all; Organic Chemistry, 6th Edition; L. G. Wade, Jr. w3.ualg.pt\~abrigas QOI 0809 A3 3
4 Kinds of Isomers w3.ualg.pt\~abrigas QOI 0809 A3 4
5 Conformational Isomers w3.ualg.pt\~abrigas QOI 0809 A3 5
6 Conformational Vs Configurational Isomers OOC O O O O O D-Glucuronic Acid OOC O O O O L-Iduronic Acid O C5-epimerase O O COO O O O L-Iduronic Acid w3.ualg.pt\~abrigas QOI 0809 A3 6
7 Configurational Isomers: Cis-Trans diastereomers w3.ualg.pt\~abrigas QOI 0809 A3 7
8 Cis-Trans Isomerism Because of restricted rotation about a C-C double bond, groups on adjacent carbons are either cis or trans to each other C 3 C C C C 3 C C 3 cis-2-butene mp -139 C, bp 4 C 3 C trans-2-butene mp -106 C, bp 1 C w3.ualg.pt\~abrigas QOI 0809 A3 8
9 Z w3.ualg.pt\~abrigas QOI 0809 A3 9
10 Sequence Rules: The E, Z Designation When the carbon double bond is tri or tetra substituted, how can we name the substituents? C C D C C C C A B A B w3.ualg.pt\~abrigas QOI 0809 A3 10
11 Configuration - E,Z higher higher C C lower lower Z (zusammen) higher C C lower lower E (entgegen) higher w3.ualg.pt\~abrigas QOI 0809 A3 11
12 Configuration - E,Z (2E, 4E)-3-chloro-4methyl-2,4-hexadiene Cl C C C 3 C C C 3 C 3 w3.ualg.pt\~abrigas QOI 0809 A3 12
13 Alkene Stability Cis alkenes less stable than trans due to steric strain Relative stability gained through catalytic hydrogenation C C C 3 C 3 C 3 C C C 3 Cis 24% Trans 76% w3.ualg.pt\~abrigas QOI 0809 A3 13
14 Tema 4. Estereoquímica Efecto de la isomería geométrica sobre las propiedades físicas 1,2-dicloroeteno Isómer o cis trans Punto Fusión ( C) Punto Ebullición ( C) buteno Isómer o cis trans Punto de Fusión ( C) Punto Ebullición ( C) 4 1 w3.ualg.pt\~abrigas QOI 0809 A3 14
15 Quiralidade w3.ualg.pt\~abrigas QOI 0809 A3 15
16 Chirality Any object that has a plane or point of symmetry is achiral (not chiral). w3.ualg.pt\~abrigas QOI 0809 A3 16
17 Chirality andedness : right glove doesn t fit the left hand. Mirror-image object is different from the original object. => w3.ualg.pt\~abrigas QOI 0809 A3 17
18 Chirality in Molecules The cis isomer is achiral. The trans isomer is chiral. Enantiomers: nonsuperimposable mirror images, different molecules. => w3.ualg.pt\~abrigas QOI 0809 A3 18
19 Stereocenters Any atom at which the exchange of two groups yields a stereoisomer. Examples: Asymmetric carbons Double-bonded carbons in cis-trans isomers => w3.ualg.pt\~abrigas QOI 0809 A3 19
20 Chiral Carbons Tetrahedral carbons with 4 different attached groups are chiral. If there s only one chiral carbon in a molecule, its mirror image will be a different compound (enantiomer). => w3.ualg.pt\~abrigas QOI 0809 A3 20
21 Mirror Trick Whenever two structures can be positioned around a symmetry plane if they aren t identical they re enantiomers. w3.ualg.pt\~abrigas QOI 0809 A3 21
22 Mirror Planes of Symmetry If two groups are the same, carbon is achiral. A molecule with an internal mirror plane cannot be chiral. Caution! If there is no plane of symmetry, molecule may be chiral or achiral. w3.ualg.pt\~abrigas QOI 0809 A3 22
23 Chirality in Molecules The cis isomer is achiral. The trans isomer is chiral. Enantiomers: nonsuperimposable mirror images, different molecules. => w3.ualg.pt\~abrigas QOI 0809 A3 23
24 Stereocenters Any atom at which the exchange of two groups yields a stereoisomer. Examples: Asymmetric carbons Double-bonded carbons in cis-trans isomers w3.ualg.pt\~abrigas QOI 0809 A3 24 =>
25 (R), (S) Nomenclature Different molecules (enantiomers) must have different names. Usually only one enantiomer will be biologically active. Configuration around the chiral carbon is specified with (R) and (S). => w3.ualg.pt\~abrigas QOI 0809 A3 25
26 Naming Enantiomers: The R,S System of Nomenclature 1. Rank groups by atomic number of the atom bonded to the chirality center. Use the same system that was used for the E and Z isomers of alkenes w3.ualg.pt\~abrigas QOI 0809 A3 26
27 Naming Enantiomers: The R,S System of Nomenclature 2. Orient molecule so that group (or atom) of lowest priority is directed into plane. 3. Draw a curve from group of highest priority through the group of second priority to group of third priority w3.ualg.pt\~abrigas QOI 0809 A3 27
28 Naming Enantiomers: The R,S System of Nomenclature R (Latin rectus) = right turn S (Latin sinister) = left turn (S)-2-bromobutane w3.ualg.pt\~abrigas QOI 0809 A3 28
29 Swap Trick If for any reason you ever wish a group were in a different position simply swap it with another group. Swap simply reverses the chirality. R for switched compound implies S for actual compound w3.ualg.pt\~abrigas QOI 0809 A3 29
30 Low Priority Group Up Trick If the low priority group in figure points up rather than down simply draw circular arrow and reverse chirality. R for reversed chirality implies S for actual chirality w3.ualg.pt\~abrigas QOI 0809 A3 30
31 Fischer Tricks If low priority group on vertical line (into plane) draw normal rotating arrow. If low priority group on horizontal line draw rotating arrow and reverse the R or S result. Rule of thumb: If group 4 is Vertical, Very true. If group 4 is orizontal, orribly wrong. (S)-2-bromobutane (R)-2-bromobutane w3.ualg.pt\~abrigas QOI 0809 A3 31
32 Fischer Tricks 90º rotation reverses all chiralities. 180º rotation maintains all chiralities everything winds up in opposite pos'n w3.ualg.pt\~abrigas QOI 0809 A3 32
33 Multi-Carbon Fischer Trick Similar C s are never more than 2 swaps diff. If 1 swap won t line up groups C s are same! top carbons have same config Cl F F Cl w3.ualg.pt\~abrigas QOI 0809 A3 33 F Cl Cl bottom carbons have opposite config's (swap and Cl) F
34 Newman Projections For front C swap low priority group to back C If swap was necessary curved arrow now gives reversed chirality; otherwise correct 4 3 Cl 3 1 Cl F 2 F Cl 4 1 Cl F2 F swap 3 and 4 Configuration is R w3.ualg.pt\~abrigas QOI 0809 A3 34
35 Two or More Chiral Carbons Enantiomer? Diastereomer? Meso? Assign (R) or (S) to each chiral carbon. Enantiomers have opposite configurations at each corresponding chiral carbon. Diastereomers have some matching, some opposite configurations. Meso compounds have internal mirror plane. Maximum number is 2 n, where n = the number of chiral carbons. => w3.ualg.pt\~abrigas QOI 0809 A3 35
36 Compounds with More Than One Chirality Center Two Pairs of Similar Groups w3.ualg.pt\~abrigas QOI 0809 A3 36
37 Compounds with More Than One Chirality Center Three Pairs of Similar Groups S R C 3 C 3 C 3 C 3 Br Br Br Br Br Br = Br Br C 3 C 3 C 3 C 3 R,R isomer S,S isomer R S meso isomer is R,S = S,R w3.ualg.pt\~abrigas QOI 0809 A3 37
38 Meso Compounds w3.ualg.pt\~abrigas QOI 0809 A3 38
39 Topology of Stereoisomers With Two Chiral Centers Two Pairs of Identical Substituents Three Pairs of Identical Substituents R,R erythro/threo E S,S erythro/threo R,R E S,S D D D R,S threo/erythro E D D D S,R threo/erythro D R,S meso D D I D D D S,R meso D E = diasteriomers = enantiomers w3.ualg.pt\~abrigas QOI 0809 A3 39 D E = diasteriomers = enantiomers I = identical (meso)
40 R,S System for isomers with more than one Chirality Center 3 C O Br C 3 C 3 O Br C 3 (2S,3R)-3-bromo-2-butanol w3.ualg.pt\~abrigas QOI 0809 A3 40
41 Relative and Absolute Configurations ( ) amphetamine is known to have the R- configuration Therefore the (+) form has S configuration w3.ualg.pt\~abrigas QOI 0809 A3 41
42 Enantiotopic, Diastereotopic, and omotopic ydrogens w3.ualg.pt\~abrigas QOI 0809 A3 42
43 Enantiotopic, Diastereotopic, and omotopic ydrogens w3.ualg.pt\~abrigas QOI 0809 A3 43
44 Enantiotopic, Diastereotopic, and omotopic ydrogens w3.ualg.pt\~abrigas QOI 0809 A3 44
45 Enantiotopic, Diastereotopic, and omotopic ydrogens w3.ualg.pt\~abrigas QOI 0809 A3 45
46 Enantiotopic, Diastereotopic, and omotopic ydrogens w3.ualg.pt\~abrigas QOI 0809 A3 46
47 Properties of Enantiomers Same boiling point, melting point, density Same refractive index Different direction of rotation in polarimeter Different interaction with other chiral molecules Enzymes Taste buds, scent => w3.ualg.pt\~abrigas QOI 0809 A3 47
48 Plane-Polarized Light Polarizing filter calcite crystals or plastic sheet. When two filters are used, the amount of light transmitted depends on the angle of the axes. => w3.ualg.pt\~abrigas QOI 0809 A3 48
49 Polarimetry Use monochromatic light, usually sodium D Movable polarizing filter to measure angle Clockwise = dextrorotatory = d or (+) Counterclockwise = levorotatory = l or (-) Not related to (R) and (S) => w3.ualg.pt\~abrigas QOI 0809 A3 49
50 Specific Rotation Observed rotation depends on the length of the cell and concentration, as well as the strength of optical activity, temperature, and wavelength of light. [α] = α (observed) c l c is concentration in g/ml l is length of path in decimeters. => w3.ualg.pt\~abrigas QOI 0809 A3 50
51 Tema 4. Estereoquímica w3.ualg.pt\~abrigas QOI 0809 A3 51
52 Chirality of Conformers If equilibrium exists between two chiral conformers, molecule is not chiral. Judge chirality by looking at the most symmetrical conformer. Cyclohexane can be considered to be planar, on average. => w3.ualg.pt\~abrigas QOI 0809 A3 52
53 Mobile Conformers Br Br Br Nonsuperimposable mirror images, but equal energy and interconvertible. Br Br Br Use planar approximation. w3.ualg.pt\~abrigas QOI 0809 A3 53 =>
54 Nonmobile Conformers If the conformer is sterically hindered, it may exist as enantiomers. w3.ualg.pt\~abrigas QOI 0809 A3 54 =>
55 Allenes Chiral compounds with no chiral carbon Contains sp hybridized carbon with adjacent double bonds: -C=C=C- End carbons must have different groups. Allene is achiral. => w3.ualg.pt\~abrigas QOI 0809 A3 55
56 Fischer-Rosanoff Convention Before 1951, only relative configurations could be known. Sugars and amino acids with same relative configuration as (+)-glyceraldehyde were assigned D and same as (-)-glyceraldehyde were assigned L. With X-ray crystallography, now know absolute configurations: D is (R) and L is (S). No relationship to dextro- or levorotatory. => w3.ualg.pt\~abrigas QOI 0809 A3 56
57 D and L Assignments * CO O C 2 O D-(+)-glyceraldehyde COO 2 N => * C 2 C 2 COO L-(+)-glutamic acid O * CO O O O C 2 O D-(+)-glucose w3.ualg.pt\~abrigas QOI 0809 A3 57
58 aminoácidos w3.ualg.pt\~abrigas QOI 0809 A3 58
59 The CORN Law Imagine looking along the ydrogen - alpha Carbon bond of an amino acid CORN is an acronym for -COO; the -R group; and -N2 Starting at the carboxylic acid group, if you move your eyes clockwise and see the mentioned - COO group then the -R group then the -N2 group: CORN. L- form w3.ualg.pt\~abrigas QOI 0809 A3 59
60 w3.ualg.pt\~abrigas QOI 0809 A3 60
61 Properties of Diastereomers Diastereomers have different physical properties: m.p., b.p. They can be separated easily. Enantiomers differ only in reaction with other chiral molecules and the direction in which polarized light is rotated. Enantiomers are difficult to separate. => w3.ualg.pt\~abrigas QOI 0809 A3 61
62 Estereoquímica das reacções O O N O * N O Talidomida 3 C * C O O 2 C OC 3 N * O (R)-naproxeno antiartrítico (S)-propanolol antihipertensivo w3.ualg.pt\~abrigas QOI 0809 A3 62
63 O N O O N O O N O O N O O O 3 C N N N N O O O C 3 O Extreme teratogen (causes birth defects) Thalidomide mild sedative convulsive narcotic Barbituate Derivatives I I C 3 C 3 O O O O I O I 2 N N I O O 2 I thyroid hormone antihypercholesterolemic Thyroxin I O I C 2 2 C 3 C C 3 odor/taste odor/taste of lemon of orange Limonene O O N C 3 β-blocker C 3 3 C Propanolol C 3 N O contraceptive O w3.ualg.pt\~abrigas QOI 0809 A3 63 C 3 O C 2 3 C spearmint O Carvone C 3 2 C C 3 caraway
64 Regioselective, Stereoselective, and Stereospecific Reactions A regioselective reaction is one in which multiple constitutional isomers possible, but more of some formed than others. Br Br major product + Br no measurable quantity formed w3.ualg.pt\~abrigas QOI 0809 A3 64
65 Regioselective, Stereoselective, and Stereospecific Reactions A stereoselective reaction can produce multiple stereoisomers theoretically, but more of some produced than others. Br + Br base (2R)-2-bromo-1,1-dimethylcyclohexane + (2S)-2-bromo-1,1-dimethylcyclohexane (1Z)-3,3-dimethylcyclohexene no E (trans) isomer is formed w3.ualg.pt\~abrigas QOI 0809 A3 65
66 Regioselective, Stereoselective, and Stereospecific Reactions A stereospecific reaction produces different stereoisomer products from different stereoisomer reactants. Br 2 (2R,3R)-2,3-dibromobutane + (2S,3S)-2,3-dibromobutane (no meso isomer formed) Br 2 (2R,3S)-2,3-dibromobutane meso isomer (no R,R or S,S isomers formed) w3.ualg.pt\~abrigas QOI 0809 A3 66
67 Syn Addition When the two substituents add to the same side Pt C C C C Addition of 2 is a syn addition w3.ualg.pt\~abrigas QOI 0809 A3 67
68 Anti Addition When the two substituents add to opposite sides w3.ualg.pt\~abrigas QOI 0809 A3 68
69 Stereochemistry of Addition CIS-SYN-ERYTRO RULE w3.ualg.pt\~abrigas QOI 0809 A3 69
70 Stereochemistry of Addition Cis-Syn-Erythro Example C 3 1. B 3 /TF 3 C C(C 3 ) O 2, O? trans methyls syn addition opposite side O put markers (methyls) in vertical pos'ns 2 + B 3 C C(C 3 ) 2 + C 3 O (C 3 ) 2 C C 3 C 3 C 3 O C(C 3 ) 2 C 3 produces ERYTRO isomers!!! w3.ualg.pt\~abrigas QOI 0809 A3 70
71 Stereochemistry of Addition Pro-Fischer Analysis C 3 3 C C(C 3 ) 2 addition reaction? up C 3 down C 3 up C(C 3 ) 2 up C(C 3 ) 2 C 3 C 3 syn addition anti addition w3.ualg.pt\~abrigas QOI 0809 A3 71
72 Biological Discrimination => w3.ualg.pt\~abrigas QOI 0809 A3 72
73 Racemic Mixtures Equal quantities of d- and l-enantiomers. Notation: (d,l) or (±) No optical activity. The mixture may have different b.p. and m.p. from the enantiomers! => w3.ualg.pt\~abrigas QOI 0809 A3 73
74 Racemic Products If optically inactive reagents combine to form a chiral molecule, a racemic mixture of enantiomers is formed. w3.ualg.pt\~abrigas QOI 0809 A3 74 =>
75 Optical Purity Also called enantiomeric excess. Amount of pure enantiomer in excess of the racemic mixture. If o.p. = 50%, then the observed rotation will be only 50% of the rotation of the pure enantiomer. Mixture composition would be => w3.ualg.pt\~abrigas QOI 0809 A3 75
76 Resolution of Enantiomers React a racemic mixture with a chiral compound to form diastereomers, which can be separated. w3.ualg.pt\~abrigas QOI 0809 A3 76 =>
77 Chromatographic Resolution of Enantiomers => w3.ualg.pt\~abrigas QOI 0809 A3 77
78 LINKS w3.ualg.pt\~abrigas QOI 0809 A3 78
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