有机化学英文课件chapter3

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1、 different compounds with the same molecular formula isomers with a different connectivity isomers with the same connectivity but a different orientation of their atoms in space from the Greek, cheir, hand an object that is not superposable on its mirror image an object that lacks chirality; one tha

2、t lacks handedness an achiral object has at least one element of symmetry an imaginary plane passing through an object dividing it so that one half is the mirror image of the other half a point so situated that identical components are located on opposite sides and equidistant from that point along

3、the axis passing through ituPlane of symmetry (contd)H H O OO O H Hm irrorm irrorplaneplaneuThe most common (but not the only) cause of chirality in organic molecules is a tetrahedral atom, most commonly carbon, bonded to four different groupsuA carbon with four different groups bonded to it is call

4、ed a all chiral centers are stereocenters, but not all stereocenters are chiral centers (see Figure 3.5) stereoisomers that are nonsuperposable mirror images refers to the relationship between pairs of objectsu2-Butanol has one chiral center here are four different representations for one enantiomer

5、 using (4) as a model, here are two different representations for the enantiomer of (4)O HCH3CCH2CH3HO HCH3CCH2CH3HHOHOH(1)(2)(3)(4)O O H H( (4 4) )O O H HO O H Hr re ep pr re es se en nt ta at ti io on ns s f fo or r t th he ee en na an nt ti io om m e er r o of f ( (4 4) )uThe enantiomers of lacti

6、c acid drawn in two different representationsC CC CH H O OC CH H3 3H HO OH H O OC CC CO OH HC CH H3 3H HO OO OH HO O H HO O H HO OO O H HH HO OO Ou2-ChlorobutaneC C H H3 3C C H H C C H H2 2C C H H3 3C C l lC C l lH HC C l l H Hu3-ChlorocyclohexeneC Cl lC Cl luA nitrogen chiral centerN NC C H H2 2C C

7、 H H3 3H H3 3C CN NC C H H3 3C C H H3 3C C H H2 2A A pair of enantiom ers pair of enantiom ers+ + +uPriority rules1. Each atom bonded to the chiral center is assigned a priority based on atomic number; the higher the atomic number, the higher the priority2. If priority cannot be assigned per the ato

8、ms bonded to the chiral center, look to the next set of atoms; priority is assigned at the first point of difference( (5 53 3) )( (3 35 5) )( (1 17 7) )( (1 16 6) )( (8 8) )( (7 7) )( (6 6) )( (1 1) )I In nc cr re ea as si in ng g p pr ri io or ri it ty y- -H H - -C C H H3 3 - -N N H H2 2 - -O O H H

9、 - -S SH H - -C Cl l - -B Br r - -I II In nc cr re ea as si in ng g p pr ri io or ri it ty y( (8 8) )( (7 7) )( (6 6) )( (1 1) )- -C CH H2 2- -O O H H- -C CH H2 2- -N N H H2 2- -C CH H2 2- -C C H H3 3- -C CH H2 2- -H H3. Atoms participating in a double or triple bond are considered to be bonded to a

10、n equivalent number of similar atoms by single bonds- -C CH H= =C CH H2 2O O- -C CH HC CC CH HO OH HC CC CO OC C- -C CH H- -C CH H2 2C CC CC CH HC CC CC CC Ci is s t tr re ea at te ed d a as si is s t tr re ea at te ed d a as si is s t tr re ea at te ed d a as s1. Locate the chiral center, identify

11、its four substituents, and assign priority from 1 (highest) to 4 (lowest) to each substituent2. Orient the molecule so that the group of lowest priority (4) is directed away from you3. Read the three groups projecting toward you in order from highest (1) to lowest priority (3)4. If the groups are re

12、ad clockwise, the configuration is ; if they are read counterclockwise, the configuration is (S)-2-ChlorobutaneC C l lH H2 23 3S S1 1 (R)-3-Chlorocyclohexene (R)-Mevalonic acidClH2 23 3R R1 12 23 34 41 1H H O OO O H HO OH H O O C C H H3 32 23 31 1R RuFor a molecule with 1 chiral center, 21 = 2 stere

13、oisomers are possibleuFor a molecule with 2 chiral centers, a maximum of 22 = 4 stereoisomers are possibleuFor a molecule with n chiral centers, a maximum of 2n stereoisomers are possibleu2,3,4-Trihydroxybutanal two chiral centers 22 = 4 stereoisomers exist; two pairs of enantiomers stereoisomers th

14、at are not mirror images refers to the relationship among two or more objectsC CC CH HO O H HC C H H O OO O H HC C H H2 2O O H HH HC CC CH HH H O OC C H H O OH H O OC C H H2 2O O H HH HC CC CH HO O H HC C H H O OH HC C H H2 2O O H HH H O OC CC CH HH H O OC C H H O OH HC C H H2 2O O H HO O H HA pair

15、of enantiom ersA pair of enantiom ers(Erythreose)(Erythreose)A pair of enantiom ersA pair of enantiom ers(Threose)(Threose)u2,3-Dihydroxybutanedioic acid (tartaric acid) two chiral centers; 2n = 4, but only three stereoisomers exist an achiral compound possessing two or more chiral centers that also

16、 has chiral isomersC CC CH HO O H HC C O O O O H HO O H HC C O O O O H HH HC CC CH HH H O OC C O O O O H HH H O OC C O O O O H HH HC CC CH HO O H HC C O O O O H HH HC C O O O O H HH H O OC CC CH HH H O OC C O O O O H HH HC C O O O O H HO O H HA pai r of enanti om ersA pai r of enanti om ersA m eso c

17、om poundA m eso com pound(pl ane of sym m etry)(pl ane of sym m etry)u2-MethylcyclopentanolH HH HC C H H3 3O O H HH HH HH H O OH H3 3C CH HO O H HC C H H3 3H HH H O OH HH HH H3 3C Ccis-cis-2-M ethylcyclopentanol2-M ethylcyclopentanol (a pair of enantiom ers) (a pair of enantiom ers)t rans-t rans-2-M

18、 ethylcyclopentanol2-M ethylcyclopentanol (a pair of enantiom ers) (a pair of enantiom ers)diastereom ersdiastereom ersu1,2-CyclopentanediolHHOH HOHHOH HOHHOOHHOHHHHOciscis- -1,2-Cyclopentanediol1,2-Cyclopentanediol (a meso (a meso compound) compound)trans-trans-1,2-Cyclopentanediol1,2-Cyclopentaned

19、iol (a pair of enantiomers (a pair of enantiomers) )diastereomersdiastereomersucis-3-MethylcyclohexanolO OH HH H3 3C CH HO OC CH H3 3utrans-3-MethylcyclohexanolO OH HH H3 3C CH HO OC CH H3 3C C o om m p po ou un nd ds s w w i it th h t th he es sa am m e e m m o ol le ec cu ul la ar r f fo or rm m u

20、 ul la aC C o on nf fo or rm m a at ti io on na al lI Is so om m e er rs sr ro ot ta at ti io on n a ab bo ou ut ts si in ng gl le e b bo on nd ds s w w i it th h c ch hi ir ra al l c ce en nt te er rs sS St te er re eo oi is so om m e er rs sM M e es so oC C o om m p po ou un nd ds sE En na an nt t

21、i io om m e er rs sC C o on ns st ti it tu ut ti io on na al lI Is so om m e er rs sC Ci is s, , T Tr ra an ns s ( (E E, , Z Z) ) I Is so om m e er rs s( (c ca an n b be e c ca al ll le ed dd di ia as st te er re eo om m e er rs s) )C C o on nf fo or rm m a at ti io on ns sr ro ot ta at ti io on n r

22、 re es st tr ri ic ct te ed dd di if ff fe er re en nt tc co on nn ne ec ct ti iv vi it ty yD D i ia as st te er re eo om m e er rs ss st te er re eo oi is so om m e er rs sb bu ut t n no o c ch hi ir ra al l c ce en nt te er rs sE En na an nt ti io om m e er rs so on ne e c ch hi ir ra al l c ce en

23、 nt te er rm m o or re e t th ha an no on ne e c ch hi ir ra al l c ce en nt te er rc ch hi ir ra al la ac ch hi ir ra al l n no ot t m m i ir rr ro or r i im m a ag ge es sm m i ir rr ro or r i im m a ag ge es sA A t tr ro op pi is so om m e er rs ss sa am m e ec co on nn ne ec ct ti iv vi it ty yu

24、Enantiomers have identical physical and chemical properties in achiral environmentsuDiastereomers are different compounds and have different physical and chemical properties meso tartaric acid, for example, has different physical and chemical properties from its enantiomers (see Table 3.1) light vib

25、rating in all planes perpendicular to its direction of propagation light vibrating only in parallel planes refers to a compound that rotates the plane of plane-polarized light plane-polarized light is the vector sum of left and right circularly polarized light circularly polarized light reacts one w

26、ay with an R chiral center, and the opposite way with its enantiomer the result of interaction of plane-polarized light with a chiral compound is rotation of the plane of polarization a device for measuring the extent of rotation of plane-polarized light the number of degrees, , through which a comp

27、ound rotates the plane of polarized light refers to a compound that rotates the plane of polarized light to the right refers to a compound that rotates of the plane of polarized light to the left observed rotation when a pure sample is placed in a tube 1.0 dm in length and concentration in g/mL (den

28、sity); for a solution, concentration is expressed in g/ 100 mLD DD DH H3 3C CC CO O H HH HC CO O O O H HC CH H3 3C CH H O OH HC CO OO O H H a way of describing the composition of a mixture of enantiomers the difference between the percentage of two enantiomers in a mixture optical purity is numerica

29、lly equal to enantiomeric excess, but is experimentally determinedx x 1 10 00 0 x x 1 10 00 0 R R + + S S R R - - S S E En na an nt ti io om m e er ri ic c e ex xc ce es ss s ( (e ee e) ) = = = % % R R - - % % S S a commercial synthesis of naproxen, a nonsteroidal anti-inflammatory drug (NSAID), giv

30、es the S enantiomer in 97% eeCalculate the percentages of the R and S enantiomers in this mixtureH H3 3C CO OC CO O O O H HC CH H3 3( (S S) )- -N N a ap pr ro ox xe en n an equimolar mixture of two enantiomers because a racemic mixture contains equal numbers of dextrorotatory and levorotatory molecu

31、les, its specific rotation is zero the separation of a racemic mixture into its enantiomersuOne means of resolution is to convert the pair of enantiomers into two diastereomers diastereomers are different compounds and have different physical propertiesuA common reaction for chemical resolution is s

32、alt formation after separation of the diastereomers, the enantiomerically pure acids are recoveredR RC CO O O OH HB BR RC CO OO O- -H HB B+ +( (R R , , R R ) )- -S Sa al lt t + + ( (S S, ,R R) )- -S Sa al lt t) )( (R R) )- -B Ba as se e( (R R , , S S) )- -C Ca ar rb bo ox xy yl li ic ca ac ci id d+

33、+: : racemic acids can be resolved using commercially available chiral bases such as 1-phenylethanamine racemic bases can be resolved using chiral acids such asN NH H2 2N NH H2 2( (S S) )- -1 1- -P Ph he en ny yl le et th ha an na am m i in ne e( (R R) )- -1 1- -P Ph he en ny yl le et th ha an na am

34、 m i in ne eH H3 3C C C CH H3 3C CO O O O H HH HO O O O C CC CH H3 3O O H HH HO OO OO OO O H HO OH HO O H HH H O OO OO OO O H H( (2 2R R, , 3 3R R) )- -( (+ +) )- -T Ta ar rt ta ar ri ic c a ac ci id d( (S S) )- -( (- -) )- -M M a al li ic c a ac ci id d( (1 1S S, , 3 3R R ) )- -( (+ +) )- -C C a am

35、 m p ph ho or ri ic c a ac ci id duEnzymes as resolving agentsH H3 3C CO OC CH H3 3O OO O E Et tO O C CH H3 3H H3 3C CE Et tO OO ON N a aO O H H , , H H2 2O O2 2. . H HC Cl l , , H H2 2O OH H3 3C CO OC CH H3 3O OO O H HE Et th hy yl l e es st te er r o of f ( (S S) )- -n na ap pr ro ox xe en nE Et t

36、h hy yl l e es st te er r o of f ( (R R) )- -n na ap pr ro ox xe en n( (n no ot t a af ff fe ec ct te ed d b by y t th he e e es st te er ra as se e) )+ +1 1. . e es st te er ra as se e( (S S) )- -N N a ap pr ro ox xe en n the 20 most common amino acids have a central carbon, called an -carbon, bond

37、ed to an NH2 group and a COOH group in 19 of the 20, the -carbon is a chiral center 18 of the 19 -carbons have the R configuration, one has the S configuration in the D,L system, all have the L configuration at neutral pH, an amino acid exists as an internal salt in this structural formula, the symb

38、ol = a side chainO O- -O OH H3 3N NR Rs si id de e c ch ha ai in nI Io on ni iz ze ed d o or r z zw w i it tt te er ri io on nf fo or rm m o of f a an n a am m i in no o a ac ci id d are long chains of amino acids covalently bonded by amide bonds formed between the carboxyl group of one amino acid a

39、nd the amino group of another amino acidO OH HN NN NH HO OR RH HN NO O- -O OO OH H3 3N NR RR RR Rn nf fo or r m m o os st t p pr ro ot te ei in ns s, , n n= = 1 10 0- -7 75 50 0uExcept for inorganic salts and a few low-molecular-weight organic substances, the molecules of living systems are chiraluA

40、lthough these molecules can exist as a number of stereoisomers, generally only one is produced and used in a given biological systemuConsider chymotrypsin, a protein-digesting enzyme in the digestive system of animals chymotrypsin contains 251 chiral centers the maximum number of stereoisomers possi

41、ble is 2251 there are only 238 stars in our galaxy!uEnzymes are like hands in a handshake the substrate fits into a binding site on the enzyme surface a left-handed molecule will only fit into a left-handed binding site and a right-handed molecule will only fit into a right-handed binding site enantiomers have different physiological properties because of the handedness of their interactions with other chiral molecules in living systems a schematic diagram of an enzyme surface capable of binding with (R)-glyceraldehyde but not with (S)-glyceraldehyde