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1、7.13 Chemical Reactions That Produce Diastereomers,In order to know understand stereochemistry of product, you need to know two things: (1) stereochemistry of alkene (cis or trans; Z or E) (2) stereochemistry of mechanism (syn or anti),Stereochemistry of Addition to Alkenes,Br2,R,S,R,S,meso,anti add
2、ition to trans-2-butene gives meso diastereomer,Bromine Addition to trans-2-ButeneFig. 7.14 (p 284),Br2,R,R,S,S,50%,50%,Bromine Addition to cis-2-ButeneFig. 7.15 (p 285),anti addition to cis-2-butene gives racemic mixture of chiral diastereomer,+,RCO3H,R,R,S,S,syn addition to trans-2-butene gives ra
3、cemic mixture of chiral diastereomer,Epoxidation of trans-2-ButeneProblem 7.17 (p 285),50%,50%,+,R,S,R,S,Epoxidation of cis-2-ButeneProblem 7.17 (p 285),syn addition to cis-2-butene gives meso diastereomer,RCO3H,meso,of two stereoisomers of a particular starting material, each one gives differentste
4、reoisomeric forms of the product related to mechanism: terms such assyn addition and anti addition refer tostereospecificity,Stereospecific reaction,.,Stereospecific reaction,a single starting material can give two or morestereoisomeric products, but gives one of themin greater amounts than any othe
5、r,+,CH3,H,CH3,H,68%,32%,Stereoselective reaction,7.14 Resolution of Enantiomers,separation of a racemic mixture into its two enantiomeric forms,enantiomers,Strategy,enantiomers,2P(+),diastereomers,Strategy,enantiomers,2P(+),diastereomers,C(+)P(+),C(-)P(+),Strategy,enantiomers,2P(+),diastereomers,C(+
6、)P(+),C(-)P(+),P(+),P(+),C(+),C(-),Strategy,7.15Stereoregular Polymers,atactic isotactic syndiotactic,Atactic Polypropylene,random stereochemistry of methyl groups attached to main chain (stereorandom) properties not very useful for fibers etc. formed by free-radical polymerization,Isotactic Polypro
7、pylene,stereoregular polymer; all methyl groups onsame side of main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions,Syndiotactic Polypropylene,stereoregular polymer; methyl groups alternate side-to-side on main chain useful properties prepared by coordi
8、nation polymerization under Ziegler-Natta conditions,7.16Stereogenic CentersOther Than Carbon,Silicon,silicon, like carbon, forms four bonds in its stable compounds and many chiral silicon compounds have been resolved,Si,Si,d,d,a,b,c,a,b,c,Nitrogen in amines,pyramidal geometry at nitrogen can produc
9、e a chiral structure, but enantiomers equilibrate too rapidly to be resolved,N,N,:,:,a,b,c,a,b,c,very fast,Phosphorus in phosphines,pyramidal geometry at phosphorus can produce a chiral structure; pyramidal inversion slower than for amines and compounds of the type shown have been resolved,P,P,:,:,a,b,c,a,b,c,slow,Sulfur in sulfoxides,pyramidal geometry at sulfur can produce a chiral structure; pyramidal inversion is slow and compounds of the type shown have been resolved,S,S,:,:,a,b,O_,a,b,O_,slow,+,+,
