Stereochemistry This is study of the 3 dimensional arrangement in space of molecules In organic chemistry,subtle differences in spatial arrangements can give rise to prominent effects. E.g.the isomers of butenoic acid: H OH HO -oh HO fumaric acid,mp287°C maleic acid,mpl38°C essential metabolite toxic irritant The cis isomer(maleic acid)is toxic,whereas the trans isomer(fumaric acid)is an essential metabolite for plants and animals This chapter deals with the stereochemical concept of chirality. Ch05 Stereochemistry (landscape) PageI
Ch05 Stereochemistry (landscape) Page 1 Stereochemistry This is study of the 3 dimensional arrangement in space of molecules. In organic chemistry, subtle differences in spatial arrangements can give rise to prominent effects. E.g. the isomers of butenoic acid: The cis isomer (maleic acid) is toxic, whereas the trans isomer (fumaric acid) is an essential metabolite for plants and animals. This chapter deals with the stereochemical concept of chirality
Chirality Chirality means"handedness". Every object has a mirror image,but if a molecule's mirror image is different from the molecule,it is said to be a chiral molecule. Chiral objects include:hands,feet,gloves,screws,cork screws Achiral objects have mirror images that are identical to the object. achiral(not chiral) chiral right hand left hand Cho5 Stereochemistry (landscape) Page 2
Ch05 Stereochemistry (landscape) Page 2 Chirality Chirality means “handedness”. Every object has a mirror image, but if a molecule’s mirror image is different from the molecule, it is said to be a chiral molecule. Chiral objects include: hands, feet, gloves, screws, cork screws Achiral objects have mirror images that are identical to the object
Common Chiral Objects mirror mirror mirror Chirality in Organic Molecules If a mirror image of a molecule can be placed on top of the original,and the 3 dimensional arrangement of every atom is the same,then the two molecules are superimposable,and the molecule is achiral. If a molecule has a non superimposable mirror image,it is chiral. Ch05 Stereochemistry (landscape) Page 3
Ch05 Stereochemistry (landscape) Page 3 Common Chiral Objects Chirality in Organic Molecules If a mirror image of a molecule can be placed on top of the original, and the 3 dimensional arrangement of every atom is the same, then the two molecules are superimposable, and the molecule is achiral. If a molecule has a non superimposable mirror image, it is chiral
Consider stereoisomers of 1,2-dichlorocyclopentane: same compound different compounds H H cis-1,2-dichlorocyclopentane trans-1,2-dichlorocyclopentane (achiral) (chiral) ●201白onEonir The cis isomer has a superimposable mirror image-achiral. The trans isomer is non-superimposable on its mirror image-chiral. Such pairs of non superimposable mirror images are called enantiomers. Every chiral compound has enantiomers. Achiral compounds do not have enantiomers. Ch05 Stereochemistry (landscape) Page 4
Ch05 Stereochemistry (landscape) Page 4 Consider stereoisomers of 1,2-dichlorocyclopentane: The cis isomer has a superimposable mirror image – achiral. The trans isomer is non-superimposable on its mirror image – chiral. Such pairs of non superimposable mirror images are called enantiomers. Every chiral compound has enantiomers. Achiral compounds do not have enantiomers
Chiral Carbon Atoms Rings are not essential for chirality,consider 2-bromobutane: mirror CH; CH; *C…H H.C* CH2CH2 Br Br CH>CH3 2-Bromobutane cannot be superimposed on its mirror image-it is chiral,and it exists in two enantiomeric forms. Any carbon bound to 4 different groups will be a chiral centre Ch05 Stereochemistry (landscape) Page5
Ch05 Stereochemistry (landscape) Page 5 Chiral Carbon Atoms Rings are not essential for chirality, consider 2-bromobutane: 2-Bromobutane cannot be superimposed on its mirror image – it is chiral, and it exists in two enantiomeric forms. Any carbon bound to 4 different groups will be a chiral centre