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Unformatted text preview: Chapter 9: Stereochemistry Handedness refers to the difference in mirror images of objects and is mainly a result of the tetrahedral stereochemistry of sp 3-hybridized carbon atoms . o Molecular handedness makes crucial interactions between enzymes and their substrates possible. Isomers are compounds that have the same molecular formula but different structures. There are two different types of isomers: o Constitutional isomers have their atoms connected in a different order. o Stereoisomers have the same molecular formula and connectivity of atoms, but have different 3D arrangements ( enantiomers , diastereomers ). 9.1 - E n a n t iomers Two Groups of Molecules: o Identical Molecules a molecule and its mirror image are the same or super-imposable meaning they can be placed on top of each other so that all atoms coincide (achiral). o Non-Identical Molecules a molecule and its mirror image are not the same or non-super-imposable meaning they cant be placed on top of each other so that all the atoms coincide ( chiral ). Enantiomers are a type of stereoisomer, where a molecule and its mirror image are non-identical & non-super imposable (Greek enantio meaning opposite). o Exhibit the same physical properties (boiling point, melting point, solubility) o Differ in biological activities & the sign of specific rotation. o Results when a tetrahedral carbon is bonded to four different substituents or groups, which doesnt always include hydrogen. 9.2 Ch i r a l i ty: T he Re ason for H a n dedness Achiral refers to a molecule and its mirror image being identical & super- imposable. o A molecule that has a plane of symmetry in any of its possible conformations must be identical to its mirror image and is said to be non- chiral. o Optically inactive Chiral refers to a molecule and its mirror image being non-identical & non- super-imposable and thus exist in two enantiomeric forms (Greek cheir meaning hand)....
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