Chem 130 Chirality

• Cis/trans isomers on rings and double bonds are stereoisomers and achiral stereoisomers
• Enantiomers are nonsuperimposable mirror images, for example: 2-butanol
• Objects with nonsuperimposable mirror images are examples of chiral molecules
• If an object and its mirror image are superposable, they are identical and there is no possibility of enantiomerism
• Objects that are nonsuperposable on their mirror images are chiral and are called enantiomers
• Enantiomers always come in pairs
• The most common cause of chirality among organic molecules is the presence of a carbon with four different groups
• A carbon with four different groups bonded to it is a stereocenter
• Objects that are superposable on their mirror images are achiral
• Molecules with chiral centers that are achiral are called mesoenantiomers and diastereomers
• For a molecule with n stereocenters, the maximum number of possible stereoisomers is 2^n
• The 2^n rule applies equally well to molecules with any number of stereocenters
• Diastereomers are stereoisomers that are not mirror images but are chiral
• The R,S system is a way to distinguish between enantiomers without having to draw them and point to one or the other
• The first step in assigning an R or S configuration to a stereocenter is to arrange the groups on the stereocenter in order of priority based on atomic number
• To assign an R or S configuration, orient the molecule in space so that 4 is directed away from you, then read the three groups from highest (1)
• Orient the molecule so that group 4 is directed away from you, then project groups 1-3 towards you
• If the order is clockwise, the configuration is R. If counterclockwise, the configuration is S
• Ordinary light consists of light waves oscillating in all planes perpendicular to its direction of propagation
• Plane-polarized light consists of light waves oscillating only in parallel planes
• A polarimeter is an instrument for measuring a compound's ability to rotate the plane of plane-polarized light
• Optically active compounds are capable of rotating the plane of plane-polarized light
• Dextrorotatory (+) means clockwise rotation of plane-polarized light
• Levorotatory (-) means counterclockwise rotation of plane-polarized light
• A pure sample of each enantiomer will result in a rotation of light in opposite directions
• A racemic (50/50) mixture of enantiomers will have no rotation of light
• Enantiomers in an achiral environment have the same properties and cannot be physically separated
• Enantiomers in a chiral environment have different properties and can be physically separated
• In reactions, both enantiomers would react in a chiral environment in life
• In reactions, only the appropriate enantiomer would react in a chiral environment in the lab
• Molecules in living systems are chiral, with usually only one stereoisomer found in nature
• Enzymes have many stereocenters, with only one stereoisomer produced and used by any given organism
• Interactions between molecules in living systems take place in a chiral environment, where a molecule and its enantiomer may elicit different physiological responses
• If two objects cannot be superimposed on each other, then they are enantiomers (mirror images)
• A molecule can be superimposed on its mirror image if there are no differences between them, but they will not be identical because their spatial arrangement is reversed
• The chiral carbon is the one that has four different groups attached to it.
• Chiral compounds can exist as pairs of mirror image forms called enantiomers
• A chiral object has no plane of symmetry
• The term "chiral" refers to an object that has non-superimposable mirror images