Fundamentals 1

• The geometric property of a molecule (or rigid object) of being non-superimposable on it’s mirror image • Contain no rotation-reflection axis- Sn • Including mirror planes- S1 and centre of inversion S2

• Proper rotation • Plane of symmetry • Center of inversion symmetry • Improper roation

• symbol = Cn (n= degree of rotation 360/n) • Element = Proper rotation axis • Operation= rotation by 360/n degrees • Principle axis - highest order proper rotation axis

• Symbol= sigma • Element = reflection plane • Operation = reflection in the plane - not the same as reflection in external mirror as that would have undergone translation

• Symbol= i • Element = inversion centre - always at centre of molecule • Operation = inversion of point x,y,z to -x,-y-z

• Sn • ELement- improper rotation axis • Operation- rotation by 360/n then reflection perpendicular to reflection axis

• S1= reflection- as rotating 360 degrees so just reflection • S2= inversion

• Used for a molecule devoid or any symmetry elements - such as tetrahedral carbon atom surrounded by 4 different substituents

• No • Chiral molecules can still possess Cn axes even when they are non-superimposable on their mirror image

• Lacking one particular symmetry element • For chiral dissymmetric molecules this is the Sn axis

• Property of chirality is to do with the molecule and is unrelated to the enantiomeric composition- which is make up of collection of molecules

• Either of a pair of chemical compounds whose molecular structures have a nonsuperimposable mirror-image relationship to each other • A molecule that possesses the property of chirality with have two possible mirror-image, non-superimposable stereoisomers known as enantiomers

• Is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms, but differ in the three-dimensional orientations of their atoms in space.

• Sometimes used as a synonym of enantiomers but it is a redundant term and strongly discouraged • Not all chiral, non-racemic compounds have measurable optical rotations

• An atom for which permutation of any two ligands generates a stereoisomer • Its substituent groups give rise to chirality

• Show identical scalar physical properties in an achiral environment • In a chiral environment (enzyme interior or chiral stationary phase) individual enantiomers may show different scalar physical properties

• Refers to stereogenic centre in a chiral molecule • Chirality is property of molecule as a whole not the atoms in it • May have stereo centres but not be a chiral molecule

• Yes- racemic distributions of chiral conformations lead to macroscopic achirality

• Butane - achiral compound but has chiral conformers • Two achiral co-planar conformations - syn and anti • But, the enantiomeric chiral conformations being rapidly interconvertible and equal in energy are always present in a 50:50 ratio- racemic • So from a macroscopic perspective butane is an achiral compound because its enantiomeric forms are far too short-lived for separation of its enantiomeric conformers to be possible.

• No • If it did it would forget which enantiomer it came from and have a 50:50 chance of then converting to the opposite enantiomeric conformation

• R/S stereodescriptors • Rank groups in order of priority • Lowest group pointing away • Highest to lowest priority- clockwise= R and anticlockwise= S

• Look down from one end of axis • Substituents that are further away are lower priority • Clockwise= R etc

• Cahn-Ingold-Prelog (CIP) priority rules • Based on atomic weights

• Each atom in the multiple bond is regarded as being associated with a phantom (duplicate atom) at the other end of the double bond • e.g. C=O is treated as though the carbon has two single bonds to two oxygens