Stereo Chemistry Flashcards
What are isomers
Molecules that have the same molecular formula but different structural formulas are called isomers
When do structural isomers occur
Structural isomers occur when the atoms are bonded together in a different order in each isomer
What is stereoisomerism
Stereoisomerism is a type of isomerism in which molecules have the same molecular formula and the atoms are bonded together in the same order but the arrangement of the atoms in space is different, making it impossible to superimpose one molecule onto the image of the other
What is the difference between trans and cis
Trans - opposite sides of the double bond
Cis - same side of the double bond
When do geometric isomers occur
- can occur when there is restricted rotation around a carbon - carbon double bond or a carbon-carbon single bond in a cyclic compound as there is no free rotation of the groups of atoms around a double bond
What groups must be attached to geometric isomers
- must have two different groups attached to each of the carbon atoms that make up the bond with restricted rotation
How can geometric isomers be labelled
can be labelled cis or trans according to whether the substituent groups are on the
same side (cis) or on different sides (trans) of the bond with restricted rotation
What differences do geometric isomers have
- have differences in physical properties, such as melting point and boiling point
- can have differences in chemical properties
Which compounds do optical isomers occur in
Occurs in compounds in which four different groups are arranged tetrahedrally around a central carbon atom (chiral carbon or chiral centre)
What type of images are optical isomers
Optical isomers are both mirror images of each other and non superimposable
Are optical isomers symmetric or asymmetric
Are asymmetric
What physical property do optical isomers differ in
However they differ in the way they affect plane polarised light. One optical isomer will rotate polarised light to the right and the other to the left
What is a racmic mixture
When mixed in equal amounts are optically inactive because the rotational effect of the plane polarised light cancels out - this is called a racemic mixture
What chemical properties do optical isomers
Have identical chemical properties except when in a chiral environment such as that found in biological systems (only one optical isomer is usually present)
How can optical isomers be described
Can be described as enatiomers
To draw the other optical isomer
Take wedge and hash bond and switch them round
