20.3 Stereoisomerism

Question 1

Types of isomers (isomer tree)

Answer 1

Question 2

How cis-trans and E-Z isomers are created

Answer 2

When free rotation in a molecule is restricted - double bond/cycle -> position of the group must be referenced to the plane

Question 3

Examples of cis-trans in alkene and cycloalkane

Answer 3

Question 4

When E-Z isomers are instead of cis-trans

Answer 4

When all the groups attached are different

Question 5

Hoe E-Z isomers distinguished

Answer 5

Cahn–Ingold–Prelog rules of priority

Rule 1: identify higher atomic number - higher priority.

Rule 2: if atoms same - same rule to the next bonded atom

If two highest priority on same side of double bond - isomer is ‘Z’ (zusammen)

If two highest priority groups on opposite sides of double bond - isomer is ‘E’ (entgegen)

Question 6

Physical properties of configurational isomers

Answer 6

Different physical properties depeding on polarity and shape -> different melting, boiling points, solubility

Question 7

What are optical isomers

Answer 7

Molecules which are mirror images of each other with chiral central carbon

Molecules are non-superimposable (do not match) - enantiomers

Question 8

Define racemate

Answer 8

Racemate/racemic mixture - mixture containing equal amounts of enantionmers - does not turn polarised light (optically inactive)

Question 9

Define diastereomers

Answer 9

Molecules which have more than one chiral center + are not complete optical isomers

Question 10

Chemical properties of enantiomers vs diastereomers

Answer 10

Diastereomers have different chemical properties

Enantiomers have identical physical and chemical properties with two exceptions:

1. Optical activity - turn plane-polarised light into different directions
2. Reactivity with other chiral molecules - enantiomers can be separated in racemate by resolution