13.2 stereoisomerism Flashcards
stereoisomerism definition
compounds with the same structural formula but with a different arrangement in space
what are the 2 types of isomerism?
- E/Z isomerism
- optical isomerism
when does E/Z isomerism occur?
occurs in compounds with a C=C double bond
why does E/Z isomerism arise?
arises because rotation about the double bond is restricted and the groups attached to each carbon atom are therefore fixed relative to each other
why does the pi bond prevent the movement of carbon bonds around the double bond?
pi- bond’s electron density above and below the plane of the sigma bond
what are the requirements for E/Z isomerism?
- C=C double bond
- different groups attached to each carbon atom of the C=C bond
what are the requirements for cis- trans isomerism?
- C=C double bond
- 2 H attached to C=C
- 2 other groups to C=C
what are the E isomer?
hydrogen atoms are diagonally opposite each other
what are the Z isomer?
hydrogen atoms are on the same side of the molecule
what are cis isomers also called?
z isomer
what are trans isomers also called?
E isomer
what are the 2 ways in assigning priority using Cahn- Ingold- Prelog (CIP) rules
- atoms attached directly to the carbon atom-> higher atomic number, higher the priority
- find the first point of difference-> higher atomic number, higher the priority
identify whether pent-1-ene shows E/Z isomerism?
no isomerism
identify whether 2-methylpent-2-ene shows E/Z isomerism?
no isomerism
identify whether 2,3- dichlorobut-2-ene shows E/Z isomerism?
isomerism
