Practice Assigning E and Z Configuration
What is the absolute configuration?
Common Questions
What do E and Z mean in organic chemistry?
E (entgegen, "opposite") means the two highest-priority groups are on opposite sides of the double bond. Z (zusammen, "together") means they are on the same side. Priority is assigned using CIP rules.
How do you assign E or Z configuration?
Rank the two substituents on each carbon of the double bond using CIP priority rules (higher atomic number = higher priority). If the two higher-priority groups are on the same side, it is Z; on opposite sides, it is E.
What is the difference between E/Z and cis/trans?
Cis/trans only works for disubstituted alkenes (two groups). E/Z works for all alkenes, including trisubstituted and tetrasubstituted, because it uses CIP priority rather than identical-group comparisons.
Why can't double bonds rotate freely?
A carbon-carbon double bond consists of one sigma bond and one pi bond. The pi bond locks the two carbons in a planar arrangement, preventing rotation without breaking the bond (which requires significant energy).