# Cos'è l'isomerismo EZ?

#### Risposta:

E-Z isomerism is a type of stereoisomerism that exists because of restricted rotation about double bonds.

#### Spiegazione:

In stereoisomers, the atoms are joined in the same order, but they have a different spatial arrangement.

In E-Z isomers you must have:

• restricted rotation, often involving a "C=C" doppio legame
• two different groups on one end of the bond and two different groups on the other end.

Un alchene come but-2-ene ha due gruppi diversi su ciascun carbonio alchenico.

Può esistere come E-Z isomeri che differiscono nelle posizioni dei sostituenti sugli atomi a doppio legame.

The substituents can be given "priorities", with atoms with higher atomic numbers given higher priorities (the Cahn-Ingold-Prelog rules).

If the highest priority groups for each carbon are on the same side of the molecule, we have the Z isomero.

If the highest priority groups for each carbon are on opposite sides of the molecule, we have the E isomero.

One way to remember the designations is to think of Z as Zame Zide (same side).

Dal "CH"_3 ha una priorità più alta di "H", it is pretty easy to determine that the butene isomers above are E e Z, Rispettivamente.

But what about the isomers of 2-methylbut-2-enoic acid (below)?

"CH"_3 ha una priorità più alta di "H" e "COOH" ha una priorità più alta di "CH"_3.

Angelic acid has the higher priority groups on the same side, so it is the Z isomero.

Tiglic acid has the higher priority groups on opposite sides, so it is the E isomero.