Difference Between E and Z Isomers

Thekey difference在E和Z之间isomersis thatE isomers have the substituents with higher priority in the opposite sides whereas the Z isomers have the substituents with higher priority on the same side.

E-Z命名法是一个符号系统，用于命名具有相同化学公式的不同异构体，但空间排列不同。此外，E和Z异构体是alkenes. These isomers get their name based on the position of the substituents attached to the double bond of the alkene.

内容

1.Overview and Key Difference
2.What are E Isomers
3.What are Z Isomers
4.Side by Side Comparison – E vs Z Isomers in Tabular Form
5.概括

What are E Isomers?

E异构体是烯烃在双键的相对侧具有更高优先级的取代基。字母“ e”来自entgegen在德语中，意思是“相反”。The basis of E-Z notation is a set of rules known as priority rules. They are the Cahn-Ingold-Prelog (CIP) rules. These are a set of rules to name the organic molecules, to specify them unequally.

使用CIP规则命名分子的步骤如下；

1. Identify chiral centers or double bonds present in the molecule.
2. Determine the priorities of the substituents attached to thechiral中心或双键。
3. Use either R/S system or E/Z system to name the compound.

The Priorities of the Substituents

• 首先考虑直接与手性中心或双键的原子 - 原子数较高，优先级较高
• If there are equal atoms present, then there is a tie. Then check the substituent groups to find a point of difference in atomic number.
• If still there is a tie, consider the atoms bonded to each of the atoms in the main chain and check whether there is a point of difference.

在上图中，E异构体在双键的相对侧具有高优先级取代基，而Z异构体则将这些取代基在同一侧。

When determining the priority of the substituents, first consider the atoms directly bonded to the double bond; in the above example, there are three Carbon atoms (C) and one hydrogen atom (H). Therefore, there is a tie because one of the two vinyl carbon atoms (carbon atoms in the double bond) have directly bonded carbon atoms. Then, to determine the high priority group, consider the atom that comes after these directly bonded carbon atoms. Since the substituent group attached to this vinyl carbon are a methyl group (-CH₃) and an ethyl group (-CH₂CH₃), the priority is given to the ethyl group. That is because the atom comes after the directly bonded carbon atom (directly bonded to the vinyl carbon) is a hydrogen atom in methyl group and a carbon in the ethyl group.

什么是z异构体？

Z异构体是烯烃在双键的同一侧具有更高优先级的取代基。字母“ z”来自Zusammenin German, which means “together”.

In the above image, the substituents with high priority are on the same side of the double bond in the Z isomer whereas the E isomer has those substituents in the opposite sides. Furthermore, the CIP rules determine the priority of these substituents. For the above example, the atoms directly bonded to the double bonded carbon are Carbon atoms (C) of methyl groups and hydrogen atoms (H). Since carbon atom (14) has a high atomic number when compared with hydrogen (1), the high priority is to the methyl group (-CH₃).

What is the Difference Between E and Z Isomers?

E Isomers vs Z Isomers
E isomers are alkenes having the substituents with higher priority on the opposite sides of the double bond.	Z异构体是烯烃在双键的同一侧具有更高优先级的取代基。
Meaning of the Nomenclature
字母“ e”来自entgegen在德语中，意思是“相反”。	字母“ z”来自Zusammenin German, which means “together”.
Relationship with other Nomenclatures
烯烃的E异构体属于跨异构体类别。	Z isomers of alkenes belong to cis isomer category.

概括–E vs ZIsomers

E-Z notation or nomenclature is used to name isomers having the same molecular formula and spatial structure, giving each isomer a uniqueness. The difference between E and Z isomers is that the E isomers have the substituents with higher priority in the opposite sides whereas the Z isomers have the substituents with higher priority on the same side.

Reference:

1. “E-Z Notation.” Wikipedia, Wikimedia Foundation, 10 Apr. 2018.Available here
2. Libretexts. “19.7: E,Z Notation.” Chemistry LibreTexts, Libretexts, 26 June 2017.Available here
3. Libretexts. “3.6 Cahn-Ingold Prelog Rules.” Chemistry LibreTexts, Libretexts, 21 July 2016.Available here

Image Courtesy:

1.’EZNotation’By Pete Davis – Own work, (Public Domain) viaCommons Wikimedia
2.’EZNotation’By Pete Davis – Own work, (Public Domain) viaCommons Wikimedia