When isomers have the same structural formula but differ in relative arrangement of atoms or groups are called

Options

A. Mesomers
B. Stereoisomers
C. Optical isomers
D. Geometrical mesomers

Answer

To answer the question, we need to identify the term used to describe isomers that have the same structural formula but differ in the relative arrangement of atoms or groups.

### Step-by-Step Solution:

1. **Understanding Isomers**:
Isomers are compounds that have the same molecular formula but differ in the arrangement of atoms. There are different types of isomers, including structural isomers and stereoisomers.

2. **Structural Formula**:
The structural formula represents the arrangement of atoms in a molecule. When isomers have the same structural formula, it means they contain the same types and numbers of atoms but are arranged differently.

3. **Relative Arrangement of Atoms or Groups**:
The key part of the question is the phrase "differ in relative arrangement of atoms or groups." This indicates that we are looking for a specific type of isomerism where the spatial arrangement of atoms or groups is different.

4. **Cis-Trans Isomerism**:
A common example of this type of isomerism is cis-trans isomerism (also known as geometric isomerism). In cis isomers, similar groups are on the same side of a double bond or ring structure, while in trans isomers, they are on opposite sides.

5. **Conclusion**:
Therefore, isomers that have the same structural formula but differ in the relative arrangement of atoms or groups are called **stereoisomers**. More specifically, when referring to the arrangement of groups around a double bond or a ring, they can be classified as **cis-trans isomers**.

### Final Answer:
Isomers that have the same structural formula but differ in the relative arrangement of atoms or groups are called **stereoisomers**.