Question

Which of the following will show geometrical isomerism? (a) 2 -methyl butene (b) Propene (c) Vinyl chloride (d) but-2-ene

Short answer

But-2-ene (d) will show geometrical isomerism.

Step-by-step solution

Understand Geometrical Isomerism

Geometrical isomerism occurs in alkenes where two, or more, different groups are attached to either side of the double-bonded carbon atoms. This results in restricted rotation about the double bond, leading to different spatial arrangements (cis and trans forms).

Analyze 2-methyl butene

2-Methyl butene can have the structure: \[ \text{CH}_2=\text{C}(-\text{CH}_3)-\text{CH}_2-\text{CH}_3 \]Here, the double bond between the second carbon atom and methyl group has two hydrogens on one carbon which do not allow for geometrical isomerism.

Analyze Propene

Propene, with the structure:\[ \text{CH}_3-\text{CH}=\text{CH}_2 \]has one hydrogen on one of the double-bonded carbons, which means only one arrangement is possible, ruling out geometrical isomerism.

Analyze Vinyl Chloride

Vinyl chloride's structure is:\[ \text{CH}_2=\text{CH}-\text{Cl} \]Here, the presence of identical hydrogen atoms on one of the sp2 carbons prevents different spatial arrangements, thus geometrical isomerism is not possible.

Analyze But-2-ene

But-2-ene has the structure:\[ \text{CH}_3-\text{CH}=\text{CH}-\text{CH}_3 \]The different groups on the doubly bonded carbon allows for two different arrangements: cis (same side) and trans (opposite side). This makes geometrical isomerism possible.

Key concepts

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). This double bond is what differentiates alkenes from alkanes, which only have single bonds. The presence of the double bond gives alkenes distinct chemical properties, such as increased reactivity compared to alkanes.
The simplest alkene is ethene, \(\text{C}_2\text{H}_4\). When naming alkenes, the position of the double bond is indicated with a number. For instance, but-2-ene has its double bond starting at the second carbon atom.

Alkenes are unsaturated hydrocarbons, meaning they have fewer hydrogen atoms than the corresponding alkane. This unsaturation allows for reactions like addition, where new atoms or groups can readily add to the carbon atoms of the double bond.

Alkenes play a significant role in organic chemistry because of their ability to form various compounds through reactions. This makes them some of the most versatile building blocks for the synthesis of other organic compounds.

• Contain at least one carbon-carbon double bond.
  
• More reactive than alkanes.
  
• Can undergo addition reactions.
  

Cis-Trans Isomerism

Cis-trans isomerism, a type of geometrical isomerism, occurs in alkenes. These isomers arise due to the restricted rotation around the carbon-carbon double bond, allowing for different spatial arrangements of groups attached to the double-bonded carbons.
"Cis" and "trans" describe the position of groups relative to each other:

• **Cis isomer**: The groups of interest are on the same side of the double bond.
  
• **Trans isomer**: The groups are on opposite sides of the double bond.
  

For cis-trans isomerism to occur, each carbon atom in the double bond must have two different groups attached. For example, in but-2-ene, the presence of methyl groups (\(\text{CH}_3\)) on both double-bonded carbons allows for these isomers. The restricted rotation around the double bond keeps the different conformations stable, unlike single bonds which can freely rotate.
This isomerism affects the physical properties significantly, such as boiling and melting points, as well as chemical reactivity. Understanding cis-trans isomerism is essential for grasping the complexities of organic molecules and their behavior in different chemical reactions.

Double Bonds in Chemistry

Double bonds are a defining feature of alkenes and several other functional groups in organic chemistry. They consist of one sigma bond and one pi bond, resulting from the overlap of atomic orbitals. These bonds limit the rotation around the carbon atoms involved, leading to phenomena like cis-trans isomerism.

The presence of a double bond impacts the physical and chemical characteristics of molecules:

• Double bonds are shorter and stronger than single bonds.
  
• They contribute to the molecule's overall energy profile, often making them sites of reactivity in organic reactions.
  
• Molecules with double bonds can partake in reactions such as hydrogenation, polymerization, and addition.
  

In a molecule such as but-2-ene, the double bond not only defines its chemical reactivity but also its structural isomer possibilities. This makes understanding double bonds crucial for students and chemists working with organic compounds.
Double bonds provide the rigidity and geometric configurations necessary to explore the vast diversity of organic materials and their potential uses.

Organic Chemistry

Organic chemistry is the branch of chemistry that studies carbon-containing compounds, typically featuring carbon-hydrogen bonds. It encompasses a variety of molecular forms and structures, from simple gases to complex macromolecules. Alkenes are just one of the vast array of organic compounds studied in organic chemistry.

The study of organic chemistry is foundational for understanding biological systems, synthetic materials, and many industrial applications. It explores and manipulates molecules to produce drugs, plastics, fuels, and more. Here's why it's important:

• It helps in understanding the structure and function of organic molecules.
  
• It is crucial for the development and production of pharmaceuticals.
  
• It aids in the creation of new materials for various applications.
  

Organic chemistry combines principles of physics and chemistry to study the behavior and characteristics of organic molecules. In academic settings, it serves as a core subject that evolves into specialized fields such as medicinal chemistry or polymer chemistry, illustrating its broad influence on science and technology.