Question

There are three different dichloroethylenes (molecular formula \(\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2}\) ), which we can designate \(\mathrm{X}, \mathrm{Y},\) and \(\mathrm{Z}\). Compound X has no dipole moment, but compound \(Z\) does. Compounds \(X\) and \(Z\) each combine with hydrogen to give the same product: $$ \mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2}(\mathrm{X} \text { or } \mathrm{Z})+\mathrm{H}_{2} \longrightarrow \mathrm{ClCH}_{2}-\mathrm{CH}_{2} \mathrm{Cl} $$ What are the structures of \(\mathrm{X}, \mathrm{Y},\) and \(\mathrm{Z} ?\) Would you expect compound \(Y\) to have a dipole moment?

Short answer

X: trans-1,2-dichloroethylene, Z: cis-1,2-dichloroethylene, Y: 1,1-dichloroethylene. Y has a dipole moment.

Step-by-step solution

- Identify the given information

We know the molecular formula is \( \mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2} \) and there are three different dichloroethylenes: compounds X, Y, and Z. Compound X has no dipole moment, compound Z has a dipole moment, and both compounds X and Z react with hydrogen to produce the same product \( \mathrm{ClCH}_{2}-\mathrm{CH}_{2} \mathrm{Cl} \).

- Analyze dipole moments and identify structures

A molecule with no dipole moment is likely to be symmetric, meaning X should be the trans-isomer. The trans-dichloroethylene molecule is 1,2-dichloroethene with the two chlorine atoms on opposite sides of the double bond.

- Identify compound Z

Compound Z has a dipole moment, which suggests asymmetry in the molecule. Therefore, Z should be the cis-isomer. The cis-dichloroethylene molecule has the two chlorine atoms on the same side of the double bond.

- Determine the remaining structure for compound Y

The remaining structure must be 1,1-dichloroethene, as it has not been assigned yet. This structure (Y) would have one double bond carbon attached to both chlorine atoms with the other carbon having two hydrogen atoms.

- Evaluate the dipole moment of compound Y

Since Y is 1,1-dichloroethene, the presence of two chlorines on the same carbon atom and two hydrogens on the other introduces a large dipole moment along the molecule's axis.

Final Answer

Compound X is trans-1,2-dichloroethylene. Compound Z is cis-1,2-dichloroethylene. Compound Y is 1,1-dichloroethylene. Compound Y would be expected to have a dipole moment due to the asymmetrical distribution of chlorine atoms.

Key concepts

molecular structure

Understanding molecular structure is crucial in organic chemistry. It refers to the arrangement of atoms within a molecule. Each molecule has a unique structure that defines its properties and behavior.
In the context of dichloroethylenes with the formula \(\mathrm{C_2H_2Cl_2}\), these molecules can have different structures called isomers. These isomers differ in the positioning of the chlorine atoms. They could be on opposite sides or on the same side of the double bond.
To identify the exact molecular structure, we examine the connectivity of atoms and their spatial arrangement. For instance, trans-1,2-dichloroethylene has chlorines on opposite sides, while cis-1,2-dichloroethylene has them on the same side.

dipole moment

The dipole moment is a measure of the polarity of a molecule. It arises from the difference in electronegativity between bonded atoms. When atoms share electrons unequally, partial charges develop, creating a dipole moment.
In dichloroethylenes, the presence or absence of a dipole moment helps differentiate isomers. For example, trans-1,2-dichloroethylene (compound X) has no dipole moment due to its symmetrical structure. In contrast, cis-1,2-dichloroethylene (compound Z) has a dipole moment because of its asymmetrical structure where partial charges don’t cancel out.
The dipole moment influences many properties such as boiling point, solubility, and reactivity with other chemicals. It is a key factor in understanding molecular interactions in organic chemistry.

isomers

Isomers are molecules with the same molecular formula but different structures. These structural differences lead to distinct physical and chemical properties.
In the case of dichloroethylenes \(\mathrm{C_2H_2Cl_2}\), the three isomers are:

• trans-1,2-dichloroethylene (compound X)
• cis-1,2-dichloroethylene (compound Z)
• 1,1-dichloroethylene (compound Y)

The trans-isomer has chlorines on opposite sides, creating a balanced, non-polar molecule. The cis-isomer has chlorine atoms on the same side, which makes it polar. The 1,1-isomer has both chlorine atoms attached to the same carbon, resulting in a significant dipole moment.
Recognizing isomers and their properties is vital in organic synthesis and understanding reaction pathways.

organic chemistry

Organic chemistry is the branch of chemistry that studies the structure, properties, and reactions of organic compounds, which contain carbon. This field is fundamental in understanding living organisms, pharmaceuticals, and many industrial processes.
A key aspect of organic chemistry includes understanding how different atoms bond and form diverse molecular structures. For example, dichloroethylenes, with the molecular formula \(\mathrm{C_2H_2Cl_2}\), showcase the importance of structural variations on chemical properties. Learning to differentiate between cis- and trans-isomers or identifying molecular geometry is crucial.
In everyday applications, organic chemistry helps design better drugs, develop new materials, and understand biological processes. A solid grasp of concepts like dipole moment, molecular structure, and isomers is essential for anyone studying organic chemistry.