Question

Draw the most stable conformation of 1,4-dichlorobutane, using wedges and dashes to represent bonds coming out of the paper and going behind the paper, respectively.

Short answer

Draw dichlorobutane with a zig-zag chain and trans chlorine positioning for stability.

Step-by-step solution

Identify the Molecular Structure

The molecule in question is 1,4-dichlorobutane. It consists of a linear chain of four carbon atoms (butane) with chlorine atoms attached to the first and fourth carbon atoms.

Draw the Tetrahedral Geometry

Each carbon atom in dichlorobutane is tetrahedral, forming 109.5° bond angles. Begin by drawing each carbon with the appropriate, realistic bond angles: dash and wedge bonds to represent bonds going behind and coming out of the paper, respectively.

Arrange in a Stable Zig-Zag Conformation

Since this is a butane chain, arrange the carbon chain in a zig-zag fashion to minimize steric hindrance and create a trans conformation for the attached chlorines.

Position the Chlorine Atoms

On the first and fourth carbon atoms, substitute one of the hydrogen atoms with a chlorine atom. To achieve maximum stability, place them in equatorial positions which are almost parallel to the plane of the paper.

Finalize the Drawing

Check the arrangement: Ensure the zig-zag carbon chain has the chlorine atoms in the most stable conformation, where they are maximally staggered and not eclipsed, usually on opposite sides of the molecule.

Key concepts

1,4-dichlorobutane

1,4-Dichlorobutane is an organic compound that belongs to the alkane family. It's named because it has four carbon atoms (butane) with chlorine atoms attached to the first and fourth carbon. To visualize, think of a straight chain of four carbon atoms. On the first carbon, there's a chlorine atom, and another chlorine on the fourth carbon. This setup creates a formula: \( \text{CH}_2\text{Cl}-\text{CH}_2-\text{CH}_2-\text{CH}_2\text{Cl} \). You can see how the chlorines are spaced at each end, influencing the molecule's structure and reactivity.
This linear arrangement is crucial for understanding how its geometry impacts stability, which we'll explore further in the context of its conformations.

Tetrahedral Geometry

Carbon atoms in organic compounds often adopt a tetrahedral geometry, which is a fancy way of saying they form a shape like a pyramid with a triangular base. In 1,4-dichlorobutane, each carbon atom forms four single bonds, which are arranged in this tetrahedral shape. The bond angles in this geometric configuration are approximately 109.5°, allowing for optimal spacing and minimizing repulsion between electrons in the bonds.
To draw this accurately in a structure, chemists use specific symbols: a solid line for bonds in the plane; wedges to show bonds coming out towards you; and dashes for those going behind the paper. This helps in visualizing the 3D structure on a 2D surface like paper.

Zig-Zag Conformation

The zig-zag conformation is a common way to depict the carbon chain in alkanes for minimized steric hindrance, which means less crowding of the atoms. This structure allows the atoms to be as far apart as possible, reducing tension and making the molecule more stable.
For 1,4-dichlorobutane, when arranging the carbon chain in a zig-zag pattern, it helps in achieving a trans conformation where the chlorine atoms are positioned on opposite sides of the molecule. This arrangement is crucial for stability, as it allows all atoms to be staggered, avoiding overlapping (eclipsing) and thus reducing potential repulsions.

Wedge and Dash Projection

The wedge and dash projection is a useful method to represent 3D molecular structures on a 2D surface. In this format, wedges are used for bonds that project coming out towards the observer, and dashes for those going away, behind the surface of the paper. This technique is essential for accurately conveying the spatial orientation of atoms in molecules.
Using this projection for 1,4-dichlorobutane, we can clearly illustrate the tetrahedral geometry of each carbon atom, showing how the chlorine atoms are positioned relative to the carbon chain. By correctly placing the wedges and dashes, one can determine the most stable conformation, where steric hindrance is minimized, thus helping predict the molecule's chemical behavior.