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 the anti conformation with one chlorine forward (wedge) and the other backward (dash) to achieve stability.

Step-by-step solution

Understanding the Molecule

1,4-dichlorobutane is an alkane with four carbon atoms and two chlorine substituents attached at the first and fourth carbon atoms. It has the formula C4H8Cl2, where the carbon chain is linear, and each end of the chain has a chlorine atom.

Identifying the Most Stable Conformation

Alkanes often adopt staggered conformations to minimize steric strain from the repulsion between atoms. For 1,4-dichlorobutane, the most stable conformation should keep the chlorine atoms as far apart as possible to reduce repulsion.

Drawing the Newman Projection

Visualizing the molecule from the perspective of looking down the C2-C3 bond will help us determine the placement of bonds. In the most stable conformation, the bulky chlorine atoms should be anti (180 degrees apart) to each other to minimize interaction.

Converting Newman Projection to Wedge-and-Dash

Translate this conformation into a wedge-and-dash drawing: place the chlorines on opposite sides of the molecule, with one projected out of the plane of the paper (using a wedge) and the other going behind (using a dash). The carbon atoms in between should be shown as connected by solid lines.

Completing the Structure

Ensure that all hydrogen atoms and the remaining bonds are correctly placed in the structure. The hydrogen atoms opposite to the chlorine atoms should be indicated in the opposite manner (dash for wedge and vice versa), maintaining the overall 3D representation.

Key concepts

1,4-dichlorobutane

1,4-dichlorobutane is a type of organic compound known as a halogenated alkane, where the chlorine atoms replace hydrogen atoms in the alkane chain. Its chemical formula is C4H8Cl2. In 1,4-dichlorobutane, the chlorine atoms are attached to the first and fourth carbon atoms. This gives it a linear four-carbon backbone. Understanding the placement of these chlorine atoms is crucial for determining the molecule's shape and reactivity. In this particular compound, being at the terminals of the chain, the chlorines introduce larger spatial dimensions and influence the molecule's conformational stability.

Alkane Conformation

Alkane conformation refers to the different spatial arrangements of atoms in alkane molecules that result from rotation around single bonds. These rotations lead to various structures that have different energy levels. For 1,4-dichlorobutane, understanding these conformations helps in identifying the most stable form. Alkanes typically achieve their least energy, or most stable conformation, in staggered forms.

• Staggered Conformation: Atoms are positioned so that they are as far apart as possible, minimizing steric strain.
• Eclipsed Conformation: Atoms line up with each other, creating higher energy and increased steric strain.

These different conformations can indeed change the hydrocarbon's physical properties and how it might behave in chemical reactions.

Wedge-and-Dash Drawing

The wedge-and-dash drawing is a method used to represent the three-dimensional structure of molecules on two-dimensional paper. This technique is fundamental in organic chemistry for visualizing the arrangement of atoms in space. In such drawings:

• Solid lines represent bonds in the plane of the paper.
• Wedges represent bonds that project out of the plane towards the viewer.
• Dashes represent bonds going behind the plane of the paper.

This technique helps chemists visualize how atoms are oriented in space, impacting how a molecule might interact with others. For 1,4-dichlorobutane, the wedge-and-dash drawing is crucial for displaying the most stable conformation accurately.

Newman Projection

A Newman projection provides a unique way of visualizing the conformation of molecules, particularly helpful for examining torsional strain. It shows a molecule looking straight down the bond connecting two carbon atoms. For 1,4-dichlorobutane, examining the C2-C3 bond helps in determining the best spatial arrangement. When drawing a Newman projection:

• The circle represents one carbon atom you are looking over.
• Lines extending from this carbon indicate bonds to other atoms.
• In the most stable conformation, bulky groups like the chlorine atoms are placed opposite each other (anti-position) to minimize steric interaction.

This projection is a powerful tool in the arsenal of any organic chemist for its ability to demystify complex molecular geometries.

Steric Strain Minimization

Steric strain is the repulsion between atoms or groups of atoms that are physically close to each other, causing increased energy in a molecular conformation. To minimize steric strain, 1,4-dichlorobutane naturally adopts conformations that spread out bulky groups, like chlorine atoms, as far apart as possible. This concept is essential because it directly affects the molecule's stability.

• Bulky atoms/groups produce significant steric strain if in close proximity.
• By placing them 180° apart in an anti-configuration, the molecule achieves its most energetically favorable state.

Focusing on steric strain minimization helps when predicting reaction pathways and understanding molecular properties.