Question

The most stable conformation of propane is

Short answer

The most stable conformation of propane is the staggered conformation, as it has the lowest torsional strain and minimizes repulsion between adjacent hydrogens.

Step-by-step solution

Draw the Lewis structure of propane

To determine the most stable conformation, we first need to draw the Lewis structure of propane. Propane has the molecular formula C3H8, consisting of three carbon atoms and eight hydrogen atoms. The Lewis structure of propane (C3H8) is: H H H | | | H-C-C-C-H | | | H H H

Analyze the bond angles and torsional strain in propane

In a single bond, the atoms can rotate freely, so we need to determine the optimal bond angles between carbons that minimize the torsional strain in propane. The tetrahedral bond angles around each carbon atom are approximately 109.5°.

Compare the different possible conformations of propane

There are two primary conformations of propane to consider: eclipsed and staggered conformations. In the eclipsed conformation, the C-C bonds are aligned with each other, and the hydrogens are closest together. This conformation results in maximum torsional strain because of the eclipsing interactions between adjacent hydrogens. In the staggered conformation, the C-C bonds are not aligned, and the hydrogens are at their maximum distance apart. This conformation has the lowest torsional strain because the adjacent hydrogens are staggered, minimizing the repulsion between them.

Identify the most stable conformation

The most stable conformation of propane is the one with the lowest torsional strain. Comparing the eclipsed and staggered conformations, we find that the staggered conformation has the lowest torsional strain. Therefore, the most stable conformation of propane is the staggered conformation.

Key concepts

Lewis Structure

Understanding the Lewis structure is essential for grasping the stable conformation of molecules like propane. A Lewis structure is a diagrammatic representation that shows the bonding between atoms of a molecule and the lone pairs of electrons that may exist. With propane, which has a molecular formula of C₃H₈, the Lewis structure depicts three carbon atoms connected linearly with single bonds and hydrogen atoms filling the remaining bonding sites.

The significance of the Lewis structure lies in its ability to visually demonstrate how atoms are bonded and in what geometric arrangement. This is the starting point for determining the most stable conformation as it gives insight into the possible rotations and interactions between bonds.

Torsional Strain

When it comes to understanding the stable conformation of propane, it's crucial to consider torsional strain. Torsional strain arises from the repulsion between electrons in bonds that are oriented close to each other. In propane, this kind of strain occurs when the bonds are rotated to an eclipsed position, meaning that the bonds on one carbon atom directly align with those on an adjacent carbon.

To visualize this, imagine the carbon atoms as the center of a clock face with the bonds pointing towards the hours. Torsional strain is at its maximum when the hands of the clock (representing bonds) overlap. In a stable conformation, molecules will adopt a shape that reduces this strain, minimizing the potential energy and leading to a lower energy state.

Staggered Conformation

In search of stability, propane prefers the staggered conformation. This is the three-dimensional arrangement where the carbon-hydrogen bonds on one carbon atom are positioned between the bonds of the adjacent carbon, akin to a zigzag pattern when viewed along the carbon backbone. This conformation takes advantage of the tetrahedral shape formed by the sp³ hybridized orbitals of the carbon atoms, which favors a 109.5° bond angle.

The staggered conformation is akin to a dance where each atom cleverly avoids stepping on the others' toes. By staggering themselves, the hydrogens stay as far apart as possible, significantly reducing torsional strain. This is the natural position of rest for propane molecules where they experience the least amount of internal energetic conflict.

Eclipsed Conformation

Conversely, the eclipsed conformation of propane is a less favorable arrangement due to the high torsional strain it exhibits. In this setup, the hydrogen atoms on one carbon are aligned with the hydrogen atoms on the next carbon, causing an increase in electron repulsion. It is like guests standing shoulder-to-shoulder in a crowded room; everyone is too close for comfort, increasing social tension or, in this case, molecular strain.

Because molecules prefer to be in a state of lowest energy, the eclipsed conformation is considered unstable compared to the staggered conformation. This higher energy state is not where propane likes to 'hang out,' making it a less common sight within a sample of the compound.

Bond Angles

Bond angles play a pivotal role in determining molecular conformation. The angles formed between bonds are a consequence of the electron pair repulsions and the three-dimensional arrangement of atoms in a molecule. For propane, with its sp³ hybridized carbon atoms, the ideal bond angles are roughly 109.5°, conforming to the tetrahedral geometry.

The concept of bond angles is like the rules of a game that dictate how the atoms can 'play' with each other — they offer a guide to the architectural layout of a molecule. By respecting the optimal bond angles, propane reduces its potential energy due to torsional and other forms of strain, rapidly settling into the staggered conformation as its most comfortable and energy-efficient form.