Greetings,
This post explores what may be considered as very short-lived variations in atomic position due to free rotation of the single (aka, sigma) bond between adjacent carbon atoms. The atoms or groups attached to those adjacent carbon atoms change position relative to each other across the single bond as they rotate. We call the different relative positions across the single bond conformations.
As the carbon-attached groups rotate they interact in two ways across the single bond; steric effects from opposing forces of atomic orbitals and electronic opposing forces from electrons in adjacent bonds. The total effect is an increase in potential energies as adjacent bonds and atoms approach each other across the single bond as they rotate.
For an arrangement of different groups across the rotating single bond, a complex set of varying potential energies arises. A good example of this is the collection of conformations obtained from rotation around the central carbon-carbon bond of the butane molecule.
The following diagram depicts conformations for ethane and butane, including potential energy variations of the butane molecule.
.png)
Note that the rate of rotation varies for the butane molecule: Rotation occurs more rapidly as the molecular rotation goes through the highest energy conformations. This has the effect of the molecule spending a greater time, on average, in the lowest energy conformations. This can effect yields and rates of certain reactions, to be covered in a later post.
That's all for now. As always, thank you for reading!
A Publication of http://ExcellenceInLearning.biz
This post explores what may be considered as very short-lived variations in atomic position due to free rotation of the single (aka, sigma) bond between adjacent carbon atoms. The atoms or groups attached to those adjacent carbon atoms change position relative to each other across the single bond as they rotate. We call the different relative positions across the single bond conformations.
As the carbon-attached groups rotate they interact in two ways across the single bond; steric effects from opposing forces of atomic orbitals and electronic opposing forces from electrons in adjacent bonds. The total effect is an increase in potential energies as adjacent bonds and atoms approach each other across the single bond as they rotate.
For an arrangement of different groups across the rotating single bond, a complex set of varying potential energies arises. A good example of this is the collection of conformations obtained from rotation around the central carbon-carbon bond of the butane molecule.
The following diagram depicts conformations for ethane and butane, including potential energy variations of the butane molecule.
.png)
Note that the rate of rotation varies for the butane molecule: Rotation occurs more rapidly as the molecular rotation goes through the highest energy conformations. This has the effect of the molecule spending a greater time, on average, in the lowest energy conformations. This can effect yields and rates of certain reactions, to be covered in a later post.
That's all for now. As always, thank you for reading!
A Publication of http://ExcellenceInLearning.biz