Objective
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In this lab, we will be understanding the potential energies involved within conformers of simple alkanes. Single bonds have the ability to rotate which varies the potential energy in comparison to the Lewis structures or line angle depictions of the compounds. While evaluating the conformers, their torsional strain, bond angles, or dihedral angles will be considered to determine their respective potential energies.
By doing this lab, I will learn about spartan and its applications as well as orientation and its relevance in chemical compounds. This lab will further my understanding of potential energy with substances as well as properties of bonds and their significance by having the ability to visualize and interact with he molecules through spartan.
Compounds of Study
Propane
Propane
BP: -42° C
Molar Mass: 44.1 g/mol
Butane
Butane
BP: -1° C
Molar Mass: 58.12 g/mol
Pre-Lab Questions
A conformer, conformational isomer, is due to the fact that single bonds can rotate within a carbon chain and exist in different shapes in 3D space. Each version of a shape is called a conformer.
3. A bond angle is composed of 3 atoms and it's the angle separating the 1st and 3rd atom in a 3 atom chain. A dihedral angle is defined by 4 atoms and it's the angle that separates the 1st and 4th atom in a 4 atom chain.
4. A 0 degree dihedral angle is known as Fully Eclipsed. A 60 degree dihedral angle is known as Gauche. A 120 degree dihedral bond angle is known as Eclipsed. A 180 degree dihedral bond angle is known as Anti-Gauche.
5. The difference between the two eclipsed conformers is both the largest groups are eclipsed with each other but within the eclipsed the carbons aren't eclipsed on top of each other and instead other atoms while in the fully eclipsed they are. This also gives the difference in Dihedral angles with fully eclipsed being 0 degrees and the eclipsed being 120.
6. The perfectly tetrahedral bond angle is 109.5 degrees.
7. The bond orbital rotating is the sp3 hybrid orbital connecting the two carbon atoms.
8.
a. They picture looking straight towards the carbon-carbon bond".
b. The 3 lines are drawn in a "Y" shape.
9. They picture looking through the carbon-carbon bonds at a downwards angle.
10.
11. I would expect the C-H bond to experience less strain than the C-C bonds being on-top of one another because they're smaller atoms with smaller bonds and smaller electronegativity therefore they experience less strain.
Quantitative Data
Propane
Butane
3-hexanol
Results
The 3 compounds of study had the highest energies while the dihedral angle was at 0 and 120 degrees and lowest energy when the angle was 60 and 180 degrees. The relative energies are directly related to the intermolecular forces experienced by the molecules. At high energy states, the atoms are closer together making it so they experience stronger repulsion forces which results in high energy as well as instability. The un-favored interactions between C-H bonds experienced within these angles creates high energy states in all 3 molecules.
The plots were different as propane experienced equal peaks and troughs while butane experienced a peak at 0 degrees and some intermediate peaks and troughs between. This is a result of their configuration and molecular structures. Propane is a smaller chemical so it has a straighter shape while Butane has extra carbon and experiences a bend. Due to the size and shape of Butane, it also has more conformers than propane making it so intermediate conformers exist and not every conformer experiences the highest or lowest respective energies.
a. 3-methyl pentane(C2-C3)
b. 3,3-dimethylhexane(C3-C4)
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