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Objective: To better understand molecular formations, potential energies, bond angles, and positions of simple alkanes using modeling software such as Spartan which allows us to better visualize organic compounds in a three-dimensional way.
Compounds of Study:
Propane
Image from UCLA
Butane
Image from UCLA
2-Methyl Propanol
Image from Sigma-Aldrich
Pre Lab:
After reading the introduction above, using your own words, describe a conformed.
A description of an isomer that tells us about a possible rotation of a single bond within a molecule.
2. Draw an octane (8-carbons) zig-zag then draw two other bent structures, drawing a blue arrow to show what bond is rotating to give the bend.
See attached below.
3. After reading the introduction above, When we talk about a bond angle, how many atoms define a bond angle? How many atoms define a “dihedral angle”?
Bond angles are composed of three atoms. Dihedral angles are composed of four atoms.
4. After reading the introduction above, what are all of the names given to each of these dihedral angles?
0: Fully Eclipsed 60: Gauche 120: Eclipsed 180: Anti-Gauche
5. Explain the difference between the two kinds of “eclipsed” conformers.
Fully eclipsed conformers have the two large atoms "eclipse" each causing a bond angle of 0 degrees. While eclipsed conformers have the largest atoms "eclipse" other smaller atoms but not the other large atoms.
6. In Wade 3.7 it is said that methane is “perfectly tetrahedral”. Every 3-atom bond angle (H-C-H) is exactly the same. What is that bond angle? How many degrees?
Bond angles are 109.5 degrees in a tetrahedral shape.
7. In Wade 3.7 look at the picture of ethane but imagine the C-C bond as if it is the two ends of pencils, the eraser ends, meeting in the middle of the bond. You can spin one of the pencils but the two erasers will still stay touching, they will still stay bonded. This is how you can think of bond rotation.
Instead of a pencil rotating to give a bent structure, what kind of bonding orbital is rotating?
Sp3 bonding orbital is rotating. The sigma bond that connects the two carbons is rotating.
8. In Wade 3.7, when drawing the Newman projection for ethane,
What bond are we looking through? You can directly quote what is said in the text for your answer.
You look straight down at the bond that connects the two carbon atoms.
What shape do we draw for the “3 lines”?
The three lines are drawn as the letter "Y."
9. In Wade 3.7, for Sawhorse drawings, instead of looking through the C-C bond and creating a drawing, what are we looking at?
You look down at an angle toward the carbon-carbon bond.
10. After Viewing the solution for the problem 3-11 in Wade section 3.7, draw each of the following Newman projections 2-methyl propane (CH3CH(CH3)CH3) from C1-C2.
See attached below.
11. After reading 3-7, describe if you would expect the eclipsing of a C-H bond over the top of another C-H bond to be higher, lower or the same torsional strain as the eclipsing of a C-C bond over the top of another C-C bond. Briefly explain.
An eclipsing C-H bond would have less torsional string than the eclipsing of a C-C bond. There is less potential energy in the C-H bond than in the C-C bond. C-C is also much larger in size than C-H due to the size of carbon compared to hydrogen and carbon tends to form four bonds while hydrogen tends to form
Images for Pre-Lab Questions Two (Left) and Ten (Right):
Experimental:
Followed all experimental procedures as outlined in the lab overview.
Results:
Propane
Propane
Butane
Butane
2 Methly-Propanolol
2 Methly-Propanolol
Propane:
Butane:
My Lab Group's Chemical (2 Methyl-Propanolol):
Post-Lab:
In one paragraph, rationalize the highest and lowest energy structures of propane and butane and your unique compound. Why does it make logical sense that certain conformers have high energy and some have low energy?
The highest energy structures of propane, butane, and 2-methyl propane would eclipsed and fully eclipsed. This is due to these formations bringing the CH3 atoms into close proximity with other atoms. We know that the shorter a bond is, the stronger it is, a similar concept applies to energy structures. The closer the CH3 is to another atom the higher the energy structure is.
In one paragraph, reflect on the difference in the plots of propane and butane. Why does butane have conformers intermediate in energy where propane conformers are all either high or low?
The shape of the propane graph is more drastic than the butane graph, having a lower lowest energy and a higher highest energy noted on the graph. The shape of these graphs can be attributed to the composition of each molecule. While butane has four carbon atoms and forms three bonds between them, propane only has three carbon atoms and can only form two bonds among all of them. Due to its additional carbon atom, butane is able to form high-energy, middle-energy, and low-energy, structures. We know that lower energy bonds are more stable, so we typically see lower energy bonds more often, which explains why butane's graph has a much narrower range of values than propane's graph.
Draw the Newman Projection, about the indicated bond, of the most stable and least stable conformer of:
a. 3-methyl pentane (C2-C3) b. 3,3-dimethylhexane (C3-C4)
CH3CH2CH(CH3)CH2CH3 CH3CH2C(CH3)2CH2CH2CH3
See attached files below for drawings, 3-methyl pentane (C2-C3) (left), 3,3-dimethylhexane (C3-C4) (right).
Reflections:
In this lab, I learned about how to use the software Spartan to better visualize atoms and how they interact within organic compounds in three-dimensional ways. I practiced using this software to understand how compounds bond and how this affects the energies these bonds possess. When we first started the experiment, my lab group and I struggled to understand what was being asked of us and to get the desired 180-degree bond angle selected on Spartan. However, after messing with the system we were able to figure out the software and easily finish the remaining two assignments. now feel more confident using 3-D modeling software and the tools in Spartan to perform similar laboratory tasks. One thing I would do in this lab is I would more time with the energy tables, and manipulating bond angles to gain a deeper understanding of how each energy structure (eclipsed, half-eclipsed, gauche, anti-gauche) looks in a three-dimensional space and to see how that affects the energies that are graphed on the table.
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