Search results
Some of the molecules will be found in the gauche conformer, because that is the second-most stable conformation. None of the molecules will be found in the eclipsed conformations, because those are points of maximum energy.
- 3.9: Conformations of Butane
If we rotate the front, (blue) carbon by 60°clockwise, the...
- Conformations of Butane
If we rotate the front, (blue) carbon by 60 ° clockwise, the...
- 3.9: Conformations of Butane
- Staggered and Eclipsed Conformations of Butane
- Focus on The Central C2-C3 Bond of Butane
- Newman Projections of Butane: Staggered and Eclipsed
- “Steric Interactions” in Butane
- The CH3-CH3 Eclipsing Interaction in Butane “Costs” About 3 kcal/mol
- Two More Eclipsed Conformations of Butane
- Not All Staggered Conformations Are Equal – The Gauche Conformation of Butane
- Graphing Out The Conformations of Butane
- Newman Projections of Butane: Conclusion
- Appendix – What About The C1 C2 Rotation of butane?
Let’s get started by drawing butane in the laziest way possible, with all carbons in the plane of the page; the line diagram drawn with the carbons zig-zagging nicely. With a bit more effort, we can also expand out the C-H bonds; if we choose to draw all the C-C bonds as staggered, we get the molecule drawn above-right. Since all the bonds in butan...
Butane has 3 carbon-carbon bonds that can each rotate freely. At first glance, that might seem intimidating to analyze. However, we’re only going to analyze rotation about the central (C2-C3) bond here. Here’s why. Say you were at a dinner party, and someone asked you to analyze the wholeconformation of butane. Your mind races. “Does the orientatio...
Now it’s time for some Newman projections. Here, we’re going to take our model of butane in the staggered conformation and look along the C2-C3 bond. When we do that we can sketch out the Newman projection like this: via GIPHY Note that the two methyl groups point up and down like the hour and minute hands on Big Ben when it strikes 6:00 . The dihe...
Let’s have a closer look at these two conformations. According to these measurements and calculations [Ref 1] the torsional strain of the C2-C3 syn conformation is about 5.0 kcal/mol higher than the C2-C3 anti conformation. Why so high? The issue here is that when electron clouds surrounding the hydrogens on the CH3 groups are brought too close tog...
If we know that the torsional strain of the CH3-CH3 syn conformation of butane is about 5 kcal/mol relative to CH3-CH3anti we can figure out how much the CH3-CH3interaction “costs”. How so? We’ve seen previously that each H-H eclipsing interaction costs about 1 kcal/mol. So if we subtract out the two H-H eclipsing interactions, that leaves us with ...
Now we can start to look at some other conformations of butane. Let’s look at the two other eclipsed conformations, ones where the dihedral angle between the methyl groups is at 120° and 240° respectively. Using the “price list” above, it’s possible to come up with a very good estimate for the torsional strain in this conformation. We just need to ...
We’re almost done. Let’s look at the two other “staggered” conformations of butane, those with a dihedral angle between methyl groups of 60° and 300° respectively. Since the substituents on C2 are staggered with respect to the three groups on C3, you might initially think the strain in these conformations is zero. That’s not quitetrue. The two conf...
Now that we’ve explored the conformational isomers of butane (in 60° increments) let’s summarize by showing a Newman projection of butane along the C2-C3 bond with the methyl groups synand sweep the back methyl group through a rotation of 360°. via GIPHY We can even graph out each of the conformations of butane and put in a diagram like this. From ...
So what did we learn? Here are some key points. 1. Steric interactions are what we call repulsions between the electron clouds of substituents that come into close contact, such as in the eclipsed conformation of butane where the two methyl groups are syn. In order to reduce steric interactions, bonds and bond angles deform ever-so-slightly from th...
The C1-C2 bond in butane has a single barrier to rotation, just like propane. The ethyl group isn’t actually that much “bigger” than the methyl group for our purposes, because the CH3at the end of the methyl group can just point away from C-C, resulting in very little additional strain: (If you’re familiar with A-values, the A-value of ethyl (1.75 ...
Aug 19, 2021 · If we rotate the front, (blue) carbon by 60°clockwise, the butane molecule is now in a staggered conformation. This is more specifically referred to as the ‘gauche’ conformation of butane. Notice that although they are staggered, the two methyl groups are not as far apart as they could possibly be.
Feb 13, 2019 · If we rotate the front, (blue) carbon by 60 ° clockwise, the butane molecule is now in a staggered conformation. This is more specifically referred to as the gauche conformation of butane. Notice that although they are staggered, the two methyl groups are not as far apart as they could possibly be.
However, in butane (C4H10, the one in this video), the front and back carbons in the Newman projections each have a methyl group, and we use those to identify anti or gauche. This means we an also identify one unique eclipsed situation.
- 10 min
- Torsional strain is the increase in potential energy in the eclipsed Newman projection due to the repulsion between the electron clouds of 2 neighb...
- Yes, but only when you have a unique functional group to differentiate them. For example, ethane (C2H6), there would be no reason to differentiate...
- It depends where the double bond is. In IUPAC naming, alcohol takes priority in naming over double bonds (i.e. you start counting carbons from the...
- He was talking about conformational analysis of ethane and propane Those are the last two videos prior to this one-conformational analysis of butan...
- I believe it means that the two eclipse conformations have the same energy.
Normally, when we rotate the molecule of butane at the axis of the C-C bond, it shows different conformation isomerism. Generally, Butane has four conformation isomers which are fully eclipsed, gauche, eclipsed, and anti butane conformational isomers. Lets us discuss these isomers below.
In the study of conformational isomerism, the gauche effect is an atypical situation where a gauche conformation (groups separated by a torsion angle of approximately 60°) is more stable than the anti conformation (180°).
