Video Solution: Identify the more stable stereoisomer in each of the followi...

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Identify the more stable stereoisomer in each of the following pairs, and give the reason for your choice: 

(a) cis- or trans-1-Isopropyl-2-methylcyclohexane  

Video Transcript

So, now let's go ahead and figure out which is more stable, cis 1-isopropyl 2-methylcyclohexane or trans 1-isopropyl 2-methylcyclohexane, so we know that we're going to have cis, right? We know we're going to have a both on the same wedge or dash and if we're going to have trans one is going to be on the wedge and the other is going to be on the dash, so I'm just going to keep our isopropyl in the wedge and our methyl is now on the dash, so let's go ahead and figure out our chair conformation because that's how we're going to figure out which one is more stable, okay? So let's say our one position is over here. So, let's give this, right? It's on the wedge, so it's going to be up, so there's our one isopropyl and then our methyl is right here, right? So now guys actually I can tell right now, we've only got one isopropyl we got one axial and one equatorial, right? Which ideally we would have, this isopropyl in the equatorial position, right? But we can do even better, right? Because here if we have, this is our one position and we did this our trans, right? We said this is up, right? This is our isopropyl coming up then trans our 2 methyl would be coming down right here in the axial position as well and that tells me that we can actually convert this into on both equatorial, right? So I can get the chair like this, where now we have our isopropyl group here, in the equatorial position and then in number two we can have this in the equatorial position, which would make this much more stable, meaning that our trans is more stable. Alright guys, so let me know if you have any questions, if not let's move on.

In the following equilibrium transformation, towards which direction does the reaction proceed the furthest as drawn (ie. left or right)?

a) A

b) B

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The change is free energy on flipping from a cyclohexane conformer with the indicated substituent equatorial to the conformer with the substituent axial is indicated in the table below: 

For each of the following cyclohexane derivatives draw the molecule in the most stable conformation. Be sure to show hydrogen atoms on the substituted ring carbons.

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Using the cyclohexane scaffold shown below, draw the structural formula of all-cis-1-ethyl-2,4 difluorocyclohexane (all-cis means that all three substituents point in the same direction). Now, draw both of the chair conformations of this molecule and circle the more stable conformation (equatiorial preference energies: –F: 0.2 kcal mol−1; –CH3CH2: −1.9 kcal mol−1).

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Draw the most stable chair conformation for the following molecule. Use the templates provided. The chloride and the numbering of carbons are already drawn in for you in the template. (*Note: D=deuterium, an isotope of hydrogen):

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Circle which isomer is more stable, cis-1,3-dimethylcyclohexane or trans-1,3-dimethylcyclohexane is more stable. To receive credit, you must include work to justify your answer.

                       cis-1,3-dimethylcyclohexane          or         trans-1,3-dimethylcyclohexane

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Draw the most stable chair conformation of the molecule shown below and explain.

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Draw the most stable chair conformer of the most stable isomer of 1,3,5-trimethylcyclohexane.

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Consider (1R, 3S)-1,3-diiodocyclohexane. Draw the two chair conformations and determine which conformation is more stable.

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For the pair drawn below, choose the MORE STABLE molecule.

Does the  UNSTABLE molecule chosen below have  ANGLE STRAIN?

Does the  UNSTABLE molecule chosen below have  TORSIONAL STRAIN?

Does the  UNSTABLE molecule chosen below have  STERIC STRAIN?

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Consider (1S, 3R)-1,3-dimethylcyclohexane. Draw the two chair conformations and determine which conformation is more stable.

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Draw the LEAST stable chair conformation of 2,3-dipropyl-1,4-dimethylcyclohexane with the following info: the propyl groups are trans to one another; the C1 methyl is cis to the C2 propyl; the C4 methyl is cis to the C3 propyl.

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Perform a ring flip on the following compound and determine which structure is more stable.

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Draw the most stable configuration.

trans-1-bromo-3-ethylcyclohexane

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Draw the LEAST stable chair conformation of 2,3-dipropyl-1,4-dimethylcyclohexane with the following info: the propyl groups are trans to one another; the C1 methyl is cis to the C2 propyl; the C4 methyl is cis to the C3 propyl.

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A. Draw the two chair conformations of cis-1,3-di-tert-butyl-cyclohexane.

B. Circle the most stable chair conformation.

C. Using complete sentences, explain why your circled chair conformation is the most stable chair conformation.

D. For the circled chair conformation, state the axial or equatorial orientation for each of the non-hydrogen substituents on cyclohexane.

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One chair conformation of the sugar galactose is given below. Complete the tetrahedral representation by filling in the missing substituent groups. It is only necessary to show bonds to groups that are not hydrogen in your tetrahedral representation. Use wedges, dashed wedges, and normal lines as appropriate to show the stereochemistry clearly and unambiguously. Consider the oxygen atom that is part of the 6-membered ring to be your “reference” atom! Then, draw the conformation that will result upon “chair flip” of the given chair. Write your answer in the empty box on the right side of the page. Remember, the 6-membered ring includes an oxygen atom! Indicate which chair is more stable by marking the appropriate box with the symbol “X”.

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Indicate the most and the least stable conformations. Give your reasoning.  

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A “planar representation” of a substituted cyclohexane ring is given below. Complete the chair conformation by filling in the missing substituent groups.  It is only necessary to show bonds to groups that  are not hydrogen in your chair conformation. To help you get started, a reference carbon is marked with an asterisk in the “planar” representation. This reference carbon is also marked with an asterisk in the chair “skeleton” that is provided. You don’t need to draw the other chair conformation, but please indicate which statement is true about the relative stability of the chair conformations by marking the appropriate box with the symbol “X”.

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For the pair of molecules drawn below, choose the letter that corresponds to the MORE STABLE molecule.

Does the UNSTABLE molecule chosen have ANGLE STRAIN? (YES or NO)

Does the UNSTABLE molecule chosen have TORSIONAL STRAIN? (YES or NO)

Does the UNSTABLE molecule chosen have STERIC STRAIN? (YES or NO)

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Which diastereomer is most stable?

 

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Which is the most stable conformation for  cis-1-bromo-3-methylcyclohexane?

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For the following cyclohexane derivative, draw the most stable chair conformation on the template provided. Be sure to attach the substituents to the corresponding numbered carbon on the template.

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Put each threesome below in order of stability from high to low using > or = signs. If two species are equal use = signs.

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Focusing on just one of the six membered rings from the structure in  avermectin, draw this portion as a cyclohexane chair below. Perform a  chair flip, and circle the more stable conformation. Provide a one sentence rationale for which conformation you circled.

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Consider a single enantiomer of trans-1-methyl-3-tert-butylcyclohexane. (For this problem, it does not matter which one.) There are two chair forms. Draw both of them. Which one is more stable? Why?

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Draw the lowest energy chair conformer for each structure (A and B). Rank these two low energy conformers as more or less stable.

 

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Draw the flipped conformation of the chair and circle the lower energy conformer.

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Complete the chair forms of the molecules shown in the box, on the templates provided as it goes through a ring flip. Indicate which conformer is the most stable.

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The preferred conformation of cis-1-isopropyl-2-methylcyclohexane is one in which:

a. the isopropyl group is axial and the methyl group is equatorial

b. the methyl group is axial and the isopropyl group is equatorial

c. both groups are axial

d. both groups are equatorial

e. the molecule exists in a twist-boat conformation

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