Video Solution: Which do you expect to be the more stable conformation of ci...

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Which do you expect to be the more stable conformation of cis-1,3-dimethylcyclobutane, A or B? Why?

Video Transcript

So, here we've got two different confirmations of cis 1,2-dimethyl cyclobutane and it's our job to figure out which one of them is more stable. So, here it might be a little bit unclear but we've got our fourth carbon, right? It's not just of cyclopropane and this one over here, so, which one of these is going to be more stable? Well, actually it's going to be the one on the right because guys they're far away from each other, right? We can think about this as analogous to a chair, these two groups up here would be the axial position but we know that they prefer to be in equatorial and, right? look it's just how far away they are from each other here versus here, okay? So, definitely because of sterics this is are more stable conformation. So guys, let me know that any questions, if not, let's move on.

Answer the following questions regarding cyclopropane and propane.

a. Provide an approximate pKa value for the C-H bond of propane.

b. Using pictures and a minimum amount of words, name and describe the types of strain associated with cyclopropane.

c. The Csp3 orbitals are able to relieve some of the strain by adjusting slightly. Draw a molecular orbital representation of cyclopropane.

d. Please provide a name for the type of “adjusted” bonds you drew in part c.

e. Due to the reorganization of the hybrid orbitals in cyclopropane, the s character of the carbon-hydrogen bonds actually increases. Do you think this will increase or decrease the pKa value of a C-H bond in cyclopropane? Why or why not?

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Draw all cycloalkanes that correspond to molecular formula C5H10, and circle the least strained of them.

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

Does the UNSTABLE molecule chosen above have ANGLE STRAIN?

A – Yes

B – No

Does the UNSTABLE molecule chosen above have TORSIONAL STRAIN?

A – Yes

B – No

Does the UNSTABLE molecule chosen above have STERIC STRAIN?

A – Yes

B – No

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Rank the following molecule in order of increasing stability (least stable to most stable)

A) 4, 1, 3, 2

B) 4, 3, 2, 1

C) 2, 3, 1, 4

D) 3, 2, 4, 1

E) 3, 2, 1, 4

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Which value is closest to the internal C-C-C bond angle in cyclohexane?

a) 90°

b) 100°

c) 110°

d) 120°

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What factor is responsible for a greater heat of combustion per CH 2 for cyclopropane than the heat of combustion per CH2 for cyclohexane?

a) Cyclohexane has a different hydrogen-to-carbon atom ratio than cyclopropane.

b) Cyclohexane is a strained ring relative to cyclopropane.

c) Cyclopropane is a strained ring relative to cyclohexane.

d) Cyclohexane has more carbon atoms than cyclopropane. 

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