cis-1-tert-butyl-4-chlorocyclohexane

[AsherLev]

On AAMC CBT 8, BS section, question 113 says that
cis-1-tert-butyl-4-chlorocyclohexane would have the tert butyl equatorial, and chlorine axial...my question is, why cant both of them be equatorial?

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[corbis11]

if they were both equatorial then it would be trans...just draw a rough chair conformation and you will see

 

[Tussis]

^^^ Right.

Also remember that T-butyl groups are considered ring "locking" groups that will "lock" the ring in that conformation, generally because of its size. It takes way too much energy for any appreciable percentage of the conformations to be out of the chair conformation with the tert-butyl group in the axial position.

 

[AsherLev]

Wow, i cant believe I didnt catch that. Thanks to both of you though! i appreciate it

 

[axp107]

Yup.. both up/down means cis, 1 up 1 down means trans. Don't go by eq or ax.

for cyclohexanes, cis = 1 eq, 1 ax trans = both eq or both ax

 

[ikester04]

On AAMC CBT 8, BS section, question 113 says that
cis-1-tert-butyl-4-chlorocyclohexane would have the tert butyl equatorial, and chlorine axial...my question is, why cant both of them be equatorial?

lol its funny, I took this test today too and put the same answer. I thought they were both at equitorial.