What conformation of cis-1-isopropyl-4-methylcyclohexane would be present in greatest amount at equilbrium?
The choices are methyl group equatorial-isopropryl group axial; both axial; both equatorial; twist boat; or methyl group axial-isopropryl group equatorial...
Please help. Thanks.
The choices are methyl group equatorial-isopropryl group axial; both axial; both equatorial; twist boat; or methyl group axial-isopropryl group equatorial...
Please help. Thanks.
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So this is your molecule:
http://www.tciamerica.com/common/img-str…
If you look at a molecule of cyclohexane, you will notice that you have cis-substituents on carbons 1 and 4 (across from each other) one will have to be equatorial and one will be axial if the ring is in its chair conformation (by far the most stable conformation for MOST cyclohexane derivatives).
If you look at this picture:
http://upload.wikimedia.org/wikipedia/co…
You'll notice that the red atom furthest to the left (axial, pointed up) and the blue carbon furthest to the right (equatorial) describe the positions of cis C1 and C4 substituents in the chair conformation.
You have methyl (1 carbon) and isopropyl (3 carbons) substituents. The general rule for choosing a "most stable" conformation of cyclohexane is to keep the larger substituents equatorial and the smaller ones axial. Since we have two, the choice is clear: we want our isopropyl group in the equatorial position because it is larger (sterics).
Consider this thought process for your options:
methyl group equatorial-isopropryl group axial -- this means its in the chair conformation (which is good), but the isopropyl (bigger) group is axial, which isn't as stable as if it were equatorial.
both axial -- This would severely strain the ring (we want as few axial groups as possible), but more importantly, its NOT POSSIBLE for our molecule! See the picture, for cis-C1 and C4 molecules, we must have one axial and one equatorial, not both.
both equatorial -- This seems ideal, but again, is not possible for out molecule for the previous reason.
twist boat -- The twist boat conformation is higher energy than the chair conformation and is not favored because it creates added stress in the ring. For some very bulky cyclohexane derivatives it can be favored (according to wikipedia, 2,5-di-tert-butyl-1,4-cyclohexanediol), but you don't have to worry about those.
methyl group axial-isopropryl group equatorial -- This is the most favorable option considering we have the chair conformation and our larger group is equatorial and our smaller group is axial.
http://www.tciamerica.com/common/img-str…
If you look at a molecule of cyclohexane, you will notice that you have cis-substituents on carbons 1 and 4 (across from each other) one will have to be equatorial and one will be axial if the ring is in its chair conformation (by far the most stable conformation for MOST cyclohexane derivatives).
If you look at this picture:
http://upload.wikimedia.org/wikipedia/co…
You'll notice that the red atom furthest to the left (axial, pointed up) and the blue carbon furthest to the right (equatorial) describe the positions of cis C1 and C4 substituents in the chair conformation.
You have methyl (1 carbon) and isopropyl (3 carbons) substituents. The general rule for choosing a "most stable" conformation of cyclohexane is to keep the larger substituents equatorial and the smaller ones axial. Since we have two, the choice is clear: we want our isopropyl group in the equatorial position because it is larger (sterics).
Consider this thought process for your options:
methyl group equatorial-isopropryl group axial -- this means its in the chair conformation (which is good), but the isopropyl (bigger) group is axial, which isn't as stable as if it were equatorial.
both axial -- This would severely strain the ring (we want as few axial groups as possible), but more importantly, its NOT POSSIBLE for our molecule! See the picture, for cis-C1 and C4 molecules, we must have one axial and one equatorial, not both.
both equatorial -- This seems ideal, but again, is not possible for out molecule for the previous reason.
twist boat -- The twist boat conformation is higher energy than the chair conformation and is not favored because it creates added stress in the ring. For some very bulky cyclohexane derivatives it can be favored (according to wikipedia, 2,5-di-tert-butyl-1,4-cyclohexanediol), but you don't have to worry about those.
methyl group axial-isopropryl group equatorial -- This is the most favorable option considering we have the chair conformation and our larger group is equatorial and our smaller group is axial.