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I have been studying the chair conformations of cyclohexane but I get confused when it comes to two substituents.

I came across an example, in which the one substituent is the ethyl group (Et) and the other one is methyl (Me). The ethyl is drawn like a solid wedge, whereas the methyl is drawn like a dashed wedge. As far as I know, I have to draw the chair and then the equatorial positions and the axial ones. I thought that since the bigger substituent is the ethyl group, that it would be better in a equatorial position and the methyl would be better in a axial position. But the example, draws the ethyl group in an axial position and the methyl in an equatorial position

Why is that?I really don't understand.

Thank you.

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  • $\begingroup$ Welcome to SE! What you have described is a trans isomer. Since one group appears to be axial and one equatorial, it sounds like the 1,3-isomer. With the ethyl axial it is the less stable of the two chair conformers. $\endgroup$ – user55119 Aug 30 '18 at 16:12
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Here are some structures to help you. You noted that one group was a solid wedge and the other a dashed wedge without mentioning the substitution pattern. I presume that this was a flat, 2-D structure. You also note that in the chair structure, one group is axial, the other equatorial. Only the 1,3-isomer 2 fits these conditions. The conformation 2a is more stable than 2b.
ADDENDUM: The 1,1-disubstituted isomer would also fit the conditions of the question. The questioner did not designate the structure. enter image description here

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