Question over Ochem Dat Destroyer #117 over cyclohexane ring

[UTlonghornDDS]

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So I came across a cyclohexane ring question, and the solution said that Hydrogen, halogens, and Tos groups all are required to be in axial position...is this true? I understand the hydrogen part, but not really the halogen or tos group. Is this always the case? Because I feel like they can be stable in the equilatoral position for some reason😕

 

[Vsno123]

So I came across a cyclohexane ring question, and the solution said that Hydrogen, halogens, and Tos groups all are required to be in axial position...is this true? I understand the hydrogen part, but not really the halogen or tos group. Is this always the case? Because I feel like they can be stable in the equilatoral position for some reason😕

Any time a cyclohexane ring undergoes an E2 reaction, it must do so in the anti-periplanar position. For a ring, always draw out the structure using the chair conformation. The leaving group and the H must be adjacent to one another and both in the axial position. E2 is a concerted rxn, meaning it occurs in one step. So as a strong base grabs a H above the axis, the arrow shows that bond moving down into the ring, and the leaving group is released from the other side. Whenever you see E2, think anti-periplanar! I'm not sure if the DAT emphasizes it for non-ring structures, but regardless E2 always occurs anti-periplanar!