[Oasis]

According to my ochem solutions manual, 2-methyl-2-pentene has a plane of symmetry. I must be missing something, because I've been staring at the question since last night and can't for the life of me find the plane of symmetry. The concept of chirality and planes of symmetry seems quite simple to me, so I'm not sure how I'm stuck on this question! Help, please?

[orgopete]

If you had 2-methyl-2-butene, all carbons would be in the same plane. If you looked at it from the top and bottom, they would be mirror images. I think that is the plane of symmetry being referred to.

[Oasis]

Thank you very much for your prompt response! I can conceptualize how 2-methyl-butene would have a plane of symmetry due to the carbons being in the same plane from the double bond. I don't, however, understand how C5 in 2-methyl-2-pentene doesn't disrupt that plane of symmetry...are you saying that 2-methyl-2-pentene does not have a plane of symmetry? I understand that it's achiral since there are no chirality centres, but I'm just feeling perplexed that my textbook says there is a plane of symmetry; I'm reluctant to move on if I'm unable to grasp what seems like a relatively simple concept!

[fledarmus]

Attached is a side view of the picture ChemDraw gives me - note that all six of the carbon atoms lie in the same plane. The carbon atom you refer to is free to rotate about the C3-C4 bond, of course, which you might claim would disrupt the plane of symmetry, but unless the rotation is restricted, the mirror image would also be free to rotate and pass through the same structure containing the plane of symmetry - the compound is identical to its mirror image.