Chiral vs. Achiral ?

Question

I don't see how 1-butene is achiral. I thought for a structure to be achiral there needs to lie an internal mirrored plane. I believe there is none for 1-butene. Can someone explain? thanks.

Answer 1

You are correct, there is no internal mirrored plane for 1-butene.  Achiral = not chiral.

Answer 2

The exact conformation of 1-butene might not contain a mirror plane, in which case the compound would be chiral.  On the other hand even in this case, the two chiral conformations of 1-butene would inter-convert rapidly at room temperature and cannot be separated.  Therefore it is rather "academic" to say it is chiral.

You can draw a conformation of the molecule that contains a mirror plane along the four carbon atoms.

H2C=CH-CH2-CH3

Answer 3

The internal plane of which you speak means the molecule would have internal symmetry  like a meso compound where one halh the molecule is the mirroe image of the other..thus one half the molecule would rotate light to the right, the other half to the left..the exact same number of degrees .Thus even if a molecule possesses chiral CARBONS the whole molecule may be symmetrical = achiral . In the case of 1 butene....none of the carbon atoms are even asymmetric l...thus in this case one need not worry about whether there is internal symmetry...it does not have the first criterion for chirality....asymmetric carbon atoms