I'm not quite sure why CH3-CH=C=C-(2 diff R groups, a methyl an ethyl) is chiral. I though a carbon had to have 4 distinct things attached. I'm sure it has to do with the cumlation of the double bond.... But why? And it doesnt matter that each has a methyl? Sorry if this has been answered my cable is out so I'm on my iphone... Not even 3G... Thanks.

this question has come up before... search the forums and you'll find the answer. it's also on wiki.

simply put allenes (the compound shown in choice A) does not require 4 different groups to be chiral.

This is such a stupid question IMO.
It is not one bit straightforward.
I don't think this could ever come up on the DAT.

Just commit it to memory, It's like the one and only exception you will ever see.