Heh, Sodium does me way to much credit. I've not actually used much chemistry since my A-levels, but as I understand it, it doesn't matter what the two functional groups are (so they can be the same (e.g. two chlorines) or totally different (e.g. chlorine and an OH). It's only their positions that matter - if they are on the same side, is a cis, and if they are on opposite sides, it's a trans. Hope that answers your question. -- DrBob |