[joshic]

i was wondering if anyone could help me with a few, i think fairly basic questions relating to sterioisomerism. If you consider a cycloalkane, for example cyclohexane, in order to work out which sides the substituents are on (to figure out cis/trans isomerism), does the ring need to be in a planar configuration (as in lying flat in one horizontal plane) as opposed to the chair conformation?

In regards to chirality, how do enantiomers interact differently with other chiral molecules, and what does the plus-minus notation denote?

thanks heaps

[Yggdrasil]

If you consider a cycloalkane, for example cyclohexane, in order to work out which sides the substituents are on (to figure out cis/trans isomerism), does the ring need to be in a planar configuration (as in lying flat in one horizontal plane) as opposed to the chair conformation?

It should not matter whether you think of the ring as being in a planar configuration or in a chair conformation.

In regards to chirality, how do enantiomers interact differently with other chiral molecules

You can think of it this way.  People's hands are chiral.  Handshakes (like molecular recognition between two chiral compounds) only work when you match a right hand to a right hand or a left hand to a left hand.  A "hand shaking" interaction fails if one hand has the wrong chirality (e.g. a right hand and a left hand).

and what does the plus-minus notation denote?

The (+) and (-) denote whether the compound rotates plane polarized light clockwise or counterclockwise.  The (+) and (-) notation do not tell you anything about the structure of either enantiomer.

[ufalynn88]

I prefer to put cyclohexanes in the chain conformation when determining cis/trans isomerism...it definitely makes the relationships between the molecules easier to see. (as up/up is cis and up/down is trans...)