Halothane is CF3 - C(H)(Br)(Cl)
Desflurane is CF3 - C(H)(F)-O-CF2H
Isofluane is CF3-C(H)(Cl)-OCF2H
The rightmost carbon of halothane is
chiral because it has four different groups attached to it: -CF3, -H, -Br, and -Cl
The second carbom from the left of desflurane and isoflurane is the "chiral center" for the same reasons.
When you draw the chiral center, you have to show the three dimensional structure or it doesn't make any sense. Unfortunately, I can't draw ;-) but Wikipedia has a page on chirality that shows some drawings:
http://en.wikipedia.org/wiki/Chirality_(chemistry))
File:Chiral.svg - Wikipedia, the free encyclopedia
The two different structrures are called "enantiomers". They are designated "L", "l", Levorotatory, or "+" and "D", "d", Dextrororatory, or "-". When you pass a polarized light through a solution of the molecule, the plane of polarization is rotated either to the left "L", or to the right, "D".
Levorotation and dextrorotation - Wikipedia, the free encyclopedia
Hope this helps.