On Jul 11, 10:19, CLASSICCMP_at_trailing-edge.com wrote:
> Stupid chemistry question from someone who took too many physics classes
> and not enough chemistry:
>
> What's the difference between trichlorotrifluoroethane and
> 1,1,2-trichloro-1,2,2,trifluoroethane? Are they different names
> for the same stuff, or two different stuffs?
Just the positions of the various halogen atoms relative to each other.
The 1,1,2 form specifies a particular arrangement, the other is
non-specific.
Schematically, this is 1,1,2-trichloro-1,2,2,trifluoroethane:
Cl F
| |
F--C---C--Cl
| |
Cl F
In other words each carbon atom has one halogen of one type and two of the
other. There's one other possible arrangement[1]; where all the chlorine
is on one carbon, and all the fluorine is on another, which would be
1,1,1-trichloro-2,2,2-trifluoroethane. I've no idea if that makes any
significant difference to any of the properties you and I would be
interested in, but I suspect not, and that most trichlorotrifluoroethane is
a mixture of the two.
[1] From my 2-D ASCII art, you might think there are other arrangements, eg
swapping the position of the fluorine for one of the chlorines on the first
carbon atom. However, if you think 3-D, and imagine the carbon as one apex
of a triangular pyramid (meeting the second carbon at the apex of another
pyramid) and also realise that the carbons can rotate relative to each
other, you'll see that all the other permutations are equivalent.
BTW, this is iso-propyl alcohol:
H
/
H O H
| | |
H--C---C---C--H
| | |
H H H
You could also call it 2-hydroxy-propane, or propan-2-ol. The O-H group is
what makes it water miscible (in fact, it's mildly hygroscopic), and of
course it's also highly flammable, unlike the chloroflurocarbons. To get
ordinary ethyl alcohol, chop off one of the carbons and two corresponding
hydrogens.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
Received on Tue Jul 11 2000 - 18:02:39 BST