Naming Compounds (1 Viewer)

[ZZZZZZ]

Why is this HCFC >>> CF3CHCL2 <<<< on the site http://hsc.csu.edu.au/chemistry/core/monitoring/chem944/944net.html named 2,2 dichloro- 1,1,1 trifluroethane and not 1,1 -ichloro- 2,2,2 trifluroethane. ???????????

 

[tristambrown]

*shrug* different naming convention to what we are taught to use ???

I always thought we had to name following alphabetical order and orienting the strarting position to whatever gave the lowest number to start with ....

i would have called it 1,1-dichloro,2,2,2-trifluroethane

 

[dral]

i don't beleive they take away marks for naming it the other way around, as long as you could redraw the molecule correctly from the name given :\ it's the same thing if you turn it upside down or revolve it.

 

[Riviet]

... there is a rule about determining which side to start numbering the branches. The rule is number from the side that gives the smallest numbers.

So in your example, 1,1-dichloro,2,2,2-trifluroethane, the numbers add up to 8 (1+1+2+2+2 = 8) but in 2,2-dichloro-1,1,1-trifluroethane, the numbers add up to 7 (2+2+1+1+1 = 7). Therefore 2,2-dichloro-1,1,1-trifluroethane gives smaller numbers and hence the correct name.

 

[phil2010]

... there is a rule about determining which side to start numbering the branches. The rule is number from the side that gives the smallest numbers.

True - but take care. It's NOT the sum of the numbers.

We have two possible set of numbers
1 1 1 2 2 OR
1 1 2 2 2
......^
NOTE - the third column. Here we see that '1' is less than '2' so the numbering is ROW one

so we have (in alpha order)

2,2-dichloro-1,1,1-trifluroethane

 

[Riviet]

Ah ok, thanks for clarifying that phil.

 

[tristambrown]

sweet thanks for sorting that out just in time for the exam too !