[lhbdan]

Hi, we are currently studying naming of organic compounds such as CFC's and HCFC's (only single chain) and the text books seem to be providing contradicting views on how to name these molecules.

One states that the most important thing is to have the smallest combined number in the 'prefix's'
eg. a) 1,1,2-trichloro-3-fluropropane
It also states that electronegativity should only be considered if there are two possible names,
eg. b) 2,2-dichloro-1,1-difluroethane instead of 1,1-dichloro-2,2-difluroethane

The other text states that electronegativity is the first thing that needs to be considered, so example a) would be named
2,3,3-trichloro-1-fluropropane

Which of these is the correct method?
I noticed as well on this wikipedia page: http://en.wikipedia.org/wiki/1,1,2-Trichloro-1,2,2-trifluoroethane that it does not follow either one of these text book rules... Is there a definitive set of rules?
Thanks for any input in advance!
Daniel.

[lhbdan]

Any ideas? further searching only leads to complex articles about naming, this wikipedia article has a complex explanation that I don't quite understand: http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry...

[kazeAaqib]

Hi
there is a set of definitive rules but i think those text books look a bit confusing.

what i know is that the prefix will come before the stem. The stem refers to the carbon in the longest chain like meth, eth, prop,

the examples you have given like 1,1,2-trichloro-3-fluropropananee or 2,3,3-trichloro-1-fluropropanane can be termed as different compounds---there should not be two possible names. The floro, chloro before the stem is the prefix but it also tells us where the chloride or fluoride atoms will be on the carbon chain.

But it is difficult to distinguish which method is correct because the structure of the compound has not been seen.

the first example shows us that there are three chloride atoms bonded to the carbon chain at position C-1, C-1 and C-2, so when you also regarded electronegativity which is right to do so by the way, you didn't move acknowledge that the prefix refers to the following atom (either flouro or chloro)

so this compund http://www.docbrown.info/page15/Image734.gif
would be called 2-bromo-1,2-chlorobutane the atoms are listed alphabetically so bromo is shown before chloro. The prefix shows that the bromide atom is on C-2 and choride atom is on C-1 and C-2