MadSci Network: Chemistry

Re: Why is CCl4 named as tetrachloromethane?

Date: Fri Oct 23 02:45:54 1998
Posted By: Scott Starling, Post-doc/Fellow, Organic Chemistry, University of Sydney
Area of science: Chemistry
ID: 907236087.Ch

Naming of chemical compounds (nomenclature) is a necessary part of 
chemistry and there are large volumes which dictate how a new compound 
should be named.  But contrary to popular belief a long name for a compound
certainly isn't instantly recognisable to a chemist which is why diagrams
are so valuable.

For 'small' molecules the rules or perhaps the convention isn't so rigid 
for CCl4 both carbon tetrachloride and terachloromethane are used 
interchangably.  It is interesting to note that CHCl3 isn't called carbon 
trichloride, but rather chloroform or trichloromethane (the former being 
the much more popular alternative) and CH2Cl2 is dichloromethane or less 
commonly methylene chloride.  CH3Cl is usually referred to as methyl 
chloride.  Confusing, yes.  This is probaby in part due to the fact that 
these 'simple' compounds were discovered long before internationally 
accepted names were decided upon and they have become almost 'slang' words
in modern chemical vocabulary.  Another fine example is 'acetone' the
proper name for this is 2-propanone but it is never called that, ethanoic
acid is always called acetic acid.  

We don't use carbon(IV) chloride because in organic compounds carbon only 
has a stable oxidation state of -4 [so in any case it would be carbon(-IV) 
chloride] so there is no ambiguity.  For example sodium chloride is never 
called sodium(I) chloride because the only stable combination of sodium and
chlorine is with sodium in the +1 oxidation state.  However, for something 
like iron chloride you have to specify either iron(II) chloride or 
iron(III) chloride because both are quite stable compounds.

As for CS2 being called carbon disulfide, this is probably another 
historical relic.  It is the direct analogue of carbon dioxide.  It is
interesting to note that if you go another row down the periodic table,
CSe2 is called carbon selenide.

I hope this clears up a few things.  It is important to learn the 
conventional naming rules, it is much like learing a new language: tackle
the regular verbs first and learn the irregular exceptions when you come 
across them!

Feel free to E-mail me if you have any other questions.

Dr. Scott Starling
University of Sydney, Australia.

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