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I read that for hydrofluorocarbons, they're named HFC-xyz, where
x = number of carbon - 1
y = number of hydrogen + 1
z = number of fluorine

I'm curious why they were named like this.
Is it better than simply putting numbers of carbon, hydrogen atoms into x and y?

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Apart from the numbering system help distinguish between various isomers (see @DrMoishePippik's answer), it also helps grouping compounds into various series:

  • 000 series: methane-based compounds

  • 100 series: ethane-based compounds

  • 200 series: propane-based compounds

  • 300 series: cyclic organic compounds

  • 400 series: zeotropes

  • 500 series: azeotropes

  • 600 series: organic compounds

  • 700 series: inorganic compounds

  • 1000 series: unsaturated organic compounds

For example: HCFC-22 is in the "000 series" of refrigerants, meaning it is a methane-based compound. R-134a is in the "100 series" of refrigerants, meaning it is an ethane-based compound.

Source: https://www.achrnews.com/articles/108910-ice-breaker-refrigerant-numbering-system-explained

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  • $\begingroup$ Does it suggest that, in order to distinguish "hydrofluorocarbons with 7 carbons" from "inorganic compounds", they gave up assigning numbers according to the amount of carbon atoms? If this is the case, then why would they add 1 to the amound of hydrogen atoms? $\endgroup$ – Wang Jun 13 at 3:36
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    $\begingroup$ @Wang (1) for a HFC to be in 700 series, number of carbon should be 8 (as x = no. of carbon - 1) and yes (2) The numbering system is done in such a way that you can also do the vice-versa (obtaining the formula from the number). Add 90 to the number to obtain a 3-digit number and each digit represent number of carbon, hydrogen and fluorine atoms and a certain calculation for chlorine atoms. Because of this simplicity and versatility in getting both the formula/number if one of the either is given, the addition and subtraction is done. Consider it a "trick". $\endgroup$ – Nilay Ghosh Jun 13 at 3:51
  • $\begingroup$ (1) I meant if they use the amount of atoms as number, 7xx would have 7 carbon atoms. (2) Wouldn't it be better and more simple if they just set the number as the formula? Then we won't need any tricks. This is exactly where my question is. What merit does the system have, that they would give up simplicity for it? $\endgroup$ – Wang Jun 13 at 8:03
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Some "hydrofluorocarbons" used in refrigeration and other applications actually are fluorocarbons, sans hydrogen. To make numbering unambiguous, even tetrafluoromethane, $\ce{CF4}$, which is "R-14" in ASHRAE parlance, would be 114 in that HFC nomenclature.

Manufacturers use proprietary and somewhat arbitrary nomenclature. For example, isomers,must be distinguished, as in 1,1,2,2-tetrachloro-1-fluoroethane, Freon R-121 vs. 1,1,1,2-tetrachloro-1-fluoroethane, Freon R-121a. Compounds with other substituents, e.g. chlorine, as in chlorotrifluoromethane, R-13 and bromochlorodifluoromethane, $\ce{CBrClF2}$, known Halon 1211 or Freon 12B1, need to be assigned names, too.

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  • $\begingroup$ Does it mean that the name does not have a certain purpose? I was wondering why they would give up the easy thought, which is assign numbers according to number of atoms. $\endgroup$ – Wang Jun 13 at 3:22
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    $\begingroup$ @Wang I imagine that having fairly simple names aids in the use of the correct chemical when they are being used by technicians skilled in other areas. Also, imagine the size of the label on a car's air conditioning refill port if it had to say "2,3,3,3-Tetrafluoropropene" instead of "HFO-1234yf". $\endgroup$ – Andrew Morton Jun 13 at 19:03
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    $\begingroup$ I wonder why it couldn't be "HFO-1324yf",with 3 for the real amount of carbon atoms, and 2 for the real amount of hydrogen atoms. What merit does the "carbon-1, hydrogen+1, fluorine" really has, compared with simple " carbon, hydrogen, fluorine". $\endgroup$ – Wang Jun 14 at 2:06
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    $\begingroup$ @Wang, There are interesting comments on haloalkane nomenclature at chemeurope.com/en/encyclopedia/Haloalkane.html . Again, because these are large-scale commercial products, a company may choose it's own naming system, rather than IUPAC's, both for convenience and to hide proprietary information. $\endgroup$ – DrMoishe Pippik Jun 14 at 18:35

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