Meaning of 1,1,1,2 in 1,1,1,2-Tetrafluoroethane & similar

What is the meaning of the 1,1,1,2 part in the compound 1,1,1,2-Tetrafluoroethane, a refrigerant commonly known as R-134a, some info:

Formula: $\ce{CH_2FCF_3}$
Structure:

The numbers indicate which carbons the substituents - the fluorine atoms - are on. The root of the molecular name is "tetrafluoro," indicating the presence of four fluorine substituents. So now where are they? That's what the numbers tell us; the "1,1,1" part indicates that there are three fluorine substituents on the first carbon, and "2" tells us there is one more fluorine substituent on the second carbon.

Which is the first carbon and which is the second carbon? The numbering scheme should be selected such that it gives the lowest number at the first point of difference.

This way, we can write "1,1,1,2" to indicate the presence of the four fluorine substituents rather than "1,2,2,2."

• Thanks for putting it in a way that I, a HS student, can understand. Also, is there a specific name for this "format"? – baharini Jun 8 '14 at 14:32
• Actually, IUPAC rules do not specify that the sum of the locants has to be minimized, but rather that the numbering scheme should be selected such that it gives the lowest number at the first point of difference. For example, 1,5,5- is chosen over, say, 2,2,6-. Q.v., the relevant section, rule 2.2, from the IUPAC Blue Book. – Greg E. Jun 8 '14 at 14:48
• Oops, good point! – Dissenter Jun 8 '14 at 20:50
• This "format" is known as IUPAC nomenclature, @baharini – Dissenter Jun 9 '14 at 22:49

1,1,1,2 in tetrafluro ethane[HFC 134a] is a position of fluorine in ethane.

This is ethane structure in which 3 hydrogen of first carbon (1,1,1) and 1 hydrogen of second carbon (2) will be replaced by fluorine

1,1,1,2 tetrafluro ethane is used instead of chlorofluorocarbon [CFC] as it is less hazardous to environment as compare to CFC