Video: EC17-18-S1-Q38

Write the displayed formula and IUPAC name for halothane.


Video Transcript

Write the displayed formula and IUPAC name for halothane.

Halothane is the common name for the haloalkane CHBrCLCF3. To draw the displayed formula, all bonds need to be explicit. So let’s start with the carbon–carbon backbone. On the first carbon atom, we have hydrogen, bromine, and chlorine. And on the second carbon, we have three fluorines. This is the completed displayed formula for halothane. Now, we can move on to the IUPAC name.

IUPAC is the International Union of Pure and Applied Chemistry basic guidelines for the appropriate naming of many chemical compounds. According to IUPAC rules, the first step for naming an organic compound is to find the longest chain of carbon atoms. In halothane, this is two. We, therefore, expect the IUPAC name for halothane to contain the name “eth,” meaning two carbon atoms. Another item in the name we expect is “bromo” because of the Br group, “chloro” because of the CL group, and “trifluoro” because of the three fluorines.

The next step on our road to the IUPAC name is to number the carbon atoms in the carbon backbone. There are two ways of doing this: left to right or right to left. The first option gives 1-bromo, 1-chloro, and 2,2,2-trifluoro as components of the name, while the second option gives us 2-bromo, 2-chloro, and 1,1,1-trifloro. For the first option, the total of these indexes is eight, while for the second option, the total is seven. IUPAC rules say that we should pick the numbering system that gives us the lowest index total. Therefore, this is the correct way of numbering the carbon atoms.

So the last step is to combine all the components we know about the name into the full name. That’s 2-bromo, 2-chloro, 1,1,1-trifluoro, and ethane. We know that the name ends in “ane” because we’re dealing with a haloalkane that’s fully saturated. Ethane always goes at the end. But now, we have to figure out what order to place bromo, chloro, and trifluoro. This is done alphabetically ignoring “tri”: b before c before f, bromo before chloro before fluoro. So the full IUPAC for halothane is 2-bromo-2-chloro-1,1,1-trifluoroethane.

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