Video Transcript
Which of the following is the
general formula of haloalkanes that contain one halogen atom? (A) C𝑛H2𝑛+1X, (B) C𝑛H2𝑛+2X,
(C) C𝑛H2𝑛-1X, (D) C𝑛H2𝑛X, or (E) C𝑛H2𝑛-2X.
The question asks for the general
formula of alkane compounds containing one halogen atom. Alkanes belong to the alkane
homologous series, in other words, the alkane family, whereas the haloalkanes belong
to the haloalkane homologous series or the haloalkane family. A homologous series is a family of
compounds with the same functional group with each compound in the series differing
from the previous or next compound by a simple structural unit. Because each compound in the series
differs from the next or previous by the same unit, every compound within the same
homologous series has the same general formula. The alkanes all have the same
general formula C𝑛H2𝑛+2, where 𝑛 is a natural number such as one, two, three,
four, et cetera.
A haloalkane is an alkane where one
of the hydrogen atoms has been removed and replaced with a halogen. Let’s call the halogen atom X. So if we remove one hydrogen atom
from an alkane, the formula becomes C𝑛H2𝑛+1. But we need to add in a halogen
atom. So we can put X into the formula
in place of the missing hydrogen atom. This formula corresponds with
answer option (A). Therefore, the general formula for
a haloalkane that contains one halogen atom is C𝑛H2𝑛+1X.
Before we end this question, let’s
have a look at two quick examples of haloalkanes. If 𝑛 is, say, two and X is, say,
chlorine, we can write the general formula as C2H2(2)+1Cl, which is C2H5Cl or
chloroethane. Here is another example. If 𝑛 is, say, four and X is, say,
bromine, then the general formula is C4H2 multiplied by four plus one Br, which is
C4H9Br, which is 1-bromobutane or any other isomer of bromobutane.
