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Recently in The Periodic Table, there was a short discussion regarding this structure:

enter image description here

At first sight, I couldn't figure out what is the structure. After a quick google search, I came to know it is trichloromethane or chloroform (chemspider). Now, I thought of the structure of dichloromethane and found out to be:

enter image description here

From the structures, It is observed that these are the skeletal formula of tri- and dichloromethane and generally in these structures, the letter C is not denoted, the C-H bond in not denoted and C-Me is denoted by a dash.

Now, following these rules, I was now curious of the skeletal formula of methyl chloride. Is it just a chlorine protruding a bond??

enter image description here

I couldn't find out this structure on the internet and this means that this formula is not valid although, this formula follow the basic rules. Am I wrong in my argument or are the rules vague?

Further, hydrocarbons are the basic skeleton of organic compounds. To draw really complex organic compound, we first have to figure what are the hydrocarbon chains. But still, methane and ethane cannot be drawn using skeletal formula. From propane onwards, you can represent them in skeletal formula.

So, there are certain ambiguities regarding skeletal formula (some simple and basic compounds cannot be drawn) but they are widely preferred. Why is this so?


I searched hard and eventually found out the structural formula of ethane. It is a dash as expected but still, it is a dash. Who would mind that it is ethane?

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It is a valid generalisation of the skeletal formula principle to draw chloromethane as you did; you may also see it drawn in the following way:

$$\ce{-Cl}$$

In a similar vein, ethane can be drawn as a simple horizontal (or $60^\circ$ ascending or descending) line, ethene as an equality sign and ethyne as a triple line.

However, the concept of skeletal formulae, which was primarily invented to simplify drawing large, complex molecules, does not extend well to these very small ones. A chlorine atom with a line can be mistaken as $\ce{Cl-}$, a horizontal line as a dash, a double line as an equality sign and so on. Thus, while formally valid, you will not see this representation used often for very small molecules. Typically, it would be used from three explicit atoms upwards — as is the case in your second example, dichloromethane.

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First of all, you didn't look in the right place to find your drawn structure. The first website I used to look for that compound showed it like this: (middle of the top table). So also basic structures are depicted like this, although writing it out is also not too much extra work, and wouldn't make it too complex.

Why they are preferred? Because you can draw complex structures without overwhelming the reader. It's a "chemical language" that's easy for trained chemists to understand. Of course, writing out all the carbons and hydrogens would be more accurate/complete, but using lines for carbon and not drawing obvious hyhdrogens cleans up structures very nicely.

For trichloromethane it's perhaps a bit silly to use this notation, but you can imagine how testosterone would look if every carbon and hydrogen atom is written as C or H.

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The formula for trichloromethane (chloroform) is $\ce{CHCl_3}$. The missing H atom in your first figure points towards you. Each angle H-C-Cl is approx $109$ degrees. The figure below is from molecule-viewer.com

CHCL3

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