Re: The chemical structure of ninhydrin?

Hi Cassie,

All of the atoms in the ninhydrin molecule are present in the image below; however, they are not all represented by their atomic symbols.

That image is what is known as a skeletal structure, which is a common way of representing the molecular structures of organic (i.e., carbon-backboned) molecules.

In a skeletal structure, carbon is not represented with the atomic symbol C. Instead, bonds between atoms are represented by straight lines, and carbon is represented by the corner at the intersection of straight lines or by the end of a straight line. Other atoms (with the exception of hydrogen, see below) are represented by their atomic symbols (like O for oxygen).

In addition, hydrogen that is bonded to carbon is not shown. Instead, each carbon is assumed to have made four bonds to other atoms. Because bonds between carbon and non-hydrogen atoms are drawn as straight lines, if a carbon is shown with fewer than four bonds, the remaining (undepicted) bonds are made to hydrogen atoms. Hydrogen bonded to other atoms is represented by their atomic symbol (H). Representing organic molecules this way makes it easier to read and draw them, because organic molecules contain a lot of carbons and hydrogens.

That may be sort of confusing, so I've drawn the carbons and hydrogens and bonds between them in blue on the image that you provided. You can compare the two images below; mine is on the right.

So in my drawing, I have numbered each carbon from 1 to 9 to make it easier to discuss them. I'll refer to the carbon that I numbered 1 as C₁, and carbon 2 as C₂, etc.

So, C₁, C₂, C₃, C₇, C₈, and C₉ are part of a six carbon ring. C₃ and C₇ each have four bonds drawn in the structure; C₃ makes a double-bond to C₇ (shown as two lines between them), and two single bonds to C₂ and C₄. So C₃ makes no bonds to any hydrogens.

C₁, C₂, C₈, and C₉ each have three bonds drawn in the structure. For example C₁ makes a double-bond to C₂ and a single-bond to C₉. That comes to only three bonds, so that means that there is one bond not drawn, which is therefore a hydrogen.

So, from my modification of the structure, you can see where all nine carbon atoms and the remaining four hydrogen atoms are. All four oxygen atoms are shown using the atomic symbol O.

Hopefully, you can see that a chemical structure that was drawn as a single straight line would represent the molecule C₂H₆!

Keep asking questions!