Re: GAMSAT Organic Chemistry Basics
Carbon, hydrogen, oxygen are the most common atoms found in organic chemistry. Carbon (C) can form four single bonds, two double bonds or one triple bond and a single bond.
Oxygen (O) can form two single bonds or a double bond and has two pairs of unshared electrons.
Hydrogen (H) can only form one single bond.
Nitrogen (N) may form 3 single bonds. It can also form double bonds and triple bonds depending on the compound.
Now let’s examine the drawing of chemical structures:
Molecules can be drawn using a variety of different styles. It is important to be able to understand the following different styles, as they are likely to show up in the GAMSAT exam.
Lewis structures are useful as they clearly show all atoms and bonds in the molecule. Each bond represents the sharing of two electrons between respective atoms.
Partially condensed structures do not show the bonds between C and H. The atoms are drawn besides each other. Three hydrogen bonds to carbon are shown as CH3.
Condensed structures do not show any single bonds. The structural arrangement of atoms is still shown.
The molecular formula does not provide information about the structural arrangement of atoms. It only shows the number of each type of atom present. Just by looking at a formula we can see that there can be many arrangements. Many previous GAMSAT questions have asked candidates to determine the number of different arrangements (constitutional isomers) that can be produced from a certain molecular formula.
For example – C2H5OH
Bond-line structures are simple and easy to read. They are drawn in a zigzag-like fashion and the endpoints and corners denote a carbon atom. The hydrogen atoms that are bonded to the carbon are not shown. It is assumed there are enough hydrogen atoms so that each carbon atom has 4 bonds. The end points will have 3 hydrogen atoms.
Double bonds and triple bonds are shown with two and three bonds respectively.
For a more extensive overview of organic chemistry check out ‘The Organic Chemistry Bible’.