Organic Chemistry (Chiral Center)

My friends asked me to discuss about the organic chemistry especially regarding the last part of the Paper 1 which mostly depicts extremely funny and sometimes complex organic substance (example menthol or even organic acid with fancy names).

Consider this structure as an example:


The IUPAC name for this structure is 3,5-dihydroxy-3-methylpentanoic acid and also called mevalonic acid (and yes it is one of those fancy names).

Upon seeing such structure, the first thing that we will notice directly are the two alcohol groups and one carboxylic acid group. You will also notice one Carbon chiral center.


Most of the questions asked will be about:
(-) Reactions of the functional group, reaction mechanism and required reagent
(-) Nature of functional group and how to identify them
(-) Number of chiral center
(-) Prediction of result of reaction

There can be more questions that can be asked, but mostly those are the stuff they will talk the most.

(+) Let's start about chiral center. First point is that if the carbon has a double bond, it will not be the chiral center. This include alkene, cycloalkene, ketone, aldehyde and benzene.

For cyclic compound, refer to these pictures:


Arrows indicates carbon atom. Picture indicates position of carbon atoms but none of them are chiral center.


Now here comes the interesting stuff. The encircled carbon atom is a chiral but the one pointed with an arrow is not a chiral center. Why? Remember the definition of chiral center. The carbon atom must be attached with 4 different functional group.

Let us magnify the picture.


Sorry for the bad quality. Left picture is the magnified carbon atom which was arrowed, while the right picture is the encircled carbon atom.

Notice at the left picture, the central carbon is attached with 2 CH2. Since it is bonded with two same structure, it will not produce enantiomer (I will explain later, much later), therefore it is not chiral.

Central carbon at the right picture is bonded with 4 different groups, making it the chiral center.

That is the end of part 1, I hope you guys understand and please comment!