Why is it said that the presence of a carbon with 4 different groups is necessary for it to exist as an enantiomeric form?
Lets take 2-fluoropropane for example.
When I draw the structure of it in such a way so that the 2 CH3 groups are adjacent to each other (on paper ) and take its mirror image I see that I got a mirror image which is not superimposable on the original structure. My teacher told me I am only allowed to rotate it in the plane of the paper and only by 180° without lifting it out.
This seems to tell me that they are a pair of enantiomers( non superimposable mirror images).
On the other hand when I draw the structure such that the 2 CH3 groups are on opposite sides of the central carbon and then take a mirror image of it , rotate it by 180° in the plane of the paper I get the original structure. This tells me that they are not stereoisomers.
Also where is the mirror supposed to be placed - up down left right? Any convention (here I have placed the mirror on the right)?