[deutdeut]

If there are no chiral centres in a compound, can the molecule be said as achiral?

[english]

An asymmetric center entails chirality in a molecule.  Loosely, an asymmetric center can be said as a "chiral" center.

[deutdeut]

So, if a molecule does not have a chiral centre, then can it and the mirror image superimpose on each other?

[english]

So, if a molecule does not have a chiral centre, then can it and the mirror image superimpose on each other?

No.  By definition they are non-superimposable.  Not all asymmetric centers are caused from 4 unique groups (sp³ hydridization).  There are compounds in which the center you are looking at may not have 4 unique groups but it can still be chiral.


Don't worry about this though.


By four unique groups I mean, by example, the boldface sp³ carbon in the following:

                     

CH₃CH₂CH(OH)NH₂

[deutdeut]

I know that in trans-but-2-ene, there is no chiral carbon. But the compound and the mirror image cannot superimpose on each other. Hence it is chiral?

[Dan]

Don't ask the same question in multiple threads, trans-but-2-ene is not chiral because the mirror image is superimposable on the original.