Chirality of 1-Pentanol and 3-Methyl-2-Pentanol

Q) Which of the following is chiral?


a) 1-Pentanol


b) 3-Pentanol 


c) 3-Methyl-2-butanol 


d) 3-Methyl-1-butanol


Answer: c)


If structure and it's mirror image are not superimposable then it's chiral.


[![enter image description here](https://i.stack.imgur.com/9iwdx.jpg)](https://i.stack.imgur.com/9iwdx.jpg)


But aren't 1st, 2nd and 4th options also not superimposable ?


I drew the 1st one '1- Pentanol' and took a mirror image of it. If I keep the second one on the 1st image it's no way superimposable. I may be wrong.


Also, is there any rule like if the molecule is optically active then it's chiral?




As [DHMO said](https://chemistry.stackexchange.com/questions/66266/chirality-of-1-pentanol-and-3-methyl-2-pentanol#comment114257_66266), you need 3D diagrams, so here they are (all taken from [PubChem](https://pubchem.ncbi.nlm.nih.gov/)):


a) **1-pentanol**:


A good rule of thumb is that a chiral carbon has four distinct substituents (you can't have more than four anyway).
This structure has no such carbon: every carbon has at least two hydrogen atoms attached.
*None is chiral*.


[![1-pentanol](https://i.stack.imgur.com/X5TmR.png)](https://i.stack.imgur.com/X5TmR.png)


b) **3-pentanol**:


This one has none either.
The carbon in the middle of the chain, bonded to oxygen, has two ethyl groups attached, so *not chiral*.


[![3-pentanol](https://i.stack.imgur.com/phhBQ.png)](https://i.stack.imgur.com/phhBQ.png)


c) **3-methyl-2-butanol**:


The carbon attached to the oxygen has four distinct groups: hydroxyl, hydrogen, methyl and *tert*-butyl.
So this carbon *is chiral*.


[![3-methyl-2-butanol](https://i.stack.imgur.com/eJTs7.png)](https://i.stack.imgur.com/eJTs7.png)


d) **3-methyl-1-butanol**:


Here every single carbon has either two hydrogen atoms or two methyl groups attached, so *not chiral*.


[![3-methyl-1-butanol](https://i.stack.imgur.com/2dNLs.png)](https://i.stack.imgur.com/2dNLs.png)


Since the only chiral carbon found is in structure c), this is the correct answer.


 2