Q:

Subscript and superscript symbols for chemical calculations

I have some very unhandy, big equations which contain quantities like 
$n_{AB}(^{13}C)$, now i would like to adapt this notation also in Mathematica so I do not need to think of a new one.
Is there a way?
Thanks
Zorg

A:

Yes, there is a way, using either Subscript[] or the keyboard notation ctrl+_
or ctrl+6 for Superscript[]
producing for example, 
Subscript[d, x] x^2

or 
Superscript[d,x] x^2

However this can end up causing effects that you weren't intending, such as:
The derivative of $\frac{\partial \left(x^2 d_x\right)}{\partial x}$ would be simply $2 x d_x$.
However without taking special care, and using D[] unintended answers can happen such as:
D[Subscript[d, x] x^2, x]

$$x^2 \text{Subscript}^{(0,1)}(d,x)+2 x d_x$$
Which certainly isn't what one intended. Because of this, it's generally better to just give your variables names such as $\left.n_{\text{ab}}(^{13}C\right)$ as nAB13C or something appropriate. Always starting with a lowercase letter as uppercase letters are reserved for commands such as D[] this will avoid any problems with future calculations dealing with variables and sub/superscripts
Have a look at this answer referring to common pitfalls awaiting new users for other tips. 

