# What is the meaning of n-Pr and i-Pr?

Apologies in advance, I have a background in physics, so this question might seem awfully simple.

Anyway, I am interested in the chiral spin selectivity effect in organic molecules, and have read a paper in which they synthesize helicene molecules with side groups R = n-Pr, i-Pr with absolutely no reference only a slight hint as to what it is an abbreviation of in either the paper or supplementary information. I thus assume that it must be some very common notation, and my guess is that Pr refers to some kind of propane/propene/propanol, and n and i refers to some normal and altered structure, respectively. But I don't know.

I would be grateful if someone could shed some light on it for me.

Propyl is a simple hydrocarbon with three carbons in it. Propane is $\ce{CH3CH2CH3}$.
Propyl is the unit formed by attaching that chain to something else (which implies replacing one of the carbons with another bond). There are two ways to do this: one attaches the propyl unit using the end carbon on the chain (giving $\ce{X-CH2CH2CH3}$); the other involves attaching the middle carbon to something else (giving $\ce{CH3CHXCH3}$). The first is called (at least in older terminology) normal-propyl, n-propyl or $\ce{n-Pr}$; the second is called iso-propyl, i-propyl or $\ce{i-Pr}$. These reduce the amount of space required to write the structure.