N heptane if derrived correctly is a isolated version of heptane without isomers or nearly no raycemic molecules.
Heptane as regular batch also refered to as heptanes is a mixture also related to spirits for thinning. It is n heptane and mixture or heptane isomers as well as who knows what off the tap generally when distilling and refining heptane(s) from a refinery it’s sorta mixed.