Example of molecular formula, semi-developed formula, structural (line-bond) formula, displayed (perspective drawing) formula

Molecular formula:

Semi-developed formula:

Structural (line-bond) formula:

Displayed (perspective drawing) formula:

Newman formula:

Distinction between identical, conformer or isomer molécules

If two molecules have the same molecular formulas, then..

they are identical if they are superimposable in all points. (1)

they are conformers, if they are superimposable after rotation around a single bond or a deformation without breaking bonds (4) (see below).(2)

they are isomers, if they are neither identical, nor conformers.(3)

Only in cases (1), (2) and (4) these molecules belong to the same substance

Rotations arouns bonds

Rotation is possible around a single bond not engaged in a cycle.

Here are two conformers, since there is no rupture of bonds, but simple rotation! Rotation is impossible around multiple bonds and single bonds engaged in a cycle.

Deformation of cycles

Without rotation around bonds, some cycles may deform (4), eg cyclohexane:

Here are three conformers, since there is no rupture of bonds!