Gnome Chemistry Utils
... GChemPaint

A 2D chemical editor

Working area

GChemPaint

Benzene mesomery

GChemPaint

A retrosynthesis

GChemPaint

The tools box with various tools selected:

GChemPaint GChemPaint

GChemPaint in Abiword: (needs Abiword-2.6.0)

GChemPaint