To export the current file to an image, use
-> .Available formats are SVG, EPS, PS, PDF, and the formats with write support in GdkPixbuf.
To choose a format, you can use an appropriate extension in the file name, or explicitly select a format in the combo box. With the first method, if GChemPaint does not recognize an extension, the exported file will be a SVG file. GChemPaint will add an extension to the file name if needed.
If what you want is a molecule image for publication in Wikipedia, you might read the next section.