Given that ISIS Draw 2.5 is an older version, you might also consider looking into more current alternatives for drawing chemical structures, such as:
It was built for older versions of Windows (98/XP/7). You may need to run it in Compatibility Mode on Windows 10 or 11. isis draw 2.5 free download
: Warns about incorrect valences, overlapping atoms, or bonds that are too short. Given that ISIS Draw 2
It featured extensive libraries for functional groups, rings, and amino acids, significantly speeding up the drawing process. and amino acids
When downloading any software, especially older versions, ensure you're using a trusted source to avoid potential security risks.