Molecular Modeling and NMR Shift Prediction ChemPen3D is the 3D molecular modeling version of ChemPen. ChemPen3D combines ChemPen's intuitive point and click molecular structure drawing program with the versatile DREIDING molecular mechanics force field to make creating 3D molecular models almost trivial. ChemPen3D includes a chemical reaction balancer, chemical reaction energetics modeling. Also included is a powerful C-13 NMR chemical shift prediction database. keys: organic chemistry, chemistry, physical chemistry, spectroscopy, molecular structure, molecules