The Molecule Calculator1 (MolCalc) is a Web application that allows students to build small molecules and estimate properties such as molecular structure, thermodynamic proper-ties, vibrational frequencies, vibrational modes, molecular orbitals, and orbital energies in a matter of seconds or minutes, depending on the size of the molecule. A video demonstrating
these features can be found on the Web site.2
MolCalc was designed to be used for teaching and for assignments in which the students build their own molecules and estimate the molecular properties, as opposed to reading from tables in textbooks. MolCalc was designed to run fast, and therefore, the estimated molecular properties will not match experimental values exactly and, in some cases, will be quite different. The idea was to have students develop a chemical intuition about how molecular structure affects molecular properties, without performing the underlying calculations by hand (which would be nearly impossible for all but the simplest chemical systems). Similar to a pocket calculator or a symbolic math program (such as Mathematica or MAPLE), MolCalc allows an instructor to assign higher-level chemical problems that are not practically possible to solve otherwise. For example, an instructor might ask students to compute the effect of a substituent on a particular vibration and then rationalize the effect using molecular orbitals. Or an instructor might ask more open-ended questions such as build a molecule with an unusually long C−C single bond.3