Answer evaluators for grading chemistry questions

Updated 30 Aug 2024

Answer evaluators compare a student’s answer to a correct or incorrect answer for a skeletal or mechanism answer type. These chemical drawing answer types use the Marvin JS chemical drawing tool. Marvin JS is an advanced chemical editor from ChemAxon, Ltd that's used in pharmaceutical and other industries.

At a minimum, you must add one evaluator and one correct answer. Additional evaluators are optional.

Set each evaluator to identify a student’s answer as correct or incorrect for the purpose of grading.
Evaluators can be combined with “and” or “or” to create a single Boolean evaluator, which must match all (and) or any (or) of its member evaluators.
Grading conditions are evaluated in order starting at the top with the first evaluator. Once a student’s answer matches a condition, no more evaluators are evaluated.
You can enter wrong answer feedback in an evaluator for when a student's answer matches an incorrect answer. Some feedback messages are also provided automatically to students.

Add a molecule/compound for comparison in some evaluators

Some evaluators need a molecule or substructure to refer to when evaluating a correct or incorrect answer. You can either draw molecules/structures using Marvin JS or copy and paste a compound sketch from another answer evaluator in the same item.

Watch a video: Student instructions for drawing with Marvin JS

Select an evaluator that requires you to add a molecule for evaluation purposes.
Either create a molecule or copy and paste a compound from another answer evaluator.
Create a molecule/compound by drawing
1. Select a bond from the left toolbar. Single bond is the default.
2. Point on the canvas to create the molecule. Carbon is active by default. Select Undo if you don’t initially get the results you want.
  H and C appearance — H is shown on the canvas only when hetero and terminal. C is shown only when the atom is terminal. (To change this default, adjust H and C visibility in the Properties area of the Answer box.)
  To change an atom on the canvas — Select an atom from the toolbar on the right. (If needed, open the Periodic table first.) Point on the atom you want to replace on the canvas.
  To get out of atom mode — Select another tool, like a bond or charge.
3. Select any other toolbar options to complete the molecule, like to add charges.
Copy and paste a molecule/compound from another answer evaluator
The molecule/compound must be in the same item.
1. Select Copy compound sketch from another answer evaluator.
2. Select Paste compound sketch in the evaluator that requires you to enter a molecule.

List of answer evaluators for correct/incorrect answers

When you draw a molecule or mechanism for a correct or incorrect answer, an MRV (Marvin) file is created.

Select an evaluator/expression below for more details about it.
Grading evaluators can apply to either or both the skeletal and mechanism answer types.

To evaluate or check for this in the student's answer...	Select this evaluator/expression	Skeletal	Mech- anism
Atoms — If the number of C atoms is more than 3	expressionOchemEvalAtoms	Skel	Mech
Bond Conformation — Whether the single-bond conformation is staggered, eclipsed, gauche, or anti (Available only when the Three dimensional Marvin JS setup property is selected.)	expressionOchemEvalConformBond	Skel
Boolean — One or more evaluator conditions using "and" or "or"	expressionBoolean (for skeletal) expressionBooleanMechanism (for mechanism)	Skel	Mech
Chair Conformation — Whether the group is axial or equatorial (Available only when the Three dimensional Marvin JS setup property is selected)	expressionOchemEvalConformChair	Skel	Mech
Charge — If the total charge of the response is exactly 1	expressionOchemEvalCharge	Skel
Contains — If no compound in the answer contains the skeleton with charge, radical, isotope states matching exactly [MRV file]	expressionOchemEvalContains	Skel	Mech
Formula — If the answer has the molecular formula H2O	expressionOchemEvalFormula	Skel	Mech
Functional Group — If the number of times the functional group chosen below appears in the answer is exactly 1	expressionOchemEvalFunctionalGroup	Skel	Mech
Is — If no compound in the answer is [MRV file]	expressionOchemEvalIs	Skel	Mech
Map Property — If the mapping numbers of the answer are exactly [MRV file] which contains mapping numbers	expressionOchemEvalMapProperty	Skel
Mechanism Counter — If the total number of boxes is less than 4, counts the number of boxes, reaction arrows, or resonance arrows	expressionOchemEvalMechCounter		Mech
Mechanism Electron Flow (arrows used correctly) — If the electron flow arrows in any step do not produce the products expected, except for the following starting materials	expressionOchemEvalMechFlowsValid		Mech
Mechanism Products or Starting Materials Is (present) — If the expected starting materials or products are present in the response	expressionOchemEvalMechProdStartIs		Mech
Mechanism Rules (used correctly) — If the student answer follows expected mechanism rules (like, an E2 reaction must contain a strong base)	expressionOchemEvalMechRule		Mech
Mechanism Substructures (present) — If expected intermediates or the transition states and curved arrows producing those species are present	expressionOchemEvalMechSubstructure		Mech
Mechanism Topology — If a linear or cyclic topology is present	expressionOchemEvalMechTopology		Mech
Number of Molecules — If the total number of compounds in the answer is exactly 2	expressionOchemEvalNumMols	Skel	Mech
Rings — If the answer has a number of rings that is exactly 2	expressionOchemEvalRings	Skel
Weight — If the exact molecular weight is exactly 2 +/- 0.01	expressionOchemEvalWeight	Skel