Mechanism Flows evaluator to grade chemistry answers

Updated 30 Aug 2024

Use the Mechanism Flows answer evaluator (expressionOchemEvalMechFlowsValid) to check for the following conditions in a mechanism question.

If a student answer uses electron flow arrows correctly
If all compounds NOT produced by electron-flow arrows are allowable starting materials

Select Grade as Correct or Grade as Incorrect, then enter the conditions you want to be checked in student answers.

Select an “if” condition for the electron flow arrows.

"If" conditions

Condition	Description
each step	If the electron flows arrows in each step lead to the compounds (This option confirms that the student has the correct electron flow arrows, so it is rarely used to provide wrong answer feedback.)
any step do not	If the electron flows arrows in any step do not lead to the compounds Tip: Before authoring custom feedback, see the "Automatic feedback reference table" section below.

Identify the compounds to use for comparison. You can either create or copy the compounds.
Create the compound sketch by drawing in Marvin JS
Select Create in MarvinJS and draw one or more compounds. (How to draw molecules using Marvin JS) Select OK when you’re done.
The file is automatically named compound(s). To rename the compound sketch, select rename.
Copy a compound sketch from another evaluator
1. Select copy compound sketch from another Mechanism Flows evaluator.
2. Select paste compound sketch in another Mechanism Flows evaluator.
View, rename, or delete the compound sketch
View a compound sketch file later:
Select its name from the evaluator condition statement.
Rename a compound sketch file:
Select rename and enter the new name. You can enter alphanumeric characters and spaces.
Delete a compound sketch file:
Select X from the condition box
Select whether the response may contain any resonance structure of the given starting materials or whether to ignore stereochemistry errors.
Specify each Mechanism Flows condition that would make an answer incorrect, then add an Atoms evaluator and set the number of carbon atoms to greater than 1. This lets multiple answers to be accepted as correct.

Using this method, a student will be marked correct if no error is made.

Add a wrong answer response (optional)

Automatic wrong answer feedback: Mastering generates automatic feedback for mechanisms with incorrect electron flow arrows. For example:

Automatic wrong answer feedback for students

Student response error	Message the student receives
If the student uses curved arrows indicating homolytic and heterolytic cleavage inaccurately	When no product is calculated: The electron-flow arrows in the highlighted step lead to products that have at least one "bond" with an odd number of electrons. All bonds should have an even number of electrons. We calculated no products of electron-flow arrows in the highlighted stage. When a product is calculated: The electron-flow arrows in the highlighted step lead to products that have at least one "bond" with an odd number of electrons. All bonds should have an even number of electrons. See the products calculated from the electron-flow arrows in the highlighted stage. NOTE: Bonds of order 0.5, 1.5, and 2.5 are indicated by •••••, •••••, and –=–=–, respectively in the product displayed in this feedback
If the electron flow arrows produce a compound with a valence error	When no product is calculated: The electron-flow arrows in the highlighted step lead to products that have at least one valence error. We calculated no products of electron-flow arrows in the highlighted stage. When a product is calculated: The electron-flow arrows in the highlighted step lead to products that have at least one valence error. See the products calculated from the electron-flow arrows in the highlighted stage.
If there are no electron flow arrows	The highlighted step has no electron-flow arrows.
If the electron flow arrows do not lead to the product in a step	When no product is calculated: The electron-flow arrows in the highlighted step do not lead to any of the products drawn in the subsequent step. We calculated no products of electron-flow arrows in the highlighted stage. When a product is calculated: The electron-flow arrows in the highlighted step do not lead to any of the products drawn in the subsequent step. See the products calculated from the electron-flow arrows in the highlighted stage.
If the electron flow arrows do not lead to the product in a step nor are they reagents in that step	When no product is calculated: The highlighted step contains a compound that is neither a product of the electron-flow arrows in the previous step nor an acceptable starting material. We calculated no products of electron-flow arrows in the stage prior to the highlighted one. When a product is calculated: The highlighted step contains a compound that is neither a product of the electron-flow arrows in the previous step nor an acceptable starting material. See the products calculated from the electron-flow arrows in the stage prior to the highlighted one.
Coproducts expected based on pKa are not present	The highlighted stage contains coproducts whose structures you have omitted, but the compounds are present nonetheless, and these compounds cannot be generated under the given reaction conditions.
If the student draws valid electron flow arrows, but they produce a compound with too many valence electrons	When no product is calculated: The electron-flow arrows in the highlighted step lead to products that have at least one atom with a total electron count more than the maximum. We calculated no products of electron-flow arrows in the highlighted stage. When a product is calculated: The electron-flow arrows in the highlighted step lead to products that have at least one atom with a total electron count more than the maximum. See the products calculated from the electron-flow arrows in the highlighted stage.
If the electron flow arrows originate from a compound that cannot be a reagent	When no product is calculated: The highlighted step contains a compound that is not an acceptable starting material. When a product is calculated: The highlighted step contains a compound that is not an acceptable starting material. See the products calculated from the electron-flow arrows in the highlighted stage.
Mechanism chain is not sustainable	Because it is the first step in a cyclic mechanism, the highlighted step should contain a compound that is produced by both of the steps preceding this one.
If the number of electrons flowing from an atom is more than the total number available	The electron-flow arrows in the highlighted step lead to products that have at least one "bond" with a negative number of electrons.
Mechanism chain has no initiation step	A chain mechanism should have an initiation part; yours does not.
Mechanism chain has initiator reacting in propagation step	In a chain mechanism, the initiator should not undergo a reaction in the propagation part of the mechanism, nor should any intermediate or product containing atoms that come from the initiator.

Your additional wrong answer responses are appended.
Select Show this response to enter wrong answer feedback for when the student’s answer matches a Grade as Incorrect condition.

Use your keyboard and options from the editing toolbar and menus. Wrong answer and follow-up text can include an image, link, and formatted text like bullets or TeX.