| Module: Aldol Condensation, Synthesis of Dibenzalacetone
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| Goals related to understanding: Given a molecular structure and molecular modeling software, students will be able to use concepts of intermolecular bonding to design another molecule that will have the shape, fit and attractions to hold the first molecule.
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| Assessment item (assignment, test item, etc.): Dibenzalacetone is used commercially in sun protection preparations. The conjugated system of sp2 carbons absorbs electromagnetic radiation in the ultraviolet and visible regions. The more planar the molecule, the better the absorption. A process that could isolate the most planar of the isomers of this reaction might be commercially useful. Using the enzyme principles of shape and intermolecular bonding, design a pocket or purse into which the most planar of your isomers will fit.
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| | Rubrics
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General Criteria
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Specific Criteria
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1. Absent or incorrect
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2. Partially developed
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3. Adequately developed
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4. Fully developed
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| Appropriate analysis and representation of the problem
| Students will: 1) draw e,e- dibenzylidene in its most linear conformation; 2) measure the length and width of the isomer; 3) calculate the volume of the pocket they must create; 4) recognize that the carbonyl presents a different bonding opportunity than the aromatic and olefinic systems; 5) recognize that non-polar groups should be on ìtop and bottomî of the pocket.
| Students: 1) draw e,z- or z,z- isomer; 2) use the diameter of the aromatic ring for the width; 3) do not calculate volume; 4) do not consider the carbonyl separately; 5) ignore any bonding with aromatic and olefinic portions of the molecule.
| 1) draw the e,e- isomer with the carbonyl bond parallel to a carbon double bond; 2) measure a diagonal for the length; 3) use inappropriate measurements for the volume; 4) recognize uniqueness of carbonyl but ignore geometry and structure; 5) assume bonding around edges.
| 1) draw the e,e- isomer in a low energy conformation; 2) measure length and width; 3) calculate volume; 4) recognize uniqueness and structural location of carbonyl oxygen; 5) recognize rigidity desirable in structure.
| 1) draw the e,e- isomer in a low energy conformation; 2) measure length and width; 3) calculate volume; 4) recognize uniqueness and structural location of carbonyl oxygen; 5) recognize planarity and rigidity required in the pocket top and bottom.
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| Appropriate chemistry-specific strategies
| Students will: 1) consider hydrogen bonding for the carbonyl group; 2) describe the structures that will provide a planar ìtop and bottomî to the pocket; 3) describe the groups that will connect the top, bottom, and sides of the pocket.
| Students: 1) do not consider hydrogen bonding for the carbonyl; 2) consider linear molecules; 3) create a structure that will bond equally well to one or both of the other isomers.
| 1) assume any hydrogen will hydrogen bond to the carbonyl; 2) ignore free rotation around the single bond; 3) assume aromatic hydrogens will hydrogen bond to any oxygen or nitrogen; 4) draw a 2D molecule that partially circumnavigates the isomer.
| 1) consider NH or OH for hydrogen bonding to carbonyl, but ignore geometry; 2) use olefinic groups to enforce planarity and rigidity; 3) do not bond top and bottom rigidly.
| 1) consider NH or OH for hydrogen bonding to carbonyl and geometry of H-bond that will form; 2) recognize planarity of aromatic or olefinic groups; 3) bond top and bottom rigidly with aliphatic carbons.
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| Appropriate execution of the plan
| Students will: 1) draw the structure they devise; 2) compare its dimensions with the required volume of the isomer: 3) check for ìfitî using space-filling models.
| Students: 1) do not implement their proposed design; 2) do not comment on any design change; 3) do not check for fit or volume.
| 1) implement proposed design; 2) do not confirm ìfitî or volume.
| 1) implement proposed design or modified design; 2) calculate volume; 3) check ìfitî with ball and stick or framework models.
| 1) implement proposed design or modified design; 2) confirm ìfitî and volume using space-filling models.
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| Critical evaluation and modification of the plan
| Students will: 1) justify the adequacy of their proposed solution or modifications; 2) use space-filling models to test them.
| Student do not comment on solution.
| Students inadequately explain their solution.
| Students explain design changes but not total revised solution.
| Students explain design and modifications and critique the fit of the pocket in those areas where ìbondingî is expected.
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