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Exp 10A: Geometric Isomers

Exp 10A: Geometric Isomers. Geometric or constitutional isomers are molecules that have the same molecular formula the same molecular mass different arrangement of the atoms in space different structures different properties

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Exp 10A: Geometric Isomers

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  1. Exp 10A: Geometric Isomers • Geometric or constitutional isomers are molecules that have • the same molecular formula • the same molecular mass • different arrangement of the atoms in space • different structures • different properties • That excludes any different arrangements which are due to rotation about particular bonds

  2. Exp 10A: Geometric Isomers Empirical formula: CHO Molecular formula: C4H4O4 Structural formula: cis and trans“conformers”

  3. Exp 10A: Geometric Isomers Empirical formula: CHO Molecular formula: C4H4O4 Structural formula: cis and trans“conformers” Maleic acid Succinic acid Fumaric acid http://www.bmrb.wisc.edu/metabolomics/mol_summary/?molName=succinic_acid

  4. Isomerizationconversion of one structure into another Strong Acid Maleic acid MP: 131oC Solubility: 788 g/L Fumaric acid MP: 287oC Solubility: 7 g/L

  5. Isomerization of Maleic Acid to Fumaric AcidMechanism

  6. IsomerizationExperimental 1 • Melting Point • Get both unknown samples A & B and 2 test tubes • Mark the tubes “A” and “B” with a Sharpie, to distinguish them from each other • Place a small amount (“pea-sized) sample of each unknown in a test tube • Hold both test tubes with a test tube clamp and heat them simultaneously in a Bunsen burner flame • Record which one melts first • Cool the test tubes, clean with DI water, and dry them

  7. IsomerizationExperimental 2 • Solubility • Place a small amount (“pea-sized) sample of each unknown in a test tube • Add 2 mL of DI water, and shake gently for 1 min • Record which sample has dissolved • Determine the identity of each sample based on melting point and solubility

  8. IsomerizationExperimental 3 • Isomerization • Put 50 mL of DI water in an ice bath for rinsing • Weigh 1.0 g of the more soluble sample and transfer to a 125-mL Erlenmeyer flask • Add 10 mL of DI water to the flask and swirl gently • Heat the flask on a hotplatein the fume hood until solution boils • Add very slowly and carefully 10 mL concentrated HCl from a graduated cylinder (do this in the fumehood on a hot plate!) • Boil 1 more minute, then take off the hotplate. • Record any changes in appearance of the solution • Remove the heat and remove the flask from the hot plate with tongs

  9. IsomerizationExperimental 3 (Cont’d) Continued • Let cool down for about 10 minutes. Cool further for about 10 minutes in an ice bath • Filter the solid by suction filtration on a filterpaper through a small Buchner filter • Continue suction for about 5 minutes • Remove the filterpaper, mark it (A or B) and set it aside Repeat the experiment with the less soluble substance • Wash and clean both test tubes • Test the solubility of the samples as described above under B. Record your observations • Confirm the identity of both samples, based on solubility and comparison with your results from B.

  10. Next Monday Oct1 • Isomerization Full lab report • Expt 12A Prelab Exercise

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