Transcript Slide 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 1 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 Fumaric acid Succinic acid 4 http://www.bmrb.wisc.edu/metabolomics/mol_summary/?molName=succinic_acid Isomerization conversion of one structure into another Strong Acid Maleic acid Fumaric acid MP: 131oC Solubility: 788 g/L MP: 287oC Solubility: 7 g/L 5 Isomerization of Maleic Acid to Fumaric Acid Mechanism 6 Isomerization Experimental 1 A. 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 Isomerization Experimental 2 B. 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 Isomerization Experimental 3 C. 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 hotplate in 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 Isomerization Experimental 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 11