Stereochemistry: Addition of Bromine to Trans-Cinnamic Acid
STEREOCHEMISTRY: ADDITION OF BROMINE TO trans-CINNAMIC ACID
Required Prelab Readings: McMurry Chapter 5, Sections 8.2 & 21.2 Morhig, Sections 7.1 and 7.3.
Previous techniques that you must know and be able to perform: Suction Filtration and Melting Point
This experiment is designed to demonstrate two concepts. First, it will provide a demonstration of how chemists can use chemical reactions to understand reaction mechanisms. Second, is the concept of multi-step synthesis. You will be performing the following reaction:
Isomer I Isomer II + Enantiomer + Enantiomer
Bromine trans-Cinnamic Acid 2,3-Dibromo-3-phenylpropanoic acid
MW 160 g/mol MW 148 g/mol MW 308 g/mol bp 60 °C mp 133-134 °C mp 93-95 °C mp 202-204 °C
When an electrophile, such as bromine, adds to an alkene, the addition can be done in a syn fashion, in which the two groups add to the same side of the molecule, or in an anti fashion, in which the groups add to opposite sides of the molecule. Depending on the mode of addition, syn or anti, and the stereochemistry of the starting alkene, various stereoisomers will result. In some cases, a racemic mixture of products is formed, other times a meso compound is produced.
The Fischer projections shown above are two possible stereoisomers that could form in the bromination reaction that you will perform. One is the result of a syn addition, the other is the result of an anti addition mode. Note that each would form as a racemic mixture, (+). You are to determine, based on the melting point of your product, which pair of enantiomers is produced. By knowing which enantiomeric pair is formed one can predict a plausible mechanism. Hint: you can predict the stereochemical outcome of a syn vs. anti addition of bromine to alkenes before you step foot into the laboratory.
The simplest example of a multi-step synthesis is to examine virtually any commercial medicine. Almost without exception that medicine was prepared by a
Required Prelab Readings: McMurry Chapter 5, Sections 8.2 & 21.2 Morhig, Sections 7.1 and 7.3.
Previous techniques that you must know and be able to perform: Suction Filtration and Melting Point
This experiment is designed to demonstrate two concepts. First, it will provide a demonstration of how chemists can use chemical reactions to understand reaction mechanisms. Second, is the concept of multi-step synthesis. You will be performing the following reaction:
Isomer I Isomer II + Enantiomer + Enantiomer
Bromine trans-Cinnamic Acid 2,3-Dibromo-3-phenylpropanoic acid
MW 160 g/mol MW 148 g/mol MW 308 g/mol bp 60 °C mp 133-134 °C mp 93-95 °C mp 202-204 °C
When an electrophile, such as bromine, adds to an alkene, the addition can be done in a syn fashion, in which the two groups add to the same side of the molecule, or in an anti fashion, in which the groups add to opposite sides of the molecule. Depending on the mode of addition, syn or anti, and the stereochemistry of the starting alkene, various stereoisomers will result. In some cases, a racemic mixture of products is formed, other times a meso compound is produced.
The Fischer projections shown above are two possible stereoisomers that could form in the bromination reaction that you will perform. One is the result of a syn addition, the other is the result of an anti addition mode. Note that each would form as a racemic mixture, (+). You are to determine, based on the melting point of your product, which pair of enantiomers is produced. By knowing which enantiomeric pair is formed one can predict a plausible mechanism. Hint: you can predict the stereochemical outcome of a syn vs. anti addition of bromine to alkenes before you step foot into the laboratory.
The simplest example of a multi-step synthesis is to examine virtually any commercial medicine. Almost without exception that medicine was prepared by a