CHM2123_manualp118
1
118 Annexe V- Example of a lab report Lab # 1 Cis/trans isomerization of 1,2-dibenzoylethylene Patrick Lagaffe, 4636251, CHM 2123, Section E TA: Yvon Travailler Due date: July 17, 2008 1 – Theory and mechanism Include a short description of the essential theoretical elements required to understand the experiment. Balanced equations and the mechanism of each reaction must be included. 1,2-Dibenzoylethylene (1,2-DBE) can exist as the cis or trans diastereomer as shown below. Typically the compound is found it its more stable trans form. The cis isomer can be prepared and isolated, but slowly reverts to the trans isomer upon standing. In this experiment, the trans isomer is converted to the cis isomer upon exposure to ultraviolet light. The cis isomer is transformed back to the trans isomer by exposure of the compound to an acidic solution. In the first reaction, the trans isomer absorbs the UV rays and becomes excited. The reactivity resembles a radical-type reaction. This isomer undergoes a π to π* transition, breaking the π bond which allows rotation about the remaining sigma bond. The molecule relaxes back to its fundamental state to give either the cis or trans compound (depending on its conformation upon relaxation). hν O O O O O O O O * * rotation about the σ bond O O hν H O O trans cis
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Transcript of CHM2123_manualp118
118
Annexe V- Example of a lab report
Lab # 1 Cis/trans isomerization of 1,2-dibenzoylethylene
Patrick Lagaffe, 4636251, CHM 2123, Section E TA: Yvon Travailler
Due date: July 17, 2008
1 – Theory and mechanism
Include a short description of the essential theoretical elements required to understand the experiment. Balanced equations and the mechanism of each reaction must be included. 1,2-Dibenzoylethylene (1,2-DBE) can exist as the cis or trans diastereomer as shown below. Typically the compound is found it its more stable trans form. The cis isomer can be prepared and isolated, but slowly reverts to the trans isomer upon standing.
In this experiment, the trans isomer is converted to the cis isomer upon exposure to ultraviolet light. The cis isomer is transformed back to the trans isomer by exposure of the compound to an acidic solution.
In the first reaction, the trans isomer absorbs the UV rays and becomes excited. The reactivity resembles a radical-type reaction. This isomer undergoes a π to π* transition, breaking the π bond which allows rotation about the remaining sigma bond. The molecule relaxes back to its fundamental state to give either the cis or trans compound (depending on its conformation upon relaxation).
hνO
O
OO OO
O
O
*
*
rotation about the σ bond
O
O
hν
H OO
trans cis
