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Hydrogenation of an alkene yields an alkane. | ![]() |
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STEP 1: Hydrogen molecules react with the metal atoms at the catalyst surface. The relatively strong H-H sigma bond is broken and replaced with two weak metal-H bonds. | ![]() |
STEP 2: The pi bond of the alkene interacts with the metal catalyst weakening the bond. A hydrogen atom is transferred from the catalyst surface to one of the carbons of the double bond. | ![]() |
STEP 3: The pi bond of the alkene interacts with the metal catalyst weakening the bond. A second hydrogen atom is transferred from the catalyst surface forming the alkane. | ![]() |
The alkane is released from the catalyst's surface allowing the catalyst to accedpt additional hydrogen and alkene molecules. | ![]() |
HEATS OF HYDROGENATIONHeats of hydrogenation correlate with structure just like heats of combustion do. The greater the heat of hydrogenation, the less stable the alkene. | ![]() |
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In the addition both groups can add to the same face of the alkene (syn addition) or they can add to opposite faces (anti addition). Hydrogenation of alkenes is a syn addition. | ![]() |
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