28.0 g of an alkene of molar mass 56.11 g/mol is hydrogenated completely…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
of an alkene of molar mass is hydrogenated completely. The heat given out is for but-1-ene and for trans-but-2-ene.
Find the heat given out for each alkene, and say by how many kilojoules per mole the trans isomer is more stable than but-1-ene.
Need a reminder? The key ideaShow
Geometrical isomers need two different groups on each carbon of the double bond. Alcoholic KOH removes HX from an alkyl halide, and the more substituted alkene is the main product (Saytzeff). The more alkyl groups on the double bond, the more stable the alkene and the less heat it gives out on hydrogenation.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Moles. .
Step 2. But-1-ene. .
Step 3. Trans-but-2-ene. .
Step 4. Stability. .
Answer: , and . The trans isomer has two alkyl groups on the double bond, and but-1-ene has one.
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