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Flashcards in Alkenes Deck (9):

How can alkenes be prepared?

-Dehydration of alcohols
-Base induced elimination of hydrogen halides from monohalogenoalkanes.


How may alkenes be dehydrated?

Passing the vapour of an alcohol over hot aluminium oxide
Treating the alcohol with concentrated sulphuric acid or concentrated phosphoric acid.


What is removed during dehydration?

An OH group and an H from the adjacent carbon, the hydrogen is usually removed from the carbon with least hydrogens.


What is an elimination reaction?

When the elements of a simple molecule are removed from the organic molecule and not replaced.


Why is concentrated phosphoric acid preferred to concentrated sulphuric acid?

With sulphuric acid, more side reactions occur and it tends to lead to charring


How is base-induced elimination of hydrogen halides from monohalogenoalkanes achieved?

By heating under reflux with ethanol potassium hydroxide ( a solution of potassium hydroxide in ethanol)


Why is the reaction referred to as base-induced elimination?

Because it tis the presence of the presence of the base which drives the reaction.


What are the 4 types of addition reactions alkenes can undergo?

Hydrogenation ----> Alkanes
Halogenation----> Dihaloalkanes
Hydrohalogenation----> Hydrogen Halides
Hydration-----> Alcohols


What does Maokovnikov's rule state?

The hydrogen atom adds to the carbon of the double bond with the larger number of hydrogen atoms already attached.