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Chemistry Unit 3 > Alkenes > Flashcards

Flashcards in Alkenes Deck (9):
1

How can alkenes be prepared?

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

2

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.

3

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.

4

What is an elimination reaction?

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

5

Why is concentrated phosphoric acid preferred to concentrated sulphuric acid?

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

6

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)

7

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.

8

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

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

9

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.