Alcohols to alkenes Flashcards
What occurs in elimination reactions?
2 sigma bonds are broken and a pi bond forms
Propan-2-ole elimination reactions explained
1) sigma bond between the C—OH bond breaks
2) carbon adjacent to it (left carbon) hydrogen breaks H—C
So One H is gone and another OH is gone forming water as well
3) a pi bond forms
forming the alkene propene and water
Whats the trend between elimination reactions in alcohols?
it always forms an alkene and water
Another example
OH bond breaks pushing C—H towards the side
the second carbon will lose its hydrogen too
Whats dehydration reaction defined as
when a molecule loses an atom from its molecule
To get an elimination reaction or dehydration reactions what do we need
state• concentrated acid catalyst
Reagent being = (concentrated sulfuric acid H2SO4) or (concentrated phosphoric acid H3PO4)
+ Heat the mixture to increase the rate of reaction
What is the name of this type of reaction?
electrophilic
as it involves breaking 1 pi bond and forming 2 sigma bonds so it’s an additional reaction as HBr acts as an electrophile
State a reagent for this dehydration reaction
H2SO4 or H3PO4
State the role of this reagent for the dehydration reaction
it’s a catalyst
The conditions needed for a dehydration reaction or elimination reaction is
concentrated acid catalyst and heat
Name the products of the dehydration reaction of propan-1-ol
propene and water
What does this arrow tell us between the reaction of H2SO4 and Propen-2-one
tells us that hydrogen hydrogen bond is formed
What does this arrow tell us
tells us a hydrogen oxygen bond is broken
What’s happening here?
the fourth molecule OH molecule on the OH2 gained a H so it gains a + charge
Whats does the arrow tell us here
this arrow tells us that the +OH2–C bond breaks so we form a carbocation
and the +OH2 broken forms water
What’s happening in the final step?
First big arrow tells us the Oxygen is forming a bond with the Hydrogen
and second small arrow tells us a pi bond is formed which forms this
Because sulfuric acid is a reagent at the beginning of the reaction and a product at the end, it’s acting as a
catalyst
another example
- OH lone pair goes to H & bond breaks oxygen bond
- OH2+ bond breaks forming water
- Carbocation occurs
- Left element H attracts the lone pair of Oxygen on sulfuric acid and bond breaks
whilst the C—H bond breaks to make a Pi bond for C—C
what’s the mechanism for ethanol to ethene?
We can replace H2SO4 by a H+ like this
This is the simplified version
so the mechanism would look like
What are these molecules examples of and what are they called?
1st molecule is called Pent-1-ene
and second molecule is called Pent-2-ene
both examples of structural isomers
Pent-2-ene has how many substituents
it has 2 substituents so it’s a z-pent-2-ene and e-pent-2-ene
When hex-3-ene undergoes elimination it can produce…
it forms hex-2-ene, hex-3-ene
which has both 2 isomers as shown
how do we write this elimination reaction
CH3CHOHCH3 —> C3H6 + H2O
if there’s the double bond only goes one way so 1 for both we write the molecular formula
write the elimination reaction of ethanol to ethene
CH3CHOH —> C2H4 + H2O
how do we write the equation for this reaction?
CH3CHOHCH2CH2CH3 —> CH3CH=CHCH2CH3 + H2O
When this alcohol undergoes elimination what will form?
First dot near OH = 1 molecule
second dot near upper tail = second molecule
How did the third molecule form?
tertiary structures are more stable than secondary
so the secondary carbocation intermediate may undergo rearrangement and carbocation rearranges to its atom to form a tertiary
