14.2 Alkenes Flashcards

1
Q

Producing alkenes

A

1) Elimination of HX from a halogenoalkane by ethanolic NaOH and heat
2) Dehydration of an alcohol, by using a heated catalyst (AI2O3) or a concentrated acid/pieces of porous pot or pumice
3) Cracking of a longer chain alkane

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2
Q

Elimination of HX from a halogenoalkane by ethanolic NaOH and heat

A

Halogenoalkane + NaOH (ethanol) with heat= Alkene + water + NaX

Rxn Conditions:
- strong base (NaOH, KOH)
- Ethanol solvent
- High temp

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3
Q

2 Different reactions depending on NaOH

A

1) NaOH (ethanol) - elimination reaction to form alkene + NaX + H2O
2) NaOH (aq)- nucleophilic substitution in which an alcohol + NaX is produced

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4
Q

Dehydration of an alcohol, by using a heated catalyst (AI2O3) or a concentrated acid/pieces of porous pot or pumice

A

Alcohol = Alkene + Water
- the smaller alkenes are all gases at room temp and can be collected over water

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5
Q

Reactions of alkenes

A

Electrophilic addition
1) Hydrogenation
2) Steam
3) Hydrogen halide (HX)
4) Halogens (X2)

  • reactions shown in notes
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6
Q

Oxidation

A
  • Acidified potassium permanganate (KMnO4) [0]

Cold, dilute
- pale purple to colourless solution
- diol produced (2 OH groups)

Hot, concentrated
- harsh conditions, therefore C=C completely breaks
- OH groups in diol are further oxidised to ketones, aldehydes, carboxylic acids and ketones
- product depends on what is bonded to C=C

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7
Q

Addition polymerisation

A
  • in notes
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8
Q

Test for unsaturation

A
  • unknown compound is shaken with bromine water
  • if the compound is unsaturated (contains C=C) addition rxn will occur and solution will go from orange to colourless
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9
Q

Electrophilic addition of HBr, Br2

A

in notes

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10
Q

Inductive effect

A
  • primary carbocation, secondary and tertiary
  • primary carbocation is the least stable
  • tertiary carbocation is most stable as they have 3 electron-donating alkyl groups which energetically stabilize the carbocation
  • due to positive charge on the C atom they are electrophiles
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11
Q

Markovnikov’s rule

A
  • in a electrophilic addition reaction of a hydrogen halide (HX) to an alkene, the halogen ends up bonded to the most substituted carbon atom, the hydrogen to the least substituted
  • applies to unsymmetrical alkenes
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12
Q

Major and minor product

A

Major- favours Markovnikov’s rule as halogen is bonded to most substituted carbon atom

Minor- favours Anti-Markovnikov’s rule as halogen is bonded to least substituted carbon atom

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13
Q

Commonly asked example with HBr

A

in notes

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