OZ - Organic reactions *03 Flashcards

1
Q

haloalkanes

A

an alkane with at least one halogen atom in place of a hydrogen atom

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2
Q

haloalkanes - naming

A
  1. longest part of carbon chain = last part of compounds name
  2. name and position of halogen atom at start
    - chloro
    - bromo
    - iodo
  3. if more then one of the same halogen atoms
    - di
    - tri
    - tetra
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3
Q

haloalkanes - boiling points down group , why?

A

increase down group

  • boiling points depends on strength of intermolecular bonds
  • down group 7 atomic radius and no. of electron shells increase
  • so there are stronger ID-ID forces between molecules
  • more energy is needed to overcome them
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4
Q

haloalkanes - carbon-halogen bond

A

polar

  • fluorine, chlorine and bromine are much more electronegative than carbon –> so the bond is polar
  • the electronegtaive atom pulls electron density away from the carbon, so the carbon is e- deficient
  • —> this means it can be attacked by a nucleophile
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5
Q

what is a nucleophile?

A

an electron pair donor

it donates an electron pair to somewhere without enough electrons

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6
Q

nucleophilic substitution - what?

A

substitution = one functional group is replaced by another functional group

nucleophilic substitution = a nucleophile attacks a slightly +ve carbon and replaces the slightly -ve group

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7
Q

nucleophilic substitution - haloalkanes + hydroxide ions

A

conditions:

  • warm aq sodium hydroxide
  • reflux

mechanism:

  • the C-Br bond is polar
  • the slightly +ve carbon attracts the lone pair of electrons on OH-
  • the C-Br bond breaks heterolytically, a new bond forms between he C and OH- ion

general equation:
R-X + NaOH —-> ROH + NaX

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8
Q

nucleophilic substitution - haloalkane + water

A

conditions:
- warming a haloalkane with water

mechanism:

  • slightly +ve carbon attracts a lone pair on H2O
  • the C-Br bond breaks
  • an intermediate forms with an oxygen that has 3 bonds —> this is unstable so one O-H bond breaks
  • an alcohol is formed

general equation:
R-X + H2O —-> R-OH + HBr

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9
Q

nucleophilic substitution - haloalkanes + ammonia

A

conditions:
warm with excess ethanolic ammonia (ammonia dissolves in ethanol)

mechanism:

  • NH3 nucleophile attacks the slightly +ve carbon atom
  • forms an unstable intermediate —> R-N+H3
  • another ammonia molecule than removes a hydrogen group to leave an amine —> R-NH2 and forms ammonium (N+H4)

general equation:
R-Br + ammonia —> R-N+H3 + NH3 < —-> R-NH2 + N+H4

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10
Q

reactivity of haloalkanes

A

carbon-halogen bonds strength decides reactivity

C-F strongest —> has the highest bond enthalpy

reactivity increase down the group

stronger bond = slower reaction

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