Halogenoalkanes Flashcards

1
Q

Preparation

A
  1. From alkenes through E.A.
    C&R :
    - X2 in CCl4 r.t.
    -dry HX(g) r.t.
    -X2(aq) r.t.
  2. From alkanes
    FRS
    C&R:
    limited X2(g), UV light
  3. From alcohols through Nu:sub
    C&R :
  4. PCl3 anhydrous, heat
  5. PCl5 anhydrous, r.t.
    3.SOCl2 anhydrous, r.t.
    4.dry HX, r.t.
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2
Q

Elimination

A

to form alkenes
- ethanolic KOH, heat

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3
Q

Physical properties

A
  1. Non polar
  2. dissolves in non polar solvents
  3. MP/BP depends on degree of branching, size of electron cloud
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4
Q

Nucleophilic substitution reactions

A
  1. Form alcohol
    - NaOH, heat
  2. Form nitriles
    - ethanolic KCN, heat
    3.Form primary amines
    - excess NH3 in ethanol and heat in a sealed tube
  3. Form quaternary amines
    -limited NH3 in ethanol
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5
Q

Nitriles reaction

A
  1. Acidic hydrolysis to form carboxylic acid
    - HCl, heat
  2. Alkaline hydrolysis to form carboxylate salt
    - NaOH, heat
  3. Reduction to form -CH2NH2
    - LiAlH4 in dry ether/ H2 /Ni catalyst and heat
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6
Q

Why halogenoarenes and alkenyl halides are resistant to nu:sub

A
  1. delocalisation of lone pair of electrons on halogen into electron rich region
  2. due to p-p orbital overlap
  3. strengthening C-X bond
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7
Q

Nu:sub mechanisms

A
  1. Sn1
    - 1 reacting particle in the slow step to generate a carbocation
    In the fast step carbocation reacts w nucleophile
    - secondary and tertiary alkyl halides undergo this mech. as they can form stable carbocations
  2. Sn2
    - 2 reacting particles in slow step
    - primary/secondary alkyl halides
    - show stereochemistry
    -product formed has inverted stereochemistry

For both, draw curly arrows and nucleophile approaching from the back

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