Chapter 15: Haloalkanes 15.1-15.2) Flashcards

1
Q

general formula of a haloalkane

A

Cn H2n+1 X

X is a halogen atom

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2
Q

functional group of haloalkanes

A

fluoro, -F
chloro, -Cl
bromo, -Br
iodo, -I

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3
Q

polarity of haloalkanes

A

C-X is a polar bond (halogens more electronegative than carbon)
C-X bond polarity decreases down the group because the electronegativity of halogens decree from F -> I
Polarity of the C-X bond attracts nucleophiles to the Cd+ atom

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4
Q

what is a nucleophile

A

an atom or group of atoms that donates an electron pair to an electron-deficient centre
usually electron rich and may be an negative ion

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5
Q

common nucleophiles

A

H20, NH3+, OH-, halogens

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6
Q

strength of C-X bond and its effect on reactivity

A

C-X bond enthalpy decreases down the group

this means that iodo-, bromo-, and chloro- alkanes are the most reactive

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7
Q

what happens in the nucleophilic substitution of haloalkanes

A

a nucleophile replaces the halogen in the haloalkane, which is lost as a halide ion

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8
Q

which aqueous alkalis are normally used for the hydrolysis of haloalkanes

A

NaOH (aq)

KOH (aq)

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9
Q

nucleophilic substitution mechanism (mechanism for hydrolysis of haloalkanes)

A
  • the OH- ion acts as a nucleophile, donating an electron pair to the d+ carbon atom
  • OH-nion attacks from the opposite side to the halide as to reduce repulsion
  • a new bond forms between the oxygen atom of the OH- ion and the carbon atom
  • the carbon-halogen bond breaks by heterolytic fission
  • an alcohol and a halide ion are formed
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10
Q

how to make haloalkanes undergo hydrolysis with water

A

haloalkanes do not dissolve in water

however in the presence of an ethanol solvent and aqueous silver nitrate, water acts as a nucleophile to form alcohol.

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11
Q

how to measure the rate of hydrolysis of different carbon-halogens

A

measuring and comparing the time for the silver-halide precipitate to form

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12
Q

which halo-alkane reacts fastest

A

idoalkanes (fastest)
bromoalkanes
chloroalkanes (slowest)

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13
Q

hydrolysis of haloalkanes which aqueous hydroxide ions OH- (aq)

A

hydroxide, OH-, ions are nucleophiles with a lone pair of electrons on the oxygen atoms, which can be donated to from a new covalent bond.
haloalkanes undergo nucleophilic substitution reactions with aqueous alkali, OH- (aq), to form alcohols.

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14
Q

What happens when you react a haloalkane with potassium cyanide and what conditions do you need?

A

C-N replaces the X and produces a nitrile and KX

Nucleophilic substitution

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