Nucleophilic substitution

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  • Created by: Hindleyc
  • Created on: 15-05-18 17:07
What do Halogenoalkanes contain?
Polar bond
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What is electronegativity? Why?
Measure of ability/tendency of an atom to attract a bonding pair of electrons in a covalent bond. Covalent bonds share electrons but not equally
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What is bond enthalpy more important than in?
Bond polarity in determining reactivity
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What is the most reactive? What does it do? What has strongest/ weakest bond?
The weakest bond. Influence rate of reaction. Carbon-Fluorine stronger, Carbon-Iodine weaker
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What does boiling point increase with? Trends?
Increased chain length. Increases going down group
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What makes a bond polar?
Electronegativity of an atom
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Why is the C-X bond always polar (X= halogen)?
Halogens are more electronegative than carbon (slightly positive C)
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Why do Haloalkanes have HIGHER boiling points than HYDROCARBON chains of similar lengths?
Greater relative molecular mass and polarity
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Why does the carbon-halogen bond enthalpy influence the rate of reaction?
The carbon-halogen bond has to be broken during the reaction. The harder the bond is to break (the higher the bond enthalpy) the slower the haloalkanes react.
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What is a Nucleophile?
Electron pair (lone pair) donor
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What is nucleophilic substitution undergone in?
Haloalkane
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Examples of 3 nucleophiles?
OH-,CN- and NH3
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WHERE DO YOU DRAW THE ARROW FROM!
THE LONE PAIR OF ELECTRONS!!!
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Describe what happens in Nucleophillic Sub with hydroxide ions and Bromoethane
The OH- nucleophile attacks the slightly positive Carbon atom that was bonded to the halogen. This then bonds to the ethane forming ethanol and a Bromide Ion
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Give overall equation for Hydroxide ion and Bromoethane
CH3CH2Br + OH- = CH3CH2OH+Br-
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Describe what happens with the nucleophilic sub with Cyanide ions and bromoethane
CN- nucleophile attacks slightly positive carbon atom that was bonded to the halogen. This then bonds to the carbon removing the Br forming propanenitrile and a Br- ion
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Give eqn for reaction of cyanide with bromoethane
CH3CH2Br+CN-=CH3CH2CN+ Br-
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Describe what happens with the nucleophilic substitution of Ammonia with bromoethane
NH3 attacks the slightly positive carbon atom bonded to the halogen and bonds with the carbon forming Br- and CH3CH2NH2-H. The nitrogen now has a positive charge as can only bond to 2 atoms and is now bonded to 3
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What next?
so the H donates both electrons to the NH2 and another NH3 bonds to the hydrogen
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Eqn for it
CH3CH2Br+2NH3=CH3CH2NH2+NH4+Br-
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What does the rate of nucleophilic substitution depend on?
Strength of carbon halogen bond rather than degree of polarisation in bond
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Which bond is weakest? so?
C-I so most readily undergo's substitution so ror highest
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Other cards in this set

Card 2

Front

What is electronegativity? Why?

Back

Measure of ability/tendency of an atom to attract a bonding pair of electrons in a covalent bond. Covalent bonds share electrons but not equally

Card 3

Front

What is bond enthalpy more important than in?

Back

Preview of the front of card 3

Card 4

Front

What is the most reactive? What does it do? What has strongest/ weakest bond?

Back

Preview of the front of card 4

Card 5

Front

What does boiling point increase with? Trends?

Back

Preview of the front of card 5
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