Halogenoalkanes

• What is the general formula of halogenoalkanes?

  CnH2n+1X

  Where X= F, Cl, Br, I
• Are halogens more electronegative than carbon

  More
• Why are the bonds polar?


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• What are the intermolecular forces in halogenoalkanes?

  Dipole-Dipole and VDW
• Are halogenoalkanes soluble or insoluble in water?

  Insoluble
• Why are they used as dry-cleaning fluids to remove oil stains?

  Both have weak intermolecular forces. Like dissolves like
• Does boiling point increase or decrease with chain length?

  Increase
• Does boiling point increase or decrease down the group?

  Increase
• Why do the boiling points increase?

  Atoms get bigger so forces get bigger
• What affect does branching have?

  Decreases the boiling point because there is less surface area contact
• Compare the boiling points or alkanes to halogenoalkanes

  Halogenoalkanes have a higher boiling point because they are bigger molecules with more electrons and therefore have stronger Van Der Waals forces so more energy is needed
• Does reactivity increase of decrease down the group? Why?

  Increase

  C-X bond gets weaker down the group, distance from nucleus increases so more unstable
• What are primary, secondary and tertiary halogenoalkanes?

  1. Primary- 1 carbon attached to the bromo carbon
  2. Secondary- 2 carbons attached to the bromo carbon
  3. Tertiary- 3 carbons attached to the bromo carbon
• What is a nucleophile?

  Electron lone pair donor
• Why do nucleophiles attack positive carbons?

  Difference in electronegativity between carbon and halogen atom
• What is substitution?

  swapping a halogen atom for another atom or group of atoms
• What is elimination?

  Removal of a small molecule from the organic molecule
• What is a reagent?

  Both a nucleophile and a base
• What are the 3 nucleophiles used in nucleophilic substitution reactions?

  Hydroxide ion (:OH-)

  Cyanide ion (:CN-)

  Ammonia (:NH3)
• Which of the nucleophiles has no charge?

  Ammonia has a neutral charge
• What are the conditions for nucleophilic substitution with :OH-

  Heat halogenoalkane under reflux with aqueous KOH or NaOH
• What does reacting a halogenoalkane with a hydroxide make

  Halogenoalkane -> Alcohol
• Mechanism for primary halogenoalkanes with :OH- (SN2)

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• Alternative mechanism for tertiary halogenoalkanes with :OH- (SN1)

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• Why do you remove the halogen first in tertiary halogenoalkanes

  Steric Hindrance- they have a bulky shape that means the nucleophile can't get in so you have to remove the halogen first create a carbocation
• What are the conditions for nucleophilic substitution with a :CN-

  Heat halogenoalkane under reflux with KCN in ethanol/water mix
• What does reacting a halogenoalkane with :CN- make

  Halogenoalkane -> nitrile
• Why are nitriles useful in organic synthesis?

  useful in lengthening the carbon chain

  nitrile functional group can be changed into other functional groups
• What are the conditions for nucleophilic substitution with :NH3

  Heat halogenoalkane under pressure with concentrated NH3 in ethanol (solvent)
• What does reacting a halogenoalkane with :NH3 make

  Halogenoalkane -> amine
• Mechanism for nucleophilic substitution with :CN-


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• Mechanism for nucleophilic substitution with :CN- (SN1)


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• Mechanism for nucleophilic substitution with :NH3 


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• What are the conditions for elimination reactions with :OH- as a base

  Heat halogenoalkane with KOH or NaOH in ethanol
• What is made in an elimination reaction with :OH- and a halogenoalkane

  Halogenoalkane -> alkene
• What does :OH- acting as a base mean?

  The H is removed from the C next to the halogen.

  H2O (proton donor) $\Leftrightarrow$ OH- (proton acceptor) + H+
• Mechanism for elimination reaction with :OH-


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• :OH- acts as a base an a nucleophile what is produced

  A mixture of an alcohol and alkene
• How can we influence this mix?

  Changing the reaction conditions

  Changing the type of halogenoalkane
• How to get the mix to leans more to SUBSTITUTION

  Dilute solution of OH-

  More water as solvent

  warm/cooler

  Use primary and secondary halogenoalkanes