Halogenoalkanes Flashcards
Halogenoalkanes:
What’s meant by Halogenoalkanes?
When H in Alkanes are replaced w Halogens
Halogenoalkanes:
What are Halogenoalkanes reacted with?
Nucleophiles
Halogenoalkanes:
What are Nucleophiles?
Species that donate electron pairs
Halogenoalkanes:
What charge are Nucleophiles?
δ- or -
Halogenoalkanes: Primary,Secondary & Tertiary Structures
What are Primary Halogenoalkanes?
Carbon-cation is found by breaking Halogen away from C
Carbon-cation is attached to 1 Alkyl Group & 2 Hydrogens
Halogenoalkanes: Primary,Secondary & Tertiary Structures
What are Secondary Halogenoalkanes?
Carbon-cation is found by breaking Halogen away from C
Carbon-cation is attached to 2 Alkyl Groups & 1 Hydrogen
Halogenoalkanes: Primary,Secondary & Tertiary Structures
What are Tertiary Halogenoalkanes?
Carbon-cation is found by breaking Halogen away from C
Carbon-cation is attached to 3 Alkyl Groups & no Hydrogens
Halogenoalkanes: Primary,Secondary & Tertiary Structures
Which Halogenoalkanane Structure is most stable?
Tertiary
Halogenoalkanes: Bond Enthalpy
How do you break Halogenoalkane?
Break halogen away from Carbon chain attaching the chain to something else
Halogenoalkanes: Bond Enthalpy in terms of IMFs
What’s the trend of Halogenoalkanes in terms of Bond Enthalpy & IMFs?
- Down G7, atomic radius increases
↳ more electrons
↳ more IMFs
↳ higher mp/bp : more energy needed to break it down
Hence C-I has the highest mp/bp
↳ hardest to break
Halogenoalkanes: Bond Enthalpy in terms of NC
What’s the trend of Halogenoalkanes in terms of Bond Enthalpy & NC?
- Down G7, atomic radius increases
↳ outer e- = further away shielded by inner e-
↳ ionise quicker : nuclear charge is reduced
↳ lower mp/bp : less energy needed to break it down
Hence C-I has the lowerst mp/bp
↳ easiest to break
Halogenoalkanes: Bond Enthalpy IMFs VS NC
Which one takes priority?
Nuclear Charge
Halogenoalkanes: Bond Enthalpy IMFs VS NC
Why does NC take priority?
Weaker Carbon-Hydrogen (e.g C-I) bonds break first
↳ they react the fastest
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What’s formed when a Halogenoalkane is hydrolysed w water?
An alcohol
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What’s the equation for this reaction?
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What type of Fission occurs?
Heterolytic Fission
↳ bond breaks unevenly, an atom receives both radicals forming 2 ions
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What’s the Nucleophile in this reaction?
Water
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
How would you identify the Halide formed in this reaction?
Add Silver Nitrate into solution
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
Why would you add Silver Nitrate to the solution?
Silver Halide precipitate is formed at different rates
↳ undissolved solid
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
How would you identify the Halide?
Identify colour change
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What colour is the AgCl Precipitate?
White
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What colour is the AgBr Precipitate?
Cream
Halogenoalkanes: Halogenoalkane Hydrolysis using Water
What colour is the AgI Precipitate?
Pale Yellow
Halogenoalkanes: Primary,Secondary & Tertiary have diff reactivities
What’s the relationship between the Type of Structure the Halogenoalkane forms & Reactivity?
- Down the table, the faster the Halogenoalkane is broken
↳ more Alkyl groups = more stable
↳ more reactive it is : quicker it breaks
Halogenoalkanes: Nucleophiles
What are 4 examples of Nucleophiles?
- Hydroxide (OH-)
- Water (H2O)
- Ammonia (NH3)
- Cyanide Ions (CN-)
Halogenoalkanes: Nucleophiles
What is considered a Nuclophile?
Anything with a lone pair of e-
↳ H2O & NH3 are neutral nucleophiles
Halogenoalkanes: Nucleophillic Substitution
What occurs in this Reactions?
Nuc replaces X
Halogenoalkanes: Nucleophillic Substitution
What does a Nucleophillic Substitution mechanism look like?
Halogenoalkanes: Nucleophillic Substitution
What does the ‘Nuc’ represent?
Nucleophile
Halogenoalkanes: Nucleophillic Substitution
What does the ‘X’ represent?
Halogen
Halogenoalkanes: Nuclophillic Substitution
What’s Nucleophillic Substitution?
When halogenoalkanes are hydrolysed to alcohols
Halogenoalkanes: Nucleophillic Substitution
What’s the 1st Step of Nucleophillic Substitution?
Nuc provides a pair of electrons to the C (δ+)
Halogenoalkanes: Nucleophillic Substitution
What’s the 2nd Step of Nucleophillic Substitution?
C-X bond breaks heterolytically
↳ bond breaks unevenly, a species gains both electrons (Halogen) forming 2 ions
Halogenoalkanes: Nucleophillic Substitution
What’s the 3rd Step of Nucleophillic Substitution?
- Nuc bonds to C
- Halogen takes both electrons
Halogenoalkanes: Forming Alcohols
What do Halogenoalkanes react w to form an Alcohol?
Aqueous KOH
↳ provides OH- group
Halogenoalkanes: Forming Alcohols
What’s the Equation for this Reaction?
Halogenoalkanes: Forming Alcohols
What’s meant by Reflux?
Continuously heating over a long period of time
Halogenoalkanes: Forming Alcohols
What is used in Reflux?
Warm Alkali (NaOH)
Halogenoalkanes: Forming Alcohols
What’s a Reflux substitute?
Water (neutral nuclophile)
↳ reaction is slower
Halogenoalkanes: Forming Alcohols
Why’s Water used as a substitute?
- Reaction is slower
- OH- can be dissolved in water
Halogenoalkanes: Forming Nitriles
What do Halogenoalkanes react w to form Nitriles?
Potassium Cyanide (CN-)
↳provides Cyanide Ions which are triple bonded
Halogenoalkanes: Forming Nitriles
What’s the Equation for this reaction?
Halogenoalkanes: Forming Nitriles
What’s a Reflux Substitute for this reaction?
Ethanol
↳ Potassium Cyanide is insoluble in water but soluble in ethanol
Halogenoalkanes: Forming Amines (NH2)
What do Halogenoalkanes react w to form Amines?
Excess Ethanolic Ammonia
↳ ammonia dissolved in ethanol
Halogenoalkanes: Forming Amines (NH2)
Why’s the Ethanolic Ammonia in Excess?
Ammonia reacts twice in this reaction
Halogenoalkanes: Forming Amines (NH2)
What’s the Reaction mechanism for this?
Halogenoalkanes: Forming Amines (NH2)
What’s the 1st Reaction w Ammonia?
Attacks the Halogen
↳ e- donated to C (δ+) which later passes it to X
Halogenoalkanes: Forming Amines (NH2)
What happens after the 1st Reaction w Ammonia?
- Dative bond is formed
- N is +
Halogenoalkanes: Forming Amines (NH2)
Why does the 2nd Reaction w Ammonia occur?
You can’t have a + on a compound
Halogenoalkanes: Forming Amines (NH2)
What happens in the 2nd Reaction w Ammonia?
Ammonia takes a proton from N+
↳ removes a H from it creating an Amine
Halogenoalkanes: Forming Amines (NH2)
How would you Identify an Amine?
Smells fishy
Halogenoalkanes: Elimination Reactions
What is an Elimination Reaction?
When a Halogenoalkane reacts w Ethanolic Alkali instead of Aqueous
Halogenoalkanes: Elimination Reactions
What’s the Equation for this reaction?
Halogenoalkanes: Elimination Reactions
Why’s Reflux required for this Reaction?
Otherwise volatile stuff will be lost
Halogenoalkanes: Elimination Reactions
What occurs in this Reactions?
- Alkene formed
- Reactants are dehydrated
