Halogenoalkanes Flashcards
(20 cards)
What is the boiling point trend of halogenoalkanes?
- Increase down a group
What does the boiling point of halogenoalkanes depend on? How?
The strength of intermolecular forces
- more electrons => stronger van der waals => more energy needed to overcome the forces
What do halogenoalkanes have that make the nucleophile attack it?
- A polar bond
- And an electron deficient centre (e.g. H+ in molecule H3C————Cl)
What is a nucleophile?
- Attacks halogenoakanes’ electron deficient centre
- Substance that is an electron pair donor
- Have a lone pair
1ST REACTION WITH HYDROXIDE IONS
What is the condition, reagent, mechanism, and equation for this reaction?
Condition: Under reflux
Reagent: Warm aqueous NaOH
Mechanism: Nucleophilic substitution
Equation: R-X + NaOH —> ROH + NaX
1ST REACTION WITH HYDROXIDE IONS
What is formed or what is the product?
- Alcohol
- Halogen
2ND REACTION WITH HYDROXIDE IONS
What is the condition, reagent, mechanism, and equation for this reaction?
Condition: Under reflux
Reagent: Warm ethanolic KOH
Mechanism: Elimination
Equation: R-X + KOH —> alkene + KCl + water
2ND REACTION WITH HYDROXIDE IONS
What does the OH- ion act as?
- acts as a base that accepts protons
- attacks H on the C that is adjacent to the C-X bond
2ND REACTION WITH HYDROXIDE IONS
What does it form?
- alkene
- water
- halogen
REACTION WITH CYANIDE IONS
What is the condition, reagent, mechanism, and equation for this reaction?
Condition: under reflux
Reagent: warm ethanolic KCN
Mechanism: nucleophilic substitution
Reaction: R-X +KCN —> RCN +KX
REACTION WITH CYANIDE IONS
What is formed?
- Nitrile
- Halogen
REACTION WITH AMMONIA
What is the condition, reagent, mechanism, and equation for this reaction?
Condition: must have excess ammonia
Reagent: Heat with ethanolic ammonia
Mechanism: Nucleophilic substitution
Equation: R-X + 2NH3 —> R-NH2 + NH4X
REACTION WITH AMMONIA
What happens in the second phase of the reaction?
excess NH3 acts as a base and reacts with H
REACTION WITH AMMONIA
What are the products?
- amine
- ammonium
What does the rate of reactions of halogenoalkanes depend on? why?
Depend on C-X (halogen) bond.
- The weaker it is, the easier is is to break, increasing the rate of reaction.
What are the roles of ozone in both upper and lower atmosphere?
upper atmosphere: removes the sun’s harmful UV radiation
lower atmosphere: a pollutant and contributes to the formation of smog
What do CFCs have that help break down ozones?
Have C-Cl bond that are broken down by radiation
- This break down produces chlorine radicals
What do chlorine radicals from CFCs do?
catalyse the decomposition/break down of ozone
What did scientists state in regards with CFCs safety?
Scientists stated that CFCs were damaging the ozone layer so CFCs are now banned
What happened now that CFCs are now banned? What is now used as an alternative and why?
Hydrofluorocarbons (HFCs) are now used for refrigerators and air conditioners because they do not have C-Cl bond.
