C.13 Halogenoalkanes

Question 1

What is a Halogenoalkane?

Answer 1

Alkanes with one or more halogens attached to them

Question 2

How do you name a Halogenoalkane?

Answer 2

Longest carbon chain, suffix; Halogenoalkane in alphabetical order, prefix

Question 3

What are the boiling point trends in the Halogenoalkane group?

Answer 3

Increase down the group; Stronger intermolecular forces down; Electron count increases down, more van der waal forces

Question 4

How does electronegativity effect Halogenoalkanes?

Answer 4

Halogens are more electronegative, creating a polar bond; Carbon is attacked by the nucleophile

Question 5

What are nucleophiles?

Answer 5

Electron pair donors; Ammonia, hydroxide ions, cyanide ions

Question 6

How do Halogenoalkanes react with hydroxide ions in aqueous solvent and what are the conditions ?

Answer 6

Nucleophilic substitution producing alcohol; Warm aq NaOH, carried under reflux

Question 7

What is the mechanism for Halogenoalkanes reacting with hydroxide ions in aqueous solvent?

Answer 7

OH- attacks delta + C; Bond C into X breaks; OH replaces X; RX + NaOH => ROH + NaX

Question 8

How do Halogenoalkanes react with cyanide ions and what are the conditions ?

Answer 8

Nucleophilic substitution producing nitriles; Warm ethanolic potassium cyanide, carried under reflux

Question 9

What is the mechanism for Halogenoalkanes reacting with cyanide ions?

Answer 9

CN- attacks delta + C; Bond C into X breaks; CN replaces X; RX + KCN => RCN + KX

Question 10

How do Halogenoalkanes react with cyanide ions and what are the conditions ?

Answer 10

Nucleophilic substitution producing an amine ; Heat w/ ethanolic ammonia, excess ammonia

Question 11

What is the mechanism for Halogenoalkanes reacting with ammonia ?

Answer 11

NH3- attacks delta + C; Bond C into X breaks; NH3 replaces X forming an intermediate; Another NH3 molecule acts as base by reacting with H; Bond H into N breaks; CH3CH2Cl +2NH3 => CH3CH2NH2 + NH4Cl

Question 12

What are the trends in reactivity with Halogenoalkanes?

Answer 12

Reactivity increases down group; Lower bond enthalpy, more reactive; Lower bond enthalpy, easier to break bonds, reactions will be more reactive

Question 13

How do Halogenoalkanes react with hydroxide ions in ethanol solvent and what are the conditions ?

Answer 13

Nucleophilic elimination producing an alkene; Warm ethanolic sodium hydroxide, carried under reflux

Question 14

What is the mechanism for Halogenoalkanes reacting with hydroxide ions in ethanol solvent?

Answer 14

OH- attacks H on C adjacent to X; OH- acts as base forming water; Electrons in bond C-H move formind C=C bond; Bond C into X breaks

Question 15

What is the difference in creating an elimination reaction and a substitution reaction?

Answer 15

Solvent; Ethanol solvent, elimination; Water solvent, substitution

Question 16

What is a base?

Answer 16

Proton acceptor

Question 17

What are CFCs and what are their attributes?

Answer 17

Chlorofluorocarbons; Molecules but all their Hs replaces by Cl and F; Stable molecule; Broken down by UV forming radicals; Break down O3(ozone) in atmosphere; C-Cl bonds are easiest to break

Question 18

What is the full equations for CFCs breaking down ozone?

Answer 18

Initiation
CCl3(g) =UV=> .CC2F(g) + Cl.(g)
Propagation
Cl.(g) + O3(g) => O2(g) + ClO.(g)
ClO.(g) + O3(g) => 2O2(g) + Cl.(g)
Termination
Cl.(g)  + Cl.(g) => Cl2(g)

Question 19

What is the simplified equation for break down of ozone with CFCs?

Answer 19

Cl.(g) + O3(g) => ClO.(g) + O2
ClO.(g) + O3 => 2O2 + Cl.
2O3 => 3O2
(2O3 =UV w/ Cl. catalyst=> 3O2)

Question 20

What are the alternatives to CFCs and why do we use them?

Answer 20

HCFs, Hydrofluorocarbons; No Cl to catalyse ozone depletion