Haloalkanes/Halogenoalkanes

Question 1

What is a nucleophile

Answer 1

A nucleophile is an atom or molecule that donates an ELECTRON PAIR to make a covalent bond.

Question 2

How do nucleophiles bind to a molecule?

Answer 2

They do this by bonding with the POSITIVELY CHARGED or PARTIALLY CHARGED parts of molecules

Question 3

Do nucleophiles bond with POLAR or NON-POLAR molecules?

Answer 3

POLAR MOLECULES as they have a partial charge

Question 4

What reagent is normally used to test for HALOGENS?

Answer 4

Silver nitrate

Question 5

What do Ag+ ions produce when they react with halide ions?

Answer 5

Ag+ ions react with halide ions to form the HALOGEN PRECIPITATE.

Question 6

What happens to the STRENGTH of the halogen carbon bond when we go down group 7.

Answer 6

The HALOGEN-CARBON decreases as we move down group 7 due to increasing atomic distances

Question 7

A HALOGENALKANE is an alkane with at least one _____in place of a halogen atom

Answer 7

Halogen atom

Question 8

The carbon-Halogen bond in Halogenalkanes is ____

Answer 8

Polar

Question 9

Why is Halogenalkanes polar?

Answer 9

Halogens are much more ELECTRONEGATIVE than carbon, so carbon-halogen bonds are POLAR.

Question 10

The s plus charge on the carbon makes it prone to attacks from the ____

Answer 10

nucleophiles

Question 11

OH-, CN_ and NH3 are all _____

Answer 11

Nucleophiles that can react with halogenalkanes

Question 12

A nucleophile can react with a _____

Answer 12

polar molecule by kicking out the functional group and taking its place.

Question 13

What are the steps for a nucleophilic substitution reaction?

Answer 13

The lone pair of electrons on the nucleophile attacks the s+ carbon. The C-X bond breaks.

The halogen leaves taking both electrons with it. A new bond forms between the cabin a nucleophile.

Question 14

Halogenoalkanes react with _____ to form Alcohols.

Answer 14

Hydroxides, This is sometimes called HYDROLYSIS because exactly the same reaction will happen with water.

Question 15

How do you convert Bromoethane to alcohol?

Answer 15

You have to use WARM AQUEOUS SODIUM or POTASSIUM HYDROXIDE -it’s a NUCLEOPHILIC SUBSTITUTION REACTION.

Question 16

Nitriles are formed by reacting Halogenoalkanes with _____

Answer 16

Cyanide

Question 17

How do you convert a Halogenoalkane to a Nitrile?

Answer 17

If you WARM a halogenoalkane with ETHANOLIC POTASSIUM CYANIDE (potassium cyanide dissolves in ethanol) you get a NITRILE.

It’s yet another NUCLEOPHILIC SUBSTITUTION REACTION-the CYANIDE ION, CN-, is the nucleophile.

Question 18

What is Hydrolysis?

Answer 18

Hydrolysis means splitting a molecule apart by reacting it with water.

Question 19

Reacting Halogenoalkanes with AMMONIA forms ____

Answer 19

Amines.

Question 20

How do you convert a Halogenoalkane to an Amine?

Answer 20

If you WARM a halogenoalkane with excess ethanolic ammonia (Ethanolic ammonia is just ammonia dissolved in ethanol) the AMMONIA swaps places with the HALOGEN.

It’s a nucleophilic substitution reaction
> The first step a normal nucleophilic substitution reaction, displacing the bromine
>In the second reaction the ammonia molecule removes a hydrogen from the NH3 group to form an Amine and an ammonium ion (NH4).
>The ammonium ion can react with the bromine ion to form Ammonium bromide.
>The AMINE GROUP in the the product still has a lone pair of electrons. This means it can also act as a NUCLEOPHILE, giving a mixture of products.

Question 21

When halogenalkanes react with HYDROXIDE IONS or WATER to form alcohols, it’s called _____

Answer 21

hydrolysis

Question 22

How quickly different halogenoalkanes are hydrolysed depends on the ______

Answer 22

Bond enthalpy

Question 23

Weaker carbon-halogen bonds break more easily, so they break more _____

Answer 23

faster

Question 24

______ have the weakest bonds, so they hydrolise the fastest

Answer 24

Iodoalkanes

Question 25

_____ have the strongest bonds, so they're the slowest at hydrolysing

Answer 25

Fluroalkanes

Question 26

Method to test the reactivity of halogenalkanes

Answer 26

When you mix a halogenalkane with water it reacts to form an ALCOHOL. If you put SILVER NITRATE SOLUTION in the mixture too, the silver ions react with the HALIDE IONS as soon as they form, giving a SILVER HALIDE PRECIPITATE. To compare the reactivity set up three test tubes each containing different halogenalkane, ethanol as a solvent and silver nitrate solution (this contains the water) A pale yellow precipitate quickly form with 2-iodopropane- so iodoalkanes must be the most reactive halogenalkane. BROMOALKANES react slower than iodoalaknes to form a cream precipitate, and chloroalkanes form a white precipitate the slowest of all.

Question 27

The halide test is used to identify which halogen is used, it can also be used to identify, what?

Answer 27

You can also use this reaction to compare the rate of hydrolysis, and therefore the activities, of PRIMARY, SECONDARY and TERTIARY HALOGENALKANES.

Question 28

What is primary Halogenalkane?

Answer 28

A PRIMARY halogenalkane has TWO HYDROGEN ATOMS and just ONE ALKYL GROUP.

Question 29

What is secondary Halogenalkane?

Answer 29

A SECONDARY halogenalkane has just one HYDROGEN ATOM and TWO ALKYL GROUPS.

Question 30

What is tertiary alcohol?

Answer 30

A tertiary HALOGENALKANE has NO HYDROGEN ATOMS and THREE ALKYL GROUPS

Question 31

Which type of haloalkaneis the most reactive?

Answer 31

Tertiary halogenalkane are the most reactive Halogenalkane.

Question 32

Which type of Halogenalkane is the least reactive?

Answer 32

Primary halogenalkane are the least reactive Halogenalkane

Question 33

What is the reaction called when you heat up a haloalkane with hydroxide ions in ETHANOL instead of water?

Answer 33

If you warm a haloalkane with hydroxide ions dissolved in ETHANOL instead of water, an ELIMINATION REACTION happens, and you end up with an alkene.

Question 34

How does an elimination reaction happen?

Answer 34

OH- acts as a base and takes a proton, H+, from the carbon on the left. This makes water. The left carbon now has a spare electron, so it forms a double bond with the middle carbon. To form the double bond, the middle carbon has to let go of the Br, which drops off as a Br- ion.

Question 35

What is an elimination reaction?

Answer 35

In an elimination reaction, a SMALL GROUP of atoms break away from a molecule. This group is not replaced by anything else.

Question 36

Why are carbon halogen bonds polar?

Answer 36

Halogens are much more ELECTRONEGATIVE than carbon, so carbon halogen bonds are polar.

Question 37

Why does iodoethane react faster than chloroethane with nucleophiles?

Answer 37

Iodoalkanes have a lower bond enthalpy than chloroalkanes and therefore react faster.

Question 38

What reagent and solvent is used in converting 2-bromopentane into pentan-2ol?

Answer 38

Reagent: NaOH/KOH Solvent: Water

Question 39

What reagent and solvent is used in converting 2-bromopentane into pentan-2-amine?

Answer 39

Reagent: Ammonia Solvent: Ethanol/Alcohol

Question 40

What reagent and solvent are used in converting 2-bromopentane into pentan-1-ene?

Answer 40

Reagent:NaOH/KOH Solvent: Ethanol/Alcohol

Question 41

Under the same conditions, 2-iodopropane was used in reaction instead of 2-bromopropane. What difference (if any) would you expect in the rate of reaction? explain your answer.

Answer 41

The rate of reaction would be faster because the c-l bond is weaker than C-Br as the BOND ENTALOPY IS LOWER.