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Chemistry > Haloalkanes/Halogenoalkanes > Flashcards

Haloalkanes/Halogenoalkanes Flashcards

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1
Q

What is a nucleophile

A

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

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2
Q

How do nucleophiles bind to a molecule?

A

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

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3
Q

Do nucleophiles bond with POLAR or NON-POLAR molecules?

A

POLAR MOLECULES as they have a partial charge

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4
Q

What reagent is normally used to test for HALOGENS?

A

Silver nitrate

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5
Q

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

A

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

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6
Q

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

A

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

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7
Q

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

A

Halogen atom

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8
Q

The carbon-Halogen bond in Halogenalkanes is ____

A

Polar

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9
Q

Why is Halogenalkanes polar?

A

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

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10
Q

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

A

nucleophiles

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11
Q

OH-, CN_ and NH3 are all _____

A

Nucleophiles that can react with halogenalkanes

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12
Q

A nucleophile can react with a _____

A

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

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13
Q

What are the steps for a nucleophilic substitution reaction?

A

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.

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14
Q

Halogenoalkanes react with _____ to form Alcohols.

A

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

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15
Q

How do you convert Bromoethane to alcohol?

A

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

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16
Q

Nitriles are formed by reacting Halogenoalkanes with _____

A

Cyanide

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17
Q

How do you convert a Halogenoalkane to a Nitrile?

A

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.

18
Q

What is Hydrolysis?

A

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

19
Q

Reacting Halogenoalkanes with AMMONIA forms ____

A

Amines.

20
Q

How do you convert a Halogenoalkane to an Amine?

A

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.

21
Q

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

A

hydrolysis

22
Q

How quickly different halogenoalkanes are hydrolysed depends on the ______

A

Bond enthalpy

23
Q

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

A

faster

24
Q

______ have the weakest bonds, so they hydrolise the fastest

A

Iodoalkanes

25
Q

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

A

Fluroalkanes

26
Q

Method to test the reactivity of halogenalkanes

A

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.

27
Q

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

A

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

28
Q

What is primary Halogenalkane?

A

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

29
Q

What is secondary Halogenalkane?

A

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

30
Q

What is tertiary alcohol?

A

A tertiary HALOGENALKANE has NO HYDROGEN ATOMS and THREE ALKYL GROUPS

31
Q

Which type of haloalkaneis the most reactive?

A

Tertiary halogenalkane are the most reactive Halogenalkane.

32
Q

Which type of Halogenalkane is the least reactive?

A

Primary halogenalkane are the least reactive Halogenalkane

33
Q

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

A

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.

34
Q

How does an elimination reaction happen?

A

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.

35
Q

What is an elimination reaction?

A

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

36
Q

Why are carbon halogen bonds polar?

A

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

37
Q

Why does iodoethane react faster than chloroethane with nucleophiles?

A

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

38
Q

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

A

Reagent: NaOH/KOH
Solvent: Water

39
Q

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

A

Reagent: Ammonia
Solvent: Ethanol/Alcohol

40
Q

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

A

Reagent:NaOH/KOH
Solvent: Ethanol/Alcohol

41
Q

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.

A

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

Chemistry (11 decks)

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