Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry #2 > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

how do alkanes react with halogens

A

in the presence of UV light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is formed when alkanes and halogens react together in the presence of UV light

A

a halogenoalkane and hydrogen halide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the reaction for the formation of halogenoalkanes and why

A

a substitution reaction

a hydrogen in the alkane is replaced by the halogen

The hydrogen lost from the alkane will join with the second half of the diatomic
halogen molecule to form HX

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what’s the mechanism for the formation of halogenoalkanes

A

free radical substitution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what’s a free radical

A

a reactive species due the presence of an unpaired electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what are the 3 stages in free radical substitution

A

1) initiation

2) propagation 1 and 2

3) termination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

explain the initiation step in free radical
substitution for formation of halogenoalkanes

A

ultraviolet light causes the covalent bond between halogen atoms to break forming 2 halogen free radicals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what happens in 1st propagation for formation of halogenoalkanes

A

the halogen radical reacts with the alkane

the halogen radical removes a hydrogen from alkane

creating a hydrogen halide and alkyl radical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what happens in 2nd propagation for formation of halogenoalkanes

A

the alkyl radical reacts with halogen molecule and

creates halogenoalkane and halogen radical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what does the halogen radical created in the end of 2nd propagation do after

A

the halogen radical created at the end of propagation 2 goes on to react with another alkane molecule and 1st propagation is repeated

there will be a chain reaction until no more halogen molecules or alkane molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what happens in termination step for formation of halogenoalkanes

A

2 radicals react to form neutral molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are chlorofluorocarbons (CFC’s)

A

they are halogenoalkanes containing both chlorine and fluorine but no hydrogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

describe short chain CFCS and what they were used for

A

they are gasses

they were used in refrigerators

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what were long chain CFCS used for

A

they are used for degreasing solvents
and dry cleaning

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how are CFC gases like under normal conditions

A

very unreactive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what happens when CFC gasses reach the atmosphere

A

they decompose to produce chlorine free radicals

17
Q

why is the ozone layer important

A

it absorbs harmful UV radiation from sun that causes skin cancer by damaging DNA in skin cells

18
Q

what layer is ozone layer in

A

stratosphere

19
Q

what do chlorine radicals do to ozone

A

chlorine radicals decompose ozone in the stratosphere creating a hole in the earths ozone layer

20
Q

name all the steps in the decomposition of ozone

A

1) the c-cl bond is broken in the presence of uv radiation to produce chlorine radical

R-Cl —> R* + Cl*

2) the chlorine radical decomposes ozone in the stratosphere

Cl* + O3 —> ClO* +O2

3) the resulting ClO3 radicals attack more ozone molecules and regenerate Cl*

ClO* + O3 —> 2O2 * + Cl*

21
Q

what can we call the Cl* in regards to the breakdown of O3

A

as the Cl* is not destroyed and is regenerated we can say it acts as a catalyst in the breakdown of ozone to oxygen

22
Q

what’s the overall equation for decomposition of ozone

A

2O3 —> 3O2

23
Q

what are the safer alternatives to CFCS

A

chemists have developed safer chlorine free compounds which is primarily used in air conditioning and refrigerators

24
Q

why are the C-X bonds polar

A

because the halogen atoms are more electronegative than carbon

the electrons in the C-X bond are more attracted to the halogen leaving it delta negative and the carbon delta positive

25
Q

what is the delta positive carbon atom attacked by

A

nucleophile

26
Q

what’s a nucleophile

A

electron pair donor

27
Q

name the 3 types of nucleophillic substitution with halogenoalkanes

A

1) NaOH/KOH (:OH ions) to form alcohols

2) KCN ( :CN- ions) to form nitriles

3) with excess ammonia (:NH3) to form primary amines

28
Q

how do we form alcohols from halogenoalkanes

A

Reagent: NaOH / KOH

Conditions : Warm and aqueous

When Halogenoalkanes are warmed with aqueous sodium hydroxide (NaOH) or potassium hydroxide (KOH), alcohols are formed. NaOH and KOH are ionic compounds containing the nucleophile: OH.

29
Q

how do we form nitriles from halogenoalkanes

A

Reagent: KCN (:CN- ions)

Conditions: warmed in aqueous ethanol

When Halogenoalkanes are warmed with an aqueous ethanol solution of potassium cyanide (KCN), nitriles are formed. This adds an extra carbon to the chain. The nucleophile in KCN is :CN-

30
Q

how are primary amines formed from halogenoalkanes

A

reagent: NH3

conditions: warmed, excess ammonia, sealed container

When Halogenoalkanes are warmed with an excess of ammonia in a sealed container, primary amines are formed (2 hydrogen atoms attached to the nitrogen). The nucleophile is ammonia, in which nitrogen atom has the lone pair of electrons:

31
Q

what mechanism is alkene formed from halogenoalkanes

A

elimination mechanism

32
Q

describe reagents and conditions elimination mechanism

describe the different roles of hydroxide ions

A

reagents: NaOH

conditions: hot in ethanol

In the reaction between aqueous sodium hydroxide and a Halogenalkane, the hydroxide ions act as a nucleophile (electron pair donor) and an alcohol is formed by nucleophilic substitution.

• However, the hydroxide ions can also act as a base (accept H*), so an alternative elimination reaction also takes place in which one of the hydrogen atom and the halogen atom are eliminated from the Halogenalkane to give an alkene.

33
Q

describe reagents and conditions elimination mechanism

describe the different roles of hydroxide ions

A

reagents: NaOH

conditions: hot in ethanol

In the reaction between aqueous sodium hydroxide and a Halogenalkane, the hydroxide ions act as a nucleophile (electron pair donor) and an alcohol is formed by nucleophilic substitution.

• However, the hydroxide ions can also act as a base (accept H*), so an alternative elimination reaction also takes place in which one of the hydrogen atom and the halogen atom are eliminated from the Halogenalkane to give an alkene.

34
Q

what are the steps in elimination reaction

A

Stage 1: The Hydroxide ion removes a hydrogen atom from an adjacent carbon to the halogen atom.

Stage 2: The electrons in the carbon-hydrogen bond move onto the carbon-carbon bond to create a double bond.

Stage 3: the electrons in the carbon-halogen bond move onto the halogen atoms, breaking the bond and creating a halide ion.

Chemistry #2 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions