Brainscape's Knowledge GenomeTM

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


See full index

Chemistry > 2.10 Halogenoalkanes > Flashcards

2.10 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

halogenoalkanes can be classified into

A

primary

secondary

tertiary

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

CH3 CH2 CH2 CH2 CH2 I

A

1 - iodopentane

primary

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

CH3 CH2 CH2 CH2 CH(Br) CH3

A

2 - bromopentane

secondary

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

(CH3)2 C Cl CH2 CH3

A

2 - cloro - 2 - methylbutane

tertiary

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

why carbon–chlorine bond is polar

A

it has more electrons and chlorine atom is very electronegative

carbon atom is slightly positive

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

why halogenoalkanes attacked by nucleophiles

A

nucleophiles attack slightly+ C atom in the carbon — halogen bond

the halogen atom gains electrons from the sigma bond and forms halides

attract electron rich nucleophiles

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

reactions of halogenoalkanes

name 3

A

elimination

substitution ( nucleophilic )

hydrolysis

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

elimination reaction
hydrogen atom is removed from carbon next to the one bonded to halogen

product is ?

A

alkene

or a mixtures of alkene

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

elimination reaction

eq
reagents
condition
product
reaction type
A

eq: refer to notes pg 2
reagents: conc potassium / sodium hydroxide
condition: heat under reflux with ethanol
product: propene ( reactant : 1 - bromopropane )

reaction type: elimination

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

elimination reaction

mechanism

draw it out

A

refer notes at pg 2

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

elimination reaction

draw diagram for heat under reflux

to prepare propene from 2 - bromopropane

A

refer notes pg 2

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

elimination reaction

why need to distill the mixture

A

to remove volatile product as it forms

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

elimination reaction

why condenser is not used in heat under reflux

A

propene has very low boiling points

will not condense at room temp

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

substitution reaction

halogen is substituted by an -OH, producing an alcohol

eq
reagents
condition
product
reaction type
A

eq : refer to notes

reagents: dilute potassium / sodium hydroxide
condition: heat under reflux in aq solution in ethanol
product: propanol ( reactant: chloropropane )

reaction type: nucleophilic substitution / hydrolysis

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

substitution reaction

why halogenoalkane is dissolved in alcohol
and alkali dissolved in water?

A

as a solvent for both aq and halogenoalkane

to allow halogenoalkane and water to mix

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

elimination and substitution

compare

conditions
type of reactions
action of OH-
product

A
  1. conditions: reflux with aq solution of KOH

type of reactions: nucleophilic substituion

action of OH- : nucleophilic

product: alcohol

2.
conditions: reflux with alcoholic solution of KOH

type of reactions: elimination

action of OH- : base

product: alkene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

2- chlorobutane in ethanolic aolution gives 3 diff alkenes

name and draw displayed formula

A

refer to notes pg 3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

mechanism of nucleophilic substitution

2 types when hydroxide ions attack a halogenoalkane

A

SN2

SN1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

the mechanism of nucleophilic substitution depends on?

A

primary secondary or tertiary halogenoakanes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

SN2 mechanism for?

A

primary and secondary

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

SN2 mechanism

draw the mechanism

involves?

A

transition state

single step mechanism

refer notes pg 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

reaction profile of SN2

A

refer notes pg 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

when does transition step occurs ?

in SN 2

A

refer to notes pg 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

the rate of order of SN2

A

idoalkane

bromoalkane

chloroalkane

C–I bond is weakest reaction faster

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

SN1 mechanism for

A

tertiary and secondary halogenoalkanes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

SN1 mechanism

draw the mechanism

involves?

A

carbocation intermediate

two steps

refer to notes pg 5

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

SN1 mechanism

reaction profile

A

refer notes pg 5

28
Q

two reasons why SN1 is more favoured by tertiary halogenoalkane

A
  1. more stable tertiary carbocation intermediate is formed
  2. presence of two alkyl groups which are bulky
    attached to slightly+ C of C–X bond
    inhibit approach of OH-
    effect is called as steric hindrance
29
Q

can primary halo undergo SN1

A

formation of primary carbocation has higher activation energy
rate of reaction is slower

30
Q

increase conc of NaOH will affect rate of which mechanism?

A

SN2

as high conc of nucleophile are requireed for the slowest step to speed up the reactoin

31
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

halogen is substituted with -NH2, producing amine

eq
reagents
condition
product
reaction type
mechanism
A

eq: refer to notes pg 6
reagents: excess ammonia in ethanol
condition: heated in a sealed tube
product: ethylamine ( reactant: chloroethane )

reaction type: nucleophilic substitution

mechanism: SN2

32
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

draw the mechanism

A

refer to pg 6

33
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

why reaction is carried out in a sealed tube rather than heat under reflux

A

ammonia gas would escape
it would not be condensed by reluc condenser

boiling point 33.43 degree celcius

34
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

alternative method to heating in sealed tube

A

conc solution of ammonia at room temp

leave for a long time

to increase rate of reaction

35
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

why ammonia is used in excess

A

there is 2 nucleophiles present

  • ethylamine
  • NH3

competition btwn them

so excess ammonia -to reduce the proportion of further substitution
ethylamine has line pairs of electrons can act as nucleophiles

36
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

why ammonia chloride salt is formed instead of HCL

A

NH3 is in excess when react with HCL forms

ammonia chloride

37
Q

further reactions of halogenoalkanes

  1. reaction with alcoholic ammonia

even in presence of alcoholic conc NH3

no elimination taek place only nucleophilic substitution why?

A

NH3 is a weak base ( slow reaction ) but a strong nucleophile and attack slightly + C in C—X bond

OH- strong base, weak nucleophile

38
Q

further reactions of halogenoalkanes

  1. reaction with water ( hydrolysis )

to study the reactivity of halogenoalkanes

the experiment procedure?

A

refer notes on G7

39
Q

further reactions of halogenoalkanes

  1. reaction with water ( hydrolysis )

same primary halogenoalkane
rate of hydrolysis
explanation

A

refer notes on pg 7

40
Q

further reactions of halogenoalkanes

  1. reaction with water ( hydrolysis )

primary, secondary, tertiary alcohol
rate of hydrolysis

explanation

A

refer notes pg 7

41
Q

test for halogenoalkanes

experiment procedure?

A

halo is warmed with some NaOH in ethanol and water

the mixture is acidified by adding dilute HNO3

Ag NO3 solution i added

42
Q

chloroalkane
bromoalkane
iodoalkane

observation with AgNO3
and ionic eq

A

refer notes pg 8

43
Q

test for halogenoalkane

halo is warmed with some NaOH in ethanol and water

the mixture is acidified by adding dilute HNO3

Ag NO3 solution i added

is actually difficult to distinguish the colours. what can you add to confirm each of these precipitate?

A

add NH3

AgCl dissolve in dilute NH3

AgBr insoluble in dilute NH3 but is soluble in conc NH3

AgI insoluble in dilute and conc NH3

44
Q

test for halogenoalkane

halo is warmed with some NaOH in ethanol and water

the mixture is acidified by adding dilute HNO3

Ag NO3 solution i added

why NaOH was added

A

to allow nucleophilic substitution

to hydrolyse the halogenoalkanes and liberate the halides

45
Q

test for halogenoalkane

halo is warmed with some NaOH in ethanol and water

the mixture is acidified by adding dilute HNO3

Ag NO3 solution i added

why the solution has to be acidic prior to addition of AgNO3?

A

neutralise NaOH

prevent from getting grey percipitate of AgOH from KOH when AgNO3 is added

46
Q

IUPAC naming

CFC - 11

A

trichlorofluromethane

47
Q

IUPAC naming

CFC - 123

A

1,1,2 - trichloro - 1,2,2 trifluroethane

48
Q

properties of CFCs ( no hydrogen atom )

A

inert

non flammable

non toxic

odourless / tasteless

volatile

49
Q

uses of CFCs

A

refrigerants - cooling liquid

aerosol propellants - perfume and insecticides spray

cleaning agent - solvent in dry cleaning and electronic industries

flame retardant - fire extinguisher

50
Q

CClBrF2

fire retardant

A

non flammable

inert due to strong C–F bond

forms a protective layer prevent underlying material from igniting and exclude O2

halogenoalkanes absorbs heat from fire

absorb free radicals in combustion propagation

51
Q

CCl2F2 as refrigerant

A

inert

low boiling point

vapourise rapidly at low temp

52
Q

inertness and stability of CFCs has a disadvantge

A

tend to persist in the atmosphere for long periods

destroy ozone layer

53
Q

structure of ozone layer

A

refer to note pg 10

54
Q

the initiation , propagation eq when UV strikes a CFC molecule producing free radicals

A

refer to note pg 10

55
Q

why chlorine radicals act as catalyst?

the consequences?

A

regenerate

so small amount can destroy thousand of ozone molecules before termination step

56
Q

replacement of CFCs called hydroclorofluorocarbon

which contain hydrogen atoms

advantages?

A

more reactive

broken down in the lower part of atmosphere and pose a lower risk to ozone layer

57
Q

replacement of CFCs called hydroclorofluorocarbon

which contain hydrogen atoms

disadvantges

A

greenhouse gas

flammable

formation of photochemical smog

58
Q

HCFC - 22
CHClF2

naming

A

chlorodifluromethane

59
Q

HCFC - 123
CF3CHCl2

naming

A

2,2 - dicloro - 1,1,1 - trifluoroethane

60
Q

why ozone is bad near earth s surface

A

harmful to respiratory systems

61
Q

why ozone is good at stratosphere

A

absorb Uv

reduce skin cancer

62
Q

why ozone is preferred than chlorine as a disinfectant

A

1.
ozone involves in a reversible reaction

turns to pure o2 when unused

leaves no harmful by products

ozone oxidation faster than chlorine

2.
chlorine is acidic in water

has a taste / unpleasant odour

63
Q

cars produce nitrogen oxide ( free radical )

but aircraft causes more damage why?

A

nitrogen oxides produce from cars are oxidised to NO2

when it rains it produced HNO3 acid rain

NO never gets a chance to reach stratosphere

aircraft fly closer to upper atmosphere, NO can reach stratosphere

64
Q

NO breaks down ozone

two propagation steps

A

refer notes pg 11

65
Q

CCl4 is a good fire retardant but pose risk to ozone
CBrF3 is not as effective but has the smallest environmental impact

why ?

A
  1. C — F in CBrF3 has the strongest bond

it takes a lot of energy to break to form radicals

C—F causes global warming

reach stratosphere

never breaks down

  1. Br : F
    1 : 3
    although C – Br can be broken, 3F is still there cannot be broken

3.
C—Br is weaker

easier to be broken before reaching the stratosphere

Chemistry (9 decks)

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