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Chemistry > halogenoalkanes > Flashcards

halogenoalkanes Flashcards

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1
Q

general formula halogenoalkanes

A

CnH2n+1Hal

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2
Q

functional group

A

C-Hal

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3
Q

what does the presence of the polar bond in halogenoalkanes mean

A

they’re more reactive than alkanes

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4
Q

3 uses of halogenoalkanes

A
  • refrigerants
  • solvents
  • pharmaceuticals
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5
Q

how are halogenoalkanes named

A

after the parent alkane with the prefix chloro, bromo, iodo etc.

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6
Q

what must be indicated if there are more than 3 carbon atoms in the molecule

A

the position of the halogen

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7
Q

what must be indicated if 2 or more halogens are present

A

their positions in the chain

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8
Q

how are the halogens named if there are 2 of them in the chain and they are different

A

in alphabetical order

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9
Q

what 2 reactions do halogenoalkanes take part in

A

nucleophilic substitution and elimination

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10
Q

what is the halogen atom replaced with in a nucleophilic substitution reaction

A

by a new group of atoms

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11
Q

nucleophile

A

electron pair donor

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12
Q

why do halogenoalkanes take part in nucleophilic substitution

A

the carbon is bonded to a halogen and so it is rendered electron deficient

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13
Q

where does the nucleophile donate its pair of electrons to in nucleophilic substitution

A

the delta plus c atom to form a new bond

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14
Q

how does the C-Hal bond break in nucleophilic substitution and what does it form

A

Heterolytic fission

halide ion formed

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15
Q

examples of common nucleophiles

A

hydroxide
cyanide
ammonia

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16
Q

what do halogenoalkanes react with aqueous hydroxides to form

A

alcohols

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17
Q

what is the reaction between halogenoalkanes and aqueous hydroxides often referred to as

A

hydrolysis

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18
Q

hydrolysis

A

the breaking of a bond using water

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19
Q

what is the reagent in nucleophilic substitution with aqueous hydroxides

A

the hydroxide

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20
Q

what conditions are needed for nucleophilic substitution using hydroxide

A

warm and aqueous

21
Q

general equation for the nucleophilic substitution between halogenoalkane and hydroxide

A

R-Hal + NaOH > R-OH + NaHal

22
Q

reagent for nucleophilic substitution between halogenoalkane and cyanide

A

cyanide ion

23
Q

conditions for nucleophilic substitution between halogenoalkane and cyanide

A

warm and ethanolic

24
Q

general equation for for nucleophilic substitution between halogenoalkane (bromo) and (potassium) cyanide

A

RBr + KCN > RCN + KBr

25
Q

what does reacting a halogenoalkane with cyanide increase

A

the length of the carbon chain

26
Q

what do halogenoalkanes react with excess ammonia to form

A

amines

27
Q

reagent for nucleophilic substitution between halogenoalkane and ammonia

A

NH3

28
Q

conditions for nucleophilic substitution between halogenoalkane and ammonia

A

ethanolic and warm

29
Q

general equation for nucleophilic substitution between halogenoalkane and ammonia

A

R-Hal + 2NH3 > RNH2 + NH4 + Hal-

30
Q

what does the rate of substitution reactions of halogenoalkanes depend on

A

the c-hal bond enthalpy

31
Q

what does a halogenoalkane react to form in an elimination reaction

A

an alkene

32
Q

elimination

A

a reaction in which an atom/group of atoms is removed from a reactant

33
Q

reagent for elimination reaction with halogenoalkanes

A

hydroxide

34
Q

conditions for elimination reaction with halogenoalkanes

A

HOT and ethanolic

35
Q

sequence of events in elimination reactions with halogenoalkanes

A
  • halogen atom always removed
  • H atom from an adjacent C atom also removed
  • double bond forms between the two C atoms
36
Q

what is the role of the hydroxide in elimination with halogenoalkanes

A

base

37
Q

substitution vs elimination using hydroxide: conditions

A

s: warm and aqueous
e: hot in ethanol

38
Q

substitution vs elimination using hydroxide: major product

A

s: alcohol
e: alkene

39
Q

substitution vs elimination using hydroxide: role of OH-

A

s: nucleophile
e: base

40
Q

what properties of chloroflourocarbons make them suitable for use as solvents and refrigerants

A

non-toxic and low reactivity

41
Q

what did the properties of chloroflourocarbons lead to

A

the depletion of the ozone layer

42
Q

where does ozone form

A

in the upper atmosphere

43
Q

how does ozone form

A

from the reaction of oxygen atoms with oxygen molecules

44
Q

equation for formation of ozone:

A

O + O2 > O3

45
Q

why is the ozone layer beneficial

A

it absorbs UV radiation that can cause skin cancer

46
Q

what did scientists discover that waste CFCs didnt do

A

break down easily and so would rise up to the upper atmosphere and break down to form chlorine radicals

47
Q

what do chlorine radicals do and what has this led to

A

catalyse the breakdown of ozone

led to a hole in the ozone layer

48
Q

equation for chlorine radicals reacting with ozone

A

O3 + Cl. > O2 + ClO.

ClO+ O3> 2O2 + Cl.

49
Q

what alternatives to CFCs are now used

A

organohalogens that don’t contain chlorine

Chemistry (42 decks)

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