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chemistry > halogenoalkanes > Flashcards

halogenoalkanes Flashcards

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1
Q

bpt trend of haloalkanes

A

increase as you go down group
the strength of intermolecular forces govern bpt
more electrons means stringer van der waals between molecules and so more energy needed to overcome forces

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2
Q

halogenoalkanes have a … bond and are attacked by …

A

polar
nucleophiles

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3
Q

why are halogenoalkanes polar

A

halogen’s are more electronegative than carbon so they pull electrons towards themselves in a covalent bond

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4
Q

what is a nucleophile

A

a substance that is an electron pair donor

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5
Q

examples of nucleophiles

A

ammonia
hydroxide ions
cyanide ions -CN

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6
Q

halogenoalkanes react with hydroxide ions via …

A

nucleophilic substitution

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7
Q

reaction with OH- conditions

A

warm aqueous sodium hydroxide
carried out under reflux

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8
Q

process of reaction with OH-

A

a nucleophile will attack delta positive carbon and will replace the halogen on the haloalkane.
the C-X breaks, both electrons move from the bond to the halogen. a new bond is formed between OH- and carbon
an alcohol is formed

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9
Q

halogenoalkanes react with cyanide ions to make …

A

nitriles

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10
Q

reaction with CN- conditions

A

warm ethanol potassium cyanide
carried out under reflux

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11
Q

process of reaction with CN-

A

a nucleophile will attack the delta positive carbon and replace the halogen.
the CX breaks, both electrons move from the bond to the halogen. a new bond is formed between CN- and carbon
a nitrile is formed

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12
Q

halogenoalkanes react with ammonia via …

A

nucleophilic substitution

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13
Q

reaction with ammonia conditions

A

heat with ethanol ammonia
must have excess ammonia

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14
Q
A

ammonia will attack delta positive carbon and will replace the halogen forming an intermediate
nitrogen is left with positive charge as it can only form three bonds and so it is unstable

another molecule of ammonia acts as a base by reacting with hydrogen (why we need excess
amine and ammonium ion is produced

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15
Q

how to identify amine

A

fishy smell

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16
Q

reactivity trend of halogenoalkane

A

more reactive as you go down the group
the bond enthalpy is lower as you go down making it easier to break and therefore react

17
Q

halogenoalkanes react wit hydroxide Iona via … using ethanol solvent

A

elimination

18
Q

condition of OH- elimination

A

warm ethanol sodium hydroxide
carried under reflux

19
Q

process of OH- elimination

A

the OH- will attack the hydrogen on a carbon adjacent to carbon with halogen on. OH- acts as a base forming water
electrons in the bond move to form a double bond in between two carbons
the C-X breaks, both electrons move from the bond to the halogen
an alkene, water and chloride ion is formed

20
Q

the … plays an important role whether its an elimination or substitution

A

solvent

21
Q

what are CFCs

A

chlorofluorocarbons are molecules that have had all hydrogens replaced by chlorine and fluorine

22
Q

what is the issue with CFC

A

they are stable but are broken down by UV ad can break down ozone in the atmosphere. radicals are formed and they catalyse the breakdown of ozone

23
Q

which halogenoalkane is easiest to break

A

C-Cl because it has the lowest bond enthalpy

24
Q

describe the process of CFC destroying zone

A

initiation
sunlight breaks the C-Cl bond and produces 2 radicals which will react with ozone molecules

propagation
the Cl* reacts with O3 to form ClO* intermediate and O2-
the ClO* reacts with more O3 to make O2 and Cl. As Cl is reformed it acts as a catalyst

termination
2 radicals react with each other

overall: 2O3 => 302

25
Q

what are the uses of CFC

A

used to be used in fridges refrigerant and propellants for deodorants

26
Q

why were CFCs banned

A

demonstrated by scientists that CFCs were damaging the ozone layer
ozone absorbs most harmful UV radiation that causes skin cancer

27
Q

what do we use instead of CFCs

A

we use hydrofluorocarbons(HFCs) and hydrocarbons
they don’t have chlorine in it so a lot safer to use

28
Q
A

chemistry (15 decks)

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