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Chemistry > 3.3.3 Halogenoalkanes > Flashcards

3.3.3 Halogenoalkanes Flashcards

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1
Q

what is the the bpt trends of halogenoalkanes

A

bpt increase down the group

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2
Q

Why do the bpt of halogenoalkanes increase down the group

A
  • down grp 7 there are increasing number of electrons in the atom
  • more electrons = STRONGER VAN DER WAALS FORCES between molecules
  • more energy needed to over come these forces
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3
Q

Define nucleophile and give 3 examples

A

electron pair donor
CN-, NH3, OH-

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4
Q

Why do halogenoalkanes have polar bonds?

A

halogens are more electronegative than carbon so they pull electrons towards themselves in a covalent bond

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5
Q

What feature of halogenoalkanes means it is susceptible to being attacked by nucleophiles?

A

it has polar bonds

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6
Q

What mechanism do halogenoalkanes undergo with hydroxide ions?

A

nucleophilic substitution

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7
Q

What are the conditions for nucleophilic substitution of halogenoalkanes with hydroxide ions?

A
  1. warm aqueous NaOH
  2. carried under reflux
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8
Q

what do halogenoalkanes form when reacted with cyanide ions (CN)?

A

NITRILES

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9
Q

what conditions are required for the reaction of halogenoalkanes with cyanide ions?

A
  1. warm ethanol potassium cyanide
  2. carried under reflux
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10
Q

What is produced when halogenoalkanes react with ammonia?

A

amine (fishy smell) + ammonium ion (NH4+)

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11
Q

What are the conditions required for halogenoalkanes reacting with ammonia?

A
  1. heat with ethanol ammonia
  2. must have EXCESS ammonia
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12
Q

Why must halogenoalkanes react with excess ammonia?

A

The ammonia acts as an electron pair donor (nucleophile in the 1st step) and a base (reacting with hydrogen) in the 2nd step.

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13
Q

What determines halogenoalkane reactivity?

A

The bond strength/ bond enthalpy

(NOT bond polarity)

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14
Q

describe reactivity of halogenoalkanes and why

A

more reactive going down the group
- bond enthalpy decreases going down the group so as you go down the lower bond enthalpies are easiest to break

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15
Q

What are the conditions for halogenoalkande undergoing elimination reaction with OH- ion?

A
  1. warm ethanolic NaOH
  2. carried under reflux
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16
Q

Whats the difference between the attack of the OH- nucleophile in elimination and nucleophilic substitution of halogenoalkane?

A

in nucleophilic substitution the OH ion attacks the carbon in which the halogen is attached to

in elimination the OH ion attacks the hydrogen of the adjacent carbon to the carbon in which the halogen is attached to

17
Q

what are the products of an elimination reaction of a halogenoalkane?

A

alkene, h20, halogen compound e.h (KBr (due to KOH being used))

18
Q

compare the elimination and substitution reaction of hydroxide ions with an halogenoalkane. ( conditions, products, how does the OH ion react)

A

when ETHANOL is solvent, undergoes elimination, produces an ALKENE. OH acts as base

when WATER is solvent, undergoes substitution, produces an ALCOHOL. OH acts as nucleophile

when both solvents are mixed you make a mixture of ALKENE AND ALCOHOL

19
Q

Why are CFC’S bad ?

A

they deplete the ozone layer (O3)

20
Q

What breaks the bonds in CFC to form radicals?

A

UV LIGHT

21
Q

How do the radicals produced from CFC’s affect the ozone layer?

A

they catalyse the break down of ozone

22
Q

Why are C-Cl bonds more likely to break that C-F bonds in CFC’S

A

C-CL bond enthalpy is much lower than C-F

23
Q

Write the steps for the depletion of the ozone layer

A

initiation : CCL3f + UV —> CCl2F + Cl.

Propogation : Cl. + O3 –> ClO. + O2
ClO. + O3 —> Cl. + 2O2

Termination : Cl. + Cl. —> Cl2

24
Q

whats the overall equation for the depletion of the ozone

A

2O3 —-> 3O2

25
Q

Why are CFC’s now banned?

A

they were damaging the ozone layer and despite being used as a refrigerant and propellant in deodorants, the Ozone is needed to absorb harmful UV radiation which can cause skin cancer

26
Q

What do we use instead of CFC’S now

A

HFC’S (CHF3)

Chemistry (16 decks)

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