Ch. 12.2: Chemical Reactions Of The Alkanes Flashcards

1
Q

Why don’t alkanes react with most common reagents?

A
  • C-C and C-H sigma bonds are strong
  • C-C bonds are non - polar
  • the electronegativity of C and H is so similar that their bind can be considered non- polar
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2
Q

What is combustion?

A

When alkanes react with plentiful supply of oxygen to produce carbon dioxide and water.

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3
Q

Why are alkanes used as fuels?

A
  • readily available
  • easy to transport
  • burn in plentiful supply of oxygen without releasing toxic products
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4
Q

Formula for balancing any combustion of alkane

A

C(x)H(y) + (x+y/4)O2 -> (x)CO2 + (y/2) H2O

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5
Q

What happens during incomplete combustion of alkanes?

A
  • hydrogen atoms are always oxidised to water

- forms toxic gas carbon monoxide (CO) or even carbon itself ( soot)

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6
Q

Describe the reactions between alkanes and halogens

A
  • They react in the presence of sunlight
  • UV radiation provides initial energy needed
  • it is a substitution reaction, as the hydrogen atom gets replaced by a halogen atom
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7
Q

What are the three stages of radical substitution?

A

Initiation
Propagation
Termination

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8
Q

What happens in initiation?

A

The covalent bond in the halogen is broken by homolytic fission. Each bonded atom takes one of the electrons, resulting into two radicals ( highly reactive species with unpaired electron ).

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9
Q

What happens in propagation?

A

1st Step: radical reacts with alkane and takes a hydrogen atom from it. This results in an alkane radical.

2nd Step : alkane radical reacts with halogen ( diatomic ) and takes one of its atoms, and leaves a halogen radical

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10
Q

What happens in termination?

A

Two radicals collide, forming a molecule with all electrons paired. There are usually three possible termination reactions.

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11
Q

What are the limitations of radical substitution in organic synthesis?

A

Further substitution: another halogen radical can collide with the halo-alkane made, substituting a further hydrogen atom to form another halo-alkane.

Substitution at different positions in a carbon chain: if a carbon chain is long, it produces a mixture of monosubstituted isomers at different positions in the carbon chain.

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