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A LEVEL CHEMISTRY > ALKENES > Flashcards

ALKENES Flashcards

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1
Q

Definition: Pi bond

A

A bond formed by the sideways overlap of two py-orbitals, with the electrons above and below the plane of the bonding atoms

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2
Q

Definition: Sigma bond

A

A bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons and with electron density centred round a line going directly between the nuclei of the two atoms

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3
Q

Why is a sigma bond stronger than a pi bond?

A

Electron density is higher in a sigma bond because it’s directly between the atoms (closer to the nuclei) however in the pi bond, the electrons are spread out so electrostatic attraction is weaker

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4
Q

Definition: Stereoisomerism

A

Molecules that have the same structural formula but a different arrangement of atoms in space

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5
Q

How does E/Z isomerism arise?

A
  • Has to have a double bond (restricted rotation)

- Has to have two different groups on each atom of the double bond

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6
Q

When is it E isomerism?

A

When the priority groups are on opposite sides

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7
Q

What is cis/trans isomerism?

A

A special case of E/Z isomerism when one of the groups on each carbon of the double bond is the same. If the identical groups are on the same side it is cis and trans if they are opposite.

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8
Q

Products and conditions for hydrogenation

A

Ni catalyst, 423K

Alkene + H2 -> Alkane

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9
Q

Alkene + Halogen

A

Dihaloalkane

Room temperature

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10
Q

Alkene + HX

A

Haloalkane

Room temperature

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11
Q

Alkene + H20 (g)

A

Alcohol

Phosphoric acid catalyst

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12
Q

Definition: Electrophile

A

An electron pair acceptor

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13
Q

Definition: Addition reaction

A

The double bond (C=C) breaks and something is added

Two reactants become one product

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14
Q

Definition: Heterolytic fission

A

The breaking of a covalent bond forming a cation and an anion (both the electrons go to the same atom)

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15
Q

Markownikoff’s rule

A

When a hydrogen halide is added to an unsymmetrical alkene, the most likely product is the one in which the H atom adds to the carbon that already has the most H atoms attached to it

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16
Q

Definition: Atom economy

A

Sum of molar masses of desired products/Sum of molar masses of all products x100. Measure of how well atoms were utilised

17
Q

Definition: Percentage yield

A

Actual yield/theoretical yield x100. Shows the percentage of how much product was made

18
Q

Reasons why 100% yield is rarely achieved

A
  1. The reaction may not have gone to completion
  2. Side reactions may have taken place
  3. Purification of the product may result in some loss of product
19
Q

How to improve atom economy

A

Find a use for other products or change the synthesis reaction so it produces fewer products

20
Q

How to improve % yield

A
  1. Use one reactant in excess to ensure completion of reaction
  2. Use a catalyst that only catalyses the reaction you want
  3. Recycle the waste product
21
Q

Problems with vast quantities of plastic used worldwide

A

Non-biodegradable so hard to dispose of because they don’t break down easily in the environment. Build up in waste disposal sites which means it can be dangerous for wildlife - at sea animals could become tangled or suffocate

22
Q

How are biodegradable and photodegradable polymers made?

A

Biodegradable polymers are made of starch or cellulose or contain additives that alter the structure so that micro organisms break them down (they contain ester groups)
Photodegradable polymers are oil based and contain bonds that are weakened by absorbing light or light absorbing additives are used

23
Q

Is combustion a good method of disposing polymers?

A
  • It can be used to produce energy for other purposes like generating electricity
  • Some produce toxic fumes but this can be rectified by installing scrubbers in chimneys that burn polymers
24
Q

How are addition polymers treated before reusing?

A

They are sorted, chopped into flakes, washed, dried and melted to then be recasted

25
Q

How can types of polymer be separated for effective processing?

A

They are given resin identification codes during manufacturing

A LEVEL CHEMISTRY (6 decks)

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