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Chemistry > properties of alkene > Flashcards

properties of alkene Flashcards

1
Q

Why do double bonds make alkenes reactive

A

sigma have a high electron density
Pi bond has a relatively low bond enthalpy
Easy to break, more reactive

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2
Q

What is different about cycloalkenes

A

Have 2 fewer hydrogens

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3
Q

What do double bonds contain

A

Pi bond and sigma bonds

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4
Q

When do sigma bonds happen

A

When 2 s orbitals overlap.

They align horizontally to give a single covalent bond

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5
Q

Sigma bond properties

A

Strong electrostatic force of attraction between nuclei and shared pairs of electrons due to high electron density between nuclei
Has a high bond enthalpy

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6
Q

What are pi bonds

A

Parallel overlap of 2 p orbitals above and below the bonding c atoms

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7
Q

Why are pi bonds weaker than sigma bonds

A

Electron density is spread out above and below the nuclei. The electrostatic attraction is weaker so they have a weaker bond enthaply making them more reactive

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8
Q

Why are alkanes less reactive

A

Only have sigma bonds

They are non polar

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9
Q

What are alkenes good for

A

Polymers and petrochemicals

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10
Q

Why are alkenes open to attack from electrophiles

A

Pi bond sticks out a little and the whole double bond has a high electron density
Electrophile adds to the molecule

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11
Q

What does stereoisomerism occur on

A

Alkenes
contain double bond
Atoms cant rotate around the double c bond and is rigid

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12
Q

Stereoisomers meaning

A

Same structural formula but the different arrangement in atoms

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13
Q

What are electrophiles

A

Electron pair acceptor

Deficient in electrons

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14
Q

Example of electrophiles

A

delta positive polar bonds, positive ions

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15
Q

Test for alkenes

A

Bromine water - orange to colorless

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16
Q

electrophilic addition hydrogen gas with ethene conditions

A

150 degrees, nickel catalyst,

make ethane

17
Q

What does the hydration of alkenes make

A

alcohol

18
Q

hydration of alkene conditions

A

steam and acid catalyst

19
Q

What do alkenes reacted with hydrogen halides make

A

halogenoalkanes

20
Q

Landfill is useful for disposing plastics that

A
  • are too difficult to recycle
  • Too difficult to separate from other materials
  • Not enough plastic to extract it
21
Q

Why is it hard to dispose of polymers

A

Not biodegradable

22
Q

what recycled plastic can be used for

A

plastics cracked into monomers and used as an organic feedstock for plastic or other substances
Some plastics can be remoulded

23
Q

When is incineration used to dispose of plastic

A

plastic cant be recycled

energy from burning used to generate energy

24
Q

Why is burning plastic bad

A

Can release toxic fumes
Chlorine-based plastics produce harmful HCL gas when burned.
Flue gas scrubbers used to neutralise acidic gases by firing a base

25
Q

what does biodegradable polymers need to biodegrade

A

good supply of oxygen and moisture

Light and water so microorganisms can digest

26
Q

what are biodegradable polymers made from

A

oil fractions and renewable sources

More expensive than non-biodegrable plastics

27
Q

Benfit to environment of biodegradable polymers

A

Less land use, decompose

Can be made from renewable materials reducing dependency in crude oil

28
Q

What is needed to break down photodegrable polymers

A

Light

29
Q

Why does bromine water go orange to colourless in presence of alkenes

A

Will undergo an electrophilic addition reaction due to the double c bond

30
Q

Shape of alkenes

A

trigonal planar

31
Q

Why the shape of an alkene trigonal planar

A

3 regions of electron density around each carbon atom
Electrons repel each other
All of the atoms are in the same plane

32
Q

Why are alkenes so rigid

A

Position of the pi bonds electron density above and below the plane of the sigma bond

33
Q

When do cis-trans isomers occur

A

One of the attached group on each carbon atom on the double bond must be hydrogen.

34
Q

What is carbocation

A

Positively charged carbon atom

35
Q

Why is tertiary carbocation the most stable

A

The more alkyl group attached to the positively charged carbon atom the more the charge is spread out making the ion more stable

Chemistry (24 decks)

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