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Chemistry A-level - organic Chem > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

what is the definition of an alkene ?

A

an unsaturated hydrocarbon

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2
Q

what is the general formula of alkenes ?

A

CnH2n

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3
Q

what does unsaturated mean ?

A

it means they contain at least 1 carbon to carbon double bond

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4
Q

what is meant by a double bond that is covalent ?

A

it means that there are 2 shared pairs of electrons
this makes them electron rich

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5
Q

what are the physical properties of alkenes ?

A
  • very similar to alkanes
  • insoluble in water
  • mpt / bpt increase with chain length
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6
Q

what is the shape of alkenes ?

A

planar (flat) due to the double bond

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7
Q

what is an additional property of the shape of alkenes ?

A

they have restricted rotation as they have a fixed shape

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8
Q

what kind of isomerism do alkenes present that is specific to alkenes ?

A

E-Z isomerism
(geometric isomerism )

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9
Q

what is an example of a functional group isomer pair that includes alkenes ?

A

alkenes and cycloalkanes

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10
Q

what are alkenes in terms of reactivity and why ?

A

they are very reactive
- due to the carbon to carbon double bond

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11
Q

what do akenes + water make ?

A

alcohols

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12
Q

conditions for the reaction of alkenes + water ?

A
  • high temp
  • high pressure
  • use a catalyst ( H3PO4)
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13
Q

what is meant by an addition reaction ?

A

when one molecule joins to another

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14
Q

what is an electrophile ?

A

lone pair acceptors

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15
Q

what are the 3 different reagents for electrophilic addition ?

A
  • HBr (HX)
  • Br2 ( any halogen )
  • H2SO4 ( sulphuric acid )
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16
Q

what is a crabocation ?

A

a positively charged carbon atom

17
Q

which molecule is the electrophile in the electrophilic addition of HBr ?

A

HBr
- because it was seeking out the negative part of the alkene = double bond

18
Q

what is the major product ?

A

the product that forms with the most stable carbocation intermediate

19
Q

state the stability of the carbocations ?

A

tertiary > secondary > primary >

20
Q

conditions for electrophilic addition with BR2 ?

A

aqueous ( bromine water)

21
Q

what is the test for unsaturation ?

A

bromine water + alkene
- shake it

22
Q

what is the positive result for the bromine water test ?

A

orange –> colourless solution

23
Q

why does the bromine water turn colourless ?

A

because the bromine combines with the alkene so that there is no more bromine in the water

24
Q

conditions for electrophilic addition with H2SO4 ?

A

cold ,concentrated H2SO4

25
Q

what does H2SO4 act as ?

A

a catalyst

26
Q
A

Chemistry A-level - organic Chem (7 decks)

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