topic 6c- alkenes Flashcards

1
Q

state the general formula for all alkenes

A

Cn H2n

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2
Q

what are unsaturated hydrocarbons?

A

compounds of ONLY hydrogen and carbon which have at least one C=C bond

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3
Q

what is the general formula for cycloalkenes

A

Cn H2n-2

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4
Q

name the two types of C=C double bonds

A

SIGMA bond= axial overlap -> strongest
PI bond= sideways overlap between 2 p-orbitals

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5
Q

what is an electrophile?

A

electron pair acceptors - anything that is attracted to a negative charge and a lot of electrons

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6
Q

give examples of molecules or ions that are electrophiles and nucleophiles

A

electrophiles= H+, H3O+, NO2+

nucleophiles= CN-, OH-, H2O, NH3

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7
Q

addition of hydrogen

name the reactants used in a hydrogenation reaction

A

C2H4 (ethene) + H2 -> C2H6 (ethane)

ethane= alkane

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8
Q

name the two conditions needed in hydrogenation

A
  • a nickel catalyst
  • 150 ‘c
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9
Q

how is margarine produced?

A
  • hydrogenation

-‘hydrogenating’ unsaturated vegetable oils
- removing double bonds -> raise MP -> solid at room temp

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10
Q

adding a halogen (Br)

describe the reactants in halogenation and the mechanism involved

A

C2H4 + Br2 -> C2H4Br2

  1. double bond repels Br2 electrons -> polarisation
  2. heterolytic fission of Br2 -> Br2 close to the C hands over electrons to Br2 farther away
  3. creates a positively charged carbocation

C2H4Br2= dihalogenoalkane = 1,2- dibromoethane

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11
Q

describe the test to identify an unsaturated hydrocarbon.

A
  1. shake an alkene with brown bromine water
  2. decolourises (due to Br is added across the double bond)
  3. 1,2- dibromoethane is formed (colourless)
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12
Q

describe the reaction of the addition of hydrogen halides

A

C2H4 + HBr -> C2H5Br

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13
Q

describe the reaction of hydration

A

C2H4 + H2O (steam) -> C2H5OH
- catalyst= phosphoric acid (H3PO4)

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14
Q

what are the conditions for hydration reaction?

A
  • steam
  • Heat 300’c 60 atm
  • catalyst (H3PO4)
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15
Q

describe the reaction of oxidation to diol

A

C2H4 + acidified potassium manganate (VII) (H+/ MnO4-) -> ethane-1,2-diol

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16
Q

describe the bromine test

A

orange/ brown to colourless

17
Q

describe the bromine water test result

A

orange to colourless

18
Q

what do curly arrows signify?

A

shows the movement of electrons