Addition Reactions of Alkenes Flashcards Preview

Chemistry 6 - Organic Chemistry > Addition Reactions of Alkenes > Flashcards

Flashcards in Addition Reactions of Alkenes Deck (35)
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1
Q

what is a C=C bond made up of

A

a sigma bond and a pi bond

2
Q

which bond is stronger and why

A
  • the sigma bond is stronger

- because it is held more tightly between the carbon atoms

3
Q

with that information does that mean that a double bond is twice as strong as a single bond and why

A
  • no, it is between 1 and 2 times stronger
  • because every single bond is a sigma bond which is stronger than a pi bond
  • so if you have a sigma bond and a pi bond like a C=C, it will be stronger but not twice as strong
4
Q

what do most reactions of alkenes generally involve in terms of the bonds

A

a double bond becoming a single bond

5
Q

what bonds change during an alkene addition reaction

A
  • the sigma bond remains unchanged

- but the electrons in the pi bonds are used to form new bonds with an attacking molecule

6
Q

what is the product that is formed compared to an alkene if it only has single bonds

A

it is saturated

7
Q

why is the product more stable than the alkene

A
  • because the product only has sigma bonds, not pi bonds

- meaning the overall bonds in the product are stronger

8
Q

what is the equation for the addition reaction between ethene and bromine

A

C2H4 + Br2 = C2H4Br2

9
Q

what is that reaction generally used for

A

the chemical test for the presence of C=C in a compound

10
Q

why is that reaction used as a chemical test

A
  • because one of the reactants has a colour (bromine water)

- but the product is colourless

11
Q

what is the correct way to describe what happens to bromine in the reaction when it reacts and the product is colourless

A

you say the bromine has been decolorised

12
Q

what is hydrogenation

A

the addition reaction between an alkene and hydrogen

13
Q

what would be the equation for the hydrogenation of ethene

A

C2H4 + H2 = C2H6

14
Q

what will the the product of a hydrogenation reaction usually be and why

A
  • an alkane
  • because the product only has single bonds
  • and has the general formula of CnH2n
15
Q

what are the two things that are required in order for a hydrogenation reaction to occur

A
  • heat

- a nickel catalyst

16
Q

what are hydrogenation reactions practically used for

A

making margarine

17
Q

how is margarine formed from hydrogenation

A
  • naturally occurring vegetable oils are unsaturated
  • so they contain C=C bonds
  • when they react with hydrogen, some of the double bonds become single bonds
  • this changes the properties of the vegetable oil and converts it into a solid
  • aka margarine
18
Q

what are monosaturated, polysaturated and satruated fats

A
  • monosaturated fats are molecules that only have one C=C bons
  • polysaturated fats are molecules that have more than one C=C bond
  • saturated fats are molecules with no C=C bond
19
Q

what is a halogenation reaction

A

a reaction between an alkene and a halogen

20
Q

what are the products of most halogenation reactiond

A

dihalogenalkanes

21
Q

what would a reaction between ethene and bromine produce if one bromine were to be bonded with one carbon atom each

A

1,2-dibromoethane

22
Q

what is hydration

A
  • adding water

- specifically, adding H and OH to the two atoms in a C=C bond

23
Q

how is a hydration react carried out

A
  • heating an alkene with steam

- passing the mixture over a catalyst of phosphoric acid

24
Q

what would a reaction between ethene and water produce

A

ethanol

25
Q

what is the difference between hydrogenation and hydration reactions

A
  • hydration reactions actually make useful products

- so they are therefore used in industry a lot more

26
Q

what are hydrogen halides often and what do they form in addition reactions

A
  • they are hydrogen bromide or hydrogen chloride

- and they form halogenalkanes

27
Q

what is the structural formula and the name for the reaction between ethene and hydrogen bromide

A
  • CH2=CH2 + H-Br = CH3-CH2Br

- bromoethane

28
Q

what is a diol

A

a compound containing two OH groups

29
Q

what is the oxidising agent in acid conditions and what acid is usually used

A
  • potassium manganate (VII)

- sulfuric acid

30
Q

what is the summation of this reaction

A
  • an oxidation reaction

- followed by an addition reaction

31
Q

how are two OH groups formed when ethene reacts with the solution and the potassium manganate

A
  • the potassium manganate provides an oxygen atom (oxidising)
  • the water in the solution provides another oxygen atom and two hydrogen atoms
  • forming the addition of two OH groups across the double bond
32
Q

what is the structural formula for this reaction

A

CH2=CH2 + [O] + H2O = CH2OH-CH2OH

33
Q

what does the [O] represent

A

the oxygen supplied by the oxidising agent

34
Q

what is the name of the product

A

ethane-1,2-doil

35
Q

why can this reaction be used to distinguish between and alkene and alkane like bromine is

A
  • potassium manganate is normally purple
  • in this reaction it changes from that to colourless
  • it only turns colourless if there is a double bond present for the reaction
  • so it can only occur with alkenes