Addition Reactions of Alkenes Flashcards Preview

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

Flashcards in Addition Reactions of Alkenes Deck (35)

what is a C=C bond made up of

a sigma bond and a pi bond


which bond is stronger and why

- the sigma bond is stronger
- because it is held more tightly between the carbon atoms


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

- 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


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

a double bond becoming a single bond


what bonds change during an alkene addition reaction

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


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

it is saturated


why is the product more stable than the alkene

- because the product only has sigma bonds, not pi bonds
- meaning the overall bonds in the product are stronger


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

C2H4 + Br2 = C2H4Br2


what is that reaction generally used for

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


why is that reaction used as a chemical test

- because one of the reactants has a colour (bromine water)
- but the product is colourless


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

you say the bromine has been decolorised


what is hydrogenation

the addition reaction between an alkene and hydrogen


what would be the equation for the hydrogenation of ethene

C2H4 + H2 = C2H6


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

- an alkane
- because the product only has single bonds
- and has the general formula of CnH2n


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

- heat
- a nickel catalyst


what are hydrogenation reactions practically used for

making margarine


how is margarine formed from hydrogenation

- 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


what are monosaturated, polysaturated and satruated fats

- 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


what is a halogenation reaction

a reaction between an alkene and a halogen


what are the products of most halogenation reactiond



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



what is hydration

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


how is a hydration react carried out

- heating an alkene with steam
- passing the mixture over a catalyst of phosphoric acid


what would a reaction between ethene and water produce



what is the difference between hydrogenation and hydration reactions

- hydration reactions actually make useful products
- so they are therefore used in industry a lot more


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

- they are hydrogen bromide or hydrogen chloride
- and they form halogenalkanes


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

- CH2=CH2 + H-Br = CH3-CH2Br
- bromoethane


what is a diol

a compound containing two OH groups


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

- potassium manganate (VII)
- sulfuric acid


what is the summation of this reaction

- an oxidation reaction
- followed by an addition reaction


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

- 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


what is the structural formula for this reaction

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


what does the [O] represent

the oxygen supplied by the oxidising agent


what is the name of the product



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

- 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