1 / 23

Booklet to help with unit 28: M2, D1 and D2

Part one of two booklets. Booklet to help with unit 28: M2, D1 and D2. Task 1 : Fill in table with what you observed from the experiments of alkanes with alkenes. Task 2: Answer the questions below.

becky
Download Presentation

Booklet to help with unit 28: M2, D1 and D2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Part one of two booklets Booklet to help with unit 28: M2, D1 and D2

  2. Task 1: Fill in table with what you observed from the experiments of alkanes with alkenes

  3. Task 2: Answer the questions below • From your results table in task 1, which hydrocarbon is more reactive: Alkanes or alkenes? • What is the functional group of alkanes? • What is the functional group of alkenes? • Try to explain why the hydrocarbon you have selected in question 1 is more reactive.

  4. M2: Reaction mechanisms • Free radical substitution of alkane • Electrophilic addition of alkene • Electrophilic addition of benzene

  5. Free radical substitution of alkanes • Free radicals: Very reactive species with an unpaired electron • Homolytic fission: When a bond is broken, each species used in the bond receives one electron from the bond that is broken. Homolyticfisson requires UV light

  6. Reaction mechanism of free radical substitution of alkanes Alkanes are substituted by halogens such as chlorine and bromine CH4 + Cl2 CH3Cl + HCl Step 1: Initiation UV provides energy to break Cl-Cl bonds homolytically producing chlorine free-readicalsCl●

  7. Step 2: Propagation The chlorine free-radicals catalyse the reaction. Free radicals are recycled in a chain reaction

  8. Step 3: Termination In this stage , free radicals are removed Free radicals react together and are removed from the reaction mixture

  9. Task 3: Draw out the reaction mechanism of free radical substitution of methane with bromine

  10. Reaction mechanism of electrophilic addition of bromine to alkene Overall reaction: Br2 + Reaction mechanism:

  11. Task 4: Draw out the reaction mechanism of electrophilic addition of chlorine to Ethene Overall reaction: Cl2 +

  12. Reaction mechanism of nitration of benzene Overall reaction: + H2O Reaction mechanism: Step 1: HNO3 + H2SO4 NO2+ + HSO4- + H2O Step 2: Step 3: HSO4- + H+  H2SO4

  13. Bonding present in alkanes Bond angles between the carbon and hydrogen atoms are 109.5◦ There is a single bond between each of the two carbon atoms where a pair of electrons is shared. This single bond is called a sigma bond (σ bond)

  14. Reactivity of alkanes • At room temperature the alkanes are unaffected by concentrated acids or alkalis. They are not affected by oxidising agents such as potassium manganate (VII) and they do not react even with the most reactive metals. • The reason for this lack of reactivity is that both the C-H and C-C bonds involve a very even sharing of electrons, since the electronegativites of carbon and hydrogen are very close. • This means that the bonds in the molecules of the alkanes are not polar to any extent, and so there are no charges to attract other polar or ionic species.

  15. Reactivity of alkanes • Almost all of the reactions of the alkanes occur due to formation of free radicals, which contain an unpaired electron. • Reactions of alkanes are: - combustion - free radical substitution

  16. Task 5: With the aid of a diagram, describe the bonding present in alkanes

  17. Task 6: Use suitable examples to analyse the types of reaction undergone in alkanes in relation to the bonding present

  18. Bonding present in alkenes Bond angles between the carbon and hydrogen atoms are 120◦ The ethene molecule CH2=CH2 is flat. The carbon-carbon double bond involves a sigma bond (σ bond) plus a second bond known as a pi bond (π bond)

  19. The π bond has electron density concentrated both above and below the plane The π bond does not allow rotation around the axis of the C=C bond. The π bond is less than twice as strong as a σ bond

  20. Reactivity of alkanes • Alkenes are reactive, due to the attraction of positively polarised groups to the electron rich π bond within the double C=C bond. • Alkenes participate in electrophilic reactions because the double bond is an electron rich area. • The π bond provides electron pairs to form new bonds with electron seeking groups

  21. Reactivity of alkanes • Types of reactions that alkenes participate in is when electron-deficient species “attacks” the electron rich C=C double bond. The electron deficient species accepts an electron pair • Addition reactions of alkenes involve the opening of the C=C double bond with the formation of a single saturated addition product • Examples of reactions of alkenes include: - Addition of bromine - Addition of hydrogen bromide - Polymerisation - Reduction with hydrogen

  22. Task 7: With the aid of a diagram, describe the bonding present in alkenes

  23. Task 8: Use suitable examples to analyse the types of reaction undergone in alkenes in relation to the bonding present

More Related