alkene mechanisms

Question 1

what are the four mechanisms in alkenes

Answer 1

halogenation
hydrohalogenation
hydration
hydrogenation

Question 2

electrophilic addition to unsymmetrical alkenes- order of stability

Answer 2

tertiary> secondary> primary

Question 3

what is Markovnilov’s rule

Answer 3

When a hydrogen halide (HX) adds to an unsymmetrical alkene, the hydrogen (H) goes to the carbon with more hydrogen atoms already attached, and the halide (X) goes to the carbon with fewer hydrogens to make it more stable.

Question 4

what happens in halogenation mechanisms

Answer 4

1)Br-Br bond breaks, making one of them negatively charged
2) The pi bond breaks and a new bond 1forms between C and Br.
3)This makes the other C atom carbocation intermediate and that attracts the negatively charged Br atom.
4)Negatively charged Br atom (nucleophile) donates a pair of e to the carbocation C and forms a new bond

Question 5

what happens in hydrohalogenation mechanisms

Answer 5

1)H-Br bond breaks, making Br negatively charged
2) The pi bond breaks and a new bond forms between C and H.
3)This makes the other C atom carbocation intermediate and that attracts the negatively charged Br atom.
4)Negatively charged Br atom (nucleophile) donates a pair of e to the carbocation C and forms a new bond

Question 6

what happens in hydration mechanisms- concentrated acids

Answer 6

1)H-OSO3H bond breaks, making OSO3H negatively charged
2) The pi bond breaks and a new bond forms between C and H.
3)This makes the other C atom carbocation intermediate and that attracts the negatively charged OSO3H .
4)Negatively charged OSO3H atom (nucleophile) donates a pair of e to the carbocation C and forms a new bond
5)The resulting alkyl hydrogen sulphate reacts with water to form an alcohol.

Question 7

What happens in hydration mechanism- dilute acid

Answer 7

1) The H+ (from H2SO4) acts as an electrophile and protonating the alkene.
2)H2O acts as a nucleophile, forming a bond to the carbocation intermediate.
3)OH-H bond breaks making the final product an alcohol (a proton is lost from the positively charged oxygen)

Question 8

What happens in catalytic hydrogenation

Answer 8

1) H2 (g) adsorbs onto the catalyst, breaking the H-H bond and producing atomic H.
2)Hydrogen atoms are then added across the double bond to form the alkane product