Alkenes

Question 1

what shape are all alkenes and why?

Answer 1

trigonal planar- there are 2 bonding pairs and 1 bonding region with no lone pairs

Question 2

what is a pi bond?

Answer 2

sideways overlap of p-orbitals only

Question 3

which bond is weaker, a sigma bond or pi bond?

Answer 3

sigma bond is weaker

Question 4

what are stereoisomers?

Answer 4

compounds with the same structural formula but different arrangement of atoms in space

Question 5

when would a molecule have E/Z isomerism?

Answer 5

1) molecule contains a C=C double bond which restricts rotation
2) both carbons in the double bond must have 2 different groups attached to them

Question 6

why do each of the molecules have respective E/Z isomerism?

Answer 6

the first one is the Z isomer because the high priority groups are both on the bottom/ top
the second is the E isomer because the high priority groups are on different sides

Question 7

what is structural isomerism?

Answer 7

molecules with the same molecular formula but different structural formula

Question 8

why do each of the molecules have cis/ trans isomerism?

Answer 8

the first one is the cis isomer because the identical groups are on the same side
the second has trans isomerism because the identical groups are on different sides

Question 9

what reactions do alkenes always do?

Answer 9

addition

Question 10

which bond breaks in an addition reaction, sigma or pi?

Answer 10

pi bond, its weaker than sigma

Question 11

give the reagants and conditions for the hydrogenation of ethene and write an equation.

Answer 11

reagant = hydrogen
conditions = nickel catalyst, high temp
C2H4 + H2 -> C2H6

Question 12

give the reagants and conditions for the hydration of ethene and write an equation

Answer 12

reagant = steam
conditions = concentrated H3PO4 catalyst, high temp + pressure
C2H4 + H20(g) -> C2H5OH (ethanol)

Question 13

give the reagants and conditions for the making of a haloalkane from ethene and write the equation

Answer 13

reagant = Cl2 or Br2
conditions = just room temp
C2H4 + Cl2 -> C2H4CL2 (1,2- dichloroethane)

Question 14

give the reagants and conditions for the making of a haloalkane with one halogen molecule from ethene and write an equation

Answer 14

reagant = hydrogen halide
conditions = room temp
C2H4 + HBr -> C2H5Br (bromoethane)

Question 15

what is an electrophile?

Answer 15

an electron pair acceptor

Question 16

what is a nucleophile?

Answer 16

an electron pair donor

Question 17

give the mechanism for the reaction of ethene with bromine + name

Answer 17

name = electrophilic addition

Question 18

give both the major and minor products of the reaction between propene and HBr, and explain why the major product is major

Answer 18

major: CH3CH(Br)CH3
minor: CH2(Br)CH2CH3
major because its formed from a secondary carbocation, which is more stable than a primary carbocation