Alkenes 4.13

Question 1

Pi bond

Answer 1

Pi bond is the sideways overlap of p orbitals. It locks the two carbon atoms in position and prevents them from rotating around the double bond.

Question 2

What is the shape of alkenes?

Answer 2

Trigonal planar. 120
The three bonding regions repel each other as far possible
All atoms are in the same plane.

Question 3

Stereoisomers

Answer 3

Stereoisomers have the same structural formula but a different arrangment of atoms in space.

Question 4

How does stereoisomerism across double bonds arise?

Answer 4

Stereoisomerism across double bonds arises because rotation around the double is restricted and the group attatched to each carbon atom are therefore fixed relative to each other.

Question 5

Entegen

Answer 5

Opposite (epposite) - trans

Question 6

Zusaman

Answer 6

Same side (zame zide) - cis

Question 7

What conditions must be satisfied for it to have E/Z isomerism?

Answer 7

• A C=C double bond
• Different groups attatched to each carbon atom of the double

Question 8

What conditions must be satisfied for a molecule to have cis-trans?

Answer 8

• C=C double bond
• Each of the carbon of the double bond must be attachment to two different groups
• One of the attached groups on each carbon of the double bond must be the same
• Each of atom of the double bond must have a H on it (for alkenes)

Question 9

What determines the priority?

Answer 9

• The higher the atomic number (protons), the higher the priority
• Look for the atom attatched to the carbon then assign priority.

Question 10

Electrophile

Answer 10

A species that must be positively charged. An electron pair acceptor.

Question 11

What does the double bond in an alkene represent?

Answer 11

The double bond in an alkene represents a region of high electron density because of the presence of the the Pi bond

Question 12

Why are alkenes more reactive than alkane?

Answer 12

A high electron density around the double bond and the fact that the pi bond is easier to break because it is weaker.

Question 13

What conditions are required for the hydrogenation of alkenes?

Answer 13

alkene + H2 —> alkane
Conditions: H2g and Ni 423K

Question 14

Halogenation of alkene

Answer 14

Alkene + X2 (halogen) —> Haloalkane

Question 15

How do you test for unsaturation?

Answer 15

Add bromine water into the solution, if the orange colour disappears (colourless) in the presence of a C=C bond in an organic compound.

Question 16

Hydration of alkenes, how is alcohol formed from alkenes

Answer 16

Alkenes react with steam H2O(g) in the presence of a phosphoric acid catalyst H3PO4

Question 17

What do curly arrows show?

Answer 17

Show movement of a pair of electrons.

Question 18

Polymer

Answer 18

Extremely large molecules made up of repeating units know as monomers.

Question 19

What happens when PVC is burnt

Answer 19

It released hydrogen chloride

Question 20

How does stability of a carbocation increase? How does this affect the major and minor product?

Answer 20

The more alkyl groups attatched to the positively charged carbon, the more charges is spread, making the ion more stable. The one that is more stable is the major product as it will be made more.

Question 21

What condition is needed for an addition reaction with a hydrogen halide? (HX)

Answer 21

Alkenes react with HX at room temperature

Question 22

How does HX react with a liquid alkene

Answer 22

HX(g) is bubbled through the liquid alkene.

Question 23

How are electrophiles attracted to Pi bonds?

Answer 23

The high electron density of the pi electrons attracts the electrophile.

Question 24

How do you reduce the negative impact of polymers?

Answer 24

• make them photodegradable or biodegradable
• recycling them - chemically reclaimed as feedstock

Question 25

What two ways of disposing polymers that can be beneficial to the environment?

Answer 25

• Combustion for energy production
• Use as organic feedstock