Lecture 8

Question 1

What is the bonding in alkenes?

Answer 1

Two sp2 orbitals overlap to form a sigma bond between two carbon atoms.
Two 2p orbitals overlap to form a pi bond between the two carbon atoms.
S orbitals in hydrogen overlap with the sp2 orbitals in carbon to form CH bonds.

Question 2

Due to the bonding in alkenes what is the resulting shape of an alkene?

Answer 2

Planar

Bond angle- 120o.

Question 3

What is the IUPAC suffix for an alkene?

Answer 3

“ene”

Question 4

What is the older nomenclature suffix for an alkene?

Answer 4

“ylene”

Question 5

What is geometric isomerism and example of?

Answer 5

STEROISOMERISM

Question 6

What causes geometric isomerism?

Answer 6

Occurs due to the RESTRICTED ROTATION around the Carbon- Carbon double bond.

Question 7

When is it E isomerism?

Answer 7

Higher ranked substituents on OPPOSITE sides.

Question 8

When is it Z isomerism?

Answer 8

Higher ranked substituents on SAME side.

Question 9

In the elimination of HX from haloalkanes, what happens?

Answer 9

There is a loss of H+ and X- ions from ADJACENT carbons, forming a new pi bond.

Question 10

What is the reagent and reaction conditions for the haloalkane to alkene (elimination)?

Answer 10

REAGENT: Alcoholic KOH/ NaOH
CONDITIONS: Reflux in alcoholic solution.

Question 11

What is the reagents for dehalogenation of vicinal dibromides?
What type of reaction is this?

Answer 11

REAGENTS: NaI and Zn/HOAc- Redox Reaction.

Question 12

What happens in the reaction of dehydration of alcohols?

Answer 12

Removal of Water.

Question 13

What is the reagent and reaction conditions for the dehydration of alcohol?

Answer 13

REAGENT: Catalytic acid- Eg. Sulfuric or Phosphoric acid.
CONDITIONS: Reflux (Depends on alcohol).

Question 14

What side reaction might occur alongside the dehydration of alcohols?

Answer 14

Rearrangement Reaction

Question 15

In the Krebs Cycle what reaction occurs between citric acid to ascontic acid?

Answer 15

Elimination of water.

Question 16

In the Krebs cycle what happens to Succinic Acid to produce fumaric acid? What reaction is it?

Answer 16

Hydrogen is removed.

Dehydrogenation reaction.

Question 17

Physical Properties: Boiling Point

Answer 17

INCREASES up the homologous series because of Van der Waals’ forces.
Trends similar to those in ALKANES.

Question 18

Physical Properties: Melting Point

Answer 18

Increases up the homologous series, but depends on the isomer, for example see fatty acids.

Question 19

Physical Properties: Solubility

Answer 19

Immiscible (don’t mix with) with WATER or some POLAR solvents.
MISCIBLE with/soluble in most organic solvents.

Question 20

Physical Properties: Density

Answer 20

LESS dense than water.

Question 21

Why are pi bonds weaker than sigma bonds in alkenes?

Answer 21

Pi electrons are FURTHER from the carbon nuclei and so are less firmly bound.

Question 22

What is the reagent for the addition reaction of Hydration (H2O)?

Answer 22

H2O- Acid Catalyst

Question 23

What is the reagent for the creation of an bromine haloalkane?

Answer 23

Eg. Br2.

Question 24

What is the reagent for the addition reaction of halohydrin formation?

Answer 24

Br2 in water.

Question 25

What is the reagent for the hydrogenation (Chemical Reduction)?

Answer 25

H2 and transition metal catalyst.

Question 26

Markovnikov's Rule: Which carbon does the hydrogen atom add to?

Answer 26

The Carbon with the Greater number of hydrogen atoms.

Question 27

Markovnikov's Rule: Why does the most stable carbocation form?

Answer 27

Alkyl groups are ELECTRON RELEASING and can “push” electrons towards the CARBOCATIONS which STABILISES them. The more alkyl groups the most electrons can be pushed towards the carbon.

Question 28

What is the major formed via?

Answer 28

The most stable carbocation.

Question 29

In biological reduction what happens during this reaction?

Answer 29

One end of the double bond has a H- transferred and the other end transfers a H+. Cofactor- H- Amino acid residue- H+

Question 30

Why does chemical reduction of alkenes require a transition catalyst?

Answer 30

The catalyst associates on the surface of the hydrogen- weakens the H-H bond. In reduction the transition metal causes the electron density to be taken out of H (partial bond to transition metal) so H more likely to react.

Question 31

What is epoxidation?

Answer 31

The addition of an OXYGEN atom in a 3 membered ring. CP450 will add the oxygen effectively.

Question 32

What is dihydroxylation?

Answer 32

2 OH groups are added to either end. (hydroxylation= HOOH) | Dihydroxylation detoxification are products of epoxidation.

Question 33

What is oxidation cleavage?

Answer 33

CORRECT oxidising agent can split the ALKENE into 2 CARBONYL groups.

Question 34

What are the reagents for diyhdroxylation reaction? Why?

Answer 34

OsO4 (Osmium Tetroxide) or cold alkaline KMnO4. | Transition Metal Catalyse to oxidise alkenes by the oxygen atom bonding to the metal which is transferred to the alkene.

Question 35

In the initiation step what is turned into a radial?

Answer 35

The Organic Peroxide.

Question 36

What are the requirements for radical polymerisation?

Answer 36

High Pressure High Temperature Catalyst

Question 37

Why is a catalyst needed in radical polymerisation?

Answer 37

Readily breaks up to form radicals which initiate a chain reaction.