Module 4: Core Organic Chemistry

Question 1

What is meant by the term homologous series ?

Answer 1

A group of compounds with similar chemical properties, whose successive members only differ by the addition of a CH₂ group.

Question 2

What is a functional group?

Answer 2

A part of an organic molecule that is largely responsible for its chemical properties.

Question 3

What is meant by the term aliphatic ?

Answer 3

Carbon atoms are joined to each other in unbranched (straight) or branched chains, or non aromatic rings.

Question 4

What is meant by the term alicyclic ?

Answer 4

Carbon atoms joined together in ring/cyclic structures, with or without branches.

Question 5

What is meant by the term aromatic ?

Answer 5

Some or all of the carbon atoms are found in a benzene ring.

Question 6

Define homolytic fission.

Answer 6

When a covalent bond breaks, each of the bonded atoms take one of the shared pair of electrons from the bond.

Question 7

Define heterolytic fission.

Answer 7

When a covalent bond breaks, one of the bonded atoms takes both of the shared pair of electrons from the bond.

Question 8

What do curly arrows represent?

Answer 8

The movement of electron pairs.

Question 9

In homolytic fission, what type of arrow is used to show the movement of electrons?

Answer 9

Half-headed/fish hook arrows.

Question 10

What is a nucleophile?

Answer 10

Electron pair donor.

Question 11

What is a electrophile?

Answer 11

Electron pair acceptor.

Question 12

What is a structural isomer?

Answer 12

Compounds with the same molecular formula but different structural formula.

Question 13

What are the three types of structural isomers?

Answer 13

1. Chain: different arrangement of carbon skeleton
2. Position: same functional group, different position
3. Functional: Different functional group

Question 14

What is a sigma/σ bond?

Answer 14

The head to head overlap of two orbitals.

Question 15

What is a pi/π bond?

Answer 15

The sideways/lateral overlap p orbitals above and below the plane.

Question 16

How do the properties of an alkane change as chain length increases?

Answer 16

• Boiling point increases
• Viscosity increases
• Volatility decreases
• Flammability decreases

Question 17

Why does the boiling point of an alkane change as branching and chain length increase?

Answer 17

• Branching: Less surface contact points, reduced London forces, lower boiling point
• Chain length: More surface contact points, increased London forces, higher boiling point

Question 18

What is stereoisomerism?

Answer 18

When compounds have the same structural formula but different arrangement in space.

Question 19

What are the conditions for stereoisomerism?

Answer 19

The molecule must have a double bond and a different group attached to each carbon in the double bond.

Question 20

Why does stereoisomerism only occur in alkenes?

Answer 20

Rotation around the double bond is restricted due to the pi bond locking the two carbons in position, so the groups attached to each carbon is fixed relative to each other.

Question 21

When is a compound an E isomer and when is it a trans isomer?

Answer 21

Groups of higher priority (higher atomic number) are placed diagonally across the double bond.

It is a trans isomer specifically when one of the groups attached to each carbon is the same.

Question 22

When is a compound an Z isomer and when is it a cis isomer?

Answer 22

Groups of higher priority (higher atomic number) are placed on the same side of the double bond.

It is a cis isomer specifically when the groups attached to each carbon is the same.

Question 23

Why are alkenes more reactive than alkanes?

Answer 23

Double bonds in alkenes are areas of high electron density, which means it can react with nucleophiles, electrophiles, water etc.

Question 24

What is a free radical?

Answer 24

Species with an unpaired electron.

Question 25

What is the problem with forming a specific product by free radical substitution?

Answer 25

The reaction forms more than one product due to having various termination steps.

Question 26

In free radical substitution, why are a variety of different compounds formed.

Answer 26

• Various possible termination steps
• Further substitution
• Substitution at different positions on the chain

Question 27

Why is UV light used in free radical substitution?

Answer 27

Provides energy for homolytic fission.

Question 28

What is the difference between a sigma/σ bond and a pi/π bond?

Answer 28

• σ bond is between bonding atoms/nuclei and π bond is above and below the bonding atoms / nuclei
• σ bond has direct/head-on overlap of orbitals and π bond has sideways overlap
• π bond has a lower bond enthalpy / is weaker than a σ bond

Question 29

What is Markownikoff’s rule?

Answer 29

In a reaction, a hydrogen will attach to the carbon with the most hydrogens.

Question 30

Why are tertiary carbocations more stable than secondary carbocations, and why are secondary carbocations more more stable than primary carbocations?

Answer 30

They’re more stable because they have more alkyl groups releasing electrons towards the positive charge on the carbon.

Question 31

How can polymers be disposed of sustainably?

Answer 31

• Burned for fuel
• Use as organic feedstock (reclaiming monomers)

Question 32

How can polymers be made more environmentally friendly?

Answer 32

• Use biodegradable polymers made from plants. These polymers can be broken down by hydrolysis.
• Use photodegradable polymers which have light-absorbing additives or are made up of bonds that are weakened by absorbing light.

Question 33

What is the difference between primary, secondary and tertiary alcohols?

Answer 33

• Primary: hydroxyl group is attached to a carbon which is attached to only one carbon
• Secondary: hydroxyl group is attached to a carbon which is attached to only two carbons
• Tertiary: hydroxyl group is attached to a carbon which is attached to three carbons

Question 34

How is the end of oxidation of alcohol reactions indicated?

Answer 34

Potassium dichromate goes from orange to green

Question 35

What are the purpose of anti-bumping granules?

Answer 35

They form smaller bubbles to prevent larger bubbles forming, to ensure smooth boiling.

Question 36

Why is it important for water in and water out of the condenser to be in the right position?

Answer 36

Ensures efficient cooling.

Question 37

When two or more halogens are present in a molecule, how is the haloalkane named?

Answer 37

Alphabetically.

Question 38

How does bond enthalpy of carbon halogen bonds change down the group?

Answer 38

Bond enthalpy decreases, so rate of hydrolysis increases.

Question 39

How can you test carbon-halogen bond strength / rate of hydrolysis?

Answer 39

Add silver nitrate and measure the rate of precipitate formed.

Question 40

How do organohalogen compounds affect the environment?

Answer 40

Disrupts the cycle of formation and breaking of ozone (O₃). Chorine radical act as catalysts, and the net reaction the catalyse is O₃ + O → 2O₂.

Nitrogen monoxide has a similar affect and it also forms radical which then acts as catalyst.

Question 41

When do bonds vibrate?

Answer 41

If they absorb light at the frequency its bonds vibrate.

Question 42

What does the clear peak at the highest m/z value on a mass spectrum represent?

Answer 42

Molecular ion peak, which shows the molecular mass of the compound.

Question 43

What is the M+1 peak ?

Answer 43

The next peak after the molecular ion peak. This is due to the fact that 1.1% of carbon exists as the carbon-13 isotope.

Question 44

What are the two types of bond vibrations?

Answer 44

1. Stretch: Distance between two atomic centres increases and decreases
2. Bend: Bond angles change

Question 45

What factors affect the amount a bond vibrates?

Answer 45

• Mass of the atoms: heavier atoms vibrate more slowly
• Strength of the bond: Stronger bonds vibrate faster