Basic Concepts of Organic Chemistry

Question 1

What is a general formula?

Answer 1

The simplest algebraic formula of a memeber of a homologous series.

Question 2

What is the structural formula?

Answer 2

• The minimal detail that shows the arrangement of atoms in a molecule.

Question 3

What is a homologous series?

Answer 3

A series of organic compounds with the same functional group and general formula. Consectutive members differ by -CH₂-.

Question 4

What are structural isomers?

Answer 4

Compounds with the same molecular formula but different structural formulae.

Question 5

What is difference between homogenous and heterogenous fission?

Answer 5

Homogenous: both atoms recieve one of the bonding electrons

Heterogenous: one atom recieves both bonding electons.

Question 6

What is a radical?

Answer 6

A species with an unpaired electron.

Question 7

Explain the trend in melting and boiling points of alkanes.

Answer 7

• Larger alkanes have higher m.p. & b.p.
• Longer chain
• More electrons per molecule + larger surface contact area
• More ID-ID interations
• More energy required to overcome these attractions

Question 8

Why do branched chain alkanes have lower m.p. and b.p. than straight-chain isomers?

Answer 8

Can’t pack as closely together and have smaller molecular surface areas so fewer ID-ID interactions.

Question 9

Why are alkanes mostly unreactive?

Answer 9

The C-C and C-H bond enthalpies are high so lots of energy is required to break them. They are also not polar so they are not susceptible to nucloephilic attack.

Question 10

What are the disadvantages of free radical substitution in synthesis?

Answer 10

• Multiple substitutions can occurs, meaning you obtain a mixture of products.
• Have to separate desired product from mixture.
• Substitution can also occur at any point along the chain, so a mixture of isomers are formed.

Question 11

Describe the formation of a pi-bond and compare their strength to that of a sigma-bond.

Answer 11

• Sideways overlap of two adjacent p-orbitals, above and below the sigma-bond.
• Weaker than a sigma-bond as electron density is much lower (spread out above and below the nuclei), therefore electrostatic attraction between shared pair of electrons and nuclei, so bond enthalpy is lower.

Question 12

Dicuss the methods and benefits of disposing of plastics.

Answer 12

• Can be melted and remoulded
• Can be cracked into monomers to use as organic feedstock for industrial chemical processes to make more plastics or other chemicals.
• Can be burned, with the heat used to generate electricity. This can produce toxic gases e.g. chlorine containing compounds produce HCl, a toxic gas, when burnt, which has to be removed. Waste gases are passed through scrubbers which neutralise gases such as HCl by allowing them to react with a base.