2.4- Organic Compounds

Question 1

(b)

Nomenclature rules relating to alkanes, alkenes, halgenoalkenes, alcohols and carboxylic acids.

Answer 1

Alkanes:
CnH2n+2
Alkenes:
CnH2n
Halogenoalkanes:
CnH2n+1X
Prefix: Fluoro-/Chloro-/Bromo-/Iodo-
Suffix: -ane
Alcohols:
CnH2n+2OH
Carboxylic acids:
CnH2n+1COOH

Question 2

(c)

Effect of increasing chain length on
melting/boiling temperature and solubility

Answer 2

Increasing Chain Length
-Increases melting/boiling temperature (stronger van der Waals forces)
-Decreases solubility in polar solvents (water)

Question 3

(c)

Effect of the presence of functional groups on melting/boiling temperature and solubility

Answer 3

Presence of Functional Groups
- Increases melting/boiling temperature if polar (due to hydrogen bonding/dipole-dipole interactions)
- Increases solubility in polar solvents if polar functional group present (due to hydrogen bonding)

Question 4

(d)

Structural isomerism

Answer 4

Structural isomers are compounds with the same molecular formula but a different structural formula

Question 5

(d)

Chain isomerism

Answer 5

The carbon chain is arranged differently (branches).

Question 6

(d)

Position isomerism

Answer 6

The functional group is in a different position in the molecule.
E.g.
CH3 CH2 CH2
Cl
1-chloropropane

CH3 CH CH2
Cl
2-chloropropane

Question 7

(d)

Functional group isomerism

Answer 7

The functional group is different

Question 8

(d)

E-Z isomerism

Answer 8

Only occurs in alkenes because there is restricted rotation around the double bond.

Question 9

(d)

Working out if the alkene is E or Z

Answer 9

Look at the atoms directly attached to each of the carbon atoms. The atom with the higher atomic number takes priority. If the higher priority atom on both carbon atoms is on the same side of the double bond, the isomer is the Z form. If the higher priority atoms are on opposite sides of the double bond, the isomer is the E form.

Question 10

Identfiying functional groups as primary/secondary/tertiary

Answer 10

Primary: Functional group attached to a carbon bonded to one other carbon.
Secondary: Functional group attached to a carbon bonded to two other carbons.
Tertiary: Functional group attached to a carbon bonded to three other carbons.

Question 11

Electronegativity

Answer 11

Electronegativity is a chemical property that describes the tendency of an atom or a functional group to attract electrons toward itself

Question 12

Non-polar covalent bond

Answer 12

Bonding electrons shared equally between two atoms. No charges on atoms. E.g. C-H, Cl-Cl

Question 13

Polar covalent bond

Answer 13

Bonding electrons shared unequally between two atoms. Partial charges on atoms. E.g. C-X (C= delta positive and X= delta negative)

(x = Cl, Br, I, O)

Question 14

Hydrogen bonds

Answer 14

Occur between a Hydrogen bonded to a N, O, F and an N, O or F atom
on another molecule

Question 15

Dipole-Dipole

Answer 15

Dipole-dipole forces are attractive forces between the positive dipole
of one polar molecule and the negative dipole of another polar
molecule

Question 16

Induced Dipole- Induced Dipole

Answer 16

These are weak electrostatic forces that attract molecules to one
another – even non-polar molecules
The more strength increases the more total electrons there are in a
molecule. So the interactions are stronger when there is a higher
surface area (i.e. longer chain length)

Question 17

Alkene bonds

Answer 17

Alkenes contain C=C bonds
These are made up of a sigma bond and a pi bond (whereas alkanes only contain sigma bonds)

Question 18

Formation of sigma bonds

Answer 18

Sigma bonds are formed from the overlap of s orbitals on each carbon

Question 19

Formation of pi bonds

Answer 19

Pi bonds are formed from the overlap of p orbitals on
each carbon

Question 20

Electrophilic addition

Answer 20

Alkenes undergo electrophilic addition reactions when they react with an electrophile

Question 21

Impact of intermolecular forces on boiling points of organic compounds

Answer 21

Melting and boiling points depend on the strength of intermolecular
forces – this is because in order for a compound to melt/boil the
intermolecular forces have to be broken

Question 22

(2)

Impact of intermolecular forces on boiling points of organic compounds

Answer 22

The stronger the interactions – the higher the melting/boiling point
This is because more energy is needed to break the molecules
apart

Question 23

Impact of intermolecular forces on solubility of organic compounds

Answer 23

When a compound dissolves the intermolecular forces between molecules break and new forces between the solute and the solvent are formed. Energy is needed to do this - all compounds are more soluble at higher temperatures

Question 24

(2)

Impact of intermolecular forces on solubility of organic compounds

Answer 24

Non-polar compounds dissolve in non-polar solvent

Polar compound dissolve in polar solvent

Question 25

Combustion of hydrocarbons

Answer 25

Burning a hydrocarbon forms two compounds:
CO2 and H2O

Question 26

Complete combustion

Answer 26

Requires excess O2
Produces only CO2 & H2O

Question 27

Incomplete combustion

Answer 27

Occurs when there is an insufficient supply of oxygen
Produces water and CO(g) and/or C(s)

Question 28

(e)

Electrophiles

Answer 28

An electrophile is a species that accepts a lone pair of electrons in a reaction.

Question 29

(e)

Nucleophiles

Answer 29

A nucleophile is a species that donates a lone pair of electrons in a reaction.

Question 30

(e)

Radicals

Answer 30

A free radical is a neutral
molecule that has an
unpaired electron.

Question 31

(e)

Heterolytic bond fission

Answer 31

Heterolytic bond fission is the breaking of a covalent bond where one of the bonded atoms gets both electrons. This produces one nucleophile and one electrophile.

Question 32

(e)

Homolytic bond fission

Answer 32

Homolytic bond fission is the breaking of a covalent bond where both bonded atoms get one electron, producing free radicals.