4.1

Question 1

a) what are the names corresponding to the first ten members of the alkanes homologous series and the corresponding alkyl groups?

Answer 1

1 : methane : methyl
2 : ethane : ethyl
3 : propane : propyl
4 : butane : butyl
5 : pentane : pentyl
6 : hexane : hexyl
7 : heptane : heptyl
8 : octane : octyl
9 : nonane : nonyl
10 : decane : decyl

Question 2

Name for alkanes?

Answer 2

-ane

Question 3

Functional group and name for alkenes?

Answer 3

C=C : -ene

Question 4

Functional group and name for haloalkane?

Answer 4

C-X (where X is a halogen) : halo- (e.g. bromo-)

Question 5

Functional group and name for alcohols?

Answer 5

C-OH : hydroxy- or -ol

Question 6

Functional group and name for aldehydes?

Answer 6

R-C=O (where R is other organic stuff) : oxo- or -al
|
H

Question 7

Functional group and name for ketone?

Answer 7

R-C=O (where R is organic stuff but not hydrogen) : oxo- or -one
|
R

Question 8

Functional group and name for carboxylic acid?

Answer 8

-C=O : -oic acid
|
OH

Question 9

Functional group and name for esters?

Answer 9

-C=O : alkyl -anoate
|
O-
With the alcohol contributing the alkyl, and the acid contributing the -anoate

Question 10

b) i) What is the general formula?

Answer 10

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

Question 11

b) ii) What is the structural formula?

Answer 11

The minimal detail that shows the arrangements of atoms in a molecule (CH3CH2CH3)
Ester: COO
carboxylic acids: COOH

Question 12

b) iii) What is the displayed formula?

Answer 12

The relative positioning of atoms and the bonds between them.

Question 13

b) iv) What is the skeletal formula?

Answer 13

A displayed formula with the hydrogens having been removed from the alkyl chains.

Question 14

c) i) What is the definition of a homologous series?

Answer 14

A series of organic compounds which have the same functional group but with each successive member differing by CH2.

Question 15

c) ii) What is a functional group?

Answer 15

A group of atoms responsible for the characteristic reactions of a compound.

Question 16

c) iii) What is an alkyl group?

Answer 16

A compound of formula CnH2n+1

Question 17

c) iv) what is an aliphatic?

Answer 17

A compound containing carbon and hydrogen joined together in straight or branched chains, or non-aromatic rings.

Question 18

c) v) What is an alicyclic

Answer 18

An aliphatic compound arranged in non-aromatic rings with or without side chains.

Question 19

c) vi) What is an aromatic?

Answer 19

A compound containing a benzene ring.

Question 20

c) vii) What is a saturated compound?

Answer 20

A compound which contains only single carbon-carbon bonds.

Question 21

e) What are structural isomers?

Answer 21

Compounds with the same molecular formula but different structural formulae.

Question 22

f) What are the different types of covalent bond fission?

Answer 22

Homolytic fission: where each bonding atom receives one electron from the bonded pair, forming two radicals.
Heterolytic fission: where one of the bonding atoms receives both electrons from the bonded pair.

Question 23

g) What is the definition of a radical?

Answer 23

A species with an unpaired electron. It is shown by a dot.

Question 24

h) What does a curly arrow represent?

Answer 24

The movement of an electron pair.

Question 25

a) What are alkanes?

Answer 25

Saturated hydrocarbons containing sigma bonds

Question 26

a) What are sigma bonds?

Answer 26

Molecular orbitals where the overlap of the orbitals are directly between the bonding atoms.

Question 27

b) What shape are alkanes?

Answer 27

The shape, determined by electron pair repulsion theory, is tetrahedral around each carbon atom with bond angles of 109.5° throughout as each carbon has four bond pairs and no lone pairs.

Question 28

c) How does boiling point change with different length and branching alkanes?

Answer 28

In straight chain alkanes, the boiling point increases with the length. This is because the number of electrons in the molecule increases, which increases the London forces, so more energy is then required to overcome the intermolecular forces. In isomeric alkanes, the boiling point decreases as the isomers become more branched. This is because they have a smaller surface area for the London forces to act through, so there is a smaller attraction between molecules.

Question 29

d) Why aren’t alkanes very reactive?

Answer 29

Alkanes are the most basic homologous series as they have no functional group. This means that they have no centre where reactions tend to happen because C-C and C-H bonds are both strong and non-polar due to their very slight differences in electronegativity. This means they attract no other charged compounds or atoms. All the covalent bonds in alkanes also have high bond enthalpy so energy is not easily released during reactions.

Question 30

Reaction mechanism for alkanes and halogens:

Answer 30

The reaction mechanism is free radical substitution: where a radical replaces a different atom or group of atoms. (CH4 + Cl -UV-> CH3Cl + HCl 1. Initialisation: where radicals are generated by UV light, homolytic fission (or 300°C): Cl2 -UV-> 2Cl• 2. Propagation: the two repeated steps in radical substitution that build up the products in a chain reaction: Cl• + CH4 -> HCl + CH3• / CH3• + Cl2 -> CH3Cl + Cl• 3. Termination: the step at the end of radical substitution when two radicals combine to form a molecule: Cl• + CH3• -> CH3Cl / 2Cl• -> Cl2 / 2CH3• -> C2H6 The possibility of multiple substitution of initially formed products exist. (Most likely: CH3Cl -> CH2Cl2 -> CHCl3 -> CCl4 :least likely). All these side products can be separated by fractional distillation or chromatography.

Question 31

What are π-bonds?

Answer 31

Molecular orbitals which have a sideways overlap of adjacent p-orbitals above and below the bonding carbon atoms. They have restricted rotations.

Question 32

Reaction mechanism for hydrogenation of alkenes:

Answer 32

Hydrogenation is an addition reaction in which hydrogen is added across a double bond. Conditions: Nickel and 150°C. Example equation: C2H4 + H2 -> C2H6

Question 33

Reaction mechanism for hydrohalogenation of alkenes:

Answer 33

Procedure: Bubble XH through alkene at room temperature. Mechanism: C=C bond -curly arrow-> Hδ+, H-X bond -curly arrow-> X (forming a carboncation) —> :Br- -curly arrow-> C+

Question 34

Reaction conditions for hydration of alkenes

Answer 34

Steam (65atm, 300°C), and H3PO4

Question 35

What is stereoisomerism?

Answer 35

When organic compounds have the same molecular formula and structural formula, but different arrangements of atoms in space.

Question 36

How do you determine E/Z isomerism?

Answer 36

Use CIP rules to determine the priority of the atoms bonded to the C=C based on their relative atomic mass. If the highest priority atoms are on the same side, the isomer is Z. If the highest priority atoms are on different sides, the isomer is E.

Question 37

How do you determine cis-trans isomerism?

Answer 37

Cis-trans isomerism is a special type of E/Z isomerism where two substituents on each carbon atom are the same. E is trans. Z is cis.

Question 38

What are alkenes?

Answer 38

A homologous series of unsaturated hydrocarbons which have the general formula CnH2n

Question 39

What is the bonding in alkenes like?

Answer 39

A σ-bond is formed between two carbon atoms using the direct overlap of electron clouds of the two atoms. The π-bond is formed by the electrons in adjacent p-orbitals overlapping above and below the carbon atoms. The π-bond has restricted rotation, so alkene molecules are planar in the region of the double bond.

Question 40

What is the shape of alkene molecules?

Answer 40

Each carbon atom in the molecule has three areas of electron density. There will be two covalent bonds to separate hydrogen atoms, and one σ-bond and one π-bond between the two carbon atoms. Each of these electron densities repel by the same amount forming bond angles of 120°, which results in a trigonal planar shape.

Question 41

Why are alkenes more reactive?

Answer 41

π-bonds have lower bond enthalpies than σ-bonds so will break more easily and react, leaving the σ-bond between the two carbon atoms. In addition to this, the double bond is an area of high electron density so is more prone to electrophile attacks.

Question 42

Reaction mechanism for halogenation of alkenes:

Answer 42

Reaction mechanism: electrophilic addition. Conditions: halogen. Mechanism: C=C bond -curly arrow-> Brδ+ (induced dipole), Brδ+-Brδ- bond -curly arrow-> Brδ- —> :Br- -curly arrow-> C+

Question 43

What is Markownikoff’s rule?

Answer 43

Markownikoff’s rule states that primary carbocations (bonded to one carbon chain) are less stable than tertiary carbocations (bonded to three carbon chains). Therefore when H-X reacts with an alkene the hydrogen will become attached to the carbon with the most hydrogen atoms to start with.

Question 44

How do we manage polymer waste?

Answer 44

-combustion for energy production. Could cause HCl if a halogenated plastic. -use as an organic feedstock for the production of other organic chemicals. -reusing. The development of biodegradable and photodegradable polymers which breaks down the polymer chains into small pieces. This would reduce dependency on finite resources and alleviate the problems from disposal.