Chapter 8 - Introduction to Organic Chemistry

Question 1

What is an alkyl group?

Answer 1

It is a substituent group derived from an alkane by removal of a hydrogen atom.

Question 2

What is an aryl group?

Answer 2

A functional group that is derived from an aromatic ring by the removal of a hydrogen atom.

Question 3

What is a substituent group?

Answer 3

An atom or group of atoms substituted in place of a hydrogen on the hydrocarbon chain.

Question 4

How are organic compounds classified into classes?

Answer 4

Depending on how many substituent groups (usually alkyl) are joined to the carbon atom which is functional group is attached to/nitrogen in the case of amines.
Primary (1^0), Secondary (2^0), Tertiary (3^0), Quarternary (4^0)

Question 5

Define homologous series.

Answer 5

It is a family of compounds containing the same functional group, and in which each successive member increases by one -CH2- unit.

Question 6

What are 4 properties of compounds in the same homologous series?

Answer 6

1) can be represented by the same general molecular formula
2) can usually be prepared by similar methods
3) shows a gradual change in physical properties as molar mass increases
4) have similar chemical properties

Question 7

What are aliphatic compounds? (3)

Answer 7

• compounds with open chains of carbon atoms (eg propane)
• may be unbranched or branched
• may contain single, double or triple bonds, or a combination of these

Question 8

What are alicyclic compounds?

Answer 8

Compounds with closed rings of carbon atoms

Question 9

What are aromatic compounds?

Answer 9

Compounds containing at least one aromatic system

Question 10

What are the 7 types of organic reactions?

Answer 10

1) addition
2) elimination
3) substitution
4) condensation
5) hydrolysis
6) oxidation
7) reduction

Question 11

What is addition?

Answer 11

it is when two substances react together to form a single product. The pi bond of the unsaturated functional group (usually present in one of the reactants) breaks to form 2 sigma bonds.

Question 12

What is elimination? (2) (opposite of addition)

Answer 12

it is when an alkene is formed by the removal of

• a molecule of H2O from a molecule of an alcohol, or
• a molecule of HX from a molecule of a halogenalkane

Question 13

What is substitution?

Answer 13

it is when one atom or group of atoms is substituted by another. There is also at least 2 products.

Question 14

What is condensation?

Answer 14

It is when 2 molecules come together to form a bigger molecule, with the elimination of a small molecule such as water or HCl. (not the same as elimination)

Question 15

What is hydrolysis?

Answer 15

A reaction in which a molecule is split into two by the action of water, often catalysed by dilute acids or dilute alkalis.

Question 16

What is oxidation [O]? (2)

Answer 16

A reaction in which

• oxygen is added to a molecule, or
• hydrogen is removed from a molecule

Question 17

What is reduction [H]? (2)

Answer 17

A reaction in which

• oxygen is remove from a molecule, or
• hydrogen is added to the a molecule

Question 18

What is heterolytic bond breaking (heterolytic fission)?

Answer 18

It is the splitting of a bond resulting in unequal sharing of the bonding electrons to each resulting fragment. It usually results in the formation of ions.

Question 19

What is heterolytic bond forming?

Answer 19

A reaction where electrons move in such a way as to create new bonds.

Question 20

What are electrophiles?

Answer 20

An electrophile is an electron-deficient species that accepts an electron pair from an electron-rich species in s reaction to form a new covalent bond. They possess either

• a positively charged centre, or
• an atom which can carry an induced/permanent partial positive charge “d+”.

Question 21

What are nucleophiles?

Answer 21

A nucleophile is a species that donates an electron pair to an electron-deficient species in a reaction to form a new covalent bond. They possess that electrons that can be shared (e.g. pi bond or lone pairs of electrons)

Question 22

What are polar mechanisms in organic reactions?

Answer 22

Bond breaking and forming processes are heterolytic - involving movement of electron pairs

Question 23

What are non-polar mechanisms in organic reactions?

Answer 23

Bond breaking and forming process are homolytic - involving movement of single electrons rather than electron pairs

Question 24

What is homolytic bond breaking (homolytic fission)?

Answer 24

It is the splitting of a single bond, giving an equal share of bonding electrons to each resulting particle. It results in the formation of radicals.

Question 25

What is the difference between an intermediate and transition state for reaction intermediates?

Answer 25

Intermediate: definite species that exists for a finite length of time; can be isolated
Transition state: hypothetical species that exists only during the time that reactants are in contact with each other (~10^-15seconds), and thus cannot be isolated.

Question 26

What are the three species that are reaction intermediates?

Answer 26

1) free radicals
2) carbocations (carbonium ion)
3) carbanions

Question 27

What are carbocations (carbonium ions)?

Answer 27

It is a species that contains a carbon atom bearing a positive charge . It is electron deficient and a strong electrophile.

• positively charged carbon atom is bonded to 3 other atoms
• has only 6 electrons in its valence shell
• no lone pairs

Question 28

What are carbanions?

Answer 28

It is a species that contains a carbon atom bearing bearing a negative charge. It is electron-rich and a strong nucleophile.

• negatively charged carbon atom is bonded to three other atoms
• has 8 electrons in its valence shell (3 bonds and one lone pair)

Question 29

What are 2 types of electronic effects? (effects that influence the distribution of electrons in a particular chemical species, hence the reactivity of the species itself)

Answer 29

1) inductive effect (polarisation)

2) resonance (delocalisation)

Question 30

What is the inductive effect (polarisation)?

Answer 30

It is the polarisation of electron density in a bond due to the electronegativity of nearby atoms.

Question 31

What 5 characteristics of the inductive effect?

Answer 31

1) is a permanent but weak effect
2) can be electron-donating or electron-withdrawing
3) occurs through sigma bonds
4) is distance dependent (can extend to 2~3 bonds away but becomes weaker the further you get from the influencing functional group)
5) as long as electronegative atoms are present, there is inductive effect

Question 32

What is resonance (delocalisation)?

Answer 32

Resonance occurs when pi electrons are allowed to flow through the overlap of neighbouring p orbitals. Such electrons are said to be delocalized.

Question 33

What are 5 characteristics of the influence of resonance?

Answer 33

1) it is a permanent effect
2) can be electron-donating or electron-withdrawing
3) occurs through pi-system, which must be in a plane
4) independent of distance
5) minimum of 3 atoms that must have continuous, sideway overlaps of p orbitals (can be distributed in a region of space)

Question 34

What are steric effects?

Answer 34

Effects that result from the number and size of substituents and the repulsion between them are called steric effects.

Question 35

What is steric hindrance and what is its effect?

Answer 35

It is when the steric effect hinders the rate and extent of a reaction. A hindered, bulky reactant could prevent easy approach of the other reactant due to the repulsion of the electron clouds of both species, making bond formation difficult.

Question 36

What is a distinguishing test?

Answer 36

It is a simple chemical test that aims to confirm the presence of a particular compound or differentiate between organic compounds, through the identification of certain key functional groups. Such tests require a detectable chemical change with minimal use of complicated set-up or equipment.