L12 - Organic Chemistry (2)

Question 1

Define Aliphatic.

Answer 1

Compounds containing an open chain of carbon atoms.

Question 2

Define Alicyclic.

Answer 2

Compounds containing a ring of saturated carbon atoms.

Question 3

Define Aromatic.

Answer 3

Compounds containing a ring where all the atoms are unsaturated (and conjugated).

Question 4

Define Heterocyclic.

Answer 4

Compounds containing a ring made up of Carbon and at least one other element, such as N, S or O.

Question 5

What is significant about the functional groups in organic compounds?

Answer 5

• Gives its characteristic chemical properties
• Acts as the site of chemical reactivity
• Serves as the basis of nomenclature
• Classifies its family

Question 6

What is the general structure of an Alkyl Halide?

Answer 6

R - X

halo

Question 7

What is the general structure of an Alcohol?

Answer 7

R - O - H

hydroxy

Question 8

What is the general structure of an Ether?

Answer 8

R - O R’

alkoxy

Question 9

What is the general structure of an Amine?

Answer 9

R - N - H2

R - N - H, R’

R- N - R’, R’’

(amino)

Question 10

What is the general structure of a Thiol?

Answer 10

R - S - H

thio / mercapto

Question 11

What is the general structure of a Sulfide?

Answer 11

R - S - R’

alkathio

Question 12

What is the general structure of an Aldehyde?

Answer 12

R - C = O, H

carbonyl

Question 13

What is the general structure of a Ketone?

Answer 13

R - C = O, R

carbonyl

Question 14

What is the general structure of a Carboxylic Acid?

Answer 14

R - C = O, OH

carboxyl

Question 15

What is the general structure of an Ester?

Answer 15

R - C = O, OR’

alkyl

Question 16

What is the general structure of an Amide?

Answer 16

R - C = O, N - R’, R’’

R - C = O, NH2

(H / Alkyl)

Question 17

What is the general structure of an Acid Chloride?

Answer 17

R - C = O, Cl

COCl

Question 18

Describe polyfunctional compounds.

Answer 18

• Contain more than one functional group
• Principle functional group determines the class
• Secondary functional groups are treated as substituents

Question 19

What is the order of preference for the principle group?

Answer 19

1) Carboxylic Acid
2) Ester
3) Acid Halide
4) Amide
5) Nitrile
6) Aldehyde
7) Ketone
8) Alcohol
9) Amine
10) Double Bond
11) Triple Bond
12) Hydrogen
13) Nitrogen

Question 20

Define Homologous Series.

Answer 20

Group of organic compounds with similar chemical properties, same functional group but differ by the length of the carbon chain; successive members differ by a CH2 unit.

Question 21

What are successive members of a homologous series called?

Answer 21

Homologues

Question 22

Describe the features of homologues.

Answer 22

• Same general formula
• Prepared by similar methods
• Similar chemical properties
• Gradual variation in physical properties with increasing molecular weight

Question 23

What does bonding in organic molecules use?

Answer 23

Linear combination of atomic orbitals

Orbitals combine to form hybrid atomic orbitals and molecular orbitals

Question 24

Describe the 2 atomic orbitals.

Answer 24

s-Orbital:

• Spherical
• Lower in energy than the other orbitals in the same shell

p-Orbital:

• Dumbbell shape
• Nodal plane passes through nucleus (no electron density at the node)
• Higher in energy than s-orbital
• 3 p-orbitals in the same shell

Question 25

Explain Hybridisation.

Answer 25

The idea that atomic orbitals fuse to form newly hybridised orbitals, which in turn, influences the molecular geometry and bonding properties.

Question 26

Explain Hybridisation, with reference to Carbon.

Answer 26

1) Carbon has 2 unpaired electrons, yet it forms 4 bonds 2) One of the 2s electrons can be promoted into the vacant p orbital in 2p - Requires energy input - Favourable because of decreased electron-electron repulsion 3) The 2s and 2p orbitals now mix to form various hybrid atomic orbitals

Question 27

Describe SP3 Hybridisation.

Answer 27

- All 4 atomic orbitals (2s, 2 px, 2 py, 2 pz) combine to give the same number of new hybrid atomic orbitals - All 4 sp3 orbitals are equivalent with the same energy (degenerate) - Orbitals point towards the corners of a tetrahedron - Overlap produces sigma bonds

Question 28

What is SP3 Hybridisation used for bonding in?

Answer 28

Used for bonding in saturated compounds

Question 29

Describe SP2 Hybridisation.

Answer 29

- The s and two p orbitals (2 px, 2 py) combine to give three new hybrid atomic orbitals - The 3rd p orbital (2 pz) remains unchanged - SP2 orbitals point towards the corners of a triangle - Used for sigma bonding - The p orbital is perpendicular to them - Used for pi bonding

Question 30

What is SP2 Hybridisation used for bonding in?

Answer 30

Used for bonding in alkenes, carbonyls and aromatic rings

Question 31

Describe SP Hybridisation.

Answer 31

- The s and one p orbital (2 px) combine to give two new hybrid atomic orbitals - The other 2 p orbitals (2 py, 2pz) remain unchanged - SP orbitals are at 180° to one another (linear molecule) - Used for sigma bonding - The 2 p orbitals are perpendicular to them - Used for pi bonding

Question 32

What is SP Hybridisation used for bonding in?

Answer 32

Used for bonding in alkynes and nitriles

Question 33

Describe the properties of hybrid orbitals.

Answer 33

- Hold electrons closer to the nucleus - Bond becomes shorter, and therefore stronger - More directional, so they have effective bonding interactions - The more s-character in an orbital, the lower the energy (leads to increased stability of an electron in that orbital)

Question 34

The overlap of orbitals forms two types of bonds depending on the ________ of the overlap.

Answer 34

The overlap of orbitals forms two types of bonds depending on the geometry of the overlap.

Question 35

How are sigma (σ) bonds formed?

Answer 35

By direct overlap

Question 36

Describe sigma (σ) bonds.

Answer 36

- Electron density is along the line of the bond - Symmetric with relation to rotation about the bond - Bond may be formed between s-s, p-p, s-p or hybridised orbitals - The bonding molecular orbital is lower in energy than the original atomic orbitals

Question 37

Describe sigma (σ) bonding in methane.

Answer 37

1) Four sp3 hybrid orbitals form a tetrahedron 2) Add four hydrogen atoms 3) Combine sp3 and 1s 4) Each molecular orbital is the same and has σ symmetry

Question 38

Describe sigma (σ) bonding in ethane.

Answer 38

1) Each carbon uses three sp3 orbitals to bond to hydrogens | 2) Remaining sp3 orbital on each carbon overlaps to form a carbon-carbon bond

Question 39

How are pi (π) bonds formed?

Answer 39

By the parallel overlap of p orbitals

Question 40

Describe pi (π) bonds.

Answer 40

- Electron density is above and below the plane of the bond - Form after sigma bonds - Higher in energy than sigma bonds, therefore weaker and more easily broken

Question 41

Describe the nature of bonding in a double bond.

Answer 41

(2 pairs of shared electrons) - Consists of 1 sigma bond and 1 pi bond

Question 42

Describe the nature of bonding in a triple bond.

Answer 42

(3 pairs of shared electrons) - Consists of 1 sigma bond and 2 pi bonds

Question 43

Describe the bonding in benzene.

Answer 43

- π electrons are delocalised around the ring, above and below the plane - All bond lengths are identical (between single and double bonds)

Question 44

Describe the different bonding types in relation to bond length and bond strength.

Answer 44

Bond Strength (Strongest to Weakest): - Triple Bond - Double Bond - Single Bond Bond Length (Longest to Shortest): - Single Bond - Double Bond - Triple Bond The stronger the bond, the shorter the bond length.

Question 45

What type of hybridisation do the different bonds undergo?

Answer 45

- Single Bond: sp3 - Double Bond: sp2 - Triple Bond: sp