Lecture 12-Organic Chemistry II

Question 1

Name the 5 types of chains + rings and whether they’re acyclic + cyclic?

Answer 1

Aliphatic (Acyclic)
Saturated + unsaturated (Acyclic)
Alicyclic (Cyclic)

Aromatic (Cyclic)
Heterocyclic (Cyclic)

Question 2

Alicyclic?

Answer 2

Compounds containing a ring of saturated carbon atoms

Question 3

Aromatic?

Answer 3

Contain a ring where all the atoms are unsaturated + conjugated

Question 4

Heterocyclic?

Answer 4

Contain a ring made up of carbon + at least 1 other element = N,S,O

Question 5

A functional group in a molecule …..

Answer 5

gives characteristic chemical properties
acts as a site of chemical reactivity
serves as the basis for nomenclature
classifies its family

Question 6

What’s a polyfunctional compounds?

Answer 6

Contain more than 1 functional group

Question 7

What determines the class in a polyfunctional compounds?

Answer 7

Primary functional group

Secondary functional group = substituents

Question 8

What is the order of preference for principal group is

Answer 8

Carboxylic acid - ester - acid halide - amide - nitrile - aldehyde - ketone - alcohol - amine - double bond - triple bond - halogen - nitro

Question 9

What is the homologous series?

Answer 9

A group of similar compounds with similar chemical properties in which members contain the same functional group ,but differ by the length of the C chain : adjacent members differ by a CH2 unit

Question 10

What are successive members of a homologous series called?

Answer 10

Homologues

Question 11

Describe the properties of homologous series?

Answer 11

• same general formula
• prepared similar methods
• similar chemical properties
• gradual variation in physical properties with increasing molecular weight

Question 12

What is a hybrid atomic orbital?

Answer 12

Combination of atomic orbitals from the same atom

Question 13

What is a molecular atomic orbital?

Answer 13

Combination of atomic / hybrid atomic orbitals from different atoms

Question 14

How so second row elements (C,O,N) hybridize using what orbitals?

Answer 14

2s , 2p —-> sp,sp2,sp3 HAOs

Question 15

Describe a s orbital?

Answer 15

spherical

lower in energy than other orbitals in the same shell

Question 16

Describe a p orbital?

Answer 16

dumb-bell shape
nodal plane passes through nucleus
higher in energy than s-orbital
3 p orbitals in the same shell

Question 17

Explain hybridisation using carbon as an example?

Answer 17

C electronic configuration = 1s2 2s2 2p2

• 2 unpaired e- ,but cC can form 4 bonds THEREFORE …
• 1 of the 2s e- can be promoted —> vacant p orbital

,But this requires energy input

it’s favourable ,because of decreased electron-electron repulsion

-the 2s + 2p orbitals now mix —> various hybrid atomic orbitals

Question 18

Sp3

Answer 18

• All 4 atomic orbitals combine —> same n.o. of new hybrid atomic orbitals
• All 4 sp3 orbitals = equivalent with the same energy (degenerate)
• Orbitals point towards the corners of a tetrahedron
• Overlap produces sigma bonds
• Used for bonding in saturated compounds

Question 19

Sp2

Answer 19

• The s + p orbitals combine —> 3 new hybrid atomic orbitals
• The 3rd p orbital = 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

Sp2 hybridisation used for bonding in alkenes,carbonyls + aromatic rings

Question 20

Sp?

Answer 20

• The s + 1p orbital combine —> 2 new hybrid atomic orbitals
• The other 2 =unchanged

Sp orbitals = 180.C to one another (linear)
-used for sigma bonding

Sp hybridisation = used for bonding in alkynes + nitriles

Question 21

What are the properties of hybrid orbitals?

Answer 21

Hold e- closer to nucleus
The bond —> shorter + stronger
More directional = more effective bonding interactions
More s-character in an orbital —> lower the energy
-increased stability of an e- in that orbital

Question 22

The overlapping of orbitals forms 2 types of bonds depending on?

Answer 22

The geometry of overlap

Question 23

How are sigma bonds formed and describe their properties?

Answer 23

Formed by direct overlap

• e- density is along the line of the bond
• symmetric wrt rotation about the bond
• bond may be formed between s-s , p-p , s-p or hybridized orbitals

The bonding molecular orbital is lower in energy than the original atomic orbitals

Question 24

How are pi bonds formed?

Answer 24

By parallel overlap of p orbitals

• electron affinity is above+below the plane of the bond
• form after sigma bonds
• higher in energy than sigma bonds —> weaker + more easily broken

Question 25

Name molecules with sigma bonding?

Answer 25

Methane

Ethane

Question 26

What type of bonding is there in a double bond? (2 pairs of shared e-)

Answer 26

1 sigma bond

1 pi bond

Question 27

What type of bonding is there in a triple bond? (3 pairs of shared e-)

Answer 27

1 sigma bond

2 pi bonds

Question 28

What is the bonding framework in ethyne (acetylene)?

Answer 28

Sigma bonds

pi overlap in ethyne

Question 29

Describe the bonding in benzene?

Answer 29

pi e- delocalised around the ring, above + below the plane

-all bond lengths identical (between single +double bonds)

Question 30

WHat type of bond has the longest length and which one has the most strength?

Answer 30

Longest = single --> double --> triple
Strongest = triple --> double --> single