Intro To Organic Chemistry

Question 1

How can C form 4 bonds when it only has 2 unpaired electrons?

Answer 1

When excited, one 2s electron can be promoted to the vacant 2p orbital, resulting in four unpaired electrons in excited state

Question 2

What is hybridisation?

Answer 2

Hybridisation refers to the mixing of atomic orbitals in various combinations to give a set of hybrid orbitals of equivalent energy for covalent bonding with other atoms

Question 3

What are the rules of hybridisation?

Answer 3

• number of atomic orbitals used in hybridisation = number of hybrid orbitals formed
• hybrid orbitals of the same type are equivalent and degenerate
• Only apply to central atoms

Question 4

What is sp3 hybridisation?

Answer 4

• One s and 3 p valence orbital
• 25% s character and 75% p character
• single bond
• tetrahedral

Question 5

What is sp2 hybridisation?

Answer 5

• One s and 2 p valence orbital
• 33.3% s character and 66/7% p character
• double bond
• trigonal planar

Question 6

What is sp hybridisation?

Answer 6

• One s and one p valence orbital
• 50% s character and 50% p character
• triple bond
• linear

Question 7

How to use hybridisation to explain the difference in bond length of why ethane bond length greater than ethene?

Answer 7

• Hybridisation of C in ethane is sp3 while ethene is sp2
• sp2-hybridised orbital has greater s character than sp3 hybridised orbital and is closer to nucleus and smaller in size
• 2sp2-1s overlap is shorter in length than 2sp3-1s overlap

Question 8

What is a saturated molecule?

Answer 8

Only single bonds

Question 9

What is unsaturated molecule?

Answer 9

Multiple bonds

Question 10

What are aliphatic compounds?

Answer 10

No aromatic ring

Question 11

What are aromatic compounds?

Answer 11

Compounds with delocalised pi electron system

Question 12

What do members of homologous series have?

Answer 12

• Same functional group thus similar chemical properties
• Have general formula

Question 13

What is 1 to 10 for root name?

Answer 13

1: meth-
2: eth-
3: prop-
4: but-
5: pent-
6: hex-
7: hept-
8: oct-
9: non-
10: dec-

Question 14

What is homolytic fission?

Answer 14

Covalent bond broken such that each bonding atom takes one bonding electron, giving rise to free radicals

Question 15

What is heterolytic fission?

Answer 15

Covalent bond broken such that one of bonding atom takes both bonding electrons while the remaining becomes a cation

Question 16

What does full arrow represent?

Answer 16

Movement of a pair of electron

Question 17

What does half arrow represent?

Answer 17

Movement of one electron

Question 18

What are isomers?

Answer 18

Compounds with same molecular formula but different arrangement of atoms in 3-dimensional space

Question 19

What are constitutional isomers?

Answer 19

Compounds with same molecular formula but different structural formula

Question 20

What are stereoisomers?

Answer 20

Same molecular and structural formula but differ in spatial arrangement of atoms

Question 21

When can cis-trans isomerism be exhibited by a molecule?

Answer 21

1. restricted rotation about a covalent bond
2. two different groups/atoms attached to each carbon of the bond of restricted rotation

Question 22

What are enantiomers?

Answer 22

Stereoisomers with non-superimposable mirror images

Question 23

What is a chiral carbon centre?

Answer 23

4 different groups attach to a carbon

Question 24

Do enantiomers have similar physical properties?

Answer 24

Yes, except their effect on plane-polarised light

Question 25

What are the effects of a pair of enantiomers on plane-polarised light?

Answer 25

Rotate plane-polarised light by equal but opposite angles

Question 26

What is a racemic mixture/racemate?

Answer 26

A mixture containing equal amounts of both enantiomers will show no optical activity as their effects on plane-polarised light cancel each other out

Question 27

Do enantiomers have similar chemical properties?

Answer 27

Yes, except when interacting with other chiral molecules, eg. chiral enzyme active sites

Question 28

How do molecules exhibit enantiomerism?

Answer 28

Chiral molecule with no internal plane of symmetry

Question 29

What is the formula for the number of optical isomers possible?

Answer 29

2^n where n is the number of chiral centres