Intro To Organic Chemistry

Question 1

What is the answering structure for 3-4m qn about hybridisation? Describe the sp2 hybridisation in propene.

Answer 1

1. Shape and bond angle of molecule
2. Bond lengths, equivalent hybrid orbitals which overlap head on with…
3. How hybrid orbitals are formed: mixing of ___ and ___ orbitals to form __ degenerate ___ hybrid orbitals
4. Unhybridised p orbitals lie perpendicular to the plane of the hybrid orbitals
5. How bonds are formed: Each C atom uses one sp2 hybridised orbital to…

Propene is trigonal planar with a bond angle of 120 degrees.
All the C-H bonds in propene have equal bond length. This implies that each carbon atom has 3 equivalent hybrid orbitals that overlap with the 1s orbital of 2 H atoms and one hybrid orbital of another carbon atom.

One 2s orbital and 2 2p orbitals are mixed, forming 3 degenerate 2sp2 hybrid orbitals. Each orbital contains one electron, and the carbon is said to be sp2 hybridised.
The unhybridised 2p orbital is perpendicular to the plane of the 3 hybrid orbitals.

Bond forming:
Propene has a C=C bond that consists of 1 sigma and 1 pi bond. Each carbon atom uses 1 sp2 hybridised orbital to overlap head on w each other to form a sigma bond. the unhyb p orbital of each C atom overlaps side on w each other to form a pi bond

Question 2

Explain why sp2-sp bond is stronger than sp2-sp2 bond.

Answer 2

Electrons in s orbitals are closer to the nucleus than electrons in p orbitals. Sp orbital has higher percentage of s character, and thus forms a shorter and stronger bond with an sp2 orbital, as compared to an sp2-sp2 bond

Question 3

Why do compounds in a homologous series have different physical properties?

Answer 3

Compounds have different molecular sizes and masses.
Each compound differs from the previous compound by one -CH2- unit, which increases its molecular size and mass

Question 4

List all the functional groups in INCREASING ORDER OF PRIORITY

Answer 4

Alkane, alkene, Arenes, amines, alcohols, ketones, aldehydes, nitriles, amides, acyl chlorides, esters, COOH

Question 5

When qn ask for displayed formula, what do you give?

Answer 5

FULL structural formula (draw everything)

Question 6

When qn ask for structural formula of eg, ethanoic acid, what can you give?

Answer 6

CH3COOH or draw it out
As long as its not C2H4O2

Question 7

Define a free radical, nucleophile and Electrophilic

Answer 7

Free radical: highly reactive, electrically neutral atom with an unpaired electron

Nucleophile: electron pair donor

Electrophilic: electron pair acceptor

Question 8

Define homolytic and heterolytic fission

Answer 8

Homolytic fission: shared pair of electrons is split equally between the two atoms, forming a free radical

Heterolytic fission: shared pair of electrons is split unequally between the 2 atoms. One atom accepts electron pair to form an anion while the other forms a cation

Question 9

Define addition reaction

Answer 9

2 reactants react together to form a single product
A pi bond is broken and 2 sigma bonds are formed

Question 10

Define a substitution reaction

Answer 10

An atom/group of atoms replaces another atom/group of atoms. One sigma bond broken, one sigma bond formed

Question 11

Define elimination reaction

Answer 11

The removal of 2 atoms (or groups of atoms) from adjacent atoms in one molecule
2 sigma bonds broken, 1 pi bond formed

Question 12

Define a condensation reaction

Answer 12

Two molecules react together to form a larger molecule and a small/simple molecule (eg, H2O, or HCl)

Question 13

What are isomers? Define constitutional isomerism and stereoisomerism

Answer 13

Isomers are compounds with the same molecular formula but with different arrangement of atoms in space

Constitutional isomers are compounds with the same molecular formulas but different structural formula

Stereoisomers have the same molecular and structural formula but different SPATIAL arrangements of atoms

Question 14

What is the shape for cis isomer and trans isomer?

Answer 14

Cis: U
Trans: like a staircase

Question 15

Why does cis isomer have lower MELTING point, but higher BP than a trans isomer?
Ie:
BP: Cis> trans
MP: Cis<trans
Cis melt more easily but is harder to boil

Answer 15

BP: Cis>Trans

Both molecules have simple molecular structures. More energy required to overcome the pdpd interactions between polar cis molecules as compared to the weaker idid interactions between non-polar trans molecules

MP: Cis< Trans
Both molecules have simple molecular structures. Trans molecules have higher symmetry and can pack more closely in its lattice structure than cis molecules. More energy is required to overcome the MORE EXTENSIVE id id interactions in trans molecules during melting.

Question 16

Describe the differences in physical, biological and chemical properties of enantiomers

Answer 16

Enantiomers have identical physical properties, except that that they rotate plane polarised light in opposite directions

Enantiomers have identical chemical properties but interact differently with other chiral compounds

Enantiomers have different biological properties and react differently with chiral molecules in our body

Question 17

Commonly tested: explain why drugs that are formed as a racemic mixture can be dangerous to consume

Answer 17

Enantiomers have different biological properties, and one of the enantiomers may interact with the chiral protein molecules in the body differently, resulting in health problems —> birth defects, etc

Question 18

Explain why molecules with an internal plane of symmetry have no effect on plane polarised light

Answer 18

Molecules w an internal plane of symmetry have a superimposable mirror image and are achiral, and thus optically inactive