Download Organic Chemistry

Organic
Chemistry
Organic Chemistry
 The chemistry of life
 The study of Carbon (C)
 More specifically, the study of the bonds formed
between Carbon (C) and (mostly), Hydrogen (H),
Oxygen (O) and Nitrogen (N).
Valency
 Number of bonds formed determined by atomic
structure
 Remember: A covalent bond is formed when two
atoms share a pair of electrons!
 Covalent bonds of Carbon form basis of Org Chem
Valency
 Sharing 1 pair of electron = single bond
 Sharing 2 pairs of electrons = double bond
 Sharing 3 pairs of electrons = triple bond
 Different atoms can form different amounts of bonds
 Why?
Valency - H
 Look at atomic structure
 H is atom no. 1
 No. of protons: 1
 No. of electrons: 1
 1 electron means it can form only 1 covalent bond
(EVER!)
Valency - H
 Look at atomic structure
 H is atom no. 1
 No. of protons: 1
 No. of electrons: 1
 1 electron means it can form only 1 covalent bond
(EVER!)
Valency - C
 C : element number 6
 => 6 protons and 6 electrons
 Electronic configuration: 1s2, 2s2, 2p2
 1s electrons not involved in bonding so 4 valence
electrons (v.e-.)
 Octet rule: C wants 8 electrons
 Must share all 4 electrons to get 8
Valency - C
 C must form 4 bonds to form stable compounds
 Can be any combination of single, double and triple
bonds
 Can NEVER exceed 4 bonds around a C atom
Valency - O
 Electronic structure: 1s2, 2s2, 2p4
 6 valence electrons available
 Wants 8 so only needs 2 more
 O can form 2 bonds; valency = 2
 This means 1 double bond or 2 single bonds
Valency - O
 Electronic structure: 1s2, 2s2, 2p4
 6 valence electrons available
 Wants 8 so only needs 2 more
 O can form 2 bonds; valency = 2
 This means 1 double bond or 2 single bonds
Valency - N
 Electronic structure: 1s2, 2s2, 2p3
 5 valence electrons available
 Wants 8 so only needs 3 more
 N can form 3 bonds; valency = 3
 This means 3 single bonds; 1 double bond and 1
single bond or 1 triple bond.
Valency - N
Drawing Organic
Compounds
 Molecular Formula: tells exactly how many of each
atom is present; Shorthand notation
 Tells nothing about how they are connected
 Structural Formula: Longhand; shows which atoms
are connected to which.
Drawing Organic
Compounds
 Consider simplest organic molecule: Methane
(natural gas)
 Molecular formula = CH4
 Only 1 way they can be connected
 Methane is an Alkane, a compound which
possesses only C and H single bonds
Drawing Organic
Compounds
 Next alkane is Ethane
 Molecular Formula: C2H6
 Structural Formula:
Drawing Organic
Compounds
 Lets skip ahead a bit;
 Pentane: C5H12
 Looks very messy (and this is still a very simple
compound)
 Too complicated to draw all molecules like this
Drawing Organic
Compounds
 Easier method: Draw C-C bonds as lines. Whenever
line ends (changes direction), that’s a C atom
 Don’t draw in H atoms. Can work out how many are
present by subtracting number of bonds visible from 4.
Implicit Hydrogens.
Vs.
Isomers
 Molecules can have the same molecular formula
but different structural formulas
 Many possible ways to connect atoms
 5 carbon alkane: C5H12
 3 possible isomers
Isomers
 Same molecular formula; different structural formula
 Can have very different properties and reactivity
 Chemically distinct molecules
Naming Organic
Molecules
 For alkanes its very easy
 Count how many C atoms in longest straight chain.
Find corresponding prefix (next slide).
 Identify any side groups off major chain. Indicate
their positions with lowest possible number.
 If all C-H single bonds then alkane. Suffix = ane
Naming Organic Molecules
No. of
C atoms
Name
Formula
Name of side
group
1
Methane
CH4
Methyl
2
Ethane
CH3CH3
Ethyl
3
Propane
CH3CH2CH3
Propyl
4
Butane
CH3CH2CH2CH3
Butyl
5
Pentane
CH3CH2CH2CH2CH3
Pentyl
6
Hexane
CH3CH2CH2CH2CH2CH3
Hexyl
7
Heptane
CH3CH2CH2CH2CH2CH2CH3
Heptyl
8
Octane
CH3CH2CH2CH2CH2CH2CH2CH3
Octyl
9
Nonane
CH3CH2CH2CH2CH2CH2CH2CH2CH3
Nonyl
10
Decane
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Decyl
If more than one side group present use di (2), tri (3) or
tetra (4) to show how many
Our isomers of C5H12
 Longest chain = 5 C atoms
 No branching
 Pentane
Our isomers of C5H12
 Longest chain = 4 C atoms
 4 = butane
 One branching group of 1 C unit = methyl group
 It’s on Carbon no. 2 so name is 2-methylbutane
 Numbers and letters are always separated by a hyphen
(-)
Our isomers of C5H12
 Can we number any other way?
 Longest chain = 4 C atoms
 4 = butane
 One branching group of 1 C unit = methyl group
 It’s on Carbon no. 3 so name is 3-methylbutane
 WRONG!! Must have lowest possible number for side
chain
Our isomers of C5H12
 Longest chain = 3 C atoms
 3 = propane
 Two branching groups of 1 C unit = 2 methyl groups
 Both on Carbon no. 2 so name is 2,2-dimethylpropane
Multiple bonds
 Alkanes are saturated compounds, all single bonds
 If 1 or more double or triple bond present then
molecule is unsaturated
 Molecules with a double bond are called alkenes
 Molecules with a triple bond are called alkynes
More naming
 Similar to alkanes
 Select longest chain containing the multiple bond.
Indicate location of multiple bond.
 Identify any side groups.
More naming
 Similar to alkanes
 Select longest chain containing the multiple bond.
Indicate location of multiple bond.
 Identify any side groups.
3-ethylpent-1-ene
More naming
 Similar to alkanes
 Select longest chain containing the multiple bond.
Indicate location of multiple bond.
 Identify any side groups.
3-ethylpent-1-ene
2-methyl-5-ethyloct-3-yne