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Organic Chemistry
Introduction
Alkanes
Nomenclature
Electron Dot structures
Li Be B C N O F
NeClass exercise 1:
Draw the electron dot structure of Carbon
Class exercise 2:
Draw the electron dot structure of oxygen and fluorine
Lewis Dot structures
Li Be B C N O F
Organic Chemistry
Chemistry of Carbon Bonding of H,O, X and N
Valence SummaryC H O N Halogen
Valence electrons
4 1 6 5 7
Valence 4 1 2 3 1
Bond types SingleDoubletriple
single Single Double
SingleDoubletriple
single
Complete Structural Formulas
Show the bonds between each of the atoms
H H
H C H H C H H H
CH4 , methane
H H Condensed Structural Formulas
H C C H CH3 CH3
H H Ethane
H H H
H C C C H CH3 CH2 CH3
H H H Propane
More Alkanes
IUPAC Names
Name # carbons Structural Formula
Methane 1 CH4
Ethane 2 CH3CH3
Propane 3 CH3CH2CH3
Butane 4 CH3CH2CH2CH3
Pentane 5 CH3CH2CH2CH2CH3
IUPAC NAMES
Name # carbons Structural Formula
Hexane 6 CH3CH2CH2CH2CH2CH3
Heptane 7 CH3CH2CH2CH2CH2CH2CH3
Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3
Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Learning Check Alk1
A. What is the condensed formula for
H H H H
H C C C C H
H H H H
B. What is its molecular formula?
C. What is its name?
Solution Alk1
A. CH3CH2CH2CH3
B. C4H10
C. butane
Properties of Alkanes
So what exactly do these things do?
Physical Properties of Alkanes
1. Combustion - Alkanes are inflammable, i.e. they burn.
CH4 O2 CO2 OH2+ +2 2
2. Boiling and melting points a. Both bp and mp increase with increasing carbon number for straight-chain alkanes with formula CnH2n+2
Carbon Number Physical State C1- C4 gases C5 – C16 liquids C17 – C30 oils and greases C30 – C50 paraffin waxes >C50 plastics (polyethylene)
b. Branching tends to lower the boiling point and raise the melting point
BP 60oC 58oC 50oC
MP -154oC -135oC -98oC
Explanation:
MP Branching reduces the flexibility of the molecule which reduces the entropy term S in the equation Tmp = H/S. Since S is in the denominator, Tmp increases.
BP Branching reduces surface area (more compact structure), and therefore London dispersion forces which control boiling point for these molecules.
3. Solubility – alkanes are nonpolar molecules and therefore insoluble in water, which is polar. Alkanes are hydrophobic.
4. Densities – alkanes are less dense than water, with densities near 0.7 g/mL. Therefore they float on water, e.g. Exxon Valdez oil spill.
Naming Hydrocarbons (nomenclature)
Drawing Structures: It’s All Good
CH3
CH
CH
CH3
CH3
CH3
CH3
CHCH
CH3
2-butene
This is called the “condensed structure”
C C C C
H
H
H
H H H
H
H
CH3 CH CH CH3
On a test, choose a method that shows all HsCH3CH=CHCH3
Using brackets can also shorten some formulas: CH3CH2CH2CH2CH2CH3 vs. CH3(CH2)4CH3
Basic Naming of HydrocarbonsHydrocarbon names are based on: 1)type, 2) # of carbons, 3) side chain type and position
1) name will end in -ane, -ene, or -yne
2) the number of carbons is given by a “prefix” 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec-
Basic Naming of Hydrocarbons
Q - What names would be given to these:7C, 9C alkane2C, 4C alkyne6C, 3C alkene
heptane, nonaneethyne, butyneHexene, propene
Mnemonic for First Four Prefixes
First four prefixes Meth- Eth- Prop- But-
Monkeys
Eat
Peeled
Bananas
?Decade
Decimal
Decathalon
Other Prefixes
Pent-
Oct-
Dec-
Hex-, Hept-, Non-
Straight chain hydrocarbonsLearning Check
Pentane
Propane
Heptane
Ethane
Octane
Numbering Carbons
Q- draw penteneA- Where’s the double
bond? We # C atoms.
Naming compounds with multiple bonds is more complex than previously indicated.
When 2+ possibilities exist, #s are needed.Always give double bond the lowest number.Q - Name these
C C C CCH3
H
H
H
H H H
HCH31
C2
C3
C4
C5
H
H
H
H H H
HCH35
C4
C3
C2
C1
H
H
H
H H H
H
ethene
3-nonyne
2-buteneCH3
CH
CH
CH3
CH3 CH3
C2H4
1-pentene
Learning Check - Numbering Carbons
ethene
3-nonyne
2-buteneCH3
CH
CH
CH3
CH3 CH3
C2H4
Name the following compounds:
CH3 CH3
CH3
CH3Naming Side ChainsThe names of molecules with
branches are based on: side chains, root
The “root” or “parent chain” is usually the longest possible hydrocarbon chain.
The root must include multiple bonds if they are present. If a cyclic structure is present it will be the root even if it is not the longest chain.
Side chains are also called “side branches” or “alkyl groups”. Their names end in -yl.
Common side chains :-CH3 methyl, -CH2CH3 ethyl, -CH2CH2CH3 propyl
2,3-dimethylpentane
CH3 CH3
CH3
CH3
IUPAC Rules for Naming Hydrocarbons1. Choose the correct ending: -ane, -ene, or -yne2. Determine the longest carbon chain. Where a double
or triple bond is present, choose the longest chain that includes this bond. If there is a cyclic structure present, the longest chain starts and stops within the cyclic structure.
3. Assign numbers to each C of the parent chain. For alkenes and alkynes the first carbon of the multiple bond should have the smallest number. For alkanes the first branch (or first point of difference) should have the lowest #. Carbons in a multiple bond must be numbered consecutively.
4. Attach a prefix that corresponds to the number of carbons in the parent chain. Add cyclo- to the prefix if it is a cyclic structure.
5. Determine the correct name for each branch (“alkyl” groups include methyl, ethyl, propyl, etc.)
6. Attach the name of the branches alphabetically, along with their carbon position, to the front of the parent chain name. Separate numbers from letters with hyphens (e.g. 4-ethyl-2-methyldecane)
7. When two or more branches are identical, use prefixes (di-, tri-, etc.) (e.g. 2,4-dimethylhexane). Numbers are separated with commas. Prefixes are ignored when determining alphabetical order. (e.g. 2,3,5-trimethyl-4-propylheptane)
8. When identical groups are on the same carbon, repeat the number of this carbon in the name. (e.g. 2,2-dimethylhexane)
IUPAC Rules for Naming Hydrocarbons
ene
Naming Side ChainsExample: use the rules on this handout to
name the following structure
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
Rule 1: choose the correct ending
ene
Rule 2: determine the longest carbon chain
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
Naming Side Chains
Rule 3: Assign numbers to each carbon
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
ene
Naming Side Chains
Rule 3: Assign numbers to each carbon
CH3 CH2 C2
CH21
CH23
C4
CH25
CH3
CH3
CH36
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
ene
Naming Side Chains
1-hexene ene
Rule 4: attach prefix (according to # of Cs)
Naming Side Chains
CH3 CH2 C2
CH21
CH23
C4
CH25
CH3
CH3
CH36
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
CH3 CH2 C2
CH21
CH23
C4
CH25
CH3
CH3
CH36
Rule 5: Determine name for side chains
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
1-hexene 1-hexene
ethyl
methyl
methyl
Naming Side Chains
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
CH3 CH2 C2
CH21
CH23
C4
CH25
CH3
CH3
CH36
1-hexene2-ethyl-4-methyl-4-methyl-1-hexene
ethyl
methyl
methylRule 6: attach name of branches alphabetically
Naming Side Chains
Rule 7,8: group similar branches
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
CH3 CH2 C2
CH21
CH23
C4
CH25
CH3
CH3
CH36
1-hexene2-ethyl-4-methyl-4-methyl-1-hexene
ethyl
methyl
methyl
Naming Side Chains
Rule 7,8: group similar branches
CH3 CH2 C
CH2
CH2 C
CH2
CH3
CH3
CH3
CH3 CH2 C2
CH21
CH23
C4
CH25
CH3
CH3
CH36
2-ethyl-4,4-dimethyl-1-hexene
ethyl
methyl
methyl
Naming Side Chains
Similar questions will be issued on Moodle and in the tutorial sheets
2-butene
propene
1-butyne
Learning Check – Naming
CH3 CH CH2
CH3 CH CH CH3CH3 CH CH C
CH3 CH3
CH32,4-dimethyl-2-pentene
CH C CH2 CH3
b) same
c) 5-ethyl-4-methyl-2-heptyne
a) 3,3-dimethyl-1-pentene
CH2 CH C CH2 CH3
CH3
CH3
CH3 C CH CH2
CH3
CH2 CH3
CH CH CH2
CH2 CH3
CC
CH3CH3
CH3