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Mr. E’s Organic Chemistry
Some organic chemicals
DNA
Essential oils
Medicines•Active Pharmaceutical Ingredients•Excipients
Materials
Fuels
Pigments
•Organic molecules = Carbon-based molecules•Organic chemistry = Chemistry of carbon-based molecules
Some properties of organic molecules
•Stability: composed of stable C-C covalent bonds
•Defined molecular structures
•Defined three-dimensional shapes
Carbon:• e.x. Methane • Four single covalent bonds:• Shape = tetrahedral.
CH
H HH
2 electrons = 1 bond
Alkanes: Saturated Hydrocarbons• Hydrocarbons are molecules composed of carbon & hydrogen
– Each carbon atom forms 4 chemical bonds– A saturated hydrocarbon is one where all C - C bonds are “single”
bonds & the molecule contains the maximum number of H-atoms– Saturated hydrocarbons are called ALKANES
‘Meth…’ = 1 Carbon
‘Eth…’ = 2 Carbons
‘Prop…’ = 3 Carbons
‘But…’ = 4 Carbons
‘Pent…’ = 5 Carbons
‘Hex…’ = 6 Carbons
‘Hept…’ = 7 Carbons
‘Oct…’ = 8 Carbons
‘Non…’ = 9 Carbons
‘Dodec…’ = 12 Carbons
‘Undec…’ = 11 Carbons
‘Dec…’ = 10 Carbons
Heptane CH3CH2CH2CH2CH2CH2CH3
‘Hept…’ implies 7 Carbons ‘…ane’ implies compound is an alkane
n
1
2
3
4
5
6
MolecularFormula
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
Structuralformula
HCH
CCH
HH
H
HH
HCH
CH
HH
CH
HH
HCH
CCH
HC
H
HH
HCH
CCH
HC
H
HH
HCH
CCH
HC
H
HH
H
H
H
HH
H
HCH
HH
H
HCH
HCH
HH
Name
methane
ethane
propane
butane
pentane
hexane
Condensedstructural
formulaCH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
Further members of the series
Heptane (7) CH3CH2CH2CH2CH2CH2CH3
Octane (8) CH3CH2CH2CH2CH2CH2CH2CH3
Nonane (9) CH3CH2CH2CH2CH2CH2CH2CH2CH3
Decane (10) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Undecane (11) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
Dodecane (12) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
Etc., etc.
Normal vs Branched Alkanes• NORMAL alkanes consist of
continuous chains of carbon atoms
• Alkanes that are NOT continuous chains of carbon atoms contain branches
• The longest continuous chain of carbons is called the parent chain
CH3
CH2CH2
CH2CH3
CH3
CH2CH
CH3
CH3
Structural Isomerism• Structural isomers are
molecules with the same chemical formulas but different molecular structures - different “connectivity”.
• They arise because of the many ways to create branched hydrocarbons.
CH3
CH2CH2
CH2CH3
CH3
CH2CH
CH3
CH3
n-pentane, C5H12
2-methlbutane, C5H12
IUPAC Rules for Naming Branched Alkanes– Find and name the parent chain in the hydrocarbon - this is
the chain with containing the most # of C atoms.– Number the carbon atoms in the parent chain starting at the
end closest to the branching– Name alkane branches by dropping the “ane” from the
names and adding “yl”. A one-carbon branch is called “methyl”, a two-carbon branch is “ethyl”, etc…
– Name Halogen branches by dropping the “ine” and adding a ”o”. Bromine Bromo
– When there are more than one type of branch (ethyl and methyl, for example), they are named alphabetically
– Finally, use prefixes to indicate multiple branches
A Little Practice
Alkane Alkyl group
Methane Methyl (CH3-)
Ethane Ethyl (CH3CH2-)
Propane Propyl (CH3CH2CH2-)
Butane Butyl (CH3CH2CH2CH2-)
Etc.
CH3 CH2 CHCH3
CH31234
2-Methylbutane
[Straight chain numbered so as to give the lower branch number]
Example 1: 2,2-dimethylpentane• The parent chain is indicated by
the ROOT of the name -“pentane”. This means there are 5 carbons in the parent chain.
CH3
CH2CH2
CH2CH3
• “dimethyl” tells us that there are TWO methyl branches on the parent chain. A methyl branch is made of a single carbon atom.
• “2,2-” tell us that BOTH methyl branches are on the second carbon atom in the parent chain.
CH31
CCH23
CH2
4
CH35
CH3
CH3
1
2
34
5
Example 2: 3-ethyl-2,4-dimethylheptane• The parent chain is indicated by
the ROOT of the name -“heptane”. This means there are 7 carbons in the parent chain.
CH3
CH2CH2
CH2CH2
CH2CH3
• “2,4-dimethyl” tells us there are TWO methyl branches on the parent chain, at carbons #2 and #4.
• “3-ethyl-” tell us there is an ethyl branch (2-carbon branch) on carbon #3 of the parent chain.
1
2
34
5
76
CH3
CHCH
CHCH2
CH2CH3
CH2CH3
CH3 CH3
Example 3: 2,3,3-trimethyl-4-propyloctane• The parent chain is indicated by
the ROOT of the name -“octane”. This means there are 8 carbons in the parent chain.
• “2,3,3-trimethyl” tells us there are THREE methyl branches - one on carbon #2 and two on carbon #3.
• “4-propyl-” tell us there is a propyl branch (3-carbon branch) on carbon #4 of the parent chain.
1
2
34
5
7
6
8
1
23
45
7
6
8
CHC
CHCH2
CH2
CH2CH3
CH3
CH3
CH3
CH3CH2
CH2
CH3
Example 4: Name the molecules shown!• parent chain has 5 carbons -
“pentane”• two methyl branches - start
counting from the right - #2 and #3• 2,3-dimethylpentane
CH3
CH2CH
CHCH3
CH3
CH3
• parent chain has 8 carbons - “octane”• two methyl branches - start counting
from the left - #3 and #4• one ethyl branch - #5• name branches alphabetically
3,4-dimethyl
43
octane
5
5-ethyl-
Alkanes Review - Cycloalkanes• A cycloalkane is made of a hydrocarbon chain
that has been joined to make a “ring”.
CH3
CH2CH3 CH2
CH2
CH2
n-propaneC3H8
cyclopropaneC3H6
60° bond angleunstable!!
109.5° bond angle
•Note that two hydrogen atoms were lost in forming the ring!•What is the general formula for a cycloalkane?
Other CycloalkanescyclobutaneC4H8 - ~90° bond angles
cylcopentaneC5H10 ~109.5° bond angles
cyclohexaneC6H12 = 109.5° bond angles
Angle (ring) Strain - results from compression of the internal bond angles. Cyclopropane has the greatest angle strain (60° bond angles) while the strain is eliminated in cyclohexane.
Alkenes & Alkynes• Alkenes are
hydrocarbons that contain at least one carbon-carbon double bond
• Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond
• The suffix for the parent chains are changed from “ane” to “ene” for double bonds and “yne” for triple bonds.– e.g. ethene, propyne
• We start numbering the carbons closest to the multiple bond.
Alkenes & Alkynes: Examples
CH2 CH2 CHCH CH2 C
H
CH3
C16
CH
CH3 CH2 CH
CH2
CH3 C C CH2CH3
CH3
ethene ethyne propene
propyne 1-butene 2-pentyne
Hydrocarbons
1
2
3
4
5
6
7
8
9
10
Number ofCarbon Atoms
AlkanesCnH2n + 2
AlkynesCnH2n-2
AlkenesCnH2n
_______
Ethyne
Propyne
Butyne
Pentyne
Hexyne
Heptyne
Octyne
Nonyne
Decyne
____
C2H2
C3H4
C4H6
C5H8
C6H10
C7H12
C8H14
C9H16
C10H18
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
_______
Ethene
Propene
Butene
Pentene
Hexene
Heptene
Octene
Nonene
Decene
____
C2H4
C3H6
C4H8
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
Name those alkenes...CH
CH
CH3 CH CH3
CH3
CH
CH
CH2
CH2
CH2
Br
4-methyl-2-pentene 2-methyl-2-hexene
cyclopentene3-heptene
2-bromo-3-methyl-2-pentene
Cis-Trans Isomerism…Again!• Like rings, alkenes and alkynes show
restricted rotation - this time about the multiple bonds
• Because of the 120° bond angles in alkenes, cis-trans isomerism is possible– If one of the carbons in the double bond
have two of the same substituents, there is NO cis-trans isomerism!
– Remember that “trans” means opposite sides of the double bond and “cis” means the same side of the bond!
– Use molar mass to prioritize the substituents to decide cis-trans isomerism
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