Mr. E’s Organic Chemistry - Eckert - homeChem...•Organic chemistry = Chemistry of carbon-based...
Transcript of Mr. E’s Organic Chemistry - Eckert - homeChem...•Organic chemistry = Chemistry of carbon-based...
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Mr. E’s Organic Chemistry
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Some organic chemicals
DNA
Essential oils
Medicines•Active Pharmaceutical Ingredients•Excipients
Materials
Fuels
Pigments
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•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
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Carbon:• e.x. Methane • Four single covalent bonds:• Shape = tetrahedral.
CH
H HH
2 electrons = 1 bond
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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
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‘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
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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
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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.
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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
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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
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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
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A Little Practice
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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]
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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
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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
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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
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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-
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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?
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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.
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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.
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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
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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
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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
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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