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Mary J. Bojan Chem 110
Organic Part 2 Hydrocarbons
1. Alkanes: all single bonds 2. Alkenes: C C
saturated v. unsaturated structural isomers geometric isomers
3. Alkynes: C C 4. Aromatic hydrocarbons
Reactivity of hydrocarbons • addition reactions • combustion reactions
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Mary J. Bojan Chem 110
HYDROCARBONS are the simplest organic compounds: containing only C and H
Alkanes saturated have the maximum number of H attached to the C skeleton.
Alkenes unsaturated Alkynes have double or Aromatic triple bonds
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Mary J. Bojan Chem 110
ALKENES Contain one or more double bonds
propene
ethene
3
CH
H
H
HC
CH
H
H
CH3
C
C CCnH2n
Rotation about double bond is restricted
Bond angle
Mary J. Bojan Chem 110
Butene: There are several possible structures for a chain of 4 carbons with one double bond.
C4H8
1-butene
2-methylpropene
2-butene
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C backbone condensed molecular formula
Mary J. Bojan Chem 110
Butene: Expand the condensed molecular formula into a structural formula, focusing on the double bond.
C4H8
1-butene CH2=CHCH2CH3
2-methylpropene (CH3)2C=CH2
2-butene
CH3CH=CHCH3
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Mary J. Bojan Chem 110
Structural isomers: same molecular formula: different structure
1-butene 2-methylpropene 2-butene
There are different classes of isomers: Structural vs. Geometric
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Geometric isomers same molecular formula: different geometry
cis-2-butene trans-2-butene
cis-isomer: same side trans-isomer: opposite side (across)
Mary J. Bojan Chem 110
ethyne propyne (acetylene)
structural isomers no geometric isomers are possible
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C C HC
H
H
C
H
H
H
C C CC
H
H
H
H
H
H
1-butyne 2-butyne
CnH2n–2
ALKYNES are hydrocarbons that contain one or more triple bonds
Mary J. Bojan Chem 110
Aromatic Hydrocarbons Contain alternating single and double C-C Bonds
Benzene is the prototypical molecule
Usually written:
Aromatic hydrocarbons are less reactive than alkenes:
We can draw resonance structures: resonance implies added stability
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CC
CC
C
C
H
H
H
H
H
H CC
CCC
C
H
H
H
H
H
H
Mary J. Bojan Chem 110
Reactivity of Hydrocarbons Same reaction: hydrocarbon + Br2
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CH3
ALKANE Heptane + Br2 Colorless red ALKENE (and ALKYNES) 2-pentene + Br2 Colorless red AROMATIC toluene + Br2 Colorless red
Mary J. Bojan Chem 110 10
Aromatic hydrocarbons have RESONANCE: resonance adds extra stability.
Alkene + Br2 reacts readily Aromatic + Br2: no reaction • alkenes are very reactive toward addition.
(alkynes even more so.) • Benzene is NOT reactive
Mary J. Bojan Chem 110
Functional Group classes: groups of molecules that contain a representative group of elements in a fixed pattern
Molecules in the class have similarities in structure and function (reactivity).
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Seemingly small changes in structure can have big affect on molecular properties
Functional Group Type hydrocarbon alcohol ether CH3!CH2!H CH3!CH2!OH CH3!O!CH3
ethane ethanol di-methyl ether gas liquid gas
bp –89°C bp 78°C bp –24 °C water soluble
Example: adding an oxygen changes a hydrocarbon into an alcohol or an ether…
Mary J. Bojan Chem 110
Functional Group Classes
Functional group classes contain a representative group of elements in a fixed pattern:
Each class has similarities in structure and function (reactivity).
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Groups which have
a carbonyl
Aldehydes Ketones (R,R’≠ H)
Alcohols R−OH R ≠ H R = alkyl group Ethers R−O−R’ R,R’≠ H
Amines
N HHR
N R'HR
N R'RR"
CO
RC
H
O
R'C
R
O
Carboxylic Ester Amide Acid
OHC
R
O
OR'C
R
O
NHR'C
R
O
Mary J. Bojan Chem 110
Focus on the atoms bonded to O and N atoms in these Functional Groups.
Alcohols R−OH hydroxyl group
hydrocarbon (alkyl) group
Ether R−O−R’
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N HHR
N R'HR
N R'RR"
Amines
Mary J. Bojan Chem 110
For these Functional Groups, notice the atoms bonded to the C in the carbonyl group.
Aldehyde
Ketone
Carboxylic Acids −COOH
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C O
RC
H
O
R'C
R
O
OHC
R
O
Mary J. Bojan Chem 110
Amines and carboxylic acids are organic Acids and Bases
AMINES weak bases, organic bases (like NH3)
CARBOXYLIC ACIDS weak acids, organic acids
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Mary J. Bojan Chem 110
Questions Which of the following hydrocarbon classes does NOT have a double or triple bond?
1 alkane 2 alkene 3 alkyne 4 aromatic
Which one of the following functional group classes does not have a double bond?
1 aldehyde 2 Ketone 3 amine 3 ester
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Mary J. Bojan Chem 110
The presence and properties of functional groups are responsible for the action of drugs.
What functional groups are present in these molecules?
Acetyl salicylic acid Acetaminophen
Ibuprofen
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C
O
O C
O
OH
CH3
HO N
H
C
O
CH3
CH3
O
OH
H3C
CH3
Mary J. Bojan Chem 110
What’s Next?
• Formulas tell us how atoms are connected to each other
• Lewis structures tell us where the electrons are.
QUESTIONS • What are the shapes of these molecules? • Can we use information about bonding,
connectivity of atoms, molecular formulas, etc. to predict the shapes (and properties) of molecules?
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