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Organic Chemistry
Chapter 20
Structure Determines Properties
• Organic compounds all contain carbon
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– CO, CO2 , carbonates and carbides are inorganic
– Other common elements are H, O, N, (P, S)
Carbon has versatile bonding patterns
– Chains, rings, multiple bonds
– Chain length nearly limitless
Carbon compounds generally covalent
– Molecular; Gases, liquids or low melting solids; Varying solubilities; Nonconductive in
liquid
C - C bonds unreactive (very stable)
Carbon Bonding
• Carbon can bond to other carbon atoms in an almost infinite chain
• Bond to a maximum of four other atoms
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Carbon
Carbon
Carbon
Carbon
or other elements
with 4 single covalent bonds = tetrahedral
with 2 single & 1 double covalent bond = trigonal planar
with 1 single & 1 triple covalent bond = linear
Hydrocarbons
• Hydrocarbons contain only C & H
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Aliphatic or aromatic
• Aliphatic hydrocarbons
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Saturated or unsaturated aliphatics
• Saturated = alkanes, unsaturated = alkenes or alkynes
• Unsaturated have double or triple bonds
May be chains or rings
• Ring molecules have two less H than chain so that ends can join
• Chains may be straight or branched
Alkanes
• a.k.a paraffins
• Aliphatic
• General formula CnH2n+2 for chains
• Very unreactive
• Come in chains or/and rings
– CH3 groups at ends of chains, CH2 groups in the middle
• Saturated
• Branched or Straight-Chain
– Straight-chain = normal
– Condensed formula has CH3 on each end and CH2 in middle
Condensed Structural Formulas
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attached atoms listed in order
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central atom with attached atoms
follow normal bonding patterns
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use to determine position of multiple bonds
() used to indicate more than 1 identical group attached to same previous central atom
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unless () group listed first in which case attached to next central atom
Structural Isomers
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Isomers are molecules with the same molecular formula but different arrangements of
the atoms
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Different chemical and physical properties
Structural isomers are isomers in which the atoms are attached differently
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Different bonding pattern
Different properties
a.k.a constitutional isomers
Naming
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Each name consist of 3 parts
1. prefix
• indicates position, number and type of branches
• indicates position, number and type of each functional group
2. parent
• indicates the length of the longest carbon chain or ring
3. suffix
• indicates the type of hydrocarbon such as- ane, ene, yne
• certain functional groups
Naming Alkanes
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The first 4 alkanes are methane (C1), ethane (C2), propane (C3), butane (C4)
After that the names come from adding Greek prefix to –ane
Naming Alkanes
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Find the longest, continuous carbon chain
Number the chain from end closest to a branch
– if first branches equal distance use next in
Name branches as alkyl groups
– Branch name related to number of C
– End in -yl
– locate each branch by preceding its name with the carbon number on the chain
List branches alphabetically
– do not count n-, sec-, t-, count iso
Use prefix if more than one of same group present
– di, tri, tetra, penta, hexa
– do not count in alphabetizing
Petroleum
• Formed when ocean microorganisms died 500 million year ago, were buried, and
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subjected to large pressures
A dark, thick liquid composed mainly of hydrocarbons
Natural gas normally found with petroleum deposits
– Mostly methane with some ethane, propane and butane
Petroleum separated into various fractions by distillation
– Separation based on boiling point
Alkane Reactions
• Combustion
• Substitution
• Dehydrogenation
Alkenes
• Also known as olefins
• Aliphatic, unsaturated
• Formula of chain alkenes - subtract 2 H from alkane formula for each double bond
• C=C double bonds
• Trigonal shape around C
• Flat
• No rotation
• Cis - trans isomerism
• Much more reactive than alkanes
• Polyunsaturated = many double bonds
Reactions of Alkenes
Naming Alkenes
• change suffix on main name from -ane to -ene
• number from end closest to double bond
• number in front of main name indicates first carbon of double bond
Naming Alkynes
• change suffix on main name from -ane to -yne
• number from end closest to triple bond
• number in front of main name indicates first carbon of triple bond
Alkynes
• Also known as acetylenes
• Aliphatic, unsaturated
• Formula of chain alkynes - subtract 4 H from alkane for each triple bond
• C-C triple bond
• Linear shape
• No rotation
• More reactive than alkenes
Aromatics
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Contain 1 or more 6 C unsaturated rings
– Benzene rings
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Chemical reactions different than alkenes
– Burn sooty instead of clean
– Undergo substitution instead of addition
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Benzene
– Liquid, BP = 80°C
– All C-C bond lengths and bond angles identical
• 120°
• Bond lengths between C-C and C=C
– Planar molecule
– Resonance hybrid
Naming Benzene Derivatives
• main name either benzene or one of the common derivatives
• ring numbered from position of main group or
• 2 = ortho (o), 3 = meta (m), 4 = para (p)
Functional Groups
• In many organic compounds, C-to-H bonds are replaced by bonds to other atoms
– C-Halogen, C-to-O, C-to-N, occasionally (C-to-S)
• These compounds are generally considered hydrocarbon derivatives
– Basically hydrocarbons with a few substitutions
• These substituted bonds are more reactive than C-H bonds
• Therefore, when molecules with the substituted bonds react, the reaction site is generally
at the substituted bonds
• These substituted atoms or groups of atoms are called functional groups, and they
generally determine the chemical reactions an organic molecule will undergo
– And also have influences on intermolecular attractions and therefore physical
properties
Alcohols
• Have an –OH group in place of a H
• Form H-bonds
– To alcohol molecules and water
• Solubility in water decreases as length of carbon chain increases
• Common reactions include substitution for OH, elimination, oxidation
Classifying Carbons
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Carbons in an organic molecule are classified based on the number of other carbons they
are attached to
Primary Carbon, 1°, = carbon attached to one other carbon
Secondary Carbon, 2°, = carbon attached to 2 other carbons
Tertiary Carbon, 3°, = carbon attached to 3 other carbons
Quaternary Carbon, 4°, = carbon attached to 4 other carbons, Very unreactive
Hydrogens are classified based on carbon they are attached to
– The hydrogens on a 1° carbon are called 1° hydrogens
Classifying Alcohols
• alcohols are classified based on the carbon they are attached to
• Primary Alcohol, 1°, = OH group on 1° C
• Secondary Alcohol, 2°, = OH group on 2° C
• Tertiary Alcohol, 3°, = OH group on 3° C
Aldehydes and Ketones
• Both contain C=O, carbonyl group
• In ketones, the carbonyl group is attached to 2 carbon atoms
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In middle of a chain or ring
In aldehydes, the carbonyl group is attached to a carbon and a hydrogen
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Or 2 H in the case of formaldehyde
Must be on the end of a chain
Ketones
• Often used as polar solvent when presence of OH cause problems
• Acetone – R1 = R2 = CH3
– Nail polish remover, paint solvent
• MEK = methyl ethyl ketone – R1= CH3, R2 = CH2CH3
– Paint solvent, gasoline additive
Aldehydes
• Often strong odors, Used as fragrances and food additives
• Formaldehyde – R1 = R2 = H
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 Gas, when dissolved in water = formalin
 Suspected carcinogen
 Used in the production of foams and adhesives
Acetaldehyde – R1 = H, R2= CH3
Naming Aldehydes
• Select the longest chain of carbon atoms containing the aldehyde group
• Number the chain calling the carbonyl C position 1
• Determine the parent name from the number of C in the chain, replace final -e with -al
• Name alkyl branches as usual
Naming Ketones
• Select the longest chain of carbon atoms containing the carbonyl group
• Number the chain from the end closest to the carbonyl group
• Determine the parent name from the number of C in the chain, replace the final -e with one
• Name alkyl branches as usual
Carboxylic Acids
• Have carboxyl group, R1-COOH
• Always on end of chain
• Acid functional group, a weak acid
• Made by oxidation of 1° alcohols
– under stronger conditions
• Formic Acid, R1 = H, as in bee and ant stings
• Acetic Acid, R1 = CH3 (vinegar)
Esters
• Replace acid H of carboxy group with R group, R1-COOR2
• Sweet, fruity odors
• Made by reacting carboxylic acid with an alcohol
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R1-COOH + R2-OH  R1-COOR2 + H2O
Not like neutralization, alcohol not a base!
Naming Carboxylic Acids
• Select the longest chain of carbon atoms containing the carboxy group
• Number the chain calling the carboxy C position 1
• Determine the parent name from the number of C in the chain, replace the final -e with –
oic acid
• Name alkyl branches as usual
Naming Esters
• Select the longest chain of carbon atoms containing the ester group
• Name R2 as alkyl group
• Name R1 and carboxy C like acid except change the –ic ending to -ate
• Put the pieces together, alkyl group first
Polymers
• Generally organic molecules
• Very large, molar masses 10,000+
• Chain-like molecules made by linking together small molecules called monomers
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Monomer units usually indicated in name with the prefix “poly-”
polyethylene, polypropylene, polystyrene
Linking Monomers
• Addition Polymerization = monomers linked by each molecule attaching to chain by a
synthesis type reaction
• Condensation Polymerization = monomers linked when a reaction occurs that splits
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out a small molecule, like water
Homopolymers all monomer units alike
Copolymers have multiple monomer units