Chapter 20 Organic Chemistry

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Chapter 20OrganicChemistry
Chemistry A Molecular Approach, 1st Ed.Nivaldo
Tro
Roy Kennedy Massachusetts Bay Community
College Wellesley Hills, MA
2008, Prentice Hall
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Structure Determines Properties

• Organic compounds all contain carbon
• 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)

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Bond Energies and Reactivities
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Allotropes of Carbon - Diamond
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Allotropes of Carbon - Graphite
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Carbon Bonding

• mainly forms covalent bonds
• C is most stable when it has 4 single covalent
  bonds, but does form double and triple bonds
• CC and CC are more reactive than C-C
• C with 4 single bonds is tetrahedral,
• 2 singles and 1 double is trigonal planar
• 2 doubles or 1 triple and 1 single is linear

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Hydrocarbons

• hydrocarbons contain only C and H
• aliphatic or aromatic
• insoluble in water
• no polar bonds to attract water molecules
• aliphatic hydrocarbons
• saturated or unsaturated aliphatics
• saturated alkanes, unsaturated alkenes or
  alkynes
• may be chains or rings
• chains may be straight or branched
• aromatic hydrocarbons

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Uses of Hydrocarbons
Number of C atoms State Major Uses
1-4 gas heating and cooking fuel
5-7 liquids, (low boiling) solvents, gasoline
6-18 liquids gasoline
12-24 liquids jet fuel camp stove fuel
18-50 liquids, (high boiling) diesel fuel, lubricants, heating oil
50 solids petroleum jelly, paraffin wax
1-4 gas heating and cooking fuel
5-7 liquids, (low boiling) solvents, gasoline
6-18 liquids gasoline
12-24 liquids jet fuel camp stove fuel
18-50 liquids, (high boiling) diesel fuel, lubricants, heating oil
50 solids petroleum jelly, paraffin wax
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Saturated Hydrocarbons

• a saturated hydrocarbon has all C-C single bonds
• it is saturated with hydrogens
• saturated aliphatic hydrocarbons are called
  alkanes
• chain alkanes have the general formula CnH2n2

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Unsaturated Hydrocarbons

• unsaturated hydrocarbons have one of more CC
  double bonds or C?C triple bonds
• unsaturated aliphatic hydrocarbons that contain
  CC are called alkenes
• the general formula of a monounsaturated chain
  alkene is CnH2n
• remove 2 more H for each additional unsaturation
• unsaturated aliphatic hydrocarbons that contain
  C?C are called alkynes
• the general formula of a monounsaturated chain
  alkyne is CnH2n-2
• remove 4 more H for each additional unsaturation

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Unsaturated Hydrocarbons
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Aromatic Hydrocarbons

• contain benzene ring structure
• even though they are often drawn with CC, they
  do not behave like alkenes

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Formulas

• molecular formulas just tell you what kinds of
  atoms are in the molecule, but they dont tell
  you how they are attached
• structural formulas show you the attachment
  pattern in the molecule
• models not only show you the attachment pattern,
  but give you an idea about the shape of the
  molecule

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Condensed Structural Formulas

• attached atoms listed in order
• central atom with attached atoms
• follow normal bonding patterns
• use to determine position of multiple bonds
• () used to indicate more than 1 identical group
  attached to same previous central atom
• unless () group listed first in which case
  attached to next central atom

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Line-Angle Formulas

• each angle, and beginning and end represent a C
  atom
• H omitted on C
• included on functional groups
• multiple bonds indicated
• double line is double bond, triple line is triple
  bond

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Formulas
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Formulas
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Isomerism

• Isomers different molecules with the same
  molecular formula
• Structural Isomers different pattern of atom
  attachment
• Constitutional Isomers
• Stereoisomers same atom attachments, different
  spatial orientation

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Structural Isomers of C4H10
Butane, BP 0C
Isobutane, BP -12C
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Rotation about a bond is not isomerism
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Possible Structural Isomers
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Ex 20.1 Write the structural formula and carbon
skeleton formula for C6H14
start by connecting the carbons in a line
determine the C skeleton of the other isomers
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Ex 20.1 Write the structural formula and carbon
skeleton formula for C6H14
fill in the H to give each C 4 bonds
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Ex 20.1 Write the structural formula and carbon
skeleton formula for C6H14
convert each to a carbon skeleton formula each bend and the ends represent C atoms
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Stereoisomers

• stereoisomers are different molecules whose atoms
  are connected in the same order, but have a
  different spatial direction
• optical isomers are molecules that are
  nonsuperimposable mirror images of each other
• geometric isomers are stereoisomers that are not
  optical isomers

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Nonsuperimposable Mirror Images
mirror image cannot be rotated so all its atoms
align with the same atoms of the original
molecule
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Chirality

• any molecule with a nonsuperimposable mirror
  image is said to be chiral
• any carbon with 4 different substituents will be
  a chiral center
• a pair of nonsuperimposable mirror images are
  called a pair of enantiomers

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Optical Isomers of 3-methylhexane
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Plane Polarized Light

• light that has been filtered so that only those
  waves traveling in a single plane are allowed
  through

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Optical Activity

• a pair of enantiomers have all the same physical
  properties except one the direction they rotate
  the plane of plane polarized light
• each will rotate the plane the same amount, but
  in opposite directions
• dextrorotatory rotate to the right
• levorotatory rotate to the left
• an equimolar mixture of the pair is called a
  racemic mixture
• rotations cancel, so no net rotation

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Chemical Behavior of Enantiomers

• a pair of enantiomers will have the same chemical
  reactivity in a non-chiral environment
• but in a chiral environment they may exhibit
  different behaviors
• enzyme selection of one enantiomer of a pair

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Alkanes

• aka paraffins
• aliphatic
• general formula CnH2n2 for chains
• very unreactive
• come in chains or/and rings
• CH3 groups at ends of chains, CH2 groups in the
  middle
• chains may be straight or branched
• saturated
• branched or unbranched

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Naming

• each name consists of 3 parts
• prefix
• indicates position, number, and type of branches
• indicates position, number, and type of each
  functional group
• parent
• indicates the length of the longest carbon chain
  or ring
• suffix
• indicates the type of hydrocarbon
• ane, ene, yne
• certain functional groups

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Naming Alkanes

• 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
• 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

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Alkyl Groups
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More Alkyl Groups
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Examples of Naming Alkanes
2-methylpentane
3-isopropyl-2,2-dimethylhexane
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Example Name the alkane

1. find the longest continuous C chain and use it to
   determine the base name

since the longest chain has 5 C the base name is
pentane
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Example Name the alkane

1. identify the substituent branches

there are 2 substituents both are 1 C chains,
called methyl
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Example Name the alkane

• number the chain from the end closest to a
  substituent branch
• if first substituents equidistant from end, go to
  next substituent in

then assign numbers to each substituent based on
the number of the main chain C its attached to
1 2 3 4 5
both substituents are equidistant from the end
2 4
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Example Name the alkane

• write the name in the following order
• substituent number of first alphabetical
  substituent followed by dash
• substituent name of first alphabetical
  substituent followed by dash
• if its the last substituent listed, no dash
• use prefixes to indicate multiple identical
  substituents
• repeat for other substituents alphabetically
• name of main chain

2,4
dimethyl
pentane
2 4
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Practice Name the Following
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Practice Name the Following
3-ethyl-2-methylpentane
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Drawing Structural Formulas
4-ethyl-2-methylhexane

• draw and number the base chain carbon skeleton
• add the carbon skeletons of each substituent on
  the appropriate main chain C
• add in required Hs

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Practice Draw the structural formula of
4-isopropyl-2-methylheptane
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Practice Draw the structural formula of
4-isopropyl-2-methylheptane
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Alkenes

• also known as olefins
• aliphatic, unsaturated
• CC double bonds
• formula for one double bond CnH2n
• subtract 2 H from alkane for each double bond
• trigonal shape around C
• flat
• much more reactive than alkanes
• polyunsaturated many double bonds

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Alkenes
ethene ethylene
propene
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Physical Properties of Alkenes
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Alkynes

• also known as acetylenes
• aliphatic, unsaturated
• CºC triple bond
• formula for one triple bond CnH2n-2
• subtract 4 H from alkane for each triple bond
• linear shape
• more reactive than alkenes

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Alkynes
ethyne acetylene
propyne
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Physical Properties of Alkynes
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Naming Alkenes and Alkynes

• change suffix on main name from -ane to -ene for
  base name of alkene, or to -yne for the base name
  of the alkyne
• number chain from end closest to multiple bond
• number in front of main name indicates first
  carbon of multiple bond

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Examples of Naming Alkenes
2-methyl-1-pentene
3-isopropyl-2,2-dimethyl-3-hexene
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Examples of Naming Alkynes
3-methyl-1-pentyne
4-isopropyl-5,5-dimethyl-2-hexyne
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Name the Alkene

1. find the longest, continuous C chain that
   contains the double bond and use it to determine
   the base name

since the longest chain with the double bond has
6 C the base name is hexene
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Name the Alkene

1. identify the substituent branches

there are 2 substituents one is a 1 C chain,
called methyl the other one is a 2 C chain,
called ethyl
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Name the Alkene

1. number the chain from the end closest to the
   double bond

then assign numbers to each substituent based on
the number of the main chain C its attached to
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Name the Alkene

• write the name in the following order
• substituent number of first alphabetical
  substituent substituent name of first
  alphabetical substituent
• use prefixes to indicate multiple identical
  substituents
• repeat for other substituents
• number of first C in double bond name of main
  chain

3ethyl
4methyl
2hexene
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Practice Name the Following
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Practice Name the Following
3
4
5
6
1
2
3,4-dimethyl-3-hexene
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Name the Alkyne

1. find the longest, continuous C chain that
   contains the triple bond and use it to determine
   the base name

since the longest chain with the triple bond has
7 C the base name is heptyne
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Name the Alkyne

1. identify the substituent branches

there are 2 substituents one is a 1 C chain,
called methyl the other one is called isopropyl
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Name the Alkyne

1. number the chain from the end closest to the
   triple bond

then assign numbers to each substituent based on
the number of the main chain C its attached to
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Name the Alkyne

• write the name in the following order
• substituent number of first alphabetical
  substituent substituent name of first
  alphabetical substituent
• use prefixes to indicate multiple identical
  substituents
• repeat for other substituents
• number of first C in double bond name of main
  chain

4isopropyl
6methyl
2heptyne
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Practice Name the Following
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Practice Name the Following
1
2
3
4
5
3,3-dimethyl-1-pentyne
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Geometric Isomerism

• because the rotation around a double bond is
  highly restricted, you will have different
  molecules if groups have different spatial
  orientation about the double bond
• this is often called cis-trans isomerism
• when groups on the doubly bonded carbons are cis,
  they are on the same side
• when groups on the doubly bonded carbons are
  trans, they are on opposite sides

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Free Rotation AroundC-C
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Cis-Trans Isomerism
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Reactions of Hydrocarbons

• all hydrocarbons undergo combustion
• combustion is always exothermic
• about 90 of U.S. energy generated by combustion
• 2 CH3CH2CH2CH3(g) 13 O2(g) ? 8 CO2(g) 10
  H2O(g)
• CH3CHCHCH3(g) 6 O2(g) ? 4 CO2(g) 4 H2O(g)
• 2 CH3C?CCH3(g) 11 O2(g) ? 8 CO2(g) 6 H2O(g)

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Other Alkane Reactions

• Substitution
• replace H with a halogen atom
• initiated by addition of energy in the form of
  heat or ultraviolet light
• to start breaking bonds
• generally get multiple products with multiple
  substitutions

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Other Alkene and Alkyne Reactions

• Addition reactions
• adding a molecule across the multiple bond
• Hydrogenation adding H2
• converts unsaturated molecule to saturated
• alkene or alkyne H2 ? alkane
• Halogenation adding X2
• Hydrohalogenation adding HX
• HX is polar
• when adding a polar reagent to a double or triple
  bond, the positive part attaches to the carbon
  with the most Hs

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Addition Reactions
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Aromatic Hydrocarbons

• contain benzene ring structure
• even though they are often drawn with CC, they
  do not behave like alkenes

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Resonance Hybrid

• the true structure of benzene is a resonance
  hybrid of two structures

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Naming Monosubstituted Benzene Derivatives

• (name of substituent)benzene
• halogen substituent change ending to o

• or name of a common derivative

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Naming Benzene as a Substituent

• when the benzene ring is not the base name, it is
  called a phenyl group

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Naming Disubstituted Benzene Derivatives

• number the ring starting at attachment for first
  substituent, then move toward second
• order substituents alphabetically
• use di if both substituents the same

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Naming Disubstituted Benzene Derivatives

• alternatively, use relative position prefix
• ortho- 1,2 meta- 1,3 para- 1,4

2-chlorotoluene ortho-chlorotoluene o-chlorotoluen
e
3-chlorotoluene meta-chlorotoluene m-chlorotoluene
4-chlorotoluene para-chlorotoluene p-chlorotoluene
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Practice Name the Following
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Practice Name the Following
1-chloro-4-fluorobenzene
1,3-dibromobenzene or meta-dibromobenzene or
m-dibromobenzene
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Polycyclic Aromatic Hydrocarbons

• contain multiple benzene rings fused together
• fusing sharing a common bond

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Reactions of Aromatic Hydrocarbons

• most commonly, aromatic hydrocarbons undergo
  substitution reactions replacing H with another
  atom or group

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Functional Groups

• other organic compounds are hydrocarbons in which
  functional groups have been substituted for
  hydrogens
• a functional group is a group of atoms that show
  a characteristic influence on the properties of
  the molecule
• generally, the reactions that a compound will
  perform are determined by what functional groups
  it has
• since the kind of hydrocarbon chain is irrelevant
  to the reactions, it may be indicated by the
  general symbol R

CH3OH
R group
functional group
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Alcohols

• R-OH
• ethanol CH3CH2OH
• grain alcohol fermentation of sugars
• alcoholic beverages
• proof number 2X percentage of alcohol
• gasohol
• isopropyl alcohol (CH3)2CHOH
• 2-propanol
• rubbing alcohol
• poisonous
• methanol CH3OH
• wood alcohol thermolysis of wood
• paint solvent
• poisonous

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Naming Alcohols

• main chain contain OH
• number main chain from end closest to OH
• give base name ol ending and place number of C on
  chain where OH attached in front
• name as hydroxy group if other higher precedence
  group present

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2
3
4
5
6
4-ethyl-4-methyl-3-hex-5-enol
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Reactions of Alcohols
Nucleophilic Substitution
Acid Catalyzed Elimination (Dehydration)
Oxidation
with Reactive Metals
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Aldehydes and Ketones

• contain the carbonyl group
• aldehydes at least 1 side H
• ketones both sides R groups
• many aldehydes and ketones have pleasant tastes
  and aromas
• some are pheromones
• formaldehyde H2CO
• pungent gas
• formalin a preservative
• wood smoke, carcinogenic
• acetone CH3C(O)CH3
• nail-polish remover

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Aldehyde Odors and Flavors

• butanal butter
• vanillin vanilla
• benzaldehyde almonds
• cinnamaldehyde cinnamon

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Ketone Odors and Flavors

• acetophenone pistachio
• carvone spearmint
• ionone raspberries
• muscone musk

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Reactions

• aldehydes and ketones are generally synthesized
  by the oxidation of alcohols
• therefore, reduction of an aldehyde or ketone
  results in an alcohol

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Carbonyl Group
CO group is highly polar many reactions involve
addition across CO, with positive part attached
to O
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Addition to CO
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Carboxylic Acids

• RCOOH
• sour tasting
• weak acids
• citric acid
• found in citrus fruit
• ethanoic acid acetic acid
• vinegar
• methanoic acid formic acid
• insect bites and stings

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Carboxylic Acids

• made by the oxidation of aldehydes and alcohols
• OH on the end of the chain
• always on main chain
• has highest precedence
• C of group always C1
• position not indicated in name
• change ending to oic acid

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Naming Carboxylic Acids
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Esters

• RCOOR
• sweet odor
• made by reacting carboxylic acid with an alcohol
• RaCOOH RbOH ? RaCOORb H2O
• name alkyl group from alcohol, then acid name
  with oate ending
• precedence over carbonyls, but not carboxylic
  acid
• number from end with ester group

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Naming Esters
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Condensation Reactions

• a condensation reaction is any organic reaction
  driven by the removal of a small molecule, like
  water

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Synthesis of Aspirin(Acetylsalicylic Acid)
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Ethers

• R O R
• ether diethyl ether CH3CH2OCH2CH3
• anesthetic
• to name ethers, name each alkyl group attached to
  the O, then add the word ether to the end

diethyl ether
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Amines

• N containing organic molecules
• very bad smelling
• form when proteins decompose
• organic bases
• name alkyl groups attached to the N, then add the
  word amine to the end

putrescine
ethylamine
ethylmethylamine
cadaverine
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Amines

• many amines are biologically active
• dopamine a neurotransmitter
• epinephrine an adrenal hormone
• pyridoxine vitamin B6
• alkaloids are plant products that are alkaline
  and biologically active
• toxic
• coniine from hemlock
• cocaine from coca leaves
• nicotine from tobacco leaves
• mescaline from peyote cactus
• morphine from opium poppies

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Amine Reactions

• weak bases
• react with strong acids to form ammonium salts
• RNH2 HCl ? RNH3Cl-
• react with carboxylic acids in a condensation
  reaction to form amides
• RCOOH HNHR ? RCONHR H2O

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Macromolecules

• polymers are very large molecules made by
  repeated linking together of small molecules
• monomers
• natural
• modified natural polymers
• synthetic
• plastics, elastomers (rubber), fabrics, adhesives
• composites
• additives such as graphite, glass, metallic flakes

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Natural Polymers

• polysaccharides
• cellulose (cotton)
• starch
• proteins
• nucleic acids (DNA)
• natural latex rubber, etc.
• shellac
• amber, lignin, pine rosin
• asphalt, tar

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Modified Natural Polymers

• Cellulose Acetate
• Rayon
• film
• Vulcanized Rubber
• Gun Cotton
• Celluloid
• ping-pong balls
• Gutta Percha
• fill space for root canal
• Casein
• buttons, mouldings, adhesives

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Polymerization

• the process of linking the monomer units together
• two processes are addition polymerization and
  condensation polymerization
• monomers may link head-to-tail, or head-to-head,
  or tail-to-tail
• head-to-tail most common
• regular pattern gives stronger attractions
  between chains than random arrangements

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Head-to-Tail
Head
Tail
Head
Tail
Head-to-Head, Tail-to-Tail
Tail
Tail
Head
Head
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Addition Polymerization

• monomers add to the growing chain in such a
  manner that all the atoms in the original monomer
  wind up in the chain
• no other side products formed, no atoms
  eliminated
• first monomer must open to start reaction
• done with heat or addition of an initiator
• chain reaction
• each added unit ready to add another

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Addition Polymerization


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Condensation Polymerization

• monomer units are joined by removing small
  molecules from the combining units
• polyesters, polyamides lose water
• no initiator needed
• chain reaction
• each monomer has two reactive ends, so chain can
  grow in two directions

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Condensation Polymerization

H2O
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Nylon

• polyamides
• good physical properties
• affected by moisture
• very good heat resistance
• excellent chemical resistance
• excellent wear resistance
• nylon 6,6 made by condensing
  1,6hexandiamine, H2N(CH2)6NH2, with
  hexandioic acid,
  HOOC(CH2)4COOH

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