Organic Chemistry

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Organic Chemistry
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What is it?

• Study of compounds involving carbon
• Carbon has the ability to make chains and rings
  with itself
• Thousands of compounds contain only Carbon and
  Hydrogen
• Millions with other elements added
• Usually, Nitrogen, Oxygen, Sulfur, Halogens

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Patterns

• Within the millions of compounds there are
  patterns that emerge
• Carbon forms 4 Bonds
• Hydrogen forms 1 Bond
• Oxygen forms 2 Bonds
• Halogens form 1 Bond

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Identifying Compounds

• Name Based on naming conventions (Usually
  IUPAC)
• Molecular Formula Shows actual number of atoms
  present C4H8O2
• Empirical Formula Shows the simplest whole
  number ratio of atoms C2H4O
• Structural Formula Shows how the atoms are
  arranged CH3COCH2CH2OH

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Cont.

• Graphical Formula Shows how the atoms are
  arranged in space and bonded
• Similar to Lewis Structures but w/o the dots
• CH3COCH2CH2OH

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Cont.

• Skeletal Formula Abbreviated form of graphical
  formula often omitting carbons and hydrogens
  CH3COCH2CH2OH

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• Example Draw the structural, graphical, and
  skeletal formula for C3H8

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• Example Draw the structural, graphical, and
  skeletal formula for C5H8O2

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• Example Draw the structural, graphical, and
  skeletal formula for C4H6

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Homework

• Organic Worksheet 1

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Alkanes

• Straight chain organic compounds containing only
  C, H, and sometimes halogens
• All carbons are sp3 hybridized
• General formula CnH2n2
• 1 C
• CH4
• 6 Cs
• C6H14

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Properties

• Nonpolar Dissolve other nonpolar compounds
• Hydrophobic Water hating
• Good Lubricants and metal preservers
• C1 to C4 (Gas) Fuels - Methane
• C5 to C8 (Liq.) Fuels - Gasoline
• C9 to C16 (Viscous Liq.) Diesel Fuel
• C17 and Up (Very Viscous) - Greases

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Cont.
http//web.mst.edu/wlf/chem381/chap11.html
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Hydrocarbons and Saturation

• Hydrocarbons are compounds that only contain
  Carbon and Hydrogen
• Alkanes are saturated hydrocarbons
• Carbons are saturated with hydrogen
• Compounds with double or triple bonds are
  unsaturated (more later)

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Alkane Nomenclature

• Alkanes are named according to the longest carbon
  chain. (per IUPAC rules)
• System of prefixes to determine the number of
  carbons that are present.
• 1 meth, 2 eth, 3 prop, 4 but, 5 pent
• 6 hex, 7 hept, 8 oct, 9 non, 10 dec
• All alkanes end in -ane

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• Example Draw the structural, graphical, and
  skeletal formula for ethane and butane

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• Example Give the name and graphical formula for
  an alkane with 7 Carbons

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Alkane Nomenclature

• Alkanes end in ane
• Alkanes without branches are named according to
  the number of carbons
• Alkanes with branches are named according to
  longest chain of carbons
• The longest chain is numbered so that
  substituents receive the lowest number

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Cont.

• When more than one of the same substituents is
  present use the prefixes di- tri-, tetra-
• If two or more substituents are present they are
  listed alphabetically (except prefix)
• Numbers are separated by commas, numbers and
  letters by hyphens

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Substituent Groups

• Alkyl Groups A hydrocarbon missing a hydrogen
• CH3 Methyl
• CH3CH2 Ethyl
• CH3CH2CH2 Propyl
• CH3CH2CH2CH2 Butyl
• Halogens
• Cl Chloro Br Bromo
• F Fluoro I Iodo

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• Name the alkane

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• Name the alkane

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• Name the alkane

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• Name the alkane

25

• Name the alkane

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• Name the alkane

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• Name the alkane

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Other Alkyl Groups

• Isopropyl
• Sec-Butyl
• Isobutyl
• Tert-butyl

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• Name the alkane

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• Name the alkane

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• Name the alkane

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• Name the alkane

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Isomers

• Same formula different compound
• Structural Isomers
• Completely different bonding pattern
• Stereoisomers
• Same bond pattern

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• Draw and name the isomers of C4H10

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Homework

• Organic Worksheet 2
• Read pages 51-60

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Dash Line Wedge Drawings

• A way of representing arragement in space
• Lines represent bonds in the plane
• Wedges come out of the plane and
• Dashed lines go into the plane
• Draw for Methane

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Newman Projections

• Another way of showing arrangement in space.
• Look at the molecule for the end view
• Draw Newman Projection for Ethane

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Alkane Confromations

• Alkanes are free to rotate because of single
  bond.
• Overlap of one orbital (sigma bond)
• Different arrangements are called rotamers.
• A Stereoisomer
• Rotate to give minimum repulsion

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• Draw the most stable conformation of chloropropane

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Cycloalkanes

• Alkanes that from ring structures
• Not necessarily a circle
• All carbons are still sp3 hybridized
• Saturated compounds
• General Formula CnH2n

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Cycloalkane Nomenclature

• Named by placing cyclo- in front of the alkane
  name of the longest carbon ring
• If there is only one substituent there is no need
  to number it
• If there are multiple substituents the must be
  numbered.
• Number by alphabetical order

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• Name the cycloalkane

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• Name the cycloalkane

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• Draw cyclopentane and cyclohexane

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• Name the cycloalkane

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• Name the cycloalkane

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• Draw 1-chloro-4-ethyl-2-methylcyclohexane

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Conformations of Cycloalkanes

• Cycloalkanes take on interesting shapes
• Consider cyclopropane
• What must the bond angles be?
• 60 degrees!
• Because 3 points determine a plane

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Cont.

• Consider cyclobutane
• What are the bond angles?
• 88 degrees
• There is a slight puckering of the bonds

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Cont.

• Consider cyclohexane
• What must the bond angles be?
• 109.5!
• Six membered rings are very common
• Takes on two puckered conformations
• Chair and boat conformations

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Chair Conformation

• Named because it looks like a chair
• Most stable conformation

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Boat Conformation

• Less stable because of repulsion

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Configurational Isomers

• Same bond pattern different arrangement in space
• Called cis- and trans- isomers
• Cis- same side Trans- opposite
• Cis and trans molecules are different molecules
• Different boiling points
• Fig. 2.7 in book. (Page 60)

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• Draw the cis and trans forms of
  2,3-dimethylcyclopropane

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Homework

• Chapter 2 s 33,34,36,37ab,41
• Organic Worksheet 3

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Reactions of Alkanes

• Alkanes are fairly boring from a chemistry point
  of view.
• Meaning they are fairly unreactive
• Make very good solvents
• Two types of reactions
• Burning
• Reacting with halogens

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Combustion

• When alkanes react with oxygen they can burn
• Complete combustion of alkanes yields carbon
  dioxide and water
• CH4 2O2 ? CO2 2H2O heat
• Incomplete combustion yeilds carbon monoxide and
  water

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Halogenation

• Process of adding a halogen to an alkane
• Process must take place in the light
• General form
• R H X X ? R X H X
• Where R is an alkane and X is a halogen
• Called a substitution reaction
• A hydrogen is substituted for a halogen
• When chlorine is added it is called chlorination
  and so on

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Cont.

• Excess halogen allows the reaction to continue
• CH4 4 X2 ? CX4 4 HX
• Reactions of straight chain alkanes gives a
  mixture of products
• C3H8 Cl2 ? ?

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Cycloalkanes

• Unsubstituted cycloalkanes give only one product
  when reacted with a halogen
• Write the balanced reaction when cyclobutane is
  reacted with bromine

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Mechanism of Substitution

• The Mechanism is a process by which the reaction
  takes place
• Halogenation is a Free Radical Chain Reaction
• Made up of three steps
• Initiation
• Propagation
• Termination

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Initiation

• Beginning step
• Energy from light is required to break the
  halogen bond (Weaker than C-C or C-H)
• Creates a radical (Free atom)

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Propagation

• Continuing the reaction
• Radicals react with the alkane and more halogens
  to create more radicals

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Termination

• Ending the reaction
• Radicals react with radicals to stop the reaction

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Problems

• 2.44