Chemistry 122 Introductory Organic Chemistry

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Chemistry 122Introductory Organic Chemistry

• Fall Quarter 2009
• Dr. Thomas H. Schultz

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What is Organic chemistry?
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What is Organic chemistry? The study of carbon
and its compounds.
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What is Organic chemistry? The study of carbon
and its compounds. First we will concentrate on
compounds just containing carbon and hydrogen,
these compounds are called hydrocarbons.
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What is Organic chemistry? The study of carbon
and its compounds. First we will concentrate on
compounds just containing carbon and hydrogen,
these compounds are called hydrocarbons. Hydroca
rbon Classification
Hydrocarbons
Alkanes
Alkenes
Cycloalkanes
Alkynes
Cycloalkenes
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• Alkanes (saturated) hydrocarbons, or aliphatic
  hydrocarbons)
• General formula of CnH2n2
• Examples
• a. CH4 b. C2H6 c. C3H?

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• Alkanes
• General formula of CnH2n2
• Examples
• a. CH4 b. C2H6 c. C3H8 d. C4H?

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• Alkanes
• General formula of CnH2n2
• Examples
• CH4 b. C2H6 c. C3H8 d. C4H10
• Draw Lewis Structures

CH4
C2H6
C3H8
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• Alkanes
• General formula of CnH2n2
• Examples
• CH4 b. C2H6 c. C3H8 d. C4H10
• Draw Lewis Structures

CH4
C2H6
C3H8
D. Polarity? Polar or nonpolar?
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• Alkanes
• General formula of CnH2n2
• Examples
• CH4 b. C2H6 c. C3H8 d. C4H10
• Draw Lewis Structures

CH4
C2H6
C3H8
D. Polarity? Polar or nonpolar?
Nonpolar
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• Alkanes (Continued)
• E. Draw three dimensional structures, bond
  angles and hybridization.

CH4
C2H6
C3H8
F. There are two different structures for
C4H 10 Structure 1
Structure 2



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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertiary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in the
• two different structures of C4H10

Primary ? Secondary Tertiary
Primary Secondary Tertiary
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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertiary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in the
• two different structures of C4H10

Primary 2 Secondary ? Tertiary
Primary Secondary Tertiary
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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertirary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in the
• two different structures of C4H10

Primary 2 Secondary 2 Tertiary ?
Primary Secondary Tertiary
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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertiary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in the
• two different structures of C4H10

Primary 2 Secondary 2 Tertiary 3
Primary ? Secondary Tertiary
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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertiary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in the
• two different structures of C4H10

Primary 2 Secondary 2 Tertiary 3
Primary 3 Secondary ? Tertiary
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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertiary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in the
• two different structures of C4H10

Primary 2 Secondary 2 Tertiary 3
Primary 3 Secondary 0 Tertiary ?
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• Types of carbon
• 1. Primary (1?) Carbon connected to one
  carbon atoms.
• 2. Secondary (2?) Carbon connected to two
  carbon atoms.
• 3. Tertiary (3?) Carbon connected to three
  carbon atoms.
• 4. How many primary, secondary, and tertiary
  carbons in
• the two different structures of C4H10

Primary 3 Secondary 0 Tertiary 1
Primary 2 Secondary 2 Tertiary 3
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Constitutional Isomers (Structural Isomers) are
different compounds of the same formula. The
different structures from the previous slide for
the formula C4H10 is an example of Constitutional
isomers.
How many isomers are there of an alkane
containing five carbons (C5H10)?
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• NOMENCLATURE
• Common system
• Works best for low molecular weight hydrocarbons
• Steps to give a hydrocarbon a common name
• Count the total number of carbon atoms in the
  molecule.
• Use the Latin root from the following slide that
  corresponds to the number of carbon atoms
  followed by the suffix ane.
• Unbranced hydrocarbons use the prefix normal, or
  n-,
• Branched hydrocarbons use specific prefixes, as
  shown on a subsequent slide

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Examples
H
n-butane
H
isobutane
H
H
H C H
H
H C C C H
H
H C H
H
H
neopentane
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2. Systematic System of Nomenclature (IUPAC)

• Find the longest continuous chain of carbon
  atoms.
• Use a Latin root corresponding to the number of
  carbons in the
• longest chain of carbons.
• Follow the root with the suffix of ane for
  alkanes
• Carbon atoms not included in the chain are named
  as
• substituents preceding the root name with Latin
  root followed
• by yl suffix.
• Number the carbons, starting closest to the first
  branch.
• Name the substituents attached to the chain,
  using the carbon
• number as the locator in alphabetical order.
• Use di-, tri-, etc., for multiples of same
  substituent.
• If there are two possible chains with the same
  number of
• carbons, use the chain with the most
  substituents.

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Substituent Names (Alkyl groups)
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Systematic Nomenclature continued.
Which one?
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Systematic Nomenclature continued.
Which one?
The one with the most number of substituents
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Systematic Nomenclature continued.
Which one?
The one with the least number of substituents
The top structure has four substituents and the
bottom has three Substituents.
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Systematic Nomenclature continued.
Which one?
The one with the least number of substituents
The top structure has four substituents and the
bottom has three Substituents.
Name ?
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Systematic Nomenclature continued.
Which one?
The one with the least number of substituents
The top structure has four substituents and the
bottom has three Substituents.
Name ? heptane
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Systematic Nomenclature continued.
Which one?
The one with the least number of substituents
The top structure has four substituents and the
bottom has three Substituents.
Name 3,3,5-trimethyl-4-propylheptane
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Another Example
Name 3-ethyl-2,6-dimethylheptane
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Another Example
Name 2,6-dimethyl-3-ethylheptane Notice
substituents are in alphabetical order di, tri,
etc. do not participate in the alphabetical order

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Line StructuresA quicker way to write sturctures
(Condensed Structure)
methyl
ethyl
(A line structure of the above condensed
structure)
methyl
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Complex Substituents

• If the branch has a branch, number the carbons
  from the point of
• attachment.
• Name the branch off the branch using a locator
  number.
• Parentheses are used around the complex branch
  name.

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1
1
2
1-methyl-3-(1,2-dimethylpropyl)cyclohexane
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Alkane Physical Properties
Solubility hydrophobic (not water
soluble) Density less than 1 g/mL (floats on
water) Boiling points increase with increasing
carbons (little less for branched chains) due to
dispersion forces being larger.
Melting points increase with increasing carbons
(less for odd-number of carbons).
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Boiling Points of Alkanes
Branched alkanes have less surface area
contact, so weaker intermolecular forces.
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Melting Points of Alkanes
Branched alkanes pack more efficiently into a
crystalline structure, so have higher m.p.
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Reactions of Alkanes
I. Combustion reaction
II. Cracking reaction
III. Halogenation reaction (substitution reaction)
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Sample problem Which isomer of C5H12 has
the most monochloro isomers?
Problem solving process Step 1 draw the isomers
of C5H12 Step 2 react each isomer with
chlorine Step 3 count the products
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Sample problem Which isomer of C5H12 has
the most monochloro isomers?
Problem solving process Step 1 draw the isomers
of C5H10 Step 2 react each isomer with
chlorine Step 3 count the products
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Sample problem Which isomer of C5H12 has
the most monochloro isomers?
Problem solving process Step 1 draw the isomers
of C5H10 Step 2 react each isomer with
chlorine Step 3 count the products
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Sample problem Which isomer of C5H12 has
the most monochloro isomers?
Problem solving process Step 1 draw the isomers
of C5H10 Step 2 react each isomer with
chlorine Step 3 count the products
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Sample problem Which isomer of C5H12 has
the most monochloro isomers?
Problem solving process Step 1 draw the isomers
of C5H10 Step 2 react each isomer with
chlorine Step 3 count the products
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Sample problem Which isomer of C5H12 has
the most monochloro isomers?
Problem solving process Step 1 draw the isomers
of C5H10 Step 2 react each isomer with
chlorine Step 3 count the products
Winner!
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Conformers of Alkanes

• Structures resulting from the free rotation of a
  C-C single bond
• May differ in energy. The lowest-energy
  conformer is most prevalent.
• Molecules constantly rotate through all the
  possible conformations.

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Ethane Conformers
Staggered conformer has lowest energy. Dihedral
angle 60 degrees
Dihedral angle
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Ethane Conformers (2)
Eclipsed conformer has highest energy Dihedral
angle 0 degrees
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Conformational Analysis

• Torsional strain resistance to rotation.
• For ethane, only 12.6 kJ/mol

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Propane Conformers
Note slight increase in torsional strain due to
the more bulky methyl group.
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Butane Conformers C2-C3
Highest energy has methyl groups eclipsed. Steric
hindrance Dihedral angle 0 degrees
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Butane Conformers (2)
Lowest energy has methyl groups anti. Dihedral
angle 180 degrees
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Butane Conformers (3)

• Methyl groups eclipsed with hydrogens
• Higher energy than staggered conformer
• Dihedral angle 120 degrees

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Butane Conformers (4)

• Gauche, staggered conformer
• Methyls closer than in anti conformer
• Dihedral angle 60 degrees

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Conformational Analysis
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Cycloalkanes

• Rings of carbon atoms (-CH2- groups)
• Formula CnH2n
• Nonpolar, insoluble in water
• Compact shape
• Melting and boiling points similar to branched
• alkanes with same number of carbons
• Slightly unsaturated compared to alkanes

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Naming Cycloalkanes

• Count the number of carbons in the cycle
• If the bonds are single then use the suffix ane
• First substituent in alphabet gets lowest number.
• May be cycloalkyl attachment to chain.

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Cis-Trans Isomerism(a type of stereoisomerism)
Cis like groups on same side of ring Trans
like groups on opposite sides of ring
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Cycloalkane Stability

• 6-membered rings most stable
• Bond angle closest to 109.5?
• Angle (Baeyer) strain
• Measured by heats of combustion per -CH2 -

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Heats of Combustion/CH2 Alkane O2 ? CO2 H2O
658.6 kJ
Long-chain
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Cyclopropane

• Large ring strain due to angle compression
• Very reactive, weak bonds

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Cyclopropane (2)
Torsional strain because of eclipsed hydrogens
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Cyclobutane

• Angle strain due to compression
• Torsional strain partially relieved by ring
  puckering

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Cyclopentane

• If planar, angles would be 108?, but all
• hydrogens would be eclipsed.
• Puckered conformer reduces torsional strain.

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Cyclohexane

• Combustion data shows its unstrained.
• Angles would be 120?, if planar.
• The chair conformer has 109.5? bond angles
• and all hydrogens are staggered.
• No angle strain and no torsional strain.

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Chair Conformer
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Boat Conformer
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Conformational Energy
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Axial and Equatorial Positions
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Monosubstituted Cyclohexanes
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1,3-Diaxial Interactions
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Disubstituted Cyclohexanes
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Cis-Trans Isomers
Bonds that are cis, alternate axial-equatorial
around the ring.
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Bulky Groups

• Groups like t-butyl cause a large energy
• difference between the axial and equatoria
• l conformer.
• Most stable conformer puts t-butyl equatorial
• regardless of other substituents.

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End of Chapter 2