Organic Chemistry Reviews
Chapter 4
Cindy Boulton
September 20, 2009
Naming Molecules
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Lewis Structure
VSEPR Structure
Bond Line
Molecular Formula
Condensed Formula
Name
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Common Name
IUPAC name
IUPAC Nomenclature
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Formal system of naming organic compounds
“Common” or old names still used
International Union of Pure and Applied Chemistry
Each different compounds should have an unambiguous
name
Locants
Prefixes
Parent Compound
Suffixes
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1) Locate the longest continuous chain of carbon – Parent
Chain
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If ring and chain have the same number of carbons, use the ring as
the parent chain
If 2 chains have the same number of carbons, use the chain with the
more groups attached
2) Number the longest chain beginning with the end of the
chain near the attached group
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If same distance to first group on either end, use the numbers that
result in the lowest sum
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Number the chain end near the group with alphabetical preference
Number the chain end near the group with suffix –ol
2 ½) Number a ring where
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the first group is the first alphabetically (2 groups)
the numbers result in the lowest sum (3 or more groups)
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3) Use the numbers to designate the location of the
attached group
4) If 2 or more attached group, each should be numbered
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Placed in alphabetic order
Disregard prefixes
5) If 2 groups are attached to same carbon, use the
number twice
6) If 2 or more groups are identical, indicate by using
prefixes:
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2: di-, 3: tri-, 4: tetra-, etc.
IUPAC Nomenclature
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Unbranched Alkanes
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Normal, single bonds
Sp3 hybridized Carbon
CnH2n+2
All end in –ane
1: meth-, 2: eth-, 3: prop-, 4: but-, 5: pent-, 6: hex-, 7: hept-, 8: oct, 9: non-, 10: dec-, 11: undec-, 12: dodec-
Alkyl Groups derived from straight chains
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1: methyl-, 2: ethyl-, 3: propyl-, 4: butyl-, 5: pentyl-, 6: hexyl-, 7:
heptyl-, 8: octyl-, 9: nonyl-, 10: decyl-, 11: undecyl-, 12: dodecyl-
Constitutional Isomers
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Branched Alkanes
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Iso- split at the end
Neo- cross shape
Branched Alkyl Groups
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Iso- split at end
Neo- cross shape
Sec- attached at secondary carbon
Tert- attached at tertiary carbon
Alkyl Halides
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Alkanes with a halogen group attached
F: fluoro-, Cl: chloro-, Br: bromo-, I: iodoIf have a halide and alkyl group attached to Parent Chain
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Number with closest group attached to end of chain-no
preference
List in alphabetical order
Alkyl Halides
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Alkyl group attached to halogen
Alcohols
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Hydroxyl group attached (-OH)
Suffix –ol indicates alcohol
Number of suffix is on Parent Compound
Numbering of the Parent Chain always begins at end
closer to group named as the suffix
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An Alcohol give priority to numbering
Parent Chain must have hydroxyl (-OH) group attached
directly
Diols
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2 hydroxyl groups attached
Suffix -diol
Monocyclic Alkanes
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Prefix cycloGroups attached to cycloalkane
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If 1 group attached, no need to indicate position
If 2 groups attached, start numbering ring beginning with the
group going to be first alphabetically and in direction of the
next group having the lowest number possible
If 3 or more groups attached, use numbering that gives the
lowest sum possible
CnH2n
Identifying Carbons
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Carbons identified by the number of Carbons directly
attached
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Primary (1o): 1 carbon directly attached
Secondary (2o): 2 carbons directly attached
Tertiary (3o): 3 carbons directly attached
Quaternary (4o): 4 carbons directly attached
Physical Properties
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More branched molecule- lower boiling point and melting
point
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Reduced molecular surface area
Less energy required to break the molecule apart
More unbranched (linear) molecule- higher boiling point
and melting point as molecular weight increases
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More molecules can bind because of larger molecular surface
More energy require to break the molecule apart
Confirmation Analysis
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Newman Projections
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View the rotation between two carbon molecules around the
sigma bond and the placement of atoms or molecules attached
to both carbons
Dihedral Angle or Torsional Angle- Angle of position between
two different atoms or molecules connected to different
carbons
Staggered Conformation- atoms/molecules attached to the
Carbons are directly bisect each other
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Dihedral Angle is 60 degrees
Eclipsed Conformation- atoms/molecules attached to the
Carbons are directly opposed to one another
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Dihedral Angle is 0 degrees
Eclipsed vs. Staggered
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Most molecules are found in staggered confirmation
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Most stable shape
Lowest energy
Less tension
Electron Pairs Repel- want to be at greatest distance apart as
possible
Potential Energy
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Staggered Confirmation- less energy
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Eclipsed Confirmation- more energy
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Anti- Largest group on both carbons are farthest apart (180 degrees)
Gauche- Largest group on both carbons are 60 degrees apart
Most energy when the largest group on both carbons are directly
opposed each other
Torsional Strain- increase energy by being eclipsed
confirmation
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How much electron pairs are repelling
Eliminate strain by being staggered confirmation
Monocyclic Alkanes
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Ring Strain = Angle Strain + Torsional Strain
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Cyclopropane
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Angle Strain- how much of a deviation from 109.5 degrees- bond
angle if Carbon is tetrahedral
Torsional Strain- if eclipsed or staggered
Smallest
Angle Strain- about 60 degrees
Torsional Strain- eclipsed
Most strained ring!!!
Cyclobutane
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Angle Strain- about 90 degrees
Torsional Strain- eclipsed
Warp along diagonal decreases torsional strain because less eclipsed
but angle strain increases to 88 degrees
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Cyclopentane
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Angle Strain- 108 degrees
Torsional Strain- eclipsed
Warp to form an envelop shape
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Decrease angle and torsional strain
Cyclohexane
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Angle Strain- 120 degrees
Torsional Strain- eclipsed
Warp to from Chair shape
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Angle Strain is 109.5 degrees and Torsional Strain is staggered
Ring Strain = 0!!!
Warp to form Boat shape
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No Angle Strain but Torsional Strain is eclipsed
Axial vs. Equilateral Positions
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Axial- hydrogen vertically attached to carbon on the ring
Equilateral- hydrogen horizontally attached to carbon on
the ring
Steric Crowding
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Crowded in axial positions
Less crowed in equilateral positions
Larger groups prefer to be in equilateral positions
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Reduce energy
More stable
13Carbon
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Nuclear Magnetic Resonance
Identifies each unique Carbon in molecule
Uses isotope of Carbon that is not radioactive
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NMR Spectroscopy
Causes the spin of Carbon molecule to be flipped on a
magnetic field
Graph
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Measure of the Chemical Shift (δ) ppm from 0-200
A peak for each different type of Carbon
Placement on graph determined by the electronegativity of
atoms attached to the Carbon
Size of peak determined by how many Carbons of that type it
is representing
Chair Conformation of Cyclohexane
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Warped 6 member ring
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No ring strain: no torsional or angle strain
Axial:
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Mountain- bond up
Valley- bond down
Equatorial: bond straight out
Ring Flip Equilibrium
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Interconvert axial and equatorial groups attached
Steric crowding in axial positions
Big groups prefer to be in equatorial positions
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More stable
Less Gibb’s Free Energy
Difference in Isomer % at Equilibrium and Free-Energy (pg. 161)
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