Organic Chemistry I |
Chapter 3 Notes |
Professor Carl C. Wamser |
Conformations
Ethane Conformations
C-H bonds on the two carbons may or may not align
eclipsed: C-H bonds are aligned
staggered: C-H bonds fit in between
Newman Projections
Potential Energy Diagrams
Butane conformations
Molecular mechanics
Types of strain:
Ring strain
Heats of combustion (normalized per CH2 unit)
Ring Size Heat of combustion (kJ/mol) Heat of combustion per CH2 (kJ/mol) 3 2091 697 4 2721 681 5 3291 658 6 3920 653 7 4599 657 larger 653 - 659
Small cycloalkane conformations
Cyclohexane
Monosubstituted cyclohexanes
PRACTICE DRAWING ACCURATE CHAIR FORMS WITH SUBSTITUENTS
equatorial generally preferred over axial
see the table in the text with delta G for axial vs equatorial
Disubstituted cyclohexanes - cis & trans isomerism
Depending on the substitution pattern, disubstituted cyclohexanes have different combinations of axial and equatorial substituents.
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Example - the two chair conformations for cis-1-chloro-3-methylcyclohexane involve either two axial substituents or two equatorial substituents. The latter is more stable.
All substituents prefer equatorial over axial
Polycyclic Compounds
spirocyclic - one carbon atom in common to two rings
naming: spiro[m.n]alkane (m,n are bridge sizes, where m<n)
number starting next to the common (spiro) atom as #1, go around smaller bridge firstexample: spiro[2.3]hexane
bicyclic - two carbon atoms in common to all three rings (bridgehead positions)
naming: bicyclo[x.y.z]alkane (x,y,z are bridge sizes, where x>y>z)
number starting at one bridgehead atom as #1, go around bridges in size order (x>y>z)example: bicyclo[3.2.0]heptane
Heterocyclic Compounds
contain one or more atoms in the ring that are not carbon
naming: special names for every case (covered later with the corresponding functional groups)
example: piperidine