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CHEM 2OA3 Lecture Notes - Conformational Isomerism, Hyperconjugation, Halogenation

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Jeff Landry

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Drawing Rotamers
If there’s a specific form he’s looking for, he has to specify more details about it, or else
you can draw any potential rotamer and it would be correct
Barrier energy is the sum from the lowest point to the highest point
Radical Halogenation and Bond Strength
Homolytic Cleavage: A:B → A’ + ‘B (radicals)
Heterolytic Cleavage: A:B → A+ + :B-
Use electronegativity to compare acidity!
o O-H bond is MUCH stronger than a C-H bond, but H2O is more acidic than CH4
because oxygen is more electronegative than carbon
CH4 bond strength > Primary > Secondary > Tertiary
More stable products when you cleave bond → weaker bond
o Product energy level changes ALSO change the energy barrier to make the break
of the bond
Hyperconjugation: p-orbital (with a single electron) overlaps with bonding molecular
orbital of neighboring C-H (or any other) bond
o Should be able to show a 3D drawing of it if asked
o More hyperconjugation → more stability
Free Radical Halogenation
H-CH3 + X-X → H3C-H + H-X
o Need energy (light or heat) to trigger this cleaving of X-X bond
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