University:
York University
Course:
CHEM 1000 | Chemical Structure
Academic year:

2021
Views:

470

Pages:

4
Author:

Niklas

Conformation of Cyclohexanes Not Planar Lowest Strain of All Rings Adopts Chair Conformations Chair is All Staggered Chair has No Angle Strain Newman Projection: Staggered No Eclipsing Bonds 1,3-Diaxial strain ↑ w/ size of axial group X/H 1,3-diaxial interaction C₁-X/C₂-H₁ are Gauche Cyclohexane Boats: Higher in E in chairs No Angle Strain (C-C-C) Torsional Strain (CH/CH & C-C/C-C) Flagpole Interaction (1,4) - Type of Steric Strain Conformational Inversion ("Ring Flip") Drawing Cyclohexane Chairs (3 Methods) DSW 1/3 Method M/W Method Conformational Inversion: Chair Boat Half-Chair Ts don't have a lifetime longer than a single vibration. Intermediate have some energy. Monosubstituted Cyclohexanes: Involves SB Rotation Low Barrier A is disfavored: 1,3-diaxial strain Gauche interaction (C₁-X/C₂-H) EXAMPLES: Ex1: 5% AX 95% EQ Ex2: K ↑ as X ↑ (becomes larger) A-values (-ΔG°) for specific group X Larger A-value is more favored Substituent A-values Ratio -OH 0.5 70:30 -CH3 1.0 83:17 -CH2CH3 1.8 95:5 -CH(CH3)2 1.9 96:4 -C(CH3)3 2.2 97:3 -t-Bu 5.5 9999:1