Evans. Breit Conformational Analysis: Cylcoheptane Chem 206 Cycloheptane Cyclooctane Chair-Boat Lowest-energy conformation Transannular strain Chair(2. 16 kcal/mol) Twist-Chair(0 kcal/mol) between C?&C Ring strain originates in eclipsing interactions and transannular van der Waals interactions (pseudoegatorial AG 182.8>4.5-0.36.1 (pseudoaxial)(kcal/mol) Underside view of boat-chair C3& C7 eclipsing interactions Boat(3.02 kcal/mol) Twist-Boat(2.49 kcal/mol) Hendrickson, J B JACS 1961. 83, 4537 See Eliel, page 762+ Olefins are preferentially orientated to eliminate eclipsing interactionsEvans, Breit Conformational Analysis: Cylcoheptane Chem 206 See Eliel, page 762+ Cycloheptane Chair (2.16 kcal/mol) Twist-Chair (0 kcal/mol) Boat (3.02 kcal/mol) Twist-Boat (2.49 kcal/mol) Hendrickson, J. B. JACS 1961, 83, 4537. Olefins are preferentially orientated to eliminate eclipsing interactions. Chair-Boat Lowest-energy conformation Cyclooctane 1 7 3 Ring strain originates in eclipsing interactions and transannular van der Waals interactions Transannular strain between C3 & C7 Methyl position 1 2 3 4 5 1.8 2.8 >4.5 -0.3 6.1 (pseudoeqatorial) (pseudoaxial) (kcal/mol) DG 5 1 7 3 Underside view of boat-chair C3 & C7 eclipsing interactions 3 7