CH ENGR 104C Lecture Notes - Lecture 6: Van Der Waals Strain, Eclipsed Conformation, Chemical Formula
7 Feb 2017
School
Department
Course
Professor
Document Summary
Strain: a decrease in molecular stability due to e- repulsion or deviation from ideal geometry. Torsional strain : strain caused by e- repulsion on one atom or group when passing by another atom or group results from bonds on adjacent atoms being eclipsed: brought about by the barrier to rotation. **important difference: torsional strain can be relieved by bond rotation, but steric strain can not. Note: ethane has no steric strain h atoms, even when eclipsed, are not close enough to each other, for each unfavorable interaction per pair of eclipsed h-h = 1. 0kcal/mol. Per pair of eclipsed ch3-ch3 = 2. 5kcal/mol. Per pair of gauche ch3-ch3 = 0. 9kcal/mol. Important concepts: most stable conformation = least van der waals repulsion. How to determine relative amounts of each conformation: relative energy difference between conformations tells us something about the relative amounts of each conformation, relate gibbs free energy to equilibrium constant g = -rtlnk.
