Strain and Stability

Translation entropy of a small molecule at 1M concentration is 30 eu

Rotational entropy of a small molecule at 1M concentration is 30 eu

Internal bond rotation costs around 3-5 eu

Bond Dissociation Energy (BDE)

C-F > C-O > C-N > C-C

C-F > C-Cl > C-Br > C-I

C-C vs. C-I????

C(sp)-H > C(sp2)-H > C(sp3)-H

50 kcal/mol difference in BDE indicates 1037 times difference in

reactivity

HO + R-H R + H2O BDE for ethane is 90 kcal/mol,

assume pre-exponential factor to be 1013, then the rate of homolytic C-C

cleavage is 1044 years

How do we know that n = 0 is most relevant for bond stretches at T= 298 K?

450-500 cm-11617-1640 cm-12260-2100 cm-1

Frequency

Heats of formation and Combustion

Application of GIM

Thermochemistry of Reactive Intermediates

stability vs. persistence

Carbocations: Hydride Ion Affinity

as a Measure of Stability

Carbanions: Proton Affinity as a Measure

of Stability

How Big is 3 kcal/mol?

The rate constant at 298 K for a 3 kcal/mol barrier is 6 X 1010 S-I . This corresponds to a half-life of 10

picoseconds.

Br > CH3> Cl > NO2> COOH > OCH3> F > H

Bredt’s Rule

S =a + b + c

Hyperstable Olefins

cis-1-methyl-4-isopropylcyclohexane

Donor-Acceptor Interactions

Contrasteric Bias Toward Axial

Ben Feringa’s Motor

Empirical Force Fieldor

Molecular MechanicsBond Stretching

Correction for Stretching Energy

Angle Bending

Correction for Angle Bending

Expansion for Torsions: -Folded interactions

Torsion

Nonbonded interactions

Electrostatic Interactions

Hydrogen Bonded Interactions