Supramolecular Interactions Flashcards
How is strength of binding measured?
Value measured by K, where K is the equilibrium constant for X + Host –> XHost in aqueous solution.
What are the different supramolecular interactions?
Ion-ion interactions, ion-dipole interactions, dipole-dipole interactions, hydrogen bonding, cation-pi and anion-pi interactions, pi-pi stacking, van der Waals forces, closed shell interactions, mechanical bonding
Tell me about ion-ion interactions.
Bond energy = 100-350 kJ/mol
Long range interactions, E = k/r
Electrostatic interactions
Tell me about ion-dipole interactions.
Bond energy = 50 -200 kJ/mol
E = k/r^2
Tell me about dipole-dipole and n-pi* interactions.
Bond energy = 4-25 kJ/mol
Alignment of dipoles can result in significant attractive interactions, fairly weak interactions. Can also have n-pi* type interactions with significant delocalisation of lone pair into antibonding orbital of another molecule, e.g. carbonyls.
Tell me about hydrogen bonding.
Bond energy = 4 - 120 kJ/mol
Strong interactions, highly directional with highest strength at 180 degrees lending selectivity, synthetically versatile and easy to build into molecular systems
How can more unusual hydrogen bonds occur?
Hydrogen bonds can also occur between polarised CH and electronegative atom, so long as CH is sufficiently polarised by an EWG, e.g. NO2.
Tell me about pi-pi stacking.
Bond energy = 0 -50 kJ/mol
Interactions between aromatic rings, where one is relatively electron rich and the other electron poor.
Edge-to-face interactions - electron-deficient hydrogen atoms of one aromatic ring and the electron-rich cloud of the other.
Face-to-face - off-set, responsible for slippery properties
Tell me about closed shell interactions.
Bond energy = variable, up to 200 kJ/mol
Aurophilic interactions - bonding between gold atoms arising between filled orbitals due to relativistic effects
Halogen bonds - lone pair donating into sigma-hole
Bridging - secondary interactions can be used to help improve stability of complexes
