[Urbanium]

Hi, I am a quantum chemistry noob and I do have one question: when somebody says that quantum mechanics is used to predict and/or explain reactivity of organic molecules, what does it mean?

Does it have to do with Hartree-Fock, Huckel method, DFT... or something else? Which quantum chemistry methods in particular are used to explore reactivity?

I would also appreciate if somebody could recommend some software used for that type of calculations and modeling.

[Schrödinger]

I guess these are some of the methods. By doing electron density calculations, you can see clearly which site on a molecule will act as the nucleophile (just an example). Similarly so for the electrophilic part of a huge molecule. Computational techniques are used to predict and optimize transition states, plot reaction coordinates, etc especially in organic systems.

[curiouscat]

I guess these are some of the methods. By doing electron density calculations, you can see clearly which site on a molecule will act as the nucleophile (just an example).mize transition states, plot reaction coordinates, etc especially in organic systems.

Even better, you can often estimate the Eact and thermodynamics to a fair degree of accuracy. At least for homogenous reactions.

Once you know activation energy and thermochemistry of a reaction, essentially you have all the reactivity information that you want.

[Schrödinger]

True. As a matter of fact, I've done some gas phase calculations of the above mentioned sort of certain organic reactions using Gaussian.

[curiouscat]

True. As a matter of fact, I've done some gas phase calculations of the above mentioned sort of certain organic reactions using Gaussian.

My point was that people often lose sight of the fact that electrophiles, neucleophiles, resonance etc. are all abstractions. The numbers on Eact etc. are the real fundamental quantities.