Some organic chemistry textbooks like to give the student a ‘solid understanding’ of the theory of chemical bond before explaining any actual chemistry. If you are into this kind of thing, you can sink very deep into quantum chemistry. But you can be a just as productive synthetic chemist without bothering with the MO stuff. There are stereo-electronic effects that are influencing the product distribution or equilibrium in some commonly used reactions and systems – and you have to memorize that this is in fact what happens. You may be curious to learn the deeper explanation – but if not you can still use the reaction.
This orbital thing is actually not hard to learn – unless you want to do it on professional level, writing a quantum-computation-based modeling programs. It is just another qualitative and visually-helpful device, not much different from the sticks and balls approach, a device that reflects some aspect of the reality but is based on simplification and memorization (“this is how electron pairs in pi orbitals look like, trust me”). I don’t have a problem with MO’s – just with the educators who try to make it into a bigger science than it really is and to intimidate the unfortunate undergrads.
The MO-based approach to teaching organic chemistry reflects the hopes of 60’s and 70’s that organic chemistry can be neatly categorized and explained by few simple principles. Woodward-Hoffmann rules were a great breakthrough not necessarily for the synthetic chemistry (the electrocyclic reaction governed by these rules are not as frequently used as for example Pd- arylations) but for the self-confidence of organic chemists. This coincided with great advances in spectroscopy and computation that allowed to make a meaningful discussion about unstable intermediates, transition states and so on. The hope at that time was that a new fundamental understanding of entire classes of reactions would emerge, that new synthetic reactions and retrosynthetic disconnecion schemes could be discovered through computation. Chemistry textbooks based on the functional group transformations were abandoned in favor of textbooks based on reaction mechanism classifcations, sometimes to a terrible effect.
So if you are in early stages of learning organic chemistry and if you are being put off by MO diagrams, you can relax. Orbitals are helpful but they are not as deep or useful as some textbooks would make you believe – definitely not usefull on the level of collected procedures in Organic Syntheses or a handbook of protective groups. Teacher, leave the kids alone.