>>9562442You can't treat it like everything is just memorization, you have to understand why things happen fundamentally so when the professor gives you a slightly different molecule on the exam you can explain why a different reaction happens.
Fundamentally, everything comes down to atomic and molecular orbitals, and figuring out which electrons go where based on relative electronegativity. Atomic orbitals consist of 1 s orbitals, 3 p orbitals, 5 d orbitals, and 7 f orbitals, while molecular orbitals consist of ?, ?, and ? (sigma, pi, and delta) along with their respective anti-bonding atomic or molecular orbitals. If a rhenium atom wants to bind with another rhenium atom, then you have filled s and d atomic orbitals which will be donated to form ?, ?, and ? molecular orbitals (molecular orbitals are the same thing as bonds). A ? bond is the interaction of one s, p, d, or f lobe to another s, p, d, or f lobe. A ? bond is the interaction of two s, p, d, or f lobes to another s, p, d, or f lobes. A ? bond is the same thing but four lobe-lobe interactions.
Often times however, molecular orbital naming convention will be ignored and the atomic orbital naming convention will be used. It's simply a change in semantics and does indicate a change in chemistry. Typically this will happen in organometalic chemistry when you are looking at metal atoms binding to organic ligands, which all bind in a ? fashion (1 d-orbital lobe to 1 p or s-orbital lobe). Because they all bind in a ? fashion, the molecular orbitals will be referred to as one of the five d atomic orbitals it came from (dxy, dxz, dyz, dz^2, or dx^2-y^2).
Most importantly, do not confuse atomic orbitals with ligands. A metal atom with 5 d-orbitals can bind to 6 organic ligands because the metal atom also has 1 filled s orbital and 3 empty p orbitals available for bonding, along with every anti-bonding version of those orbitals.
Look up molecular orbital diagrams for more information.