Maybe it is easier to just think of reduction in terms of electronegativity
Li is a stronger reducer than Na because Li donates an electron more easily
Al is a stronger reducer because it has a weaker bond as a result Al being less electronegative than B
Alkyl substituents it a stronger reducing agent because they donate in electrons making the hydride opt to leave. (Also add sterics for stereoselectivitiy)
Electronegative substituents like CN and O-alkyl make the hydride less reactive as the try to pull in the negative charge on the hydride
Could someone check my logic. I'm taking a synth course that is almost exclusively reductions and I rogue memorization wont be enough to get by so I am establishing trends.
If anyone as studying methods for the reduction reactions please let me know. If I had to memorize something it would be about this much per week haha
http://www.chem.harvard.edu/groups/myers/handouts/1_Reduction.pdfThanks