Leaving Groups, Nucleophiles, & bases

order the following in increasing order of best LG: R-OH2, OH, R-NH2

R-OH2> OH> R-NH2

Why?? B/c the R-OH2 has a (+) charge, so if it leaves it will be neutral, which a better LG is one that is more stable when it leaves, aside from that between N & O, N would be the better base thus making it the weaker LG, after R-OH2, OH is a base, so it’s an intermediate LG, finally, R-NH2 is just the better base overall, thus it’s the worst LG

between CH3NH2 & CH3OH, which one is the better nucleophile??

CH3NH2 is the better Nu(-) b/c it is the better base (see the trend on the periodic table)

in P.A the LG ability increases…

F- > Cl- > Br- > I-

b/c it takes F- less time to get thru solvent & attack electrophile than I- (due to size)

in P.P, LG ability increases…

I- > Br- > Cl- > F-

b/c it takes more H-bonding to cage I than to cage F (due to size difference)