[physstudent1]

I have an exam coming up about the Sn1 Sn2 E1 and E2 reaction pathways, I understnad most of the rules but one thing that I'm unsure of is how can I tell if a base is a strong base can anyone help me,  also how can I tell a strong nucleophile?

[macman104]

A base in the sense of Sn1, Sn2, E1, E2 are categorized by the ability to pull of hydrogens.  Right now, you will probably see only a few common strong bases.  They would be lithium diisopropylamide, n-butyllithium, um...yea.  Strong bases are ones that have a negative charge that is destabilized, or very strong, with lots of electron donators (however, I think most of that will be over your head).

Strong nucleophiles are those that have a large-polarizable electron shells that can easily penetrate to attack.

[physstudent1]

so the easier a nucleophile can delocalize it's negative charge the stronger it is right?  and weak bases are strong nucleophiles?  I also am confused I thought a weak acid's conjugate base was a strong base but this is not right?  There are 2 other factors that affect nucleophile strength but I don't know them anyone have any idea?

[azmanam]

Your question is very nuanced.  It depends on the substrate, the solvent, and the conditions (heat?).

start here:

http://www.cem.msu.edu/~reusch/VirtTxtJml/alhalrx1.htm#hal2

here's an excerpt:

(i) For a given element, negatively charged species are more nucleophilic (and basic) than are equivalent neutral species.
(ii) For a given period of the periodic table, nucleophilicity (and basicity) decreases on moving from left to right.
(iii) For a given group of the periodic table, nucleophilicity increases from top to bottom (i.e. with increasing size), although there is a solvent dependence due to hydrogen bonding. Basicity varies in the opposite manner.

[physstudent1]

thanks a lot