[vnaraya3]

I just finished two semesters of undergraduate organic chemistry, and looking back I was wondering why SN1/SN2 aren't used more for making C-C bonds? I'm assuming these reactions don't work (if so, why?) or rather they're not important enough to include an organic chemistry textbook.

For example, why can't you make octane from adding n-butyllithium to 1-chlorobutane? Shouldn't n-butyllithium be a strong nucleophile?

Also, in discussing the synthesis of esters, we never discussed the possibility of using carboxylate ions as nucleophiles to attack alkyl halides. Even if carboxylate ions are weak nucleophiles, could they potentially participate in SN1? For example, could you add sodium acetate to tert-butyl chloride to make tert-butyl acetate by SN1?

[orthoformate]

I just finished two semesters of undergraduate organic chemistry, and looking back I was wondering why SN1/SN2 aren't used more for making C-C bonds? I'm assuming these reactions don't work (if so, why?) or rather they're not important enough to include an organic chemistry textbook.

For example, why can't you make octane from adding n-butyllithium to 1-chlorobutane? Shouldn't n-butyllithium be a strong nucleophile?

Also, in discussing the synthesis of esters, we never discussed the possibility of using carboxylate ions as nucleophiles to attack alkyl halides. Even if carboxylate ions are weak nucleophiles, could they potentially participate in SN1? For example, could you add sodium acetate to tert-butyl chloride to make tert-butyl acetate by SN1?

Vnaraya3,

carbanions like n-butyl lithium are very basic, and do not make good nucleophiles. Remember that basicity increases up the periodic table and nucleophilicity increases down the periodic table.

For example, the reaction you propose would most likely yield 1-butene, butane, and lithium chloride in an E2 type reaction.

As for carboxylates nucleophiles, they are used in substitution reactions as you suggested, but there are better ways to make an ester. As I mentioned before oxygen anions are usually not nucleophilic, so the yield would most likely be low. Also people avoid reacting carboxylates with alkyl halides if they can, because alkyl halides are toxic and often pricey.

[orgopete]

Re: esters and SN1/SN2
Because SN1 reactions require more easily formed carbocations, such as tertiary halides, they suffer from competing elimination reactions. Although I can't say never, but I cannot think of any preparative SN1 reactions.

SN2 alkylation of carboxylates is a common method to make esters.

Re: coupling reactions
Good question, but I don't know the answer. If I had to guess, I'd be inclined to think it has to do with several issues. Alkyl lithium reagents are generally coordinated as tetramers, hexamers, etc and that may reduce their ability to act as nucleophiles. Another reason may be the degree they may catalyze elimination reactions as well as attack on the halide. In order to attack a carbon, polarization of the bond would probably be helpful, however the more electro withdrawing the atom is, the greater the attack on the halide is likely to be. That is, while an iodide would be a good leaving group, it may also increase elimination and transmetallation reactions.

For the above reasons, use of organometallic reagents may explain their use. If there were a prior transmetallation reaction with a transition metal, this may avoid some of the conditions I have wondered about.

[Babcock_Hall]

Gilman reagents may be better choices for the type of coupling reactions you are envisioning.