Organic Chemistry: Sub/Elim Reactions

[atavistic]

Homework Statement

1)$$(CH_3)_3CCH(OH)CH_3$$+ HBr ->

[hide=My View]I believe reaction should be elimination because $$Br^ -$$ is a weaker nucleophile than $$OH^ -$$ so it cannot substitute it.[/hide]

2)$$CH_3CH_2CHBrCH_3$$ + $$EtO^ -$$->

[hide]Substitution?[/hide]

3) Compare the nucleophilicity of$$NH_3$$ and $$PH_3$$

[hide]$$NH_3$$ has more $$e^ -$$ density so $$NH_3 > PH_3$$[/hide]

Will the following reactions be primarily substitution or elimination?

$$CH_3CH(Br)CH_3 + OH^ - (H_2O) - >$$

[hide]$$OH^ -$$is stabilized in water so can't go Sn2,it can go Sn1 though and maybe some elimination.[/hide]

$$CH_3CH(Br)CH_3 + OH^ - (Ethanol) - >$$

[hide]Isnt this case almost the same as above?[/hide]

 

[Spirochete]

edit: mental note- Edit does not equal quote

 

[Spirochete]

I've helped with these questions but you should probably review the rules for the criteria for Sn2/E2 and Sn1/E1. Remember that Sn2 and Sn1 are both substitutions but they happen under very different conditions. Same with E2/E1.

1) Nope. In the mechanism HBr protonates the alcohol to make a good leaving group. With secondary carbons the protonated hydroxyl group can leave as water, forming a carbocation that's attacked by bromine. This makes the overall mechanism. . . .

2) Secondary alkyl halide plus strong base gives a mix of substitution/elimination

3) Depends on the solvent type. NH3 is more basic, making it a better nucleophile in aprotic solvents. PH3 is less basic but is also larger and more polarizable. In protic solvent PH3 would be the better nucleophile because NH3 is tied up more by the protic solvent.

4) I forget which type of solvent (protic or aprotic) facilitates substitution. You'll have to look that up. I can tell you that you're not going to get any Sn1/E1 with such a strong base. This is a general rule.

5) Looks similar except hydroxide could deprotonate ethanol giving you a mixture of products.

edit: misread first question.