2 - sn2 questions. re: nu-

[wall1two]

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Which of the following anions is the most nucleophilic in polar aprotic solvents?
a. iodide anion
b. hydroxide anion
c. water
d. chloride anion

correct: a
your answer: b
feedback: Incorrect. Hydroxide, with a negative charge, is more basic and more nucleophilic than water, but it is not the most nucleophilic anion shown here.For additional study, review: textbook section 11.6

I thought in a polor APROTIC nucleophilicity increases going up a group, so maybe the Cl or the hydroxide was what was i thinking (the Cl due to electronegativity reasons)



10
Which of the following undergoes the most rapid reaction with methyl iodide?
a. cyanide anion
b. methoxide anion
c. water
d. acetate anion
status: incorrect (0.0)
correct: b
your answer: a
feedback: Incorrect. When comparing the reactivity of nucleophiles with the same attacking atom, the nucleophilicity generally parallels basicity. Cyanide is not the strongest base shown here and it is not the most nucleophilic.For additional study, review: textbook section 11.6


meth-oxide i thought would would favor elimination and this is a primary halide so we are def talking SN2 here i would think. and i thought the cyanide anion is strong as hell, only hydrosulfide would be stronger?


please help me out i thought i had this down but now i'm not so sure

 

[FredDurst]

You didn't choose methoxide because of elimination? You can't have elimination on methyl iodide.

 

[wall1two]

correct, i did not choose methoxide because of elimination,we have a primary substrate so we are dealing with bi-molecular substitution. i just don't understand their reasoning.

 

[yappy]

Where are these Q's from?

 

[MrFantastik]

For the first question I completely agree with you. In polar aprotic you have a naked ion so its definitely the OH-. And like you said, even the Cl- is stronger than the I- in polar aprotic.

For the second question i think youre focusing too much on SN2 vs E2. You already know its gonna be SN2 so dont worry about if something favors elimination or not cuz theres no way thats gonna happen. Just pick the strongest nucleophile. So its between CN- and CH3O- ...and i think CH3O- is a stronger nucleophile (but im not 100%)

Either way I dont know how helpful this book is gonna be. Cuz for the first question is seems like its just plain wrong and for the second question it says "When comparing the reactivity of nucleophiles with the same attacking atom, the nucleophilicity generally parallels basicity." which is true but doesnt apply here cuz not all of the answers have the same attacking atom. So what book is this?

And dont worry...seems to me like you know your stuff. You knew when the book was wrong and why it was wrong too

 

[wall1two]

these are from the Mcmurry organic chem website the link is

http://www.brookscole.com/cgi-brook...uct_isbn_issn=0534389996&discipline_number=12

the website is based on the 6th edition, i have the 7th of the textbook (can be found cough illegally cough online along with the solution manual and they are great i suggest it) and in thier sn2 section they have a ranking of nucleophiles and their reaction rates (no units though, so must just be for comparison) and im guessing it is in a PROTIC solution based on their value for I-

nuc: rate
NH3 700
MeO- 10,000
I- 100,000
CN- 125,000
HS- 125,000