SOLVENTS???? confusion. please help

[navneetdh]

I must have gone over solvents so many times but i just dont get it.

there are polar solvents and non polar solvents

then protic and aprotic

then polar protic and is there polar aprotic?

then nucleophillic solvents??


I am extremely confused. which one is which. And what and where are they helpful in terms of SN1 SN2 E1 and E2 reactions.

is there some sort of a list of names i should memorize?


please help. thanks

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[Talib]

Polar Protic solvents are the ones that have O-H, N-H, and S-H bonds ( can form hydrogen bonds and solvate cations and anions).
These are preferred in Sn1 reactions because they can solvate both the cation and the anion that are formed in the rate determining step
R-X ----> R+ + X-
In these solvents, the larger the nucleophile the faster the reaction.
Ex: water, methanol, ethanol, amines.


Polar aprotic and nonpolar are the ones that do not have O-H, N-H, and S-H bonds ( can not form hydrogen bondings and solvate only the cations).
These are preferred in Sn2 reactions because the leave the anion (Nucleophile) unsolvated which increaseas the reaction rate since the Nucleophile appears in the rate determining step.
In these solvents, the smaller the nucleophile (more basicity) the faster the reaction.
Ex: DMSO, DMF, HMPA, Acetone.

Hope this will help, send me if u need anything else buddy.

 

[navneetdh]

Polar Protic solvents are the ones that have O-H, N-H, and S-H bonds ( can form hydrogen bonds and solvate cations and anions).
These are preferred in Sn1 reactions because they can solvate both the cation and the anion that are formed in the rate determining step
R-X ----> R+ + X-
In these solvents, the larger the nucleophile the faster the reaction.
Ex: water, methanol, ethanol, amines.


Polar aprotic and nonpolar are the ones that do not have O-H, N-H, and S-H bonds ( can not form hydrogen bondings and solvate only the cations).
These are preferred in Sn2 reactions because the leave the anion (Nucleophile) unsolvated which increaseas the reaction rate since the Nucleophile appears in the rate determining step.
In these solvents, the smaller the nucleophile (more basicity) the faster the reaction.
Ex: DMSO, DMF, HMPA, Acetone.

Hope this will help, send me if u need anything else buddy.

o wow that makes a lot more sense now. Thanks a ton. 🙂

 

[prsndwg]

Polar Protic solvents are the ones that have O-H, N-H, and S-H bonds ( can form hydrogen bonds and solvate cations and anions).
These are preferred in Sn1 reactions because they can solvate both the cation and the anion that are formed in the rate determining step
R-X ----> R+ + X-
In these solvents, the larger the nucleophile the faster the reaction.
Ex: water, methanol, ethanol, amines.

I always thought that the polar protic solvents w/ strong nucleophile were E2 rxns! corret me if i am wrong please..


Polar aprotic and nonpolar are the ones that do not have O-H, N-H, and S-H bonds ( can not form hydrogen bondings and solvate only the cations).
These are preferred in Sn2 reactions because the leave the anion (Nucleophile) unsolvated which increaseas the reaction rate since the Nucleophile appears in the rate determining step.
In these solvents, the smaller the nucleophile (more basicity) the faster the reaction.
Ex: DMSO, DMF, HMPA, Acetone.

Hope this will help, send me if u need anything else buddy.

.

 

[nze82]

I always thought that the polar protic solvents w/ strong nucleophile were E2 rxns! corret me if i am wrong please...

.

You are wrong!
Polar protic solvents are those solvents capable of forming hydrogen bonds. The fact that these solvents are polar (hence attracted to charge) and can establish hydrogen bonds allows them to stabilize the charge on the carbocation. E2 reaction mechanism doesn't involve any intermediate carbocations. Therefore, polar protic solvents won't do much in such reactions. On the other hand, they stabilize the charge of the intermediate carbocation that forms during E1 reactions (1st order reaction rates in general E1/SN1). By doing so, they lower the activation energy of the reaction and favor the reaction to proceed faster.

 

[navneetdh]

i was going through solvents again and I was wondering if E2 also uses polar aprotic solvents??? coz they may not need the stabalization of an carbocation either.

polar aprotic are specified as sn2 solvents, are there any specifications for E2?

 

[nze82]

i was going through solvents again and I was wondering if E2 also uses polar aprotic solvents??? coz they may not need the stabalization of an carbocation either.

polar aprotic are specified as sn2 solvents, are there any specifications for E2?

All 2nd order reactions (SN2/E2) are favored by polar aporotic solvents, while all 1st order reactions (SN1/E1) are favored by polar protic solvents.