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![[Post New]](/templates/default/images/icon_minipost_new.gif) 7 Dec 2007 11:48:52 IST
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Given any conjugate base, how to determine whether it acts predominantly as a base or as a nucleophile?Does it depend on the nature of solvent ( polar protic or aprotic)
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God has given you one face, and you
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~William Shakespeare
You were born an original. Don't die a copy.
~John Mason |
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7 Dec 2007 11:59:30 IST
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A polar protic solvent is one that contains an O-H or N-H bond. A polar aprotic solvent is one that does not contain an O-H or N-H bond. Water (H-O-H) or acetic acid (CH3-C(=O)OH) are representative polar protic solvents.
A polar aprotic solvent is acetone (CH3-C(=O)-CH3).
In chemical reactions the use of polar protic solvents favors the SN1 reaction mechanism, while polar aprotic solvents favor the SN2 reaction mechanism.
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7 Dec 2007 12:07:40 IST
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As far as i remember, the answer of this question will depend on the basicity as well as the structure of the substrate.
A strong base will favour elimination.
A 1 degree substrate favours substitution.
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7 Dec 2007 14:01:56 IST
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Hey guys, u havent answered my q ...................at the first place how to distinguish between a base and a nucleophile?
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God has given you one face, and you
make yourself another.
~William Shakespeare
You were born an original. Don't die a copy.
~John Mason |
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7 Dec 2007 14:05:31 IST
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A nucleophile is a Lewis base, i.e. an electron pair donor. Any reagent that contains an atom with at least one lone pair of electrons is a potential nucleophile.
Common examples include halide ions such as -:I and -:Br, hydroxide ion , -:OH, water, H2O:, and ammonia, :NH3.
is ur doubt regarding when SN1 or SN2 takes place????/
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7 Dec 2007 14:14:03 IST
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Nope bro..............
I have read in my notes that 1,2 Dimethyl halide when reacted with ROH gives Prop-1-ene as the major product . Here ROH acts as a base
The same compound when reacted with water gives an alcohol(prpan 2- ol) as major product. Here Water acts as a nuclophile.............
My question is how can we say whether a given conjugate base acts as a base or a nucleophile
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~William Shakespeare
You were born an original. Don't die a copy.
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the first reaction is an elimination reaction that takes place in an alcoholic media
the second reaction is a substitution reaction that takes place in aqueous media
the answer depends on the medium of solvent generally water favours subs and alcohol favours elimination
as in both reactions OH- is the base cum nucleophile
in alcohol R is a +I group so electrons are slightly displaced towards OH- so OH- gets a strong -ve charge and hence can act as a base which is not in the case of water
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7 Dec 2007 14:29:55 IST
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Thank u......i got it.........
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God has given you one face, and you
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~William Shakespeare
You were born an original. Don't die a copy.
~John Mason |
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