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Organic Chemistry

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27 Jun 2007 21:29:36 IST

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484

NUCLEOPHILE

None

plz tell which of the following is most reactive nucleophile & why?

1 CH3O-

2 (CH3)2CHo-

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MOHNISH

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Joined: 7 Jan 2007

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27 Jun 2007 21:52:27 IST

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I think the most reactive nucleophile among the two is:
(CH3)2CHO-
It is so because there are more +I groups present on it which increases the charge on the carbanion and decreases its stability.It is also due to the steric effect of these groups being more than the other carbocation,which makes it less stable.Less stability means more Reactivity.So (CH3)2CHO- is more reactive and less stable than CH3O-

Khinar Thukral

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27 Jun 2007 23:01:15 IST

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Hey see for all the nucleophillic substitutions reactions to be feasible the nucleophile should be reactive(i.e.more unstable) so that the reaction order as well as reaction rate.now the answer to Ur question is Ur second option.this is because since two ch3 groups are attached to the carbonyl group they will delocalize the negative charge (more than their ability to localize the partial charge on carbon atom due to the oxygen group) and hence it would attack more fiercely in search of the + charge.In general, the more basic the ion (the higher the pKa of the conjugate acid), the more reactive it is as a nucleophile. Polarizability is also important in the determination of the nucleophilicity: the easier it is to distort the electron cloud around an atom or molecule, the more readily it will react. e.g., the iodide ion (I?) is more nucleophilic than the fluoride ion (F?).

arun-rashi

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Joined: 19 Oct 2006

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28 Jun 2007 00:28:07 IST

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Nucleophilicity & Basicity r relaled but r diff terms Basicity is the affinity for a proton but Nucleophilicity is the ability to form bonds with C atoms it must be kept in mind that Basicity is thermodynamically controlled where as nucleophilicity is kinetically controlled for e.g iodide ion is weakest base amomg halides but it is best nucleophile due to solvation effect Similarly in the case given C₂H₅O^-1 is a better nucleophile although it is a weaker base than (CH₃)₂CHO^-1later even being a stronger base is a weaker nucleophile bec its large bulk hinders it from closely approaching the substrate.

syrap hat

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28 Jun 2007 08:50:11 IST

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the answer depends on the conditions of the reactions.
in normal cases (ch3)2-cho- is the answer on reasons stated above.

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