If carbon is a highly electronegative element, why are alkyl groups considered to be electron donating groups?

Asked by deepti_walvekar | 22nd Oct, 2010, 12:00: AM

Expert Answer:

Dear student
An alkyl group is a monovalent group ( R- ), whenever it is bonded to some other group or part of some other molecule it has a tendency to donate electrons. It is an electron donating group.
(except in case of Metal carbides or Grignards reagent where it is electron attracting group)
In an alkyl group, for example, in methyl group carbon is linked to three hydrogen atoms. Carbon is more electronegative than hydrogen. So carbon pulls bonded electrons nearer to itself and accquires very slight negative charge (delta-) and correspondingly hydrogen lose hold over bonded electrons and acquires  slight positive charge (indicated by delta +). Thus electron density increases near carbon, which can be transfered to the next attached group.

Thus alkyl group are electrin releasing or electron donating in nature. In ethyl group (CH3-CH2-) this effect will be more than methyl group. The CH3 part releases elecrons to the next carbon plus two hydrogens also make contributions. The net electron releasing effect of ethyl group is more than that of a methyl group.
We hope that clarifies your query.
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Answered by  | 22nd Oct, 2010, 09:50: AM

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