IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry - plz tell me the concept n explanation of...

sonal_01

please explain me about carbanions n carbocations
how to identify n reacn based on this concept

sandeepramesh

the pathway in which the more stable carbocation is formed will be the favoured pathway Mr. Green

iberis22

A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents and a total of eight valence electrons.

A carbocation is an ion with a positively-charged carbon atom with a "sextet", i.e. it has only six electrons in its outer valence shell instead of the eight valence electrons.

To identify the reactions involved, first of all learn the methods of generation of carbocations and carbanions. Once you know what reagent generates which species, you will get to know which ion is involved in the given

reaction.

sandeepramesh

That is bcos the transition state is stabilised

I have a sneaky feeling that u asked sth else in ur ques. What are the full forms of the abbrvs u used in the question?

viswanath

carbocations and carbanions are the products of heterolytic fission. carbocations have +ve charge and carbanions have -ve charge. the carbon in carbocation is a sextet so its tertiary form is stabler than secondary which inturn is stabler than primary due to the electron releasing properties of the alkyl groups.
carbanions have negative charge and has charge donating ability and so its primary form is stabler than secondary form which is stabler than tertiary

iberis22

Carbocations

Stability:

The general stability order of simple alkyl carbocations is: (most stable) 3^o > 2^o > 1^o > methyl (least stable)

This is because alkyl groups are weakly electron donating due to hyperconjugation and inductive effects. Resonance effects can further stabilise carbocations when present.

Structure:

A simple representation of a carbocation

Alkyl carbocations are sp² hybridised, planar systems at the cationic C centre.
The p-orbital that is not utilised in the hybrids is empty and is often shown bearing the positive charge since it represents the orbital available to accept electrons.

Reactivity:

As they have an incomplete octet, carbocations are excellent electrophiles and react readily with nucleophiles (substitution).
Alternatively, loss of H⁺can generate a p bond (elimination).

iberis22

Reactions involving carbanion :

1. Aldol condensation

2. Claisen condensation

3. Reformatsky reaction

4. Wittig reaction

5. Alkylation/Acylation

eistien

lemme see!!!

these are certain imp reactions you need to be sure of !!!!

illustrate using examples these named reactions

1> bergius reaction

2> pthalien reaction

3>Mulliken Barker reaction

4> strecker's synthesis

5>EOSIN

6>Darzen

7>Sommelet

8>Vilsmeir formylation

9>Zeisel's method

plz post your answers and lemme know what you dunno so that i can post the answers for those reactions lets start!!!! i hope this will be useful for everybody!!!

tarinbansal

Mr. eistien,

R U sure these reactions are is our syllabus, becoz except Sommlet, I hav not even heard the names of these reactions.

sandeepramesh

ive heard of all of them

One referrence id give you all is this

http://wikipedia.org/

if you know where and what to search, it becomes easy :D

tarinbansal

Its not abt whether U hav heard abt them or not.
The main ques is whether these reactions are there in JEE syllabus or not?

sandeepramesh

i dont care whether they are or not, i read it for the sake of learning the subject rather than for the specific and narrow minded of thought of the jee itself Razz

tarinbansal

Its gud that U R not narrow minded but it wud hav been better if U wud hav answered my ques straightaway.

I just wanted to know whether they are there or not, if U dont know then simply say that.

sandeepramesh

they arent there happy?! Razz

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