E-StoreSome important and lesser known points in Organic chem.
Hey frnds,
I have collected some important and not-so-known points of organic chemistry from my notes and assembled them here.
GOC
1-Carbocation stability- Ring expansion should always be given higher priority than tertiary carbocation.
2- If some unknown reactants are given to U and if U cant decide how to start, always give first priority to an acid-base reaction.
3- Carbene(:CCl2)- Triplet is more stable than singlet.
For :CF2- Singlet is more stable than triplet as it can have back-bonding in singlet carbene due to the presence of an empty orbital.
4- Benzyne - The inductive effect(and not resonance) of the group attached to benzene decides the orientation of incoming reagent becoz the triple bond of benzyne is sigma bond and not pi-bond.
5- In Ph-NH3+, NH3+ is slightly more para directing than meta(EXCEPTION).
ISOMERISM
1-Tautomerism - Acidic H should be released only from saturated C and not from unsaturated C.
2-Geometrical isomerism is not applicable in alkynes.
3- For a compound to be optically active, it should lag both plane of symmentry as well as centre of symmetry.If anyone of them is present in compound, it wud become optically inactive.
ALCOHOL,PHENOL & ETHER
1- 1,2 v/s 1,4 addition
Mechanisms are shown in figure.
1,4 product - Thermodynamically stable and is produced in long duration(for example-in reaction with NaBH4).
1,2 product- kinetically stable and is produced in short duration(for example- in reaction with LiAlH4).
=> Generally thermodynamically stable product is given.
2- U all must have read the preperation of alcohol by ketone and grignard reagent. There's an exception to this reaction-
Ketone = Me2CH - CO - CHMe2
Grignard Reagent = Me2CH-MgBr
In the reaction with these reagents, alcohol is not formed by the usual mechanism in which R- attacks C=O. In this reaction, the ketone is reduced by H- from grignard reagent. The concerted mechanism in shown in figure.
If we take a ketone/G.R. bigger than this one => No reaction.
If we take a ketone/G.R. smaller than this one => Normal reaction
Means, the steric hindrance of both the molecules matter and not only anyone.
3 - Luca's test- We all know that 3o alcohols give immediate turbidity with luca's reagent. BUT there are 2 more alcohols which are not 3o but still give immediate turbidity with Luca's reagent(dont ask me the mechanism 
). They are-
Ph-CH2-OH and CH2=CH-CH2OH
4- Williamson's Etherification - The halide used should not be aryl halide becoz the reaction wont take place due to partial double bond character of C-X bond by resonance.
Till now I have been able to collect only these points. Will post more as soon as I assemble them.
Hope these points help U in ur exams.
All the best!!! 
Comments (20)
Lemme get his reply and then I wud confirm whether its sigma or pi.
Now some facts to support me-
1-The extra bond doesnt effect the aromaticity of the ring(given in Jerry March's advanced organic chem). It wud have effected only when it was pi but as it doesnt effect, it means it is not pi.
2-This bond is between sp2 hybridised orbitals. Now sigma bonds are formed between hybridised orbitals and pi bonds are formed between unhybridised orbitals. And here hybridised orbitals are taking part in bonding, so it shud be sigma.
This concept was taught to me by my sir and if U all are saying that its pi and NOT sigma, its OK. I have asked it from some more teachers and will tell U the correct answer as soon as I get their replies.
the third bond is not formed by pure p-orbitals. Its formed by sp2 orbitals.
The extra bond in benzyne NEITHER SIGMA NOR PI.
Bond is formed when orbitals overlap. In case of benzyne, orbitals DONT overlap. Its just that as C-H bonds are broken, so the sp2 orbitals are tilted and the electron cloud density becomes high in that region and we denote it by showing a bond.
Think urself, if it was a legal bond, means its a triple bond, means C is sp hybridised. And if C is sp hybridised, how can it bend? But the angles of benzene remain almost same. Means it is NOT a triple bond and that third bond is not a legal bond.
Now why it is effected by inductive effect and not resonance? Its becoz its the inductive effect which pushes/pulls the electron cloud and hence the incoming nucleophile is directed accordingly.
Now, alteast I am pretty sure abt this answer becoz this teacher is a post-graduate in chem from IIT-D and is one of the best teacher for Organic at Brilliant Tutorials, Delhi.
It was never there in the course. :P It wasnt there this yr also. But this topic is generally taught everywhere.
Refer to Organic chemistry by morrison and boyd (page no. 998 of sixth edition)
And if you don't have it ,here is a quote from the book page 998
" The sideways overlap of sp2 orbitals forms a pi bond out of the plane of the aromatic pi cloud "
PS : dont say u dont even believe morrison and boyd
Its OK buddy,havent U read my last comment on this thread?
I have accepted that its NOT a sigma bond and have posted the correct answer there.
But again, sorry. My teacher is higher than Morrison boyd for me.
He said that many books and ppl call it a pi bond but its NOT actually a pi. Actually it is neither a sigma nor a pi............ Read my explanation in my last post. I am not explaining the whole thing again here. :-|
Preparing for IIT-JEE ?
Arihant Revision Package for IIT JEE - Books, Practice Tests + Rank Predictor
@ INR 1,995/-
For Quick Info
|
|
|
|
|
| 35,229,755 Engineering Questions Attempted |
6,69,530 Visitors Monthly |
79 Engg. Exam Covered |
508 Students Currently Online |
Connect with Us  |
 |
