39They generally work but yeah, they should not be thought of as the benchmark to products...the benchmark is stability alone. An old dialog of mine..."Everything in organic is attributed to, or wants a piece of, stability" :P
1I want some explanation on
1."wat is bulkiness"?
2."how bulky is sufficiently bulk to turn the tables around for an expected reaction which does not take place the expected way!"(i mean to change major products to minor products in a reaction)
1
vishuboy
·2011-05-13 07:02:12
Bulk is the same as its literal sense. Like in case of a nucleophilicity, lets compare it with a fat man (bulkier), he can't run faster than a slim man. So when you see some huge molecule acting as a nucleophile, you can be sure that it won't react as fast as other lighter molecules.
Now how much bulk is bulkier is a matter of experience. Most of the times, chemists do experiments and devise a mechanism to it. So, if some product is found to be major, we can think out some conditions why that happened over the other product. Maybe the temp? or catalyst's presence or the SIZE of the molecule!
There may be some factors which i am not vary of, but as far as what I've learnt yet from my teachers and books, this is what I can say :). :)
39
Pritish Chakraborty
·2011-05-13 10:11:50
1. What vishu said.
2. Sometimes even one methyl group can be enough to lessen %age of major product by a reasonable margin! Such is the world of organic chemistry. Let me give you an example -:
(In the original substitution reaction, there was no beta methyl group present. In that case, 90% substitution product and 10% elimination product had formed. Hence this is a sizeable difference)
1
chinmaya
·2011-05-13 12:15:39
The example u gave was exatly i was looking for....during exams we have to make PREDICTIONS.And i don't think that having a methyl at B-Carbon in all the reations would have same effect!...so u see i m feeling pity at myself as a chemistry student[2]
39
Pritish Chakraborty
·2011-05-13 12:50:03
Depends on the reaction. SN2 requires axial backside attack, and the methyl group at the beta position is a bit of a hindrance. Note that beyond the beta position, bulkiness doesn't really matter.
Go through my notes...you'll get lots of info to satisfy your hunger.
1
chinmaya
·2011-05-13 12:56:24
hmm...downloading them Thanks for the effort u put in scanning and uploading them!
waise how are u dong with ur semester exams,and yeah....m waiting for 17th[3][3]