CSIR, GATE, JAM, IISc, and all other Chemistry Higher studies Exams has been changed their syllabus. If we analyze them quite precisely and it’s seems that many advanced are of research has been included. The previous year’s questions from those type exams are clearly indicated that, students must understand the fundamentals, and they must have reasoning ability to answer the question. In this view we wish to collect most important exam based reasoning questions and we discussed answer for them. It’s not only useful for competitive exams also for your interviews.
Today's Question:
2,4-pentanedione(A) in hexane exit 8% of keto tautomer and 92% of the enol tautomer.
Q1. Why (A) prefer to form B??
Q2. Give Reason: In water 2,4-penatanedione consist of 84% of keto and 16% enol tautomer.
Answer:
A1. Hydrogen Bonding.
A2. In water, The Keto tautomer is stabilized by hydrogen-bonding of its two carbonyl-oxygen atoms with the solvent, effectively nullifying one of the stabilizing influence in the enol tautomer.
The boiling point of ethanol is very much higher than that of its isomer, dimethyl ether. Why?
Answer:
Hydrogen Bonding. Hydrogen-bonding leads to an increase in intermolecular ‘aggregation’ forcesand is manifested particularly in the boiling point and solubility of organic compound. The boiling point is raised because energy is required to separate H –bonded molecules. That’s why ethanol boiling point is higher than that of dimethyl ether.
We can see other questions tomorrow.
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