ISOMERISM STRUCTURAL

DEAR STUDENTS 

To begin,i want to focus  on metamer .It  is observed that due to

difference in the in the nature of alkyl grps attached to polyvalent 

atom or functional group, we generally get confused with meta merism

and positional isomerism for e.g 2, Pentanone and 3, Pentanone appears

to be more than positional isomerism but we generalize this fact for metamer.

One should always remember the fact that more than one type of isomerism

is possible between two isomers similarly we can also notice that ring chain

isomers are also always functional isomers. 

I therefore advice you all to be very cautious will deciding the structural

isomer in the multiple option question .I have generally noticed that we have

a very casual attitude while  dealing with structural isomerism but it is often

seen that easy questions makes us feel  helpless.

Now taking up the second topic which is tautomerism, we the generally study

keto-enol from this section where importance of hydrogen bonding

(more enol content  in non polar solvent),extended conjugative system

(reactive methylene group) and the most important of them is the Aromatic

structure(1,3,5- Trihydroxy benzene from cyclohexane-1,3,5trione.)which

shifts the equilibrium in the desired direction. I would like to point out fudamental

difference between resonance and tautomerism that in resonance contributing

structure cannot be isolated whereas tautomeric structures can be isolated.

One should also check other branches  of tautomerism like Enamine-Ketimide,

Nitroso -isonitroso,Lactam-lactim and not to forget nitrous acid and

hydrocyanic acid form where latter is known for the dyad  system other are triad form.

Question : 2-pyridone is in equilibrium with 2-pyridonol,

which is the stable form between the  two?

Question:Why Cyclobutenone does not Enolize?

Question: Comment on  Diethyl malonate tautomeric form?