Question

Keto-enol Problems 21.9 Among each pair, which keto molecule will have the most enol content? Hint: draw the enol for each and then decide which will have more enol. alla mo 21.10 Write reasonable mechanisms to explain the following racemization rxns. 21.11 Write reasonable mechanisms for the following rxns. como mi B-addition Problems 21.12 Draw the product for the following B-addition rxns.

Answer 1

the equillibrium forms. The two (8.19) Keto-end tautomerism is nothing but that exists between the keto and end forms are also known as tautomers. for eq; " R%&M end form kelo form : The two forms are interconverted to each other by shift in hydrogen. Keto form is the one having cao, and the end form contains c= c adjacent to Oh. *The keto form is regarded as most thermodynamically stable forme as compared to end As in keto The bond energies of The bond energies of (= c-c c-H) y > (c=ct c-oto-H) 7 S * But stable which in various tece cases the end forms becomes more due to eat and various stabilising factores shifts the equillibrium towards the end form:

1. The most famous example to show this is of Phanol is making BD LA end form Keto form . The end form is very much stable as it - the species aromatic here. Now here get to our question to apply the . concept Please note here that the Keto end tautomerism requires the presence o of cidic of hydrogen. And here the L- carbon do not contain any H . -hydrogen.. . DO NOT show keto end I tautomerism . Keto here a- carbon hai 1-4-hydrogen : This displays keto eno! tautomerism.

ont of 18 ) ,l) has more and content no H at this a OH conjugated in and form in non conjugated Keto form - in brefers to have more and content than (1) as in enda form of (w, it is very much stabilised by conjugation -

Therefore o all aro e od H bond cal H - enol form In this the end form is very much stabilised by the hydrogen bonding that makes a stable 6-memin ring. This can shift eqh almost comoletely towards end from oro-oro here no such t-banai stabilisation is present

Therefore enol content other corre