Questions tagged [tautomer]

Tautomers are constitutional isomers of (usually organic) compounds that readily interconvert into each other. This tag is also suitable for tautomerization, the isomerization by which tautomers are interconverted. It may synonymously specified for questions about tautomerism.

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Acid hydrolysis of Birch-reduced Anisole

The following is a question from Advanced problems in organic chemistry by MS Chouhan: Product $A$ is rather straightforward: and on acidic hydrolysis, the following reaction takes place: Here the ...
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2 answers
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2-Pyridone tautomer ratio

The following excerpts from different textbooks about keto–enol tautomerism in pyridones seem to be contradictory. Could someone explain which one is right? MARCH’S ADVANCED ORGANIC CHEMISTRY pg-103 ...
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Do ketdione molecules have diol tautomers?

In my chemistry textbook there's a keto-enol tautomerism example: But will it also be in equilibrium with pent-1,3-dien-2,4-diol in a reaction like this or will it just be a functional isomer?
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Number of enol forms of acetylacetone

Here is what I tried: These are the two enolic forms that I could make. So according to me, the total number of distinct enol forms of acetylacetone is $2$. But the answer is 3, what am I missing?
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Tautomerism between cyclohex-2-en-1-one and cyclohex-3-en-1-one

I think cyclohex-2-en-1-one and cyclohex-3-en-1-one should undergo tautomerism as shown below: I'm calling it tautomerism because of it's similarity with the tautomerism mechanism in basic medium. I ...
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4 votes
3 answers
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Finding the major contributing tautomer of 1-(propan-2-yl)-1,2,3,5-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-one [closed]

I am having a problem generating the correct tautomer for 1-(propan-2-yl)-1,2,3,5-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-one. I am told by my collaborator that the one I am generating is wrong. I am ...
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Keto-Enol tautomerism acidity of α Hydrogen vs stability of double bond [duplicate]

If I consider a ketone that has an ethyl group and a methyl group attached to it. The α-Hydrogen of the methyl group would be more acidic than that of the ethyl group due to -I effect of the adjacent ...
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Keto-enol tautomerism in a bicyclo compound

Question Which one is more stable- the keto or enol form. The compound given is this: Solution The enol form would violate Bredt's Rule and would therefore be unstable. Hence the keto form is more ...
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Determining the most stable enolic form of 1-phenylbutane-1,3-dione?

Question Which form of 1-phenylbutane-1,3-dione is more stable? Answer 3-hydroxy-1-phenylbut-2-en-1-one My question I've been told that between the above two, 3-hydroxy-1-phenylbut-2-en-1-one is ...
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Comparing the boiling points of common organic molecules

The order I was provided with is(comparing molecules of similar molecular mass from each); alkanes< ethers< esters< aldehydes< ketones<< alcohols<< carboxylic acids<< ...
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On the stabler tautomer in amide-imidic acid tautomerism

In the section on acid-catalysed hydrolysis of nitriles, this webpage has the following line of reasoning; ...the more stable amide tautomer predominates the (following) equilibrium. (credit) How ...
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Why is quinone mono oxime more stable than 4-nitrosophenol?

When we do nitrosation of phenols, we get para-nitrosophenol as the major product, which tautomerises to quinone mono oxime. This article states that it largely exists in the quinonoid form. My ...
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Is tautomerism in ketimines possible?

In a reaction between an aliphatic primary amine and a ketone, I could expect a ketimine as a product or intermediate. My question regards tautomerization of this intermediate: has tautomerization ...
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Which enol form is more stable?

I came across an example today while I was studying tautomerism. It is an example of tautomerism exhibited by acetylactone/1,3-diketone; given under the keto-enol systems under 1-3 migration/triad ...
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Find the major products when these cyclohexenone bromides react with caustic potash in alcoholic medium:

Question: Also find the order of the rates of the given reactions. Answer: The answer of this question is given as option 'D' ie. all products are identical, however I am getting the answer as ...
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Is a tautomer's stability compared with refernce to its initial compund [closed]

Considering the following example while comparing the enolic content in the product, am I supposed to compare its stability with reference to its initial state or am I supposed to compare it between ...
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Tautomerism in 3,5‐dimethyl‐4H‐pyrazole

How would tautomerism take place in 3,5‐dimethyl‐4H‐pyrazole? I am aware of nitro–aci nitro and keto–enol, but I haven't seen such a compound before. I recognize that a hydrazone formation was done ...
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Phenol vs 4-hydroxypyridine - Enol Content [duplicate]

Which has a higher enol content; phenol or 4-hydroxypyridine? The solution to this question in my book says that phenol has a higher enol content due to aromaticity. But 4-hydroxypyridine is also ...
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Which has a higher enol content between 4-Pyridone and Cyclohexa-2,5-dien-1-one?

I am new to organic chemistry but here is what I feel. 4-Pyridone will have a lower enol content as in its keto form it has higher resonance stabilisation due to the involvement of lone pairs on ...
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1 answer
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Why doesn't keto enol tautomerism take place in acid derivatives?

Why does keto enol tautomerism take place only in ketones and aldehydes? Why doesn't it take place in carboxylic acids, esters, amides, anhydrides and acid chlorides?
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2 answers
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Tautomer of acrolein

Are $\ce{CH2=CH-CH=O}$ and $\ce{CH2=C=CH-O-H}$ tautomers? There is only a shift of a hydrogen atom and a pi bond. So why are these two not tautomers?
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Why Nitroso tautomer is more stable than its oxime counterpart? [closed]

As I was looking for the answer of the question I found that it is explained using the Electronegativity difference concept. That's correct but I am unable to prove the same through the bond energy ...
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3 answers
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Which compound will have the most stable enol form?

Which compound will have the most stable enol form, Phloroglucinol or 4-Pyridone? My Thoughts: Both in their enol form are aromatic. I am not sure how do I compare their stabilities. The answer ...
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Stability of 4-pyridone vs 4-pyridinol

In kryptomerism assignment, there was a question to compare more stable tautomeric form between 4-pyridone (1) and 4-pyridinol (2): Answer: 4-pyridone. My friend gave two plausible reasons: $\ce{C=...
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Role of tautomerism and its difference from hyperconjugation [closed]

I would like to know the role of tautomerism, if any, in increasing stability of an organic compound. Moreover, how is it different from that of hyperconjugation? I know that hyperconjugation ...
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Do alpha hydroxy ketones give iodoform test

So, we know that alpha hydroxy ketones give tollens test as the tautomerise into their enol form and the then have an equilibrium between the 2 keto forms. So going ahead with the same logic. Do ...
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1 vote
1 answer
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Why does coumarin predominantly exist in keto form?

By applying the logic that phenol exists in enol form rather than keto form as it attains aromatic character, why is it not the case in coumarin?
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2 votes
2 answers
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How are there three possible tautomers of 2,2,4-trimethylheptane-3,5-dione? [closed]

The answer for the above question is three. But I am able to draw four structures: Where am I getting it wrong?
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3 votes
2 answers
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Which has the highest enol content?

Which of the following compound has highest enol content? The answer is an option (c) and I think the reason behind it is that there are two phenyl groups attached to it, hence there will be a good ...
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-1 votes
1 answer
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Enol content tautomers

I have figured out that 4 one will have the highest enol content of all, and the 1 structure would come after 4 in enol content, i.e 4 > 1. Then I got confused between the 2nd and the 3rd structures. ...
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2 votes
2 answers
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Will (3R,4S,5R)-1,3,4,5,6-pentahydroxyhexan-2-one tautomerise in nitric acid?

The following question was sent to me .The question is " Which of the following is A ?" The given answer was a,b,c Background If both ends of an aldose chain are oxidized to carboxylic ...
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2 votes
0 answers
140 views

Chirality with tautomers

This molecule has 6 peaks in its proton NMR. I think this is due to the following tautomerisation: However, I am unsure as to whether this molecule would be chiral, as it can freely interconvert ...
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What will be the major enol form of methyl acetoacetate?

I presume the best enol form would have a double bond between the two $\ce{C=O}$ so they're conjugated, but I'm not sure how the resonance would play out.
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1 answer
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Equilibrium Constants For Phenol Tautomers

I encountered the following equilibrium constant values for the keto-enol interconversions of phenol in Organic Chemistry (Solomons, Fryhle, Snyder, 3rd Edition): I wonder what could explain the ...
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1 answer
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Tautomerism in alkenes

Why doesn't but-2-ene exhibit tautomerism like alkenols? By transfer of 1 hydrogen from terminal CH₃ to the middle carbon and forming a double bond between the two?
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0 answers
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Acid catalyzed enolization and alpha hydrogen

In acidic catalyzed enolization of butan-2-one: We have 2 alpha hydrogens available. From the mechanism of acid catalyzed enolization there is a certain carbocation character at the carbonyl carbon ...
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2 votes
0 answers
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Number of enolizable hydrogens in 2-methylcyclohex-2-en-1-one [duplicate]

The number of enolizable hydrogen atoms according to me is four, but the answer given for the question says it has seven enolizable hydrogens. Where are the rest of them?
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-1 votes
2 answers
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What is the predominant enol tautomer of 1-phenylbutane-1,3-dione?

In 1-phenylbutane-1,3-dione (1), which enol tautomer will be predominant? Both carbonyl groups possess α-hydrogens, so can undergo keto-enol tautomerism. In particular, the carbonyl group on the ...
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3 votes
2 answers
654 views

Compound having the highest enol content will be?

The answer written in book is 3 but no solution is given. After referring to some other question I think that hydrogen bonding can take place in compounds like 3 but am not sure about it. Am I right ...
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13 votes
1 answer
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Stability of keto-enol vs. conjugation

I am trying to figure out which tautomer of creatinine: is more stable. We see that the enol tautomer is more highly conjugated: the $\pi$ electrons from the alcohol to the double bond to the $\pi$ ...
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5 votes
1 answer
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What is the most stable structure amongst the keto-enol tautomers of pentane-2,4-dione?

I was assigned the following question and I cannot decide which is the correct answer. Which is the most stable structure? (a) pentane-2,4-dione (b) 4-hydroxypent-4-en-2-one (c) (Z)-4-...
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3 votes
3 answers
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Why enol content of ethyl acetoacetate is more in toluene than water?

Ethyl Acetoacetate has enol content of 0.4% in water and 19.8% in toluene. What is the reason behind this? Does this anything have to do with the intramolecular hydrogen bonding in the enol form?
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4 votes
2 answers
503 views

Structure of the compound C9H7O2Cl?

A compound having formula $\ce{C9H7O2Cl}$ (O = oxygen) exists predominantly in enol form (A) and also in keto form (B). On oxidation with $\ce{KMnO4}$ it gives m-chlorobenzoic acid as one of the ...
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What anions does the loss of a proton from HOCN and HNCO produce? Are they same or different?

What anions does the loss of a proton from $\ce{HOCN}$ and $\ce{HNCO}$ produce? Are they same or different? Once, I had asked my teacher if $\ce{HCN}$ and $\ce{ HNC }$ are different or same compunds, ...
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2 votes
1 answer
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Deuteration of enone - mechanism?

What happens when the above compound is mixed with D2O (deuterated water)? As a result of tautomerism, I'd expect the 4H atoms, one alpha to carbonyl carbon, and three at gamma position; to be ...
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5 votes
1 answer
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In the bicarbonate ion, why can the hydrogen not bond to the carbon?

I've been studying electrophiles and nucleophiles recently, including how the carbonate ion ($\ce{CO3^2-}$) is stabilised through resonance. While drawing the model for bicarbonate, however, I ...
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5 votes
3 answers
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What is the keto form of a hexahydroxybenzene?

159. The keto isomer of the following compound is: The answer has been given as (c). I cannot seem to understand why is it not possible for the keto form to only have one OH convert into keto form ...
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7 votes
2 answers
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Ring chain tautomerization of hydroxyacetone

My chemistry textbook says that hydroxypropane-2-one and 1,2-epoxy-2-hydroxypropane are ring chain tautomers, but it did not mention the steps for conversion of one into the other. I tried to figure ...
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2 votes
1 answer
978 views

Rates of Keto-Enol Tautomerism

Are there any databases with rate constants for keto-enol tautomerism in small molecules? I'm looking for rate constants if possible.
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1 answer
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Enol or Keto form?

Which will be the major form among the two tautomeric forms? According to me, it should be enol form due to resonance stabilization as well has five membered ring formes througj hydrogen bonding. On ...
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