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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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Which one is more stable? Keto or enol form?

The image shows the structure of the compound in consideration. I am confused if the enol form is stabler due to aromatic ring presence or the keto form due to extended conjugation. Also the enol form ...
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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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154 views

Which has more enol content?

According to me, resonance in {a} is more effective than {b}. And for monocyclic ketones, enol has very less content. I say {1} has lesser enol than {2}. Which is right?
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Tautomerism in phenyl substituted compounds

Why doea phenyl substituted compounds have more enol content? For example, in almost all benzyl glyoxals and diarylmethanes, the enol content range up to a 100% I tried to see the effect of ...
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148 views

Number of enolizable hydrogen in 2-methyl cyclohex-2-en-1-one? [duplicate]

The number of enolizable hydrogen according to me are four , but the answer given for the question says it has 7 enolizable hydrogen . Where are the rest of them ?
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138 views

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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2answers
152 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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1answer
178 views

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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247 views

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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2answers
282 views

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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1answer
175 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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1answer
147 views

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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1answer
574 views

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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1answer
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What is the keto form of a hexahydroxybenzene?

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 shown below:
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2answers
590 views

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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1answer
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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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1answer
201 views

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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Enol content of acetylacetone and ethyl acetoacetate

Why is the enol content of acetylacetone higher than that of acetoacetic ester? Hydrogen bonding stabilisation is present in enol form of both of them. I cannot figure out which factor makes one ...
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How can an α,β-unsaturated ketone tautomerise?

I was taught that for aldehydes and ketone to exhibit keto-enol tautomerism, it is essential that there must be at least one α-hydrogen. For example, acetophenone and butan-2-one show keto-enol ...
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1answer
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Why are the secondary alpha hydrogens more acidic than primary alpha hydrogens (keto-enol tautomerization)?

I learned in organic chemistry that secondary/tertiary carbanions are less stable than primary carbanions and therefore primary hydrogens are MORE acidic than secondary/tertiary hydrogens. But lets ...
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Why is the thione tautomeric form of 2-Mercaptopyridine favoured?

During some organic chemistry studies (through an old online course material) I ran into a doubt about the equilibrium in tautomeric forms of some heteroaromatics. First, the context: On the course ...
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Why oxime is more stable corresponding nitroso tautomer?

We know,generally, keto tautomeric is more stable corresponding enol.(please explain it apart from thermodynamic explanation) Nitroso is analogous to keto form and oxime is analogous to enol form. ...
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On the oxyacids of +III pnictogens and +IV chalcogens

Phosphorus in its $\mathrm{+III}$ oxidation state is known to exist as the phosphonic acid tautomer rather than phosphorous acid one. All salts isolated containing $\ce{H2PO3-}$ are (to the best of my ...
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Sulfurous acid tautomerisation

In the structure of $\ce{H2SO3}$ there is a lone pair on sulfur. Why can't sulfur make a bond with one of the hydrogen atoms and a double bond with oxygen to avoid lone pair?like given below because ...
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Is carbonyl-enol tautomerization only intermolecular or can it be intramolecular?

During workup of a conjugate addition reaction, it is likely that protonation occurs at the oxygen of the enolate formed. See discussion here: Do enolates get protonated at the carbon or oxygen atom? ...
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Is there any possibility of tautomerisation to en-ol form?

In the picture, you can see the bridge whose end points are in para relation (for making the image clear). Now, what my friend said is that there is no possibility of tautomerisation as there is no H ...
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1answer
934 views

Comparison of enol content

How can we find the order of percentage of enol form of the compounds in the following equilibria? Percentage of enol form in x is highest as due to aromaticity. But how can we compare that for y and ...
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3answers
737 views

Which tautomer of hexane-2,4-dione is more stable?

Which tautomer will be more stable? Both 1 and 2 show intramolecular hydrogen bonding and form 6 membered cyclic ring, thus increasing the stability. I think I need to compare the effect of the two ...
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1answer
1k views

Which of the following has higher enol content?

Which of the following has higher enol content? The enol form of (A) and (B) is: Both the enols have hydrogen bonding. If the oxygen were to accept the pi electrns from carbon forming a carbocation ...
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1answer
475 views

Are Isopropyl Alcohol (2-Propanol) and 1-Propanol tautomers? [closed]

They both are structural isomers, but are they tautomers too?
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What is the enol form of 4-methylcyclohex-2-en-1-one?

What is the enol form of this compound? I have made an attempt, but it doesn't look quite right. Also which hydrogen should be taken off (left or right hand side of the carbonyl)? And I dont think ...
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1answer
420 views

What is the role of acid in keto enol tautomerism [closed]

I have heard about an acid acting as a catalyst in keto enol tatutomerism.I have yet to understand the mechanism of the reaction though.pictorial depictions are welcome.
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According to a condtion for tautomerisation to take place , what does one mean by, A-H bond should be in conjugation with polar pi bond?

What does one mean by, A-H (where A is sp3 hybridised) bond should be in conjugation with polar pi bond and Hydrogen with it should most acidic in the compound ?
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Can a tertiary enamine tautomerize to an imine?

Which of the following compounds does not show tautomerism? The correct answer is (a), and I'm curious if this is because to show tautomerism, there can't be any net charge. For instance, ketones ...
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1answer
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Dieckmann condensation's final protonation step

This is the Wikipedia image for the reaction mechanism: In the final protonation step, why does the enol tautomerize to the keto form? In the enol form the carbon-carbon double bond is in ...
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1answer
222 views

Why interconversion in tautomers is so rapid?

Looking at the examples in Tautomer on Wikipedia, it seems that the hydrogen needs to travel a significant distance (~20Å) for the interconversion to take place. What lets it happen so fast? Why ...
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1answer
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Why tautomers are considered to be the same chemical compound?

Because of the rapid interconversion, tautomers are generally considered to be the same chemical compound. (Wikipedia) But looking at the examples provided on that same Wikipedia article, it is ...
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2answers
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alpha-hydrogen atom and keto-enol tautomerism

The following is an extract from my book- For an aldehyde or a ketone to exhibit keto-enol tautomerism, it is essential that it must have atleast one $\alpha$-hydrogen atom. Thus, acetophenone, ...
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1answer
390 views

Dependence of steric hinderance on enol content

The following is extract from my book- To illustrate this, let us consider the enol contents of acetyacetone and $\alpha$ - methylacetylacetone. Although both the enols are stabilized by H bonding ...
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1answer
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Why do only ketones exhibit keto-enol tautomerism?

Why can't esters or acids or their derivatives exhibit tautomerism? I mean if they did, then there would be a conjugation between lone pair electrons of oxygen and pi electrons adding to their ...
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2answers
611 views

Can Ketones next to a Nitrogen hetero atom tautomerise?

I worry that the electronegative N will stabilise keto form so much that equilibrium will be so far towards keto it would be unreasonable to call the enolisiation process a factor
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1answer
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Enolizablity of pyruvate and lactate

I understand that to create an enol, you simply eliminate a proton alpha to the relevant $\ce{C=O}$ and then tack the proton onto the $\ce{O}$ and there you have it — an alkene and an alcohol — or ...
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Which is the more stable enol form?

If I understand correctly, when we go from a keto to an enol form, we simply abstract an alpha proton and thereby create a double bond to a carbon bearing the hydroxyl functional group. When ...
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1answer
309 views

Major form of methyl 3-hydroxy pent-2-enoate?

I came across this question in a test: The enol form is the ________ form for 3-hydroxy pent-2-enoate? (major/minor) My argument is that the enol form must be more stable because of hydrogen ...
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How large is the energy difference between keto- and enol-form of guanine and uracil?

The nucleobases in DNA and RNA are generally present in the keto-form, and not in the enol-form. As an interesting historical note, James Watson and Francis Crick did initially believe them to adopt ...