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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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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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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150 views

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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2answers
88 views

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 ...
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1answer
62 views

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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1answer
106 views

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 acids the ...
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49 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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74 views

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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120 views

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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107 views

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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101 views

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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702 views

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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356 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
271 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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322 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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1answer
558 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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749 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
287 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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233 views

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
240 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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865 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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339 views

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 ...
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772 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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678 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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223 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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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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930 views

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 is the oxime tautomer more stable than its corresponding nitroso isomer?

We know, generally, that the keto tautomer is more stable than the corresponding enol tautomer. I would appreciate an explanation that goes beyond the thermodynamic reasoning, too. In the nitroso-...
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278 views

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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462 views

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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587 views

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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479 views

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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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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999 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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2k 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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571 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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713 views

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
529 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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92 views

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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201 views

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
348 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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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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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
496 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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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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701 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