Questions tagged [stability]

Applied to a chemical species, the term expresses a thermodynamic property in reference to a standard, stating that one state is lower in energy than another. The tag should be applied to questions seeking answers with respect to the stability (or instability) of a certain chemical species, molecular entity and/or electronic structure. It must not be applied to questions about the reactivity of particular chemical species.

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55
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3answers
12k views

Why doesn't H₄O²⁺ exist?

I know this question has been asked previously but I cannot find a satisfactory explanation as to why is it so difficult for $\ce{H4O^2+}$ to exist. There are explanations that it is so because of $+2$...
37
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5answers
110k views

Difference between thermodynamic and kinetic stability

What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?
28
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3answers
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What is the reason for the exceptional stability of the cyclopropylmethyl carbocation?

Can someone explain this to me by drawing resonance structures for the cyclopropylmethyl carbocation please? Also one more question, is the tricyclopropylmethyl carbocation more stable than tropylium ...
26
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2answers
2k views

Which of the following is the more stable carbocation?

Which of the following is the more stable carbocation? I thought the 1st carbocation would be the more stable one as the pi-electron density of phenyl group can overlap with the vacant orbital on ...
26
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1answer
12k views

Relative stability of cis and trans cycloalkenes

Why is the stability of (Z)-cyclodecene 2 greater than that of (E)-cyclodecene 1? I'd think that since 1 contains a trans double bond instead of a cis double bond, it should experience less steric ...
26
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1answer
4k views

Why is cyclooctateraene shaped like a “tub” rather than a “chair”?

I understand that for cyclooctatetraene (COT) to "escape" the horrible prospect of becoming an anti-aromatic molecule, it must adopt a non-planar conformation. The widely touted conformation of COT ...
24
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4answers
5k views

Which molecule is more acidic: CHF3 or CHBr3?

I know that fluorine is more electronegative than bromine. However, because of the size of bromine, it is more stable with a negative charge. In the case of $\ce{HF}$ vs. $\ce{HBr}$, to me, $\ce{HBr}$ ...
24
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2answers
22k views

Carbocation stability order

I was wondering whether the following order (from here) is correct: In the first inequality, why did 9 hyperconjugations dominated resonance effect of benzene ring? In the last inequality doesn't ...
23
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3answers
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Why are noble gases stable

I was recently asked the question "Why are noble gases stable? with the expectation of providing an answer beyond the general explanation of "they have full valence layers" and I couldn't think of one....
22
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3answers
5k views

What makes an epoxide stable?

Overall ring strain seems to be a big issue when it comes to organic chemistry. That is why cyclopentane may be in an "envelope form" or why cyclobutane may be in a kinked, kite form. Both of these ...
22
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2answers
6k views

Are geminal disubstituted alkenes more stable than their cis/trans isomers?

I know for a fact that cis alkenes are less stable than trans alkenes due to steric repulsions. But what bugs me is the fact that why systems such as 2-methylprop-1-ene, where I believe steric ...
21
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1answer
11k views

Stability Comparison between the Tropylium and Tricyclopropylcarbinyl Carbocation

Why is the Tropylium carbocation less stable than the tricyclopropylcarbinyl carbocation? The tricyclopropylcarbinyl carbocation undergoes a sigma-tropic rearrangement whereas tropylium is highly ...
21
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2answers
494 views

Why are lithides not known?

In the last few decades, many alkalides - anions of alkali metals - have been synthesised. The most famous is undoubtedly that of sodium: $\ce{[Na(\text{2.2.2-cryptand})]+Na-}$, but the alkalides $\ce{...
20
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5answers
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Is the t-butyl carbocation more stable than the benzyl carbocation?

Various authors have different views regarding stability order of the benzyl and t-butyl carbocations. $$\ce{PhCH2+ ; (CH3)3C+}$$ In my opinion, resonance effect dominates, so the benzylic ...
20
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5answers
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Comparing the stabilities of allylic, benzylic, and tertiary radicals

Which is the most stable free radical among the given species? (1) $\ce{CH2=CH-CH2^.}$ (allyl radical) (2) $\ce{C6H5-CH2^.}$ (benzyl radical) (3) $\ce{(H3C)3C^.}$ (t-butyl radical) (4) $\ce{...
20
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2answers
4k views

What is the favoured geometry of chlorine trifluoride?

Why is the first structure on the left more stable than the second one on the right? In the first one the angle between the two pair of nonbonding electrons is about 120° which is a lot less than ...
20
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2answers
4k views

For a given element do heavier isotopes form stronger bonds than lighter isotopes?

I know that $\ce{C-D}$ and $\ce{C-T}$ bonds are stronger than $\ce{C-H}$ bonds, but is this generally true for isotopes of all elements? (By isotopes I mean stable ones with large half lives.)
18
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2answers
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How do the molecules know the future? How do they proceed to form “Most Stable” compound?

I'm tutoring few students for Chemistry. During the course, I many times use the phrase "Out of these possibilities this one is stable. So it is formed". I get questions like, "How do the molecules ...
18
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3answers
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What exactly is “B-strain”?

On factors that influence the stability of carbocations, I came across this peculiar one: Bulky groups attached to the positively charged $C$-atom (of the carbocation), stabilize it by B-strain, ...
18
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1answer
6k views

Stability of carbocations: CF3+ vs CH3+

Is $\ce{CF_3+}$ more stable than $\ce{CH_3+}$? In $\ce{CF_3+}$, there is $\ce{C-F}$ back bonding that increases stability of the carbocations. But -I effect of $\ce{F}$ dominates +R effect and this ...
18
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1answer
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What dictates the lifetime of a solvated electron in a given solvent?

Solvated electrons have a long lifetime in ammonia solutions, but their counterparts in water (called hydrated electrons) have a much smaller lifetime, of the order of microseconds in very pure water. ...
17
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1answer
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Why is 2-methylpropene less in energy than its alkene counterparts?

Other isomers include 1-butene, cis 2-butene, and trans 2-butene. Why would 2-methylpropene be less in energy if there is more steric hindrance?
17
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1answer
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What are the g-block's predicted properties?

I have been researching for a Physics/Chemistry exam and thought; what will the future periods in the periodic table (periods 8 and above) would entail? Each block contains its own properties that ...
16
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3answers
20k views

How does Resonance stabilize a molecule?

How does resonance lower the potential energy of the molecule? Take $\ce{O3}$ as an example.
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2answers
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What makes heat resistant proteins heat resistant?

We were doing the chapter Biomolecules in class the other day, and a doubt popped up once we reached the section on proteins. We were taught that the stuff that keeps proteins together are: Ionic ...
15
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4answers
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Why is formic acid a stronger acid than acetic acid?

I am told that because the methyl group is electron donating in the conjugate base of acetic acid, this destabilizes the conjugate base by exacerbating the existing negative formal charge on the ...
15
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5answers
1k views

Define, (actually define) the “stability” and “energy” of a compound

When we say a conformer or compound is of "higher energy" than another, are we quantifying energy in terms of the bond strength? Or are we going off of how much energy it takes to break the bond? I ...
15
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2answers
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Why is cis-1,2-dichloroethene more stable than trans-1,2-dichloroethene?

Why is cis-1,2-dichloroethene more stable than trans-1,2-dichloroethene? Usually, trans compunds are more stable than cis ones, due to less strain and its non-polarity. But, in this case it's quite ...
15
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5answers
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Is oxygen with a positive charge more stable? (comparison of canonical structures)

Which of the contributing structures of the resonance below is more stable? I'm watching a video lecture by a professor of my college where he puts this question to the class. The class ...
15
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2answers
8k views

Exocyclic vs. endocyclic double bonds in E1 elimination

What will be the major product of this elimination reaction? The exocyclic product has more substituent groups on the alkene which should make it more stable but I have heard that exocyclic alkenes ...
14
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2answers
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Why is sulfur hexafluoride more stable than selenium or tellurium hexafluoride?

I was just reading about p Block elements from two different books. Both books say that $\ce{SF6}$ is extremely stable in 16th group due to steric reasons but my question is why is it more stable than ...
14
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2answers
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Why are aromatic compounds so stable?

I've never actually been told deeper reasons for this. In organic chemistry classes (1 and 2) we're usually told that aromatic compounds are very stable whereas anti-aromatic ones are not, and also, ...
14
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6answers
68k views

How to determine the most stable carbanion?

Which of the following carbanions is the most stable? I think the answer is either a or c, as in d there are no chances for the carbanion to have its charge become less. In b I think there is a ...
14
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1answer
577 views

Why can't antiaromatic compounds just escape planarity and become non-aromatic to avoid destabilization?

Why can't just all anti-aromatic systems lose planarity (and hence conjugation) and be non-aromatic like cyclooctatetraene ? ...
13
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2answers
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Why is isoindole unstable?

According to this paper, isoindole is unstable because the 1-carbon in the isoindolidine tautomer is very electron-deficient. I figured that the electron-deficiency of this carbon must be because it ...
13
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6answers
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How to determine the least stable resonance structures out of a given set?

So I was "happily" doing organic chemistry homework when I came across this question: For 1-methoxy-1,3-butadiene, which of the following resonating structure is the least stable? $$\begin{...
13
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2answers
14k views

The effect of hyperconjugation on the stability of alkenes with MO theory

Hyperconjugation stabilizes carbocations and that makes sense because electrons are given to the empty p orbital. But how does it stabilize alkenes? Can molecular orbital theory be used to explain it?...
13
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1answer
3k views

Thermodynamic stability of meta-xylene over ortho- and para-isomers

When talking about the example of the alkylation of toluene by chloromethane in the presence of $\ce{AlCl3}$, Hepworth, Waring and Waring (2002) mentioned that: At room temperature, a mixture of 1,...
13
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2answers
8k views

Resonance stability: ester vs. thioester

My problem set solution cites: "Although sulfur is less electronegative than oxygen, overlap is a more important consideration. Sulfur is a member of the third period. As a consequence, a ...
13
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1answer
309 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 $\pi$ ...
13
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1answer
2k views

Stability of cyclobutyl methyl carbocation

I know that cyclopropyl methyl carbocation is exceptionally stable compared to say, benzyl carbocation. But I want to know how stable is cyclobutyl methyl carbocation compared to say, tertiary/...
12
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3answers
977 views

Can a molecule contain a linear series of conjugated pi bonds twisted through 180 degrees?

Imagine a long chain of carbon atoms connected by single and double bonds in conjugated fashion. All of the p orbital pi bonds would normally be aligned to either side of the carbon atoms forcing the ...
12
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1answer
1k views

Is BCl₅ possible?

Is $\ce{BCl5}$ possible? I saw it in book. As far as we can see there is no way to get 5 chlorine atoms with boron.
12
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1answer
7k views

Why would sulfuric acid turn gray/black?

About 2 years ago I purchased 2 liters of 98% concentrated sulfuric acid. It's in a standard poly bottle with leakproof lids, and originally was clear. Recently I noticed the acids have turned a dark ...
12
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1answer
1k views

Why are inert gas (especially Xenon) compounds powerful oxidizing agents?

I am curious as to why compounds with inert gases, such as $\ce{XeF4}$, $\ce{XeF2}$, and $\ce{XeO3}$ are considered powerful oxidizing agents. I would attribute the phenomenon to the highly oxidized ...
12
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2answers
471 views

Why quaternary nitrogen but not tertiary oxygen?

Why do quaternary ammonium ions with a partially positive nitrogen form fairly readily and are often stable but tertiary oxygens, apparently called oxonium ions, are more rare/less stable? The trend ...
11
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2answers
758 views

By what mechanisms can molecules with the same empirical formula be so different?

I understand the difference between empirical and chemical formula. But I always thought that compounds and molecules took their specific shape because it's the lowest energy configuration. How then, ...
11
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2answers
10k views

Why Cu+ is unstable in aqueous medium?

This was one of the question that was given in the school exam. But what I am expecting is that $\ce{Cu+}$ attains a $d^{10}$ configuration by losing one electron from s-subshell. Since it has fully ...
11
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1answer
6k views

Why are 7-membered rings less likely to form than 5- and 6- membered rings?

I see 5- and 6-membered ring products as the major products even when 7-membered rings are possible. Why is that 5- and 6-membered rings are more likely to form than 7-membered rings? Is it even true? ...
11
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3answers
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Why are acetals stable to bases and nucleophiles?

Why are acetals stable to bases and nucleophiles? Could it be due to electronic effects? Lone pairs on the two oxygen atoms create an unfavorable environment for the approaching nucleophiles and ...