Questions tagged [radicals]

Radicals are highly reactive species, that have one or more unpaired electrons. Whether a species has unpaired electron(s) can be experimentally determined through electron pair resonance spectroscopy. Radicals are paramagnetic. This tag should be applied to questions that involve free radicals as a species or radicals in reactions and their mechanisms.

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28
votes
3answers
577 views

What makes a radical 'free'?

The qualifier 'free' seems to be ubiquitously attached to discussion of radicals as highly reactive species with unpaired spins. What, precisely (or imprecisely, as the case may be) does 'free' really ...
22
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3answers
3k views

What is the geometry of an alkyl radical?

I encountered this question which asks how many possible radicals are formed when $\ce{CH3CH2C(CH3)3}$ is monosubstituted by $\ce{Br2}$. The answer given is 3 while I think it should be 4, reasoning ...
20
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5answers
14k views

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{...
19
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3answers
2k views

Why doesn't TEMPO react with itself?

TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl, or (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) has the following structure: Given that it's a free radical, why doesn't it react with itself, despite ...
19
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1answer
11k views

Structure of Br3O8

What is the structure of $\ce{Br3O8}$? It has an odd number of electrons; does that make it a free radical? The structure given in my book shows Where did the 7th electron of the central atom go? ...
14
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3answers
9k views

Why don't free radicals undergo rearrangement like carbocation/carbonium ions do?

Why don't free radicals and carbanions undergo rearrangement like carbocation/carbonium ions undergo in a reaction?
14
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1answer
707 views

Can we synthesize alcohols by the photolysis of hydrogen peroxide?

As I was going through my revision of organic chemistry, I came across free radical substitution of alkanes with halogens. In a similar process where we use hydrogen peroxide, instead of chlorine, so ...
13
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1answer
183 views

Ring opening of aziridinylmethyl and oxiranylmethyl radicals

When a radical is alpha to a three-membered ring, it is common for the ring to open via β-scission (to relieve ring strain): When the ring contains a heteroatom there are a couple of different ...
12
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1answer
660 views

Exceptions to motif: nucleophile attacks electrophile

I hear this motif - nucleophile attacks electrophile - all the time with regard to organic chemistry. Are there any exceptions? I think this statement is always true in general because it's a ...
11
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3answers
2k views

How to check if azobisisobutyronitrile (AIBN) is still active?

I will have some samples of azobisisobutyronitrile and I want to perform Barton-McCombie reaction. The problem is that the reagent is quite old and I need to know whether it has not decomposed. Do ...
11
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1answer
195 views

Mechanism of radical cyclisation to form hydroazulene core

Recent studies on radical-induced cyclisation reactions have led to a simple, one-step method for the preparation of hydroazulenes from appropriately substituted cyclopentanone precursors. Treatment ...
10
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2answers
170 views

Carbon tetraradical

I was just reading through Reactions: The private life of atoms by Peter Atkins and I noticed that in Chapter 3, the chapter on the combustion reaction, the author writes: As we watch we see $\ce {...
10
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1answer
914 views

Formation of radicals from C-H and C-C bonds

Why do radical mechanisms favor the homolytic dissociation of a $\ce{C-H}$ bond over a $\ce{C-C}$ bond? The $\ce{C-H}$ bond is stronger in magnitude (and it's also slightly polarized), so why would ...
10
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1answer
156 views

Naming of asymmetric organic molecules with two nitroxides

When writing my diploma thesis I had to name my molecules following IUPAC nomenclature rules. There were several molecules like the following one, that contained two TEMPO groups, but were not ...
9
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1answer
29k views

What is the major product on chlorination of 2-methylbutane?

I came across a question asking for the major product on chlorination of 2-methylbutane. The answer in the back of the book says it will be 2-chloro-3-methylbutane. However, I thought the major ...
9
votes
1answer
968 views

What exactly does it mean for the reaction of superoxide with non-radicals to be spin-forbidden?

From Wikipedia: The reaction of superoxide with non-radicals is spin forbidden. In biological systems, this means its main reactions are with itself (dismutation) or with another biological ...
8
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2answers
746 views

Can an organic molecule have a triplet ground state?

Can the ground state of an organic molecule be a triplet. This would imply something like a "HOMO" formed by 2 degenerate levels and less than 4 electrons to fill them. If yes, what are the conditions?...
8
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2answers
10k views

Why is O2 a biradical?

$\ce{O2}$ has a double bond in its normal form. That is $\ce{O=O}$. There are no unpaired electrons in this case are there since there are 2 lone pairs on each oxygen. However 1 resonance structure ...
8
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1answer
3k views

How to find if the unpaired electron is placed in hybrid orbital or pure orbital in odd electron species?

Odd electron species contain an unpaired electron which can either be placed in hybrid orbital or in pure orbital. Example: In the case of $\ce{.CF3}$ radical, the unpaired electron is placed in $\...
7
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2answers
3k views

How does neutralization of free radicals by $\beta$-carotene work?

In my understanding, by bonding to the free radical species, say by one of the double bonds, a new free radical on the $\beta$-carotene develops.
7
votes
1answer
240 views

Geometries of methyl and silyl radicals

The $\ce{.CH3}$ radical is planar but the $\ce{.SiH3}$ radical is a trigonal pyramid. Why are they different? After all, $\ce{C}$ and $\ce{Si}$ are in the same group.
7
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1answer
183 views

Why does the light catalyzed radical addition of tetrachloromethane to an alkene produce only a single regioisomer?

This reaction always occurs in the following, regiospecific way: $$\ce{CCl4 + R-CH=CH2 ->[$h\nu$] R-CHCl-CH2-CCl3}$$ The same should apparently also happen when there is a carbon that has two ...
7
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1answer
1k views

Why is free radical chlorination exothermic whereas bromination is endothermic?

In the energy profile diagrams below, it can be clearly seen that the free radical chlorination of an alkane $$\ce{RH + Cl2 -> RCl + HCl}$$ is exothermic. However, the corresponding bromination $...
7
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1answer
672 views

Which singlet dihalocarbene has the strongest carbon-halogen bond?

There are three singlet carbenes - difluorocarbene, dichlorocarbene and dibromocarbene. Which has the strongest carbon halogen bond? Obviously backbonding is a point to be considered, as carbene is ...
6
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1answer
3k views

Why can UV light initiate a reaction between hydrogen and chlorine gas?

Can someone explain me how does UV light help combine chloride gas and hydrogen to produce hydrochloric acid? $$\ce{Cl2(g) + H2(g) -> 2HCl(g)}$$
6
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3answers
122 views

Determining the product which is not possible in the reaction

This is an objective type question I encountered in a objective test. NBS (N-bromosuccinimide) is used for the allylic substitution of $\ce{Br}$ in a reaction. In this reaction, since the allylic ...
6
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1answer
8k views

What is the hybridisation of CF3 free radical?

Having 3 sigma bonds in a similar manner to CH3 free radical it should also have hybridisation sp2. However, if we look at its shape, it is pyramidal and not planar unlike CH3 free radical(which is ...
5
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3answers
7k views

Is a carbon-fluorine bond stronger than a carbon-chlorine bond?

In hydrolysis/nucleophilic substitution of haloalkanes, the bond enthalpy indicates the rate of hydrolysis (e.g. the $\ce {C-I}$ bond is weaker than the $\ce {C-Cl}$ bond so in hydrolysis the alkane ...
5
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1answer
1k views

Which C-C bond would break first, the one in ethane, or 2,2-dimethylpropane?

I have drawn the figures and determined intuitively that the larger molecule's $\ce{C-C}$ would break first. I made this assumption that ethane has the stronger $\ce{C-C}$ bond and I am correct, ...
5
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2answers
973 views

What is the mechanism for thermal decarboxylation of a generic carboxylic acid (not special cases like beta-ketocarboxylic acid or malonic acids)?

I am looking for the mechanism for thermal decarboxylation for any RCOOH, and I am guessing that its possible for the thermal energy to cleave the R-C bond homolytically leaving a R• and •COOH. Then I ...
5
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2answers
136 views

Atmospheric methane to carbon [closed]

I read an article by popsci that talked about huge fans forcing methane over a catalyst. Now that got me wondering, can't we produce hydroxyl radicals with powerfull uv lasers blasting the sky, ...
5
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1answer
217 views

Photolysis of N-bromo compound in acidic conditions (radical cyclisation)

For the proposed mechanism, I believe that the N-Br bond is firstly broken by the absorbed light hv, then the radical formed on the N will perform an intra-molecular attack on the end of the carbon ...
5
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1answer
518 views

Why does chlorine replace a hydrogen in propene instead of adding to the double bond?

I read about the following reaction in my book: $$\ce{CH3-CH=CH2->[Cl2][\pu{773 K}] (Cl)CH2-CH=CH2}$$ It surprises me that the $\ce{Cl}$ doesn't attack the $\pi$ bond, rather it attacks the $\...
5
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1answer
5k views

Why is it possible to form bromoalkanes but not iodoalkanes from free radical substitution?

For a free radical substitution (FRS) reaction between iodine $\ce{I2}$ with ethane and bromine $\ce{Br2}$ with ethane $\ce{CH3CH3}$: $E_\mathrm d(\ce{H-I})=299\ \mathrm{kJ\ mol^{-1}}$ $E_\mathrm d(\...
5
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2answers
1k views

Reactions in water radiolysis - producing hydroxyl radicals

There’s an excellent question on Stack Exchange regarding the radiolysis of water here but I have one simple outstanding question that perhaps someone might now; in radiobiology, a common DNA damaging ...
5
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1answer
4k views

Why is the methyl radical planar?

Why is the methyl radical planar? The VSEPR theory would predict an angle between 120 and 109.5 degrees, while it is actually 120 degrees.
5
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2answers
956 views

Thermodynamic vs kinetic reaction control with radical substitution

Doing a revision for a chemistry class test tomorrow, I stumbled upon thermodynamic and kinetic reaction control in the context of radical substitution. Here, my chemistry teacher said, that ...
5
votes
1answer
128 views

Why is a 7-endo radical cyclisation favoured over a 6-exo in this synthesis?

Normally, according to Baldwin's rules, 3-exo to 7-exo cyclisations are preferred over endo cyclisations. But in the following example, a 7-endo-trig reaction is favoured over a 6-exo-trig and I am ...
5
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1answer
120 views

Explaining differences in rate of propagation based on monomer structure

The values given below have been taken from my lecture hand out, and they weren't cited so I don't know where my instructor got them from The $k_\mathrm{p}$ (rate constant for propagation in radical ...
5
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2answers
3k views

Stability of cyclic radicals

How do we arrange the following in increasing order of stability? The answer given is: $5<3<1<2<4$ (numbering according to their order in the image). My Approach: I can figure that in ...
4
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4answers
535 views

Can a free radical be created by chemical reaction of non-radical species?

Here's my thinking: Atomic oxygen in its ground state is a free radical because there are two unpaired electrons in p-orbitals. When species react new orbitals are formed, and perhaps a situation ...
4
votes
1answer
423 views

Why doesn't the N-Br bond dissociate quickly in NBS?

NBS is used to provide a constant, small amount of $\ce{Br2}$ which then dissociates to give $\ce{Br^.}$ free radical. Why doesn't the $\ce{N-Br}$ bond simply dissociate to give $\ce{Br}$? This ...
4
votes
1answer
378 views

Major product of radical fluorination vs bromination

I understand what structure is formed by using $\ce{Br2}$ to brominate this alkane, and I know that $\ce{F2}$ will be less selective in its abstraction of hydrogen. However, how can I know where $\ce{...
4
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1answer
3k views

Why are radicals unstable?

Why are unpaired electrons especially reactive? Does pairing electrons decrease the reactivity of the electrons? But then doesn't forcing two electrons into the same orbital cost energy?
4
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1answer
1k views

Rank the following radicals in order of decreasing stability

Question Rank the following radicals in order of decreasing stability Aromaticity makes a cyclic compund more stable. Here, 1 and 3 are aromatic since they follow Huckels rule(Or am I wrong ...
4
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1answer
2k views

Free radical vs radical cation

What is the difference between a free radical and a radical cation? Are they different thing or do they mean same?
4
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1answer
399 views

Why is antimony oxide used as a flame retardant?

What is the mechanism of action of antimony oxide as a flame retardant? Is this to do with radical absorption?
4
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2answers
778 views

What determines the high degree of selectivity in free radical brominations?

In my organic chemistry class, we were asked what determines the relatively high degree of selectivity in the reaction of a bromine radical with primary, secondary, and tertiary C–H bonds. I said it ...
4
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1answer
8k views

Formation of azobenzene from nitrosobenzene and N-hydroxyaniline

I'm trying to create a reasonable reaction mechanism for the reaction of nitrosobenzene and N-hydroxyaniline, which happens as part of the reduction of nitrobenzene to azobenzene using magnesium as ...
4
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1answer
390 views

Is propanone responsible for photochemical smog?

Many volatile organic compounds (VOC) are responsible for photochemical smog. Propanone is a VOC. It's produced in a great amount for industrial purposes. So, propanone can be a potential contributor ...