Questions tagged [organic-chemistry]

Use this tag for questions relating to organic molecules and their properties (structure of organic molecules, spectroscopic properties, reaction mechanisms, stereochemistry etc). DO NOT use this tag as the only tag in your question, as this tag by itself cannot appropriately classify your question. Always use this tag in addition to other more specific tags.

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55
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6answers
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Ortho-effect in substituted aromatic acids and bases

When comparing o,m,p-toluidine basicities, the ortho effect is believed to explain why o-toluidine is weaker. But when comparing o,m,p-toluic acid basicities, the ortho effect is stated as a reason ...
31
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2answers
8k views

Why does cyclopropane react with bromine?

In my exam, I was asked why cyclopropane could decolourise bromine water (indicating that it reacted with the bromine). All I could guess was that it is related to the high angle strain in ...
26
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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 ...
16
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2answers
11k views

Why are vinylic and arylic carbocations highly unstable?

I have checked the internet and read quite a few books, but I still am not able to understand why vinylic and arylic carbocations are highly unstable. What I found while surfing the internet is: For ...
13
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2answers
4k views

What is the perfect definition for chirality?

Why is chirality defined differently for organic and inorganic compounds? Why are inorganic compounds deemed to be optically active if they have more than one of the same ligands attached to the ...
18
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1answer
1k views

What makes C=O more stable that C(OH)₂

When there are $2$ hydroxy groups on same carbon, they tend to undergo dehydration ( of course with exceptions like chloral where $\ce H$ bonding prevails). Why does this happen? We are breaking a ...
30
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3answers
9k views

IUPAC nomenclature: “Smallest sum of locants”?

While naming any compound, the numbering should be done such that position of substituted groups gives smallest sum. I'm struggling with the IUPAC naming for cyclic compounds. How exactly does this ...
26
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4answers
43k views

What's the difference between a nucleophile and a base?

Obviously it depends on the context whether you would call a particular species a nucleophile or a base but are the two terms largely synonymous or is there a difference?
25
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2answers
11k views

Which carbocation is more stable, the ethyl- or 1-propyl-carbocation?

$\ce{C2H5+ vs \ C3H7+}$ There are two conflicting trends here. Inductive effect of ethyl will be higher than that of methyl so carbocation attached to ethyl (3 carbons in total) should be more stable....
40
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1answer
23k views

Mechanism of arene side chain oxidation by permanganate

When treated with hot, concentrated acidic $\ce{KMnO4}$, arenes are oxidised to the corresponding carboxylic acids. For example, toluene is oxidised to benzoic acid. I've tried to examine how this ...
9
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1answer
28k 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 ...
27
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4answers
29k views

Why does alcoholic KOH prefer elimination whereas aqueous KOH prefers substitution?

What is the basic difference between aqueous and alcoholic $\ce{KOH}$? Why does alcoholic $\ce{KOH}$ prefer elimination whereas aqueous $\ce{KOH}$ prefers substitution?
21
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3answers
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What is Y-aromaticity? Is the trinitromethanide anion aromatic?

The wikipedia article on trinitromethane claims that: There is some evidence that the anion (which obeys the $4n+2$ Hückel rule) is aromatic. Unfortunately the citation is behind a paywall so I ...
16
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1answer
1k views

Ring contraction in a carbocation due to ring strain and back bonding

Today our teacher told us that the following carbocation rearrangement occurs due to back bonding. I could not really follow what he meant. Can someone please explain what is actually happening during ...
15
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1answer
11k views

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?
11
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2answers
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How do you name an alkene using IUPAC rules if the longest carbon chain in this alkene does not include the double bond?

For example, which is the right way to name this compound: Is it 2-bromo-4-methylenehexane or 4-bromo-2-ethylpent-1-ene? Does the larger number of carbon in a chain take priority, as in the former, ...
20
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2answers
8k views

How to rationalise the resonance structures and hybridisation of the nitrogen in a conjugated amine?

I was given the first structure, and then drew the other 5 resonance structures: First of all, are they correct? ChemBioDraw had some complaints, but as far as I can see there's the same number of ...
8
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2answers
5k views

1,6-dimethylcyclohexene and 2,3-dimethylcyclohexene

Is there a difference between these two molecules? If so how does one tell? What is the correct nomenclature for cycloalkenes? I know that the double bond is assumed to be between C1 and C2 but why ...
17
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2answers
4k views

Is the ring or the chain chosen as the parent structure in octan-2-ylbenzene?

How would you name the above compound according to IUPAC rules? I see some sources say it is 2-phenyloctane, but ChemDraw and a few other sources say it is 2-octanylbenzene.
21
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5answers
190k views

How to determine number of structural isomers?

I have come across many questions where I'm asked to give the number of possible structural isomers. For example number, structural isomers of hexane is 5, while the number structural isomers of ...
30
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1answer
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Why does the unstabilised Wittig reaction selectively form cis alkenes?

This question is meant for a simple unstabilised ylide. The mechanism of the Wittig reaction, as given on ChemTube3d, involves a concerted formation of the oxaphosphetane (this is generally favoured ...
15
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3answers
39k views

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 ...
14
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3answers
3k views

Explanation for the trends in nucleophilicity—Orbital interactions or electrostatic attraction

The trend of halide nucleophilicity in polar protic solvents is $$\ce{I- > Br- > Cl- > F-}$$ The reasons given by Solomons and Fryhle[1], and by Wade[2] are basically as follows. Smaller ...
27
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5answers
11k views

Is pyrene aromatic despite failing Hückel's rule?

Pyrene doesn't seem to be aromatic. However, sources claim that it is aromatic. Considerations: Pyrene is cyclic. ✓ Pyrene is flat (planar). ✓ Pyrene has 16 π electrons. Every atom in the ring ...
13
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1answer
3k views

What makes carbon special and versatile?

My teacher told me that carbon's tetravalency and high catenation ability makes it special and is the reason why there are millions of compounds of carbon. 1) Silicon is tetravalent too but doesn't ...
22
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3answers
5k views

Can heteroatoms with lone pairs be chiral centres?

If a compound has a carbon atom with four different groups covalently bonded to it, it is called asymmetric and enantiomers of the compound can exist. But imagine if one has a different central atom, ...
14
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3answers
7k views

Do lone pairs on substituents (e.g. in aniline) count towards Hückel's rule?

Why is aniline aromatic? Doesn't it have 8 π electrons including the lone pair on nitrogen, thereby violating Hückel's rule? The way I see it, there are 6 π electrons from the benzene ring, and an ...
11
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1answer
9k views

Relative acidities of alkanes, alkenes, and alkynes

How does one explain the trend in bond lengths and acidity of the following hydrocarbons? $$\begin{array}{ccc} \hline \text{Species} & \ce{C-H}\text{ bond length / Å} & \mathrm{p}K_\mathrm{a} ...
8
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1answer
298 views

Why do dianions (such as malonate) bind cations more strongly than anions?

Why does a dianion (such as malonate) bind cations more strongly than its equivalent anion (acetate)? Is it simply because of the proximal availability of another $\ce{O-}$ group that can bind to ...
101
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1answer
4k views

Is there a general consensus on the causes of the alpha-effect?

There have been various explanations posited for the α-effect. The α-effect refers to a phenomenon wherein nucleophiles with lone pairs on atoms adjacent (i.e., in the α- position) to the atom bearing ...
24
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1answer
19k views

Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

The reaction of one equivalent of hydrogen bromide with 1,3-butadiene gives different products at under different conditions:1 The addition of hydrogen chloride also gives rise to similar products.2 ...
19
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1answer
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Thermodynamic vs Kinetic Sulphonation of Naphthalene

The left hand isomer is clearly the kinetically favoured product and the right hand isomer is the thermodynamically favoured product. However, I have no idea why. Can you explain?
22
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1answer
13k views

Is cyclobutadiene antiaromatic?

Cyclobutadiene is very unstable. But, some sources claim that this instability can be attributed to other factors such as ring and angle strain rather than antiaromaticity. According to some, ...
20
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5answers
6k views

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 ...
17
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4answers
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Why is acetic acid more acidic than phenol?

Acetic acid (ethanoic acid, $\mathrm pK_\mathrm a \approx 5$) is more acidic than phenol ($\mathrm pK_\mathrm a \approx 10$), which is reflected in their reactivity with a weak base such as sodium ...
19
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1answer
44k views

Why does fructose reduce Tollen's reagent and Fehling's solution?

Even though fructose is a ketohexose (ketone-containing hexose, a six-carbon monosaccharide), it reduces Tollen's reagent and Fehling's solution. Generally, a ketone does not reduces Tollen's reagent ...
18
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1answer
3k views

Molecular chirality and optical rotation

Why does having molecular chirality result in optical rotation? The dissymetry or chirality of molecules translates to the rotation of plane polarized light, the magnitude and direction depending on ...
15
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3answers
2k views

IUPAC name for 1,2,3-trichlorocyclopropane?

What is the IUPAC name for the two isomers of 1,2,3-trichlorocyclopropane? Similarly what is the name for isomers of 1,2,3,4-tetrachlorocyclobutane, 1,2,3,4,5-pentachlorocyclopentane, etc? 1,2,3-...
13
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3answers
4k views

Number of diastereomer pairs of 1,3-dichloro-1,2,3-triphenylpropane

How can I determine the number of possible pairs of diastereomers here? My first guess was two: RR with RS and SS with RS. But what about the potential chirality center middle carbon? There are two ...
21
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2answers
15k views

Products of Reimer–Tiemann reaction of 4-methylphenol

p-cresol (4-methylphenol), undergoes the Reimer–Tiemann reaction upon treatment with chloroform ($\ce{CHCl3}$) in alkaline medium. Which of the following is the major and minor product? A. 2-...
12
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1answer
56k views

What is the definition of organic compounds?

According to the definition of organic compounds on Wikipedia: An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. ...
11
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3answers
30k views

Why do molecules having a higher relative molecular mass have stronger inter-molecular forces?

Why do molecules like alkanes with higher relative molecular mass ($M_\mathrm r$) have stronger intermolecular forces? For example, methane ($\ce{CH4}$) has a weaker intermolecular force than pentane (...
23
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3answers
46k views

Rationalising the order of reactivity of carbonyl compounds towards nucleophiles

This is immediately following ron's answer from Why is a ketone more nucleophilic than an ester? One of the most simplest questions you can ask, how can you rationalise the order of reactivity ...
48
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2answers
14k views

Regioselectivity of acid-catalyzed ring-opening of epoxides

Not to be confused with what is the mechanism of acid-catalyzed ring opening of epoxides. What is the correct order of regioselectivity of acid-catalyzed ring-opening of epoxides: $3^\circ$ > $2^\...
23
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1answer
17k views

Is the ammonium substituent (-NH3+) really meta-directing in electrophilic substitution?

If we make a resonance structure for the anilinium ion, with positive charge at either the ortho or the para position, we get a pentavalent nitrogen, which is not possible. So, how is the $\ce{-NH3+}$ ...
27
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2answers
12k views

Inductive effect of hydrogen isotopes

Why does the electron-donating inductive effect (+I) of the isotopes of hydrogen decrease in the order $\ce{T} > \ce{D} > \ce{H}$? (where T is Tritium and D is Deuterium) Google has nothing to ...
16
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2answers
7k views

Is the cyclopropenyl anion antiaromatic?

According to my book, a compound is antiaromatic if it is cyclic, planar, and possesses a fully conjugated system of p-orbitals with $4n$ π-electrons. However, I have also been told that the ...
22
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2answers
1k views

Which is the currently accepted mechanism of a Wittig reaction?

The Wittig reaction is one of the most significant advances in synthetic organic chemistry in the 20th century and rightfully won its discoverer, Georg Wittig, the Nobel Prize in Chemistry. A Wittig ...
18
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2answers
9k views

Comparing acidities of substituted and aromatic carboxylic acids

When comparing the acidities of carboxylic acids, we primarily see the electropositivity of the carboxylic acid carbons, i.e. we see how effectively the negative charge on the carboxylate ion is ...
14
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2answers
63k views

Reaction of alcohols with PCl5 and PCl3

The reaction of alcohols $\ce{ ROH }$ with $\ce{ PCl5 }$ and $\ce{ PCl3 }$ yields an alkyl halide $\ce{RCl}.$ With $\ce{ PCl5 }$, the reaction is quite simple leading to the formation of $\ce{ RCl }$ ...