# Tag Info

54

I'd like to throw a tentative explanation for the ortho effect into the ring: In the molecules in question, an interaction between the protons of the methyl group and the lone pair of the amine nitrogen and the negative charge on the carboxylate, respectively, can be assumed. In the first case, the electron density on the N atom is (slightly) reduced and ...

38

I would like to back up Klaus' answer with some Quantum Theory of Atoms in Molecules (QTAIM) results, based on a DF-BP86/def2-SVP calculation. Note that these are results, obtained without the consideration of solvation or condensed phases. I believe they still prove a valid point in the case of electronic structure theory. I revisited this question in ...

38

I will start my answer with a preface that the website linked to in the question is a pseudoscience website (and I am glad that it has vanished from the face of this earth, only accessible via the Wayback Machine). These people use scientific-sounding jargon that sounds impressive to the lay reader, but any actual scientist will know that it is simply ...

26

It can be explained another way: o-toluidene is less basic than aniline cause of a different reason. See, what happens is: when aniline acting as a base becomes $\ce{NH3+}$ (on top of a benzene ring), it is usually stabilised by solvation. But if there is a substituent on the ortho-position, it inhibits solvation. Thus the tendency to act like a base is ...

26

You were on right path; tert-butyl carbocation is quite stable$\ldots$ so stable that the acylium cation, which normally reacts as an electrophile itself, instead decomposes via decarbonylation (loss of stable carbon monoxide molecule). The t-butyl carbocation isn't as stable as the acylium cation (which is stabilised by resonance), but the difference is ...

25

Like aniline, phenol too reacts to a very less extent during Friedel-Crafts reaction. The reason being that the oxygen atom of phenol has lone pair of electrons which coordinate with Lewis acid. In fact most substituents with lone pair would give poor yield. The two pathways involved in the reaction with phenol reduce the overall yeild: Phenols ...

25

In contrast to many other electrophilic aromatic substitution reactions, aromatic sulfonation is reversible, in other words it is an equilibrium. If you use a large excess of $\ce{SO3}$ you push the reaction to the sulfonation side; if you heat the sulfonated product in the absence of $\ce{SO3}$ it will de-sulfonate. This makes sulfonation a nice method to ...

22

how is anilinium ion meta directing for electrophiles? Actually, anilinium is not meta directing (I know it is often taught that way), but rather it inductively deactivates the entire aromatic ring. To explain the electrophilic substitution pattern observed with any aromatic system we must consider both resonance and inductive effects. Resonance Effects: ...

22

The mechanism of the Cannizzaro reaction is illustrated below. The first step involves attack by the nucleophilic hydroxide ion on the positively polarized carbonyl carbon to form a tetrahedral intermediate. Once the tetrahedral intermediate is formed, substituents on the aromatic ring can have little resonance interaction with the former carbonyl carbon ...

22

It's all about the 3D structure of double bonds. If we look at the tub form we see that all dihedral C-C=C-C angles are 0°. the C=C-C angles are 125°, also pretty close to the optimal value. Everything works out fine, there's basically no strain on the whole molecule. I tried to build the chair form of all cis, but every optimization ended up in either the ...

20

First, Hückel's rule is only valid for monocyclic systems: Hückel's rule is not valid for many compounds containing more than three fused aromatic nuclei in a cyclic fashion. For example, pyrene contains 16 conjugated electrons (8 bonds), and coronene contains 24 conjugated electrons (12 bonds). Both of these polycyclic molecules are aromatic even though ...

20

In fact I find a more simple reasoning with resonance structure. When phenol loses the $\ce{H+}$ the phenolate ion is stabilized due to the resonance effect, as shown below: The energy of the dissociated form is lower and so phenol has more chance to be in the solution dissociated with the phenolate ion. Aliphatic alcohols are not stabilized by resonance so ...

20

It indeed can be named quite nicely using the recent "phane" nomenclature from the Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013, here is the example* By abstracting to the bicyclo phane composed of nine benzene nodes ("superatoms") of three kinds, we get 1,5(1,3,2),2,4,6,8,9(1,4),3,7(1,2)-nonabenzenabicyclo[3.3.1]...

19

The linked article is a short summary of a Science article: "A Tricyclic Aromatic Isomer of Hexasilabenzene" by Kai Abersfelder, Andrew J. P. White, Henry S. Rzepa, and David Scheschkewitz; Science 2010: 327 pp. 564-566. They propose a new term, "dismutational aromaticity": The highly dispersed $\ce{^29Si}$ nuclear magnetic resonance shifts in solution ...

18

What are the precise conditions under which Benzene undergoes ozonolysis? In Über das Ozobenzol, an early German publication on the reaction of benzene with ozone, Ber. Dtsch. Chem. Ges., 1904, 337, 3431-3433 (DOI) , the authors write Leitet man in solches Benzol 1–2 Stunden lang bei einer Temperatur von 5–10° einen 5-procentigen Ozonstrom, so scheidet ...

18

Hueckel's rule (i.e. that aromatic compounds have $4n+2$ $\pi$ electrons) places limits on aromaticity in cycles with less than 6 carbons. As there are only 3 cases to look at, let's enumerate them: 5 carbons: cyclopentadiene ($\ce{C5H6}$) is not aromatic, but the cyclopentadienide anion ($\ce{[C5H5]^{-}}$) is. This species is well known in organometallic ...

18

The key point to understanding why fluorides are so reactive in the nucleophilic aromatic substitution (I will call it SNAr in the following) is knowing the rate determining step of the reaction mechanism. The mechanism is as shown in the following picture (Nu = Nucleophile, X = leaving group): Now, the first step (= addition) is very slow as aromaticity is ...

18

The effect is indeed amazing, if you compare the $\mathrm{p}K_\mathrm{a}$ of tert-butanol (17.0) with that of phenol (9.95). Deprotonation is facilitated when the reaction goes downhill (energywise). In order to obtain stabilization of the anion, the negative charge needs to be distributed over a larger number of centres. This distribution (only) is ...

18

ChemDoodle 8 can name this via the extended von Baeyer system, although the name is quite long. Thanks for putting up this nice example though! Undecacyclo[18.18.6.22,5.212,15.221,24.231,34.240,43.06,11.016,44.025,30.035,39]tetrapentaconta-1(39),2,4,6,8,10,12,14,16(44),17,19,21,23,25(30),26,28,31,33,35,37,40,42,45,47,49,51,53-heptacosaene

18

Yes, this graphical representation of a substituted benzene is in accordance with Graphical Representation Standards for Chemical Structure Diagrams (IUPAC Recommendations 2008). GR-9.4 Variable attachment location In addition to allowing the type of attachment to vary, it may also be convenient to indicate that the attachment’s location is variable ...

18

Here the bond connecting the substituent with the center of the ring suggests that the substituent may be located on any of the three positions (ortho-, meta-, para-). From Graphical representation standards for chemical structure diagrams (IUPAC Recommendations 2008), section GR-9.1 Small substituents [1, p. 393] (emphasis mine): Parent structures with a ...

17

Yes, it is all about the absorption of light at specific wavelength. Azobenzene, the parent compound has an absorption maximum around $\lambda$= 430 nm in the visible spectrum. The interesting part is: The absorption can be tuned by substitution of the arenes. This is done before the azo coupling. Some examples are Allura Red (1), Chrysoine Resorcinol (2),...

17

The nitrogen in aniline is somewhere between $\mathrm{sp^3}$ and $\mathrm{sp^2}$ hybridized, probably closer to the $\mathrm{sp^2}$ side. We are correctly taught that the nitrogen in simple aliphatic amines is pyramidal ($\mathrm{sp^3}$ hybridized). However in aniline, due to the resonance interaction between the aromatic ring and the nitrogen lone pair, ...

17

First, the methoxy- group can be demethylated by $\ce{AlCl3}$, beginning with $\ce{AlCl3}$ coordination to the ether oxygen, followed by an $\mathrm{S_N2}$ reaction: $\hspace{3.6cm}$ $\hspace{0cm}$ The oxygen activates naphthalene's position 1, and the acid chloride will undergo a Friedel-Crafts acylation (as you noted): $\hspace{.5cm}$ Being a strong ...

17

The reaction of benzene over $\ce{V2O5/ PtAu}$ catalyst at lower temperatures, can convert benzene to phenol with some success. See this book here Direct hydroxylation of benzene [The original question before editing was: What is the Ratta Maar Reaction?] Someone has played a prank with you with the named reaction. "Ratta maar" is a slang for "rote ...

16

For resorcinol, the naming is covered in a footnote to the Wikipedia article: "Wir nennen den neuen Körper, da wir gefunden haben, dass er auch aus dem Ammoniakgummiharz erhalten werden kann, Resorcin, um an seine Entstehung aus Harzen und seine Beziehung zum Orcin zu erinnern." (We name the new substance, since we've found that it can be obtained from ...

16

Let's look at nitrosobenzene. In order to be delocalized (participate in resonance), the lone pair on the nitrogen needs to be in a $\ce{p}$ orbital. As I have draw it above, the lone pair is in a $\ce{sp^2}$ orbital, and the $\ce{N=O}$ pi bond is conjugated with the ring: If the lone pair on the nitrogen atom is delocalized, then yes the nitrogen atom is ...

16

It doesn't stop, it just gets a lot slower the more chlorine atoms you add. From the abstract of an article titled Photochemical side-chain chlorination of toluene[1]: Where $k_1$, $k_2$, and $k_3$ are the rate consts. for the successive reactions: $\ce{PhMe}$ → $\ce{PhCH2Cl}$ → $\ce{PhCHCl2}$ → $\ce{PhCCl3}$, resp.; $r = \frac{k_1}{k_2}$ and \$s = \frac{...

15

The Reimer-Tiemann reaction is known as the ortho-formylation of phenols under strongly alkaline conditions. It's not an addition of a carbene to a double bond, like the Simmons-Smith reaction, the pyrrole to pyridine ring enlargement or the Buchner expansion, which is catalyzed by transition metals. As ron already pointed out, pH is one crucial ...

15

Starting with a short and blunt answer to the title’s question: Yes. But you likely already knew that, otherwise you wouldn’t have written the rest. One might argue that the reader understands what is being portrayed or that this is done in aims of saving time, but that doesn’t sit right with me. The entire point of nomenclature, drawing a chemical, or ...

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