59 votes
Accepted

Why is fluorine a gas, but lithium isn't?

A lithium atom has one valence electron, easily lost (shared), so it is connected to other atoms by a metallic bond. This is a bit like the shell game where a pea (electron) is hidden under a walnut ...
DrMoishe Pippik's user avatar
52 votes

Why do compounds like SF6 and SF4 exist but SH6 and SH4 don't?

TL;DR Fluorine is electronegative and can support the extra negative charge that is dispersed on the six X atoms in $\ce{SX6}$, whereas hydrogen cannot. First, let's debunk a commonly taught myth, ...
orthocresol's user avatar
49 votes
Accepted

What is the molecular structure of xenon hexafluoride?

TL;DR Xenon hexafluoride has a fluxional structure in the gas phase, with multiple rapidly interconverting conformers. The three most important conformers have $C_\mathrm{3v}$, $O_\mathrm{h}$, and $C_\...
orthocresol's user avatar
38 votes

Storing hydrofluoric acid before the invention of plastics

In the original 1771 experiment, Scheele used a very simple setup consisting of a glass retort with a glass receiver (round-bottom flask). Yes, the glass was etched to some degree by the fumes, but ...
andselisk's user avatar
  • 37.6k
24 votes
Accepted

Why is WF6 stable whereas CrF6 is unknown?

The answer has to do with two things. Note that HSAB theory is dubious at best and doesn't have very useful predictive power, so I am going to avoid talking about it. (1) The accessibility of the high ...
orthocresol's user avatar
23 votes
Accepted

Reasons for negative iodoform test

As @Waylander pointed out, it appears this reaction has not been performed and/or recorded in any literature, so it is quite dangerous to speculate. But keeping that aside, A 3D perspective reveals ...
William R. Ebenezer's user avatar
23 votes
Accepted

Can fluorine ever have a positive oxidation state?

As noted in the referenced question, fluorine is not in the +1 oxidation state in hypofluorous acid (which, incidentally, is the only hypohalous acid that has been isolated) nor in any other compound ...
Oscar Lanzi's user avatar
  • 56.9k
22 votes

Has anyone sysnthesized perfluorocubane (AKA octafluorocubane)?

[Caveat: This is not so much a question-and-answer as a desire to share Derek Lowe's article in his inimitable style. Given enough down-votes, I'll delete both Q-&-A. But enjoy the synthesis ...
DrMoishe Pippik's user avatar
21 votes
Accepted

Is there a haloalkane for astatine?

Part of the reason why there has been very little research done on organoastatine chemistry is the extreme radioactivity of astatine; the half-life of $\ce{^210At}$, the longest-lived isotope, is ...
JSK's user avatar
  • 1,141
21 votes
Accepted

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

This is a rather intellectually-stimulating question and one that is also very difficult to answer. You have constructed a very good case for why the nucleophilicity order would not be expected to ...
Tan Yong Boon's user avatar
19 votes
Accepted

Why do XeO and XeF8 not exist?

$\ce{XeF8}$ is not known to exist though O.N is +8. Why is this so? At least 2 compounds have been reported that contain the $\ce{XeF8^{2-}}$ unit. See, for example: $\ce{(NO^+)2[XeF8]^{2-}}$ (...
ron's user avatar
  • 84.7k
19 votes
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What is hybridisation of XeF6 in solid state?

Forget about applying hybridization outside the second row, especially in 'hypervalent' compounds. I know, that it is common to use and sometimes works, but it is incorrect. The $\ce{XeF6}$ molecule ...
permeakra's user avatar
  • 21.6k
19 votes
Accepted

Why does chlorination of toluene stop at two chlorine atoms?

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 $k_3$ ...
ringo's user avatar
  • 24k
18 votes

Why is thionyl chloride preferred for preparing alkyl chlorides from alcohols?

Preparation of alkyl chlorides from alcohols by thionyl chloride is preferred over other methods mentioned because of the following reasons : $$\ce{R-OH + PCl5 → R-Cl + POCl3 + HCl ↑}$$ $$\ce{...
Resorcinol's user avatar
  • 1,439
17 votes
Accepted

Why is thionyl chloride preferred for preparing alkyl chlorides from alcohols?

Thionyl chloride is preferred for preparing alkyl chlorides from alcohols because the by-products formed in the reaction are $\ce{SO2}$ and $\ce{HCl}$ which are in gaseous form and escape into the ...
Vishnu JK's user avatar
  • 1,254
17 votes
Accepted

Why is the dipole moment of chloromethane larger than the dipole moment of fluoromethane?

Dipole moment is not just about charges, it also has $L$ term. Bond length of $\ce{C-Cl}$ is greater than $\ce{C-F}$ and in this case, that is more dominating factor. The dipole moment is in order ...
Black Jack 21's user avatar
16 votes
Accepted

Why isn't a polar protic solvent used in the Finkelstein reaction?

The key point is driving the equilibrium where you want it. You could do it by relative reaction rates. The Finkelstein reaction, however, uses a better method: precipitation of one of the products. ...
Jan's user avatar
  • 68k
15 votes
Accepted

Why is cis-1,2-dichloroethene more stable than trans-1,2-dichloroethene?

Here's a pre-MOT rationalisation of the cis form being more stable than the trans form for 1,2-dihaloethylenes: The lone pair of chlorine atoms is involved in resonance with the double bond, as it ...
Archer's user avatar
  • 5,453
15 votes
Accepted

Storing hydrofluoric acid before the invention of plastics

Based on research inspired by andselisk's answer, chemists stored it in glass vessels coated in wax (similar to the receiver setup Scheele used to prove the silicon dioxide precipitate was from the ...
Doktor J's user avatar
  • 266
15 votes
Accepted

How can AuCl3 exist?

Gold(III) chloride does not exist as $\ce{AuCl3}$. According to Wikipedia, the name gold trichloride is a simplification of the name, which is referring to the empirical formula, $\ce{AuCl3}$. The X-...
Mathew Mahindaratne's user avatar
14 votes
Accepted

Friedel–Crafts alkylation of benzene with tetrachloromethane

Fonken1 says that the reaction doesn't occur, but it is not due to steric hindrance or instability of tetraphenylmethane since the molecule is actually thermally stable. Instead, it argues that the ...
Nilabro Saha's user avatar
14 votes

Reasons for negative iodoform test

There have been a few answers for this question, which make sense on steric hindrance preventing the idoform formation. However, one thing I wouldn’t agree with is almost everybody’s claim of not ...
Mathew Mahindaratne's user avatar
13 votes
Accepted

Geometry of the pentachloridoindate(III) anion

TL;DR Initially published crystal structure of $\ce{[NEt4]2[InCl5]}$ [1] according to the further investigations [3], is not valid. The $\ce{InCl5^2-}$ ion does not have $C_\mathrm{4v}$ symmetry, and ...
andselisk's user avatar
  • 37.6k
13 votes
Accepted

Which one of the following is NOT a haloalkane?

I have went through each option: A) Freon is $\ce{CCl2F2},$ which is derived from methane B) Teflon is a polymer of $\ce{-F2C-CF2 -}$ (or) $\ce{(C2F4)_n},$ derivative of 1,2-difloroethene. Here, ...
Math_Whiz's user avatar
  • 349
13 votes

(E)-2-bromo-1,4-difluoro-3-iodobut-2-ene or (E)-3-bromo-1,4-difluoro-2-iodobut-2-ene

As per the official IUPAC guidelines, namely Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book): P-14.4 NUMBERING When several structural features appear ...
orthocresol's user avatar
13 votes

Why does potassium bifluoride exist whereas bichloride does not?

The bichloride ion $\ce{HCl2^-}$ does exist, but it requires other environment than usual solutions in water. E.g. solution of $\ce{[N(CH3)4]Cl}$ salt and undissociated $\ce{HCl(solv)}$ in ...
Poutnik's user avatar
  • 41.3k
13 votes

How to distinguish silver chloride, bromide and iodide?

Nilay Ghosh's method is excellent, but it does not work if the original deposit is a mixture of the three precipitates $\ce{AgCl, AgBr, AgI}$. In this case, it is first necessary to get rid of the ...
Maurice's user avatar
  • 28.2k
12 votes
Accepted

Is it possible for halogens to show oxidation states less than -1?

Yes, they can show oxidation states lower than -1. For example in hyperlithiated compounds, like $\ce{Li3Cl}$, the chlorine would formally have an oxidation state of -3. However, a word of caution, ...
Philipp's user avatar
  • 17.8k
12 votes
Accepted

Why would this rearrangement happen?

Is methanol even a strong enough reagent for such a reaction? Methanol is a very poor nucleophile, so the rate of the $\mathrm{S_N2}$ pathway will be extremely slow. This is much likelier to be a $\...
orthocresol's user avatar
12 votes
Accepted

Alphabetization rule in case of consecutively placed substituents

Rule P-45.2.2 in the 2013 IUPAC Recommendations reads: The preferred IUPAC name is based on the senior parent structure that has the lower locant or set of locants for substituents cited as ...
orthocresol's user avatar

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