87 votes
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How do people know HCN smells like almonds?

The odour threshold for hydrogen cyanide $(\ce{HCN})$ is in fact quite a bit lower than the lethal toxicity threshold. Data for $\ce{HCN}$ can be found in many places, but here and here are a couple ...
long's user avatar
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66 votes
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Why is '-ethane' in 'methane'?

meth vs eth [OP] Why is '-ethane' in 'methane'? This is a coincidence. Methyl is ultimately from Greek methy "wine" + hylē "wood. Source: https://www.etymonline.com. The terminology ...
Karsten's user avatar
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63 votes
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How do organic chemistry mechanisms become accepted?

Great question! When I was teaching, Anslyn and Dougherty was a decent text for this. Here are some general comments: First, please note that you cannot be sure about a mechanism. That's the real ...
Zhe's user avatar
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60 votes
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What's the biggest organic molecule that could have a smell?

I'll quote from $\ce{[1]}$: The general requirements for an odorant are that it should be volatile, hydrophobic and have a molecular weight less than approximately 300 daltons. Ohloff (1994) has ...
theorist's user avatar
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50 votes
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Do molecules with bridges through rings exist?

I'm not sure about the existence of molecules with bridges through rings. However, there are several publications of synthesis of molecules mimicking wheels and axles ([2]rotaxanes; The “[2]” refers ...
Mathew Mahindaratne's user avatar
47 votes
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What does the circle inscribed in a benzene ring represent?

The circle, if anything, represents the inability of our everyday physical intuition to cope with the quantum phenomena. See, you would often encounter those two pictures with "double bonds this way" ...
Ivan Neretin's user avatar
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43 votes
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Why is pyrimidine less basic than pyridine?

It is not the number of lone pairs that in any way explains basicity. Take a random sugar and it will have ten times the number of lone pairs (albeit on oxygen, not on nitrogen) without being ...
Jan's user avatar
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38 votes
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Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

Thermodynamic and kinetic control This is a classic example of the concept of thermodynamic versus kinetic control of a reaction. Take a look at this energy profile diagram.1 The horizontal axis is a ...
orthocresol's user avatar
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38 votes
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Why is −78 °C a magic temperature for organic reactions?

Dry ice (solid carbon dioxide) sublimes at −78 °C. Dry ice and acetone are a common cold bath for chemical reactions. The melting point of acetone is -95 °C so the bath never gets cold enough to ...
MaxW's user avatar
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37 votes

How do organic chemistry mechanisms become accepted?

This doesn’t exactly concern the actual mechanism you asked for, but as part of my PhD thesis, I performed an amide alkyne coupling the mechanism of which had been researched by Arndt et al.[1] ...
Jan's user avatar
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36 votes
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Why is 1-ethylidene-4-methylcyclohexane chiral?

The strict criterion for a compound to display chirality is that it must not be superimposable upon its mirror image. Let's ignore the chair conformation of the ring for a while, and assume it adopts ...
orthocresol's user avatar
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35 votes
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Why does chocolate melt so easily?

tl;dr The main structural component of chocolate is cocoa butter, which is a blend of fatty acids (primarily oleic, palmitic, and stearic acids). Cocoa butter has multiple crystal structures, and ...
chipbuster's user avatar
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35 votes
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Which is the currently accepted mechanism of a Wittig reaction?

tl;dr: I don't think there is any mechanism that is 100% correct, and, in cases like this especially, I think it would completely depend upon what set of carbonyl/ylid/base/solvent etc. was used. But, ...
NotEvans.'s user avatar
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35 votes

Five-pointed crown alkane C25H40: does it exist?

These polyspiro compounds such as the one you gave are known as [m,n]rotanes, where m is the size of the central ring and n is the size of the decorating rings. So, your compound would be called [5,5]-...
orthocresol's user avatar
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35 votes

How do people know HCN smells like almonds?

Recognize that a whiff of most toxins, even in high concentration, will probably not kill you. You need a sufficient concentration in your blood - which means you have to actually get a certain number ...
Floris's user avatar
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34 votes

What is the "‡" symbol meaning in a reaction mechanism?

The symbol is called "double dagger" (sometimes also "double cross") and is used to denote transition state (a maximum in an energy diagram; also often denoted with "*" or "TS") or a related physical ...
andselisk's user avatar
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33 votes
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Is cis-1,2-dimethylcyclohexane a meso compound?

cis-1,2-Dimethylcyclohexane is achiral, not because there is a plane of symmetry, but because it consists of two enantiomeric conformations which interconvert rapidly via ring flipping at normal ...
orthocresol's user avatar
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32 votes
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Raw green onions are spicy, but heated green onions are sweet. Why is this?

Onions caramelize, becoming sweet as various complex saccharides are broken down to more "tasty" sugars. For instance, in onions, green (scallions), yellow, red or other, chains of fructose ...
DrMoishe Pippik's user avatar
32 votes
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Does IUPAC nomenclature have the ability to name all organic compounds?

Definitely not. You got yourself in trouble specifying all organic compounds, because there is a truly immense, mind-boggling number of possible compounds. No one even knows how to accurately ...
Nicolau Saker Neto's user avatar
32 votes

When are two orbitals orthogonal?

Unfortunately, the sense in which orbitals are orthogonal is more or less impossible to define rigorously without recourse to functions of some kind. So, I'll give an explanation a shot using some ...
hBy2Py's user avatar
  • 17.3k
31 votes

Is the t-butyl carbocation more stable than the benzyl carbocation?

I am using a very simplistic quantum chemical approach of the following isodesmic reaction: I have used Gaussian 16 Rev. A.03 and the DF-B97D3/def2-TZVPP level of theory. The summaries of the ...
Martin - マーチン's user avatar
31 votes
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What is the perfect definition for chirality?

The correct definition of chirality is given in the IUPAC gold book as follows: chirality The geometric property of a rigid object (or spatial arrangement of points or atoms) of being non-...
Martin - マーチン's user avatar
31 votes

Why is acetone so cold?

Evaporation is an endothermic phenomenon, i.e. it absorbs heat in order to proceed. Acetone is a volatile solvent (it evaporates easily) so it absorbs much heat when evaporating, and your skin gets ...
SteffX's user avatar
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30 votes

Do molecules with bridges through rings exist?

A variation on this theme is Ice VII, in which two cubic ice structures are intertwined with hydrogen bonds from each component structure passing through the hydrogen-bonded rings formed by the other ...
Oscar Lanzi's user avatar
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29 votes
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Can heteroatoms with lone pairs be chiral centres?

Generally, amine nitrogens will not behave like a normal asymmetric carbon. Simple amines are roughly $\mathrm{sp^3}$ hybridiized and the molecules you use as examples do have 4 (we include the lone ...
ron's user avatar
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28 votes
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Chlorination by SOCl2 vs SO2Cl2

The reactivity patterns of $\ce{SO2Cl2}$ and $\ce{SOCl2}$ are quite different. $\ce{SOCl2}$ is a good electrophile, and can be thought of as a source of $\ce{Cl-}$ ions. These ions can go on to react ...
StevieD's user avatar
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27 votes

What is the perfect definition for chirality?

I think Martin has provided an excellent answer, and I would like to supplement it with a few additional details and examples that might prove insightful. So as I already mentioned in the comments, ...
getafix's user avatar
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26 votes
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Does Br2/H2O oxidize all aldehydes including carbohydrates?

Aldehydes, including aldoses, are oxidized to their respective carboxylic acids in the presence of $\ce{Br2}$ in $\ce{H2O}$. The reason this reaction is often discussed with carbohydrates is that it ...
ringo's user avatar
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26 votes
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Does trans-decalin really have a plane of symmetry?

It's not easy to see from a diagram, because it distorts bonds and angles. I recommend building it with a balls-and-sticks model set. You can also use a molecular viewer to model it; there are a ...
Martin - マーチン's user avatar

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