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
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Why is there inconsistency about integral numbers of protons in NMR in the Clayden: Organic Chemistry 2nd ed.?

The error in the integrals in the 100 MHz 1H NMR spectrum of the diethyl acetal of dichloroacetaldehyde is only one of the problems. The spectrum is simulated and it is incorrect. ChemDraw produces a ...
user55119's user avatar
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11 votes
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What is the correct IUPAC nomenclature for this compound?

In the present case, more atoms is a criterion to be considered earlier than the one of maximum of multiple, than double bonds. IUPAC's brief guide illustrates this by the following flow chart: (...
Buttonwood's user avatar
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Why is the ketone not attacked by the Grignard reagent/cuprate in this case but a double bond is?

The book is correct. This is a classic example of a 1,4-addition (also called a conjugate addition) of an alkyl nucleophile to an α,β-unsaturated ketone. Normally, a Grignard reagent such as MeMgBr ...
HarvestTheNight's user avatar
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Why does burnt milk on bottom of pan have 'vaguely' cork-like pattern?

Milk comprises sugars and fats, with the sugars being prone to caramelization upon exposure to heat from stovetop. You can see the developing brown color and if you scrape further, you will see burnt ...
AChem's user avatar
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Does a slippery liquid leak through pipe fittings?

Potassium hydroxide ($\ce{KOH}$) makes skin feel slippery because it saponifies oils in your skin, changing them to soap. It is called caustic potash because of the damage it does to tissue. However, ...
DrMoishe Pippik's user avatar
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Mechanism of formation of nile blue dyes

You are correct that the first step of the mechanism involves protonation of the nitroso group. Be aware that protons are being exchanged on the amines during the course of the condensation. There are ...
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9 votes

Question about the differences of white and grey NaH properties

Sodium hydride on mineral oil is grey. When it reacts with water, for example from air humidity it reacts to NaOH which leads to discolouration which is white. One can wash NaH with hexane or THF to ...
raptorlane's user avatar
9 votes

Why do ketoses undergo dehydration more rapidly than aldoses?

Seliwanoff's Test - The Favouritism for Ketoses TL;DR The Seliwanoff's Test is a method to distinguish ketoses and aldoses. The test uses resorcinol + dil. $\boldsymbol{\ce{HCl}}$ as the reagent. ...
Harikrishnan M's user avatar
9 votes

Acidity of metronidazole

There are no acidic groups in metronidazole. The $\mathrm{p}K_\mathrm{a}$ you are quoting relates to the protonated form of the molecule (usually hydrochloride or benzoate). The most easily removed ...
Waylander's user avatar
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9 votes

Why are "vinylic" and "allylic" carbons named so?

Actually, word roots in organic chemistry aren't of much help because the origins have little connection with the actual molecular structure. There are entire books dedicated to these topics of you ...
AChem's user avatar
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Does Grignard reagent on reaction with PbCl2 give PbR4 and not PbR2?

More is involved here than the simple nucleophilic exchange normally associated with Grignard reagents. Essentially, the proposed dialkyl lead disproportionates with displacement of metallic lead. ...
Oscar Lanzi's user avatar
8 votes
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What is the criss-cross C-N bond in furazolidone?

It means it is a double bond without specifying whether it is E or Z From Wikipedia A crossed double-bond has been used sometimes; it is no longer considered an acceptable style for general use but ...
Waylander's user avatar
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Geometrical isomerism in 1-(chloromethylidene)-3,5-dimethylcyclohexane

There are four stereoisomers of the compound (two pairs of enantiomers), shown in the first row. If you swap the chlorine with the hydrogen (second row, swap from structure right above), you don't ...
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Reaction of cyclohexene with HCO3H

According to this patent Performic acid is unsatisfactory as an epoxidizing agent for cyclohexene because the reaction leads preferentially to hydroxy-formoxy cyclohexane with small amounts and thus ...
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Why does the measured CO2, TVOC and CH2O increase rapidly when I cook/bake?

Many raw foods naturally contain formaldehyde according to the Hong Kong Center for Food Safety and other sources. Dried Shiitake mushrooms have over 100 mg/kg of formaldehyde, for example. So ...
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Product of oxymercuration-demercuration reaction

Well, the answer is correct except instead of -OH it must be -OMe because the reagent used is Hg(OAc)2/ MeOH and not Hg(OAc)2/H2O. Here's an illustration of the rection using methanol
daf's user avatar
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Why is there inconsistency about integral numbers of protons in NMR in the Clayden: Organic Chemistry 2nd ed.?

In general, you should not expect NMR integrals to be perfect. There are several reasons for this. Two main ones are: The integral in the spectrum depends on the proportion of the spins that are ...
orthocresol's user avatar
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7 votes
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What is 'spray foam' or 'expanding foam'?

Single component spray foams work differently to two-component spray foams The Wikipedia article on spray foams is somewhat misleading because it mostly talks about the characteristics of industrial ...
matt_black's user avatar
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7 votes

FTIR Spectra: Did I synthesize ethyl gallate from gallic acid?

The short answer: consider a technique complementary to IR spectroscopy, for instance $\ce{^1H}$-NMR spectroscopy. Your have good luck, as the public AIST spectral database holds records of IR spectra ...
Buttonwood's user avatar
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Nomenclature of C6H5CO-O-NH2

According to the last printed version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), the retained name hydroxylamine was used for the construction ...
Loong's user avatar
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7 votes

Using Thionyl Chloride with tertiary alcohol

There is no real barrier against thionyl chloride reacting with a tertiary alcohol. The mechanism described by Ouellette and Rawn[1] does not depend on cleavage of a carbon-hydrogen bond and is even ...
Oscar Lanzi's user avatar
7 votes

Why does burnt milk on bottom of pan have 'vaguely' cork-like pattern?

The pattern has everything to do with the interacting of opposing forces such as in convection, combined with mass transport, precipitation, and agglomeration of particles in the fluid. The same ...
Zak's user avatar
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which is more acidic thiols or carboxylic acid?

Some $pK_a$ values: $\ce{H3C–SH}$: 10.4 $\ce{H3C–C(O)–OH}$: 4.8 This comparison clearly indicates that the carboxylic acid group imparts stronger acidity than the thiol group. The determinimg factor ...
Oscar Lanzi's user avatar
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NMR and dienes to isolate certain isotopes?

There are at least two glaring problems: Look at the energy scales on which NMR operates (for example, take the resonance frequency $\nu$ and calculate the associated energy $h\nu$)... and compare it ...
orthocresol's user avatar
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Class vs Functional Group: Imprecise Language?

In some cases, there is a clear correspondence between class and functional group. Alcohols are a class of compounds that all contain a hydroxyl functional group. The carbonyl functional group is an ...
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What do we get when we joint two α- glucoses via an α1,4 bond?

The anomeric carbon of of the second glucose unit of maltose interconverts between the alpha and the beta form in aqueous solution (just like glucose). The stereochemistry of the anomeric carbon in ...
Karsten's user avatar
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Why does silver have more affinity for chlorine and bromine rather than fluorine in Swarts reaction?

Silver actually does prefer fluorine over heavier halogens. But this preference involves less (free) energy difference than the preference for the alkyl groups for fluorine. As a result, transfer of ...
Oscar Lanzi's user avatar
6 votes

How do I reduce this ketone to two double bonds on the carbo chain?

This can be done (on paper) by alpha-selenation of the starting ketone followed by selenoxide elimination to form the alkene (Wikipedia). The product from this can be reduced by Luche reduction ($\ce{...
Waylander's user avatar
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Chlorination of 2-phenylbutane

First of all, welcome to ChemSE! I presume that you are a student, which I am not, and that this problem arises from a preparatory examination. Too many of these types of questions are ambiguous at ...
user55119's user avatar
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