25 votes
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Which compound reacts faster in the Cannizzaro Reaction?

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 ...
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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 ...
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22 votes
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Does a Grignard reagent react with enones to give the 1,2- or 1,4- product?

The correct answer is the 1,2-addition product (i.e. the allylic alcohol 1). In general, Grignard reagents and organolithium reagents add directly to the carbonyl carbon, while organocuprates (...
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21 votes

Why do BH3 and NaBH4 have different selectivities?

Your assertions are correct, for the most part. $\ce{BH3}$ is a Lewis acid, and it does not reduce carbonyl groups by directly donating a hydride group like $\ce{NaBH4}$ does. The $\ce{NaBH4}$ ...
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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 ...
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Is an ester or a ketone more acidic?

So, shouldn’t the order be the other way round? Yes, it is the other way around. Ketones (pKa ~ 20) are more acidic than esters (pKa ~ 25). The figure below shows the resonance structures for the ...
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Can an amide nitrogen be a hydrogen bond acceptor?

If I understood you correctly, you are talking about the peptide bond nitrogens ($\ce{R-C(=O)-\color{red}{N}H-R}$). This is, reduced to its significant chemical functional group an amide, more ...
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Mechanism of a dephenylation reaction

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: $\hspace{3.6cm}$ $\hspace{0cm}$ ...
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Does folic acid contain a benzyl or a phenyl group?

Does folic acid contain a benzyl or a phenyl group? This is the question asked in the title. At the first glance to the structure, one would say folic acid consists of phenyl function but not benzyl ...
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18 votes

Why is a ketone more nucleophilic than an ester?

The ester carbonyl carbon is a stronger nucleophile and less prone to nucleophilic attack than the carbonyl carbon in a ketone. I think you are trying to understand why the carbonyl in a ketone ...
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Clarifications about the mechanism of the Wittig reaction

1) Why is only triphenyl phosphine used here. Why not some stronger nucleophile like say trimethyl phosphine? Trialkyl phosphines can particpate in the Wittig reaction just fine, but they create ...
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Does acetic acid give a positive result with the iodoform test?

The iodoform reaction proceeds by the mechanism shown below. (The final proton transfer need not occur between the two partners, any other hydroxide could abstract the acid’s proton and any water ...
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Why does LiAlH4 reduce an amide to an amine, but only reduce a ketone/aldehyde to an alcohol?

You've got it correct in your comment with the $\ce{N}$ lone pair assisting. The reason why the $\ce{N}$ lone pair kicks oxygen out, and not the other way round, is because oxygen-based groups are ...
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Mechanism for basic hydrolysis of α-chloronitrile to ketone?

Your analysis is slightly incorrect, actually. If you do a $\mathrm{S_N2}$ on the chloride, hydrolyse the nitrile, and decarboxylate, you end up with the wrong oxidation state: Instead, if you ...
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18 votes
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Can hydrogen on platinum reduce carboxylic acids and esters?

This is based off my memory, as far as I can remember what my teacher taught me. Note, instead of $\ce{Pt}$, you can go for $\ce{Ni}$ (or Raney Nickel) or even $\ce{Pd}$ as a catalyst. Functional ...
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In what way could benzoin give Tollen's test?

Of your three "thoughts", you are correct that an aldol reaction is not an option. Not only is the product "crowded", but the reaction is reversible. [BTW, an aldol condensation occurs when water is ...
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How can benzaldehyde have a pKa of 14.9?

Significant amount of geminal diol of benzaldehyde exists in an aqueous solution of benzaldehyde at 25 °C because $\mathrm{p}K_{\text{hyd}} = 2$ (Ref. 1) The $\mathrm{p}K_{\mathrm a}$ of benzyl ...
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Mechanism for reaction of Tollens' reagent with aldehydes

Here are the two half reactions: $$\begin{align} \ce{[Ag(NH3)2]+ + e- &-> Ag^0 + 2NH3} \\ \ce{RCHO + 3OH- &-> RCO2- + 2H2O + 2e-} \end{align}$$ which together yield the overall ...
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Rationalising the order of reactivity of carbonyl compounds towards nucleophiles

Here is my "old school" explanation. Below is a drawing of the reaction coordinate for nucleophilic attack at a carbonyl carbon. The energy well for the starting carbonyl compound is shown on the ...
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ICHO Synthesis Problem 2018

You have asked quite a number of questions in your post so let's tackle it one by one. Why does the oxidation take place at that particular nitrogen atom? To understand this, we first need to ...
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Why is a ketone more nucleophilic than an ester?

Looking at the partial charges of esters and ketones, unfortunately ron's answer is only half true. For a simple model I have chosen 3-pentanone and ethyl acetate. You can see, that the carbonyl ...
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Which factors determine the keto:enol ratio for aldehydes, ketones, and 1,3-dicarbonyl compounds?

Your reasoning is along the right lines, but it is incomplete. enol of B is more stable because of more substituted alkene. The methyl group in acetone does stabilize the carbon-carbon double bond ...
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Rationalising the order of reactivity of carbonyl compounds towards nucleophiles

For this approach I am basically employing Frontier Molecular Orbital Theory (FMO) to predict the reactivity of carbonyl compounds towards nucleophiles. For the purpose of this explanation I have ...
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Rearrangements of α-aminoketones in Clemmensen reduction

Regarding this question, there are two things that should be stated beforehand. Firstly, the mechanism of the Clemmensen reduction is not well-understood. There are two plausible pathways that have ...
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Is tropone aromatic?

Tropone, or 2,4,6-cycloheptatrien-1-one, is an aromatic, non-benzenoid hydrocarbon. If you look at the resonance structures in the drawing below you'll see that structure B depicts a molecule with ...
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Why are beta-ketoacids better at decarboxylation than gamma or delta?

It has to do with the stability of the electrons that are ejected from the bond that breaks. In B-ketoacids, the electrons can resonate onto the oxygen and form an enol/enolate intermediate, which is ...
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Why can enolizable aldehydes undergo Cannizzaro reactions?

There is never an either–or in chemistry; it is typically a both instead. In the case of a hydroxide ion approaching an aldehyde with an α-hydrogen, it can both deprotonate the hydrogen creating ...
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What is the significance of the 2 and 4 positions in 2,4-DNP?

Probably any DNP could work if you could get it. But, because of the directing character of substitutents in electrophilic substitution you inherently favor the 2,4 isomer: the hydrazine group (or ...
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