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12 votes

Regioselectivity of deprotonation of 1,4-dicarbonyl

Here, both the α-$\ce{CH2}$ and α-$\ce{CH3}$ groups have very similar acidities since they are both α to only one carbonyl group. [This is different compared to, for example, a 1,3-dicarbonyl such as ...
orthocresol's user avatar
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8 votes
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Why cyclohexane-1,4-dicarbaldehyde does not give aldol condensation?

Your claim is worded very poorly, and taken in the broadest sense, is not true. However, it's more complex than an outright yes or no. If we're interested in fundamental reactivity, it suffices to ...
orthocresol's user avatar
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8 votes

Why does acetate aldol with Evans auxiliary give almost no diasteroselectivity?

1. The acetate aldol reaction Before looking at selective variants, its worth pointing out what an acetate aldol is. An acetate aldol (below), is the simplest kind of aldol in which the β-...
NotEvans.'s user avatar
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What is the correct reaction mechanism?

I see what went wrong. Such questions are often confused with aldol or cannizarro as they have a carbonyl group and a base is given. Actually this is a completely different name reaction called ...
WhySee's user avatar
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7 votes
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Will 2-methylbutanal undergo aldol condensation

There is no reason why the aldehyde cannot undergo an aldol reaction with itself. Enolates are not rendered unstable by the presence of additional alkyl substituents; in fact they are considered to be ...
orthocresol's user avatar
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7 votes

Aldol Condensation with Cyclic Molecule

It certainly could undergo the acid-base equilibrium you described, if there's enough energy in the system. Your problem is omitting an important piece of information, which is the temperature at ...
Dennis Cao's user avatar
6 votes

Base-promoted rearrangement of β-ketoester

This problem has probably been on everyone's mechanistic chemistry exam at some time or another. Does the alkyl (allyl) just "jump" from one side of the carbonyl group to the other? In most examples, ...
user55119's user avatar
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6 votes

Will cinnamaldehyde undergo self-aldol condensation?

Not every α-hydrogen automatically means that a ketone is enoliseable. It would need to be an α-hydrogen capable of aligning with the π system of the $\ce{C=O}$ bond such that ...
Jan's user avatar
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6 votes
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Regioselectivity in Claisen condensation and aldol reaction

Claisen and aldol condensations are thermodynamically controlled,* so it is not a question of which enolate forms, it is a question of which product forms. In your first example, product A can be ...
orthocresol's user avatar
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6 votes

What does the intramolecular aldol condensation of 6-oxoheptanal form?

Intramolecular-Aldol reactions involves heat, as you have mentioned, and the base used (NaOH) isn't much affected by steric factors. Therefore, the preferred product should be thermodynamically ...
ba-13's user avatar
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What does the intramolecular aldol condensation of 6-oxoheptanal form?

B.Anshuman has given a short answer, but I felt more explanation is needed to understand this situation. This reaction can be done in kineticlly controlled conditions (e.g., using $\ce{LDA/THF}$ as a ...
Mathew Mahindaratne's user avatar
5 votes
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Reduction using hydrazine and glycol in alkaline medium

If you look carefully, the reagent for the first step is $\ce{O3/H2O}$, which is used for Oxidative ozonolysis. If the mechanism of ozonolysis is drawn, you will realise that a molecule of Hydrogen ...
Soumik Das's user avatar
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5 votes

Chelation-controlled aldol: why is the α substituent pseudo-axial?

Having the methyl group psuedo-axial means that when the nucleophile approaches, the transitiation state is chair-like. The energy penalty for having the methyl group initially in the less favourable ...
NotEvans.'s user avatar
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Acidity of aldehydes and ketones and enolate formation

I would like to first comment on the reasoning given as to why aldehydes are more acidic than ketones. The usually provided reasoning is, as stated here: H atoms are regarded as having no electronic ...
Tan Yong Boon's user avatar
4 votes
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Which Alpha-H will be extracted in intramolecular condensation rxn between ester and ketone

Your immediate concern seems to be which hydrogen is abstracted, 1 or 2, in structure 1 (see below). Examination of pKa’s is useful. pKa’s: EtOH, 16; alkyl ketone, ~20; aliphatic ester, ~25; and β...
user55119's user avatar
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Why do Zr, Sn, and Ti enolates form syn aldols selectively?

For most aldol reactions, the relative 1,2-diastereoselectivity is a consequence of the enolate geometry.* Both tin and titanium enolates are easily formed, and have been shown to exist predominantly ...
NotEvans.'s user avatar
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4 votes

Why is only the (E,E)-isomer obtained in Claisen-Schmidt condensation?

If your Claisen condensation was run with lots of heat (reflux?), as is typical, then you will obtain the thermodynamic product. For the alkenes, the (E)-isomer is more thermodynamically stable (...
orthocresol's user avatar
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Does 4-methylbenzaldehyde give haloform and aldol reactions?

First, Cannizzaro reaction is not given by ketones (your statement says ketones give cannizzaro reaction). Counter to your analysis, the following reaction will not occur since $\ce{H}$ bonded to ...
Chakravarthy Kalyan's user avatar
3 votes
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How does dehydration of an alcohol occur in alkaline medium?

The commonly accepted mechanism for the base-catalysed aldol example here is that the alpha hydrogen (shown in blue on your scheme) is removed by OH- present in the reaction medium, and the negative ...
Waylander's user avatar
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Major product for aldol condensation between acetophenone and acetaldehyde

I would expect the aldehyde to be the major electrophile in this reaction. The reason is that the steric demands for a nuelophile coming close to the carbonyl carbon are lower than for the same ...
Nuclear Chemist's user avatar
3 votes

How does this ring expansion on a steroid system occur?

It is clear that the first step is ozonolysis with a slightly reductive workup, yielding two ketones. You seem to have already established that. The second step features a base and an alcohol as a ...
Tan Yong Boon's user avatar
3 votes

Deciding which α-Η gets abstracted in aldol condensation

There have been tons of articles, review articles and even books written on the subject. The tl;dr version is that it depends on the conditions you use. In general, the less-hindered enolisation (in ...
Jan's user avatar
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3 votes

Aldehyde and ketone reactions

Step P is std base-driven alpha alkylation of ketone. Step Q Wacker details here takes the terminal alkene to methyl ketone then step R is base-catalysed internal aldol mechanism here gives the ...
Waylander's user avatar
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3 votes
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Decide major product for first order elimination reaction

The product that you have drawn is very unlikely to be the major product of a mixed aldol condensation. The actual major product in said reaction would be (assuming I get the substrates right) would ...
Safdar Faisal's user avatar
3 votes

Effect of +I on the alpha hydrogen in aldol reaction

Is the alpha hydrogen acidic enough to react with base? The answer is yes. As you said +I effect of the methyl group stabilizes the carbocation. It is weakly acidic but not weak enough to not be ...
WhySee's user avatar
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3 votes
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Acidity of alpha hydrogens in enolate formation

I'm interested in the OP's curiosity. I'd agree with Waylander about disfavoring to make 4-membered rings. Yet, it is possible to have two six-membered ring products. The first $\alpha$-proton ...
Mathew Mahindaratne's user avatar
2 votes
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What products did this aldol condensation create?

Straightforward aldol between benzaldehyde and acetone. Enolate of acetone adds to benzaldehyde (which cannot enolise) then eliminates water to give the enone. Product recrystallised from EtOAc.
Waylander's user avatar
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2 votes

Regioselectivity of deprotonation of 1,4-dicarbonyl

You can actually take either. The other two $\alpha$ hydrogens are more acidic thermodynamically, but if you used a hindered (kinetic) base at a low temperature, you can predominatly de-protonate at ...
Zhe's user avatar
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2 votes

Which Alpha-H will be extracted in intramolecular condensation rxn between ester and ketone

TL;DR The hydrogen near the ketone will be plucked. Comparing positive charge characters Ketones and esters both have carbonyls. The oxygen of the carbonyl pulls electrons away from the carbonyl ...
Eashaan Godbole's user avatar
2 votes
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Determination of major product in crossed aldol condensation

There are two main steps in any aldol condensation:- 1. Formation of enolate ion 2. Using the enolate ion as a nucleophile. The 1st step is a reversible step. If you think that the kinetically ...
Ankit Kumar's user avatar

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