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18 votes
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Why are lactones more acidic than esters?

Overview The only interesting thing about lactones is that if the ring size is relatively small, they necessarily adopt the (E) conformation. Therefore, the question essentially boils down to: for a ...
orthocresol's user avatar
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12 votes
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Baldwin's rules exceptions: cations

The acetal formation in question is actually an example of a 5-endo-trig cyclisation, which, according to Baldwin's rules should be unfavourable. The first thing to realise about Baldwin's rules is ...
NotEvans.'s user avatar
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11 votes
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Gauche effect and bond length

Actually, the more the polarization of a bond, the stronger it is, since both the atoms are drawn close together due to electrostatic attraction, decreasing the bond length and increasing the bond ...
FreezingFire's user avatar
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9 votes

How are SN2 transition states stabilised by adjacent double bonds and carbonyl groups?

Unsaturated groups conjugated to the site of attack (aromatic rings, alkenes, carbonyl groups) all tend to have the effect of increasing the rate of an SN2 reaction at that centre. As an example, ...
NotEvans.'s user avatar
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8 votes
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Regioselectivity in iodolactonisation of γ,δ-unsaturated carboxylic acid

There are several arguments. Firstly, five-membered ring formation is generally kinetically more favourable than 6-membered ring formation. As ring size increases, the entropy of activation also ...
orthocresol's user avatar
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8 votes

Stereoelectronics of the Houk model

1. Origins of the Houk model The initial idea behind the Houk model was infact provided by Kishi, who proposed that alkenes with a chiral centre on the adjacent carbon adopted a 'reactive conformation'...
NotEvans.'s user avatar
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7 votes
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Steric hindrance of an unbonded electron pair

Since I just covered this material in depth in my physical organic chemistry class, I figured I'd write up an answer. Electronegative elements lower the energies of all molecular orbitals to which ...
ringo's user avatar
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6 votes
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Why is methyl α-D-glucopyranoside preferentially formed from glucopyranose in acidic methanol?

In general, if there is overlap between a filled orbital and an unfilled orbital, a stabilising interaction will take place between the two. A simple example is the resonance present in esters, where ...
orthocresol's user avatar
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6 votes
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Stereoelectronic effects in torquoselectivity of 4π electrocyclic opening

The torquoselectivity of the above reactions is dictated by stereoelectronic effects, which (in this case) are significant enough to take precedence over steric effects. In general, electron-donating ...
orthocresol's user avatar
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6 votes
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Mechanism of three-membered lactone hydrolysis in base

According to Organic Chemistry: Second Edition,[1, pg 934](from which I assume that the question was taken): Enantiomerically pure (R)-2-bromopropanoic acid reacts with concentrated sodium hydroxide ...
Safdar Faisal's user avatar
5 votes

Why is a 7-endo radical cyclisation favoured over a 6-exo in this synthesis?

I'm the co-first author of this paper. I want to thank Mathew Mahindaratne for the helpful and thoughtful discussion. I just want to add one more result when I was doing the synthesis, please see the ...
Maomao He's user avatar
4 votes

Hydrolysis of Sucrose over Sn1Ac or Sn2Ac

The mechanism supplied in the question statement is wrong according to this paper, where the evidence favored Carbon-Oxygen bond cleavage on the fructosyl-side instead of the glucosyl-side of the ...
Tony M's user avatar
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4 votes

Gauche effect and bond length

Many of these cases hinge on some weird effect. Evidently the gauche form of 1,2-Difluoroethane is more stable than the anti form which is sort of weird. This wikipedia article on the Gauche Effect ...
MaxW's user avatar
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4 votes

Stabilisation of carbocations through hyperconjugation

Hyperconjugation Hyperconjugation, as you point out, is able to stabilise carbocation intermediates, IUPAC define this as: the interaction is ... between σ-bonds and an unfilled or partially ...
NotEvans.'s user avatar
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3 votes
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Why is a 7-endo radical cyclisation favoured over a 6-exo in this synthesis?

Before make any suggestion for the sought cyclization mechanism, let’s look at some rules and guidelines set by peers in their early studies on radical cyclizations. Specifically, Beckwith and ...
Mathew Mahindaratne's user avatar
3 votes

Regioselectivity in iodolactonisation of γ,δ-unsaturated carboxylic acid

Although both 5- and 6- membered rings are thermodynamically stable, 5-membered rings are kinetically faster to form. See the referenced JACS paper and figure for an example. You may also be ...
Vice Chemist's user avatar
2 votes

A question about geometry of benzenetetrol

The melting point of 1,2,4,5-benzenetetrol is 210C (https://www.chemicalbook.com/ProductChemicalPropertiesCB41307665_EN.htm), so there is very probably significant intermolecular attraction between ...
James Gaidis's user avatar
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2 votes

Why is 1-bromotriptycene inert to nucleophilic substitution?

Sn1 reaction proceed through carbocation intermediate which has planar structure. The structure of 1-bromo triptycene is cage like structure so the bridgehead carbon cannot assume planarity , hence,...
Hemant's user avatar
  • 21
1 vote

lowest energy conformation of butan-2,4-diol

I presume it is in the gauche form that its energy is minimun because of possible hydrogen bonding between the hydroxy groups
SubZero's user avatar
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