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Questions tagged [stereoelectronics]

For questions where the reactivity/conformation of the molecule is defined/controlled by a specific orbital arrangement/alignment (for example the unusual conformation of sugars because of the anomeric effect). This tag cannot be the only tag on a question. Tags such as [tag:conformation], [tag:organic-chemistry] must also be applied.

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

Normally, according to Baldwin's rules, 3-exo to 7-exo cyclisations are preferred over endo cyclisations. But in the following example, a 7-endo-trig reaction is favoured over a 6-exo-trig and I am ...
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Regioselectivity in iodolactonisation of γ,δ-unsaturated carboxylic acid

In the last step of the iodolactonisation of 3,3-dimethylpent-4-enoic acid,[1,2] why does the carboxylate attack the iodonium to form a 5-membered ring, when a more stable 6-membered ring is possible? ...
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Rationalising diastereoselectivity of hydroboration using stereoelectronics

Using bulky reagents such as 9-BBN, hydroboration is often highly diastereoselective, giving rise to the 1,2-anti diastereomer: This is easily explained using a steric argument, with the major ...
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2answers
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Why is 1-bromotriptycene inert to nucleophilic substitution?

According to my textbook, 1-bromotriptycene is inert to any nucleophilic substitutions. Due to steric hinderance we can say SN2 reactions cannot occur, but I think SN1 reactions should be favoured as ...
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1answer
502 views

Why is methyl α-D-glucopyranoside preferentially formed from glucopyranose in acidic methanol?

According to my textbook Organic Chemistry 2e by David Klein, the formation of a glycoside from glucopyranose favors the α form (see picture below). Why does this happen? Shouldn't the equilibrium ...
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1answer
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Stereoelectronic effects in torquoselectivity of 4π electrocyclic opening

Thermal 4π electrocyclic ring openings of cyclobutenes to form butadienes are known to proceed in a conrotatory manner, consistent with the Woodward–Hoffmann rules. However, there are two different ...
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1answer
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Stereoelectronics of the Houk model

In Clayden's Organic Chemistry it gives the Houk model as a way for predicting selectivity for alkene reactions where an existing stereocentre is present (diastereoselectivity). Unlike the ...
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1answer
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Stabilisation of carbocations through hyperconjugation

Our teachers told us that greater the number of alpha H, greater is the stability of carbocation. But consider this: $\ce{CH3CH2+}$ and. $\ce{CH3CH2CH2+}$ The first one has 3 alpha H ...
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2answers
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lowest energy conformation of butan-2,4-diol

Do the OH groups want to be furthest apart? or the CH3 groups? I'm trying to determine the lowest energy conformation - and I don't know which group has the bigger steric effect?
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2answers
687 views

Gauche effect and bond length

Which of the following compounds has the longest bond length? (A) $\ce{H3C-CF3}$ (B) $\ce{FCH2-CH2F}$ (C) $\ce{F2CH-CHF2}$ (D) $\ce{F3C-CF3}$ My logic was based on the relative ...
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1answer
468 views

Baldwin's rules exceptions: cations

Why do cations violate Baldwin's rules? For example, the following acetalization mechanism is plausible even though it contains a 5-endo-trig step: Image taken from: Clayden, J. Organic Chemistry; ...
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Steric hindrance of an unbonded electron pair

This question is half inspired by this question, and half inspired by the structure of molecules like hydrazine and hydrogen peroxide. When I was looking at the aforementioned molecules, I started ...
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1answer
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Hydrolysis of Sucrose over Sn1Ac or Sn2Ac

In "March's Advanced Organic Chemistry" I have read about the general mechanism of the acetal hydrolysis. It names the acid-catalyzed SN1 or SN2 as a possible mechanism for a Acetal-hydrolysis. Now I ...
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3answers
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How are SN2 transition states stabilised by adjacent double bonds and carbonyl groups?

It is my understanding that transition states in an SN2 reaction have some filled and some empty orbital character, as we have the backside of the C-X σ* beginning to fill with electrons from the HOMO ...
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1answer
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How can the gauche-effect be explained?

Generally, anti-conformations are more stable. But in the case of 2-fluoroethanol, the gauche confirmation is more stable. It's given in March's advanced organic chemistry book that intramolecular ...
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1answer
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Stereoelectronic effects in carbamate carbonyl oxygen attack on halide

2-Bromoethyl (2-bromoethyl)carbamate can react through either Path A or Path B to form salt 1 or salt 2. In both instances the carbonyl oxygen functions as the nucleophile in an intramolecular ...
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Why are lactones more acidic than esters?

Lactones ($\mathrm pK_\mathrm a \sim 25$) tend to be more acidic than esters ($\mathrm pK_\mathrm a \sim 30$). I know that the lactone is fixed in a (E)-conformation, due to the ring: and that in ...
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4answers
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Why are DCM and chloroform so resistant towards nucleophilic substitution?

In the book Organic Chemistry by J. Clayden, N. Greeves, S. Warren, and P. Wothers I found the following reasoning: You may have wondered why it is that, while methyl chloride (chloromethane) is a ...
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3answers
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Which conformer of beta D-glucose is more stable?

I drew the two chair conformers of $ \beta $-D-glucose: Which one is more stable? I think it's the one with all of the OH groups in the equatorial position because of less steric hindrance, but I ...