All Questions
Tagged with stereoelectronics organic-chemistry
18 questions
4
votes
1
answer
567
views
Mechanism of three-membered lactone hydrolysis in base
I was reading up on the participation of neighboring functional groups and in the reaction below, I was wondering why hydroxide attacks the C–O bond instead of the carbonyl group of the lactone. ...
- 732
2
votes
0
answers
49
views
Solvent shell collapse
In "advanced organic chemistry part A" book page:306&307 , the author uses the term 'solvent shell collapse' when talking about the reason for retention of conformation in tertiary ...
- 567
0
votes
1
answer
100
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A question about geometry of benzenetetrol
In the 3d conformation of 1,2,4,5 - benzenetetrol, how could i determine the direction to which hydrogen atoms of hydroxyl groups would point? and if there were tertiary butyl groups in positions 3 &...
- 567
4
votes
2
answers
1k
views
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 ...
- 488
5
votes
2
answers
264
views
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? ...
- 5,532
12
votes
0
answers
246
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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 ...
- 17.2k
6
votes
2
answers
2k
views
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 ...
- 2,239
5
votes
1
answer
2k
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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 ...
- 1,796
10
votes
1
answer
730
views
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 ...
- 71.9k
6
votes
1
answer
5k
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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 ...
- 326
4
votes
1
answer
6k
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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 ...
- 49
18
votes
2
answers
2k
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 electronegativities of ...
- 379
7
votes
1
answer
1k
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; ...
- 14.4k
3
votes
1
answer
4k
views
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 ...
- 411
25
votes
3
answers
7k
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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 ...
- 498
13
votes
1
answer
685
views
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 ...
- 14.4k
20
votes
1
answer
7k
views
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 ...
- 963
30
votes
4
answers
14k
views
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 ...
- 18k