8
votes
Nucleophilicity in polar aprotic solvent (DMSO)
let me start with nucleophilicity of halides. In protic polar solvent, $\ce{F^-}$ is more solvated (hydrogen bonding) than $\ce{I^-}$ and hence less reactive.
In polar aprotic solvent $\ce{F^-}$ ...
- 4,394
7
votes
Accepted
Comparing the rates of hydrolysis of different haloalkanes
This confusion arise because OP did not look at the energy profile of $\mathrm{S_N}$1 mechanism. The first order kinetics of $\mathrm{S_N}$1 reactions (e.g., reactions given in the question) suggests ...
- 42.1k
7
votes
Accepted
Possible dehydration after nucleophilic addition
Similar to to last step of aldol condensation to give $\alpha, \beta$-unsaturated ketone, the last elimination step at sought reaction is also supposed to undergo elimination of water molecule through ...
- 42.1k
6
votes
Is hydrazine a better nucleophile than ammonia?
Yes, hydrazine is a better nucleophile than ammonia. This is the case in both water (a protic solvent) as well as acetonitrile (an aprotic solvent). A quantitative approach may be found in the Mayr ...
- 71.9k
6
votes
Order of Nucleophilicity
Please remember that nucleophilic substitution at a saturated carbon atom does not directly correlate with pKa.
The pKa of a substance (in the Bronsted-Lowry definition) relates to the substance's ...
- 811
5
votes
Which will give faster SN2 reaction
There is no sense of comparing the reaction rate when one of the compound doesn't show SN2 mechanism. And, that compound is $\ce{CH2=CHBr}$, due to the fact that it is a vinyl halide.
$\ce{CH2=CHBr}$ ...
- 3,081
5
votes
Comparing the rates of hydrolysis of different haloalkanes
One way to interpret the solvent effect in this particular problem is that, as you mentioned, the iodide could attack the carbocation if it weren't trapped as much as the other halides were. But, that ...
- 115
4
votes
Will "soft nucleophiles" undergo 1,4-conjugate addition even if the β-carbon is sterically hindered?
Your line of thought possibly is influenced by the Walden inversion which is characteristic for the nucleophilic substitution mechanism of $\mathrm{S_N2}$ where steric hindrance affects the rate when ...
- 31.4k
4
votes
In hydroboration oxidation reaction .. why do not we use sodium hydroxide alone as a nuclophile?
The combination of hydroxide and peroxide is essential for the oxidation of boranes to alcohol, both components are needed. Firstly the hydroxide deprotonates peroxide to give peroxide anion - a good ...
- 23k
3
votes
Why is the reaction rate of tert-butyl chloride solvolysis faster in 80% water/20% acetone, than in 70% water/30% acetone?
Water is more polar than acetone, so 80/20 water/acetone is a more polar solvent than 70/30 water/acetone. Since the SN1 reaction has a positively charged carbocation intermediate, more polar ...
- 22.6k
3
votes
When does Alcohol act as Solvent and as a Nucleophile?
The proposed solution to this roadmap problem has several errors. I am assuming that $\ce{K2Cr2O7}$, methanol and $\ce{LiAlH4}$ are employed in excess. In the oxidation of 1 (A), chromic acid, $\ce{...
- 17.5k
3
votes
Why is fluoride the most nucleophilic halide in aprotic solvents?
When talking about elements of a group, the size of the atom is more effective than the electronegativity factor.
As $\ce{F-}$ size is too short so its electron density will be much higher than other ...
- 31
3
votes
Which is a better nucleophile: hydroxide anion or amide anion?
I was not able to find data on this nucleophilicity of $\ce {NH2^-}$ and $\ce {OH^-}$ in dimethylformamide, $\ce {Me2NCHO}$. However, I have a plausible explanation as to why the answer may not be ...
- 10.8k
3
votes
Nucleophilicity with respect to the solvent
Actually nucleophilicity is inversely proportional to electronegativity when comparing compounds across the period, and inversely proportional to size when comparing in the same group. This condition ...
- 124
3
votes
Nucleophilicity in polar aprotic solvent (DMSO)
The negative charge is actually not all on the oxygen on for the phenolate on the right. It can be delocalized in the ring, which makes the whole molecule less basic. The negative charge is fully ...
- 1,618
3
votes
Accepted
Why polar aprotic solvents don't surround negatively charged nucleophiles?
Found a good explanation in Oxford University presentations.
It appears that partially positive side of aprotic solvents is hindered in the middle of the molecule. Only negative charge is on the ...
- 1,567
3
votes
Accepted
Bromination of an alkene in presence of water
While there is no formal carbocation intermediate, the cyclic bromonium intermediate has a few different resonance forms (reference):
As you can see on the right, in the structure representing the ...
- 700
2
votes
Accepted
Which one is the stronger nucleophile? CH3CH2O or CH3CO2
Since a nucleophile is a species that is donating a pair of electrons, it’s reasonable to expect that its ability to donate electrons will increase as it becomes more electron rich.
As electron ...
- 558
2
votes
Accepted
Why is N- a better nucleophile than S-?
I think it would be nice to consider the charge density. The S- is more stable than N- because it has more electron shells, so the negative charge density is better distributed in the atom. It makes ...
- 46
2
votes
Accepted
Order of Nucleophilicity
It has been established here that basicity and nucleophilicity are distinct concepts. Why then is basicity often used as a measure of nucleophilicity?
To answer this question, we have to consider the ...
- 10.8k
2
votes
Accepted
Which will give faster SN2 reaction
$\ce{CH3-CH-Br}$ will give faster $\mathrm{S_N2}$ reaction because when a nucleophile will approach $\ce{CH2=CH-Br}$ for $\mathrm{S_N2}$ reaction the double bond between $\ce{CH2=CH}$ will hinder its ...
- 79
2
votes
Is hydrazine a better nucleophile than ammonia?
Yes hydrazine is a better nucleophile than ammonia (ignoring solvent effects) and this is called the "alpha effect" which states that the nucleophilicity of an atom increases if it has an adjacent ...
- 3,042
2
votes
Why does using NaI as a nucleophile and acetone as solvent lead to an SN2 reaction mechanism instead of SN1? Is I- not considered a weak nucleophile?
As Jan wrote, there isn't a hard and fast rule encompassing every mechanism, so there may not be a definitive answer to the question. Nevertheless, I found an interesting site that talked a little bit ...
- 1,668
2
votes
Why are Grignard reagents nucleophiles and not ambiphiles?
In fact a Grignard reagent reacting with, let us say, a ketone, is ambiphilic. However, the electrophilic component of the reaction, in which the positively charged magnesium combines with the ...
- 62.6k
2
votes
Do ambident nucleophiles form functional isomers?
Yes, ambident nucleophiles show functional isomerism. Two examples are:
Cyanide ($\ce{CN}$) and isocyanide ($\ce{NC}$)
Nitrite ($\ce{ONO}$) and Nitro ($\ce{NO2}$)
- 556
2
votes
Iodide ion is good leaving group and a good nucleophile. How can both be correct?
Nucleophilicity
Because smaller anions are very well solvated in polar protic solvents, such as water and methanol, iodide is a very good nucleophile:
$$
\textbf{Polar Protic Solvents}\\
\begin{align}
...
- 2,364
2
votes
Accepted
Does the nucleophilicity of an alkene increase with increase in alpha hydrogen or hyperconjugative structures?
When the number of alpha carbons increases, the +I effect causes the electron density on the carbon of the C=C bonds to increase, making this double bond act like a nucleophile. Note that if the ...
- 36
1
vote
What is the product when alcohol is added to carbonyl compounds?
As already pointed out in the comments, the second reaction reagent is not exactly an alcohol but an alkoxide. For example, $\ce{EtONa}$ and not $\ce{EtOH}$.
This makes the reaction condition for the ...
- 3,161
1
vote
Stereochemical outcomes for hydrohalogenation when there is a carbocation rearrangement
This is correct. Since the methyl rearrangement can occur at either side of the planar carbocation, and Cl- can attack either side of the resulting planar tertiary carbocation, all four possible ...
- 11
1
vote
Comparing Rate of Hydrolysis of Acyl halides
The high reactivity of acyl chlorides towards nucleophilic attack is due to the highly polarised situation of the carbon-oxygen/chlorine bonds i.e.
As you have mentioned due to the phenyl ring being ...
- 558
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