For each pair, predict the stronger nucleophile in the SN2 rea...

Question

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction.

g. (CH₃)₂CHO^– or CH₃CH₂CH₂O^–

h. I^– or Cl^–

Accepted Answer

All right. Hello everyone. So this question is asking us to determine which is the stronger between the two N files using alcohol as the solvent in the SN two reaction. Explain. And here we have two different pairs of nucleo files which we'll discuss further throughout this video. But for now, let's talk a little bit about the SN two reaction in general. And what makes an effective nuc file? Now, a nucleo file is a term that can be used to describe a Lewis base because a Lewis base is a species that donates a pair of electrons towards a different species. In this case, the electro and in the S and two reaction, in particular, the nucleo file or Lewis base must be considered strong. So now lets talk about a few different factors that determine the strength of a nucleo phi first, we have the charge because recall that a negatively charged nucleo file is stronger than a neutral one. So that's the first factor that comes to mind. But after that, we can also consider the electron negativity or e for short because as the electron negativity of an atom increases. So does its nucleo Felicity. Now, nuc Felicity also increases as polaris ability increases. So in addition to these first three factors, we can also talk about the effects of resonance and strix. So with respect to resonance, the stabilization of a negative charge or loan pairs of electrons via resonance actually makes the Nile less reactive because that stability is increased. And on the topic of steri hindrance, a less hindered nucleo is considered stronger than the more hindered ones because the more hindered or the bulkier N files are going to have a harder time approaching the electro file. And last but not least if this information is provided, we can also talk about the effect of the solvent on nuc Felicity because N Felicity decreases with increased salvation of an anion in a particular solvent. Now an alcohol, if you recall is an example of a polar pro solvent because it's capable of hydrogen bonding in a polar product solvent, then the nucleic anions can be salted. And because smaller nucleo files are solved more effectively because theyre physically smaller and therefore easier to surround larger NUC files are more effective in polar product solvents. By contrast, a polar a product solvent such as DMSO or Acetone does not solv the nucleo. So a smaller nucleo file is more effective in that context. But now that we've talked a little bit about NUC files and what factors determine their strength. Let's go ahead and talk about each respective pair starting off with number one or part one, we can see here that we have two nuc files in which oxygen has a negative charge. Now both have a negative charge which does make them relatively strong. And in this case, we cannot compare electronegativity because the same element or the same atom bears the negative charge. However, we can talk about the structure of the carbon chain that's attached to each one because even though both N files have a four carbon chain, one of them has branching considering there's a metal substituent. Whereas the second one does not have any branching. It is a straight four carbon chain now because branching adds an element of STAIC hindrance. Then the first nucleo file is more sternly hindered and therefore weaker because a more hindered nucleo file is going to have a harder time approaching an electro file. This means that the second nuc file in which oxygen is attached to a four carbon straight chain is the stronger NUC file since it is less dely hindered. So here I'm going to briefly pause the recording so I can write out the final answer to part one. All right. So here I've resumed the recording and the answer to part one is as follows. The stronger NUC file is CH three CH two CH two CH 20 negative because it is less sternly hindered. So now we can go ahead and talk about the second pair in which we're comparing the bromide and fluoride ions. Now, once again, they both have a negative charge, which means that they're both relatively strong nucleo files. However, it's worth mentioning that bromine is physically larger than fluorine. And because we're dealing with a pro solvent nucleic actually increases as the size increases, which means bromide would be the stronger nucleo. And also we can talk about electron negativity. Now, I do want to go ahead and correct a statement that I made earlier in this video talking about electron negativity because in actuality, n Felicity decreases as electron negativity increases. So it's actually an inverse relationship because of this fluorine being more electron than bromine is going to be a less effective nucleo file as well. So the answer to part two is bromide and the explanation is as follows because bromide is larger, endless electron negative then fluoride and there you have it. So with that being said, thank you so very much for watching. And I hope you found this helpful.

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction.
g. (CH₃)₂CHO^– or CH₃CH₂CH₂O^–
h. I^– or Cl^–

Key Concepts

Nucleophilicity

Solvent Effects in SN2 Reactions

Steric Hindrance

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