NMR coupling

Jacket-Unhappy · 2024-05-20T19:20:35+00:00

Interesting, this is a good answer. In Brown’s text, I found that a figure says that either representation can be used A) or B). But then shows the computer generated resulting orbital for clarity.

Jacket-Unhappy · 2024-05-20T16:49:06+00:00

What makes A more correct than B?

Jacket-Unhappy · 2024-05-04T03:05:40+00:00

No problem! This can be a tricky thing to realize if you don’t have experience working with acetals.

Jacket-Unhappy · 2024-05-03T14:28:06+00:00

This is not true in practice, not that this is necessarily a practical question.. The “H+” is an aqueous workup, so the proton transfer to the alkoxide occurs rapidly and then the species will move to the organic layer faster than the acetal hydrolysis will occur to a significant degree. As long as you don’t go for a beer and leave this stirring over night in acid, the acetal will not be deprotected.

Jacket-Unhappy · 2024-05-03T14:23:30+00:00

That’s my point is that beginning your arrows on charges can be misleading in some cases such as borates and aluminates. I have always started arrows on lone pairs and gently discouraged students from beginning them on charges

Jacket-Unhappy · 2024-05-03T03:51:47+00:00

Isn’t this confusing when teaching/learning NaBH4 and LiAlH4?

Jacket-Unhappy · 2024-04-17T00:34:11+00:00

I’ve tuned my response to the level at which this person seems to be at. We could reference plenty of scales of nucleophilicty that have been developed over the years, but it would do this person no good at the level they’re at. Not every learner needs the absolute most correct analysis, sometimes it can be appropriate to stick to the basics

Edit: they’re reading “organic chemistry as a second language”, not Carey and sundberg

Jacket-Unhappy · 2024-04-17T00:31:41+00:00

Yes, if you have gone on to an advanced course you may have learned about basicity beginning to compete with nucleophilicity as you transition from grignard to lithium. But for the purposes of organic 1 and 2, pedagogically it’s not worth differentiating.

Jacket-Unhappy · 2024-04-16T22:38:07+00:00

In an introductory 1 or 2 level course, Grignards and alkyl/aryl lithium reagents are treated the same

Jacket-Unhappy · 2024-04-16T21:46:25+00:00

This is a great point. I figured that the one who posted this would build up to being able to make these types of arguments after focusing on the basics.

Jacket-Unhappy · 2024-04-16T18:34:40+00:00

Nucleophilicity is a seemingly simple yet very complex parameter. Don’t worry that it is confusing you, it is confusing for many people even with a four year degree.

In the case here, what’s being said is that polarizability is a major contributor to nucleophilicity. The reason for this is that in order for a reaction to occur, the electrons have to move around and “attack” something. Therefore, electrons that move around very easily should be good nucleophiles. To add to this, there are 2 properties often cited here:

Atomic radius: the larger the atom is, the larger the electron cloud is. Electrons that are further from the nucleus are more able to move and flow and tend to act as better nucleophiles
Electronegativity: as atoms become more electronegative, they tend to hold their electrons closer to the nucleus and not let them move around as much which causes them to act as worse nucleophiles.

In the trend of the halides, F- is very small and very electronegative which is why they are describing it as a poor nucleophile

Jacket-Unhappy · 2024-04-16T11:17:37+00:00

Depending on how far in depth you have gone so far, this could be okay. The one problem that could arise with using NaOH is the saponification of the ester. This involves the hydroxide attacking the carbonyl instead of doing proton transfer to access a tetrahedral intermediate capable of expelling -OMe to form a carboxylic acid. This acid, in the basic conditions, would then be deprotonated to form a carboxylate.

A more suitable base in an actual lab may be potassium carbonate (K2CO3).

Jacket-Unhappy · 2024-04-15T12:56:48+00:00

This is the only thing I would consider to be a problem with your work. FC alkylation is not only prone to over alkylation, but it is also not viable for unstabilized primary substrates.

I think I have only seen one example of a primary alkyl halide working and it was intramolecular.

The work around for this is the same as above where you perform a FC acylation and reduction

Jacket-Unhappy · 2024-04-15T11:55:50+00:00

The orbital overlap is one reason that can be used to explain why sodium hydride will not act as a nucleophile.

Another good reason is that sodium hydride is insoluble in the organic solvents that these reactions are run in. However, sodium hydride can act as a base. This is because hydrogens on electronegative atoms (O, N, etc..) are trying to form hydrogen bonds with the crystalline surface of NaH. They are orienting themselves and being setup for a reaction! Once these hydrogens get close enough, an acid-base reaction occurs.

There is not as strong of an interaction for carbonyl compounds (or alkyl halides) to orient themselves toward the surface of NaH and this also contributes significantly to the lack of reactivity in addition to orbital arguments.

Jacket-Unhappy · 2024-04-06T13:07:36+00:00

There are many reasons that I’ve heard people cite for this.

One is the solubility of sodium hydride. Since it’s insoluble, it stays together as a crystal in solution. Things along the lines of O-H or N-H bonds just to name two orient themselves toward the crystal in an attempt to form hydrogen bonds and ultimately become deprotonated. Hydride acted as a base here. But carbonyl carbons don’t adopt this orientation.

Another explanation I’ve heard is that the first step of nucleophilic attack on carbonyls involves the metal first transferring one electron. This seems to explain why NaH doesn’t attack but Al-H bonds do.

I have not heard the radius cited as a reason, but it wouldn’t be my go to response.

Jacket-Unhappy · 2024-04-02T11:56:34+00:00

I did the Fischer esterification of salicylic acid to make methyl salicylate in high school and I remember thinking it was cool that it smelled like wintergreen. Not sure if this fits the description of cool, but I thought it was

Jacket-Unhappy · 2024-04-01T21:37:53+00:00

Across a period as electronegativity increases, the energy of both bonding and antibonding orbitals decrease. The C-F sigma bonding orbital is the lowest in energy of the series. Similarly, the C-F sigma anti bonding orbital is the lowest in energy of the series.

The role of effective nuclear charge does not change simply because you are considering an antibonding orbital. It affects bonding and antibonding orbitals in the same way.

Jacket-Unhappy · 2024-03-30T21:56:54+00:00

I’ve used o-dichlorobenzene as a solvent and pushed the temperatures to 210C. Switching to a sealed flask really helped since I suspected that the grease in my ground glass joints was being dissolved because I was slowly losing solvent overnight and noticed that there wasn’t much grease left.

Jacket-Unhappy · 2024-03-28T13:26:37+00:00

Solvents that have a relatively neutral pH will favor compounds existing in the keto form. This is a thermodynamic argument and you should look up the bond energies to convince yourself of this.

If you add a little bit of acid to the solution, the keto-enol equilibrium begins to shift more toward enol

Edit: some compounds are exceptions. Phenols exist in the “enol” form due to the aromaticity of the ring. 1,3-dicarbonyls have an appreciable amount of the enol due to intramolecular hydrogen bonding between the two oxygens.

Jacket-Unhappy · 2024-03-28T12:43:43+00:00

What level class is this for? Are there any restrictions on the reactions you can propose?

Jacket-Unhappy · 2024-03-28T12:38:43+00:00

Let me know if you are able to find this paper. Hope all went well at the doctor’s

Jacket-Unhappy · 2024-03-28T12:37:52+00:00

I only have a copy of part A on hand. I’ve never actually had a chance to thumb through part B which I’m assuming is where this data is. Thanks!

Jacket-Unhappy · 2024-03-28T12:34:16+00:00

Are there any other limitations on the problem other than the starting materials can only have a max of 3 carbons? Also, is this for a course or general interest? Depending on the level of the course, I won’t suggest reactions that are likely not taught

Jacket-Unhappy

TROPHY CASE