May 18, 2024, 04:49:36 PM
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Organic Chemistry Forum / Re: Cahn-Ingold-Prelog ACS Question on YouTube
« Last post by benz0icacid on Today at 03:44:04 PM »
I agree. Also, it doesn't make sense for it to be 2R, 3S and it's cis. It would be 2R, 3R, if I'm not mistaken.
Thanks!
edit: exactly, @Hunter2. Thank you!
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Organic Chemistry Forum / Re: Cahn-Ingold-Prelog ACS Question on YouTube
« Last post by Hunter2 on Today at 03:43:44 PM »
It should be the cis - 4-bromo-2R,3R epoxy- butan-1-ol.
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Organic Chemistry Forum / Re: Cahn-Ingold-Prelog ACS Question on YouTube
« Last post by Babcock_Hall on Today at 03:07:26 PM »
The video looks incorrect to me.
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Organic Chemistry Forum / [Solved] Cahn-Ingold-Prelog ACS Question on YouTube
« Last post by benz0icacid on Today at 02:12:36 PM »
Hello!
I'm watching an ACS Ochem 2 Exam Review: https://www.youtube.com/watch?v=OQctLH-psYc&list=PL3A1cf8LCsnlSRO3HEygntDa4cd9tQh2U&index=1

At timestamp 4:30, we are assigning R and S configuration for the epoxide's carbon #3. We are comparing the carbon with O, C, H, and the carbon connected to Br, H, H. The carbon connected to OCH is given 2nd priority, and the carbon with BHH is given 3rd priority. Why is that? I thought since Br has the higher mass, it would have 2nd priority?

I also found a similar question on R/MCAT: https://www.reddit.com/r/Mcat/comments/91mzf1/br_or_oh_higher_priority/

I would appreciate the clarification. Thank you for your time and patience!
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Organic Chemistry Forum for Graduate Students and Professionals / Re: Sulfamidophosphonate synthesis via n-butyllithium: ratio of starting materials
« Last post by rolnor on Yesterday at 05:37:15 PM »
Quote from: Babcock_Hall on Yesterday at 09:42:36 AM
https://pubs.acs.org/doi/10.1021/acs.jmedchem.8b01523 
Granberg KL, J. Med Chem. 2019, 62, 3, 1385-1406. 

One thing that attracted me to this method is that the ratio of the methyl sulfonamide to base to the chlorophosphate is 1:2:1; in other words, there is not the approximate twofold of excess of the methyl sulfonamide over the phosphorylating agent that I found in most other protocols.  As to what is different, my speculation is that the steric bulk of this base prevents it from removing a proton from the product, which is more acidic than the starting material.

Or maybe the product becomes a TMS enol? I know that ethyl acetate is best lithiated by LiHMDS it gives better yields, better than LDA. Its interesting. I dont know if steric bulk stops deprotonation, maybe it does
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High School Chemistry Forum / Re: Why does removing valence electrons increase effective nuclear charge?
« Last post by Corribus on Yesterday at 05:12:04 PM »
Quote from: sd79812 on Yesterday at 04:54:49 PM
As far as I know, Valence shell electrons don't shield other valence shell electrons from the proton in the nucleus, and outer shell electrons don't shield inner shell electrons.
This is incorrect. Valence shell electrons do shield other valence shell electrons; the effect is not as strong as the shielding effect by inner shell electrons, but it is not negligible. An outer shell electron may even spend some of its time closer to the nucleus than an inner shell electron, meaning a valence shell electron may exhibit a small shielding effect on an inner shell electron. Depending on your level of study, you may want to review structural models of the atom to have a better understanding of why this is the case.

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High School Chemistry Forum / Why does removing valence electrons increase effective nuclear charge?
« Last post by sd79812 on Yesterday at 04:54:49 PM »
If effective nuclear charge is net pull inwards by all the protons in the nucleus on outer electrons, why does removing a outer electron increase the net pull by the protons on outer electrons inwards? As far as I know, Valence shell electrons don't shield other valence shell electrons from the proton in the nucleus, and outer shell electrons don't shield inner shell electrons.

I'm learning about cations smaller than their neutral atoms.

If F_electrostatic=kq_1q_2/r^2. Let q_1 be charge of nucleus' proton(s) which is constant if you make a neutral atom a cation. AFAIK: If q_2 is negative and becomes smaller because you pulled out an electron to form some cation, then you're decreasing attractive force inwards towards the nucleus, which means that quite absurdly you're decreasing effective nuclear charge contrary to what my source says.
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Analytical Chemistry Forum / Re: RSD Volumetric Solutions (European Pharmacopeia)
« Last post by marquis on Yesterday at 11:16:55 AM »
Yes, it is difficult.  It's best to read all the related paragraphs, because sometimes there's a bit of an out.  But that value is not too strange for either the EP or the USP.  It can make titration quite interesting.  There are some tricks played.  Some of the techs would make sure their weights were always as close to identical as possible ( before dissolving a reference standard, if done by weight). Then the titration volumes should be nearly the same, as well.  And trying to get by with the minimum amount of indicator and using white surfaces, as well as good volume reading, helps a lot.  The automated equipment was only helpful if doing many identical standardizations.  It was usually more of a pain than it was worth to us.  Good luck.
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Organic Chemistry Forum for Graduate Students and Professionals / Re: Sulfamidophosphonate synthesis via n-butyllithium: ratio of starting materials
« Last post by Babcock_Hall on Yesterday at 09:42:36 AM »
https://pubs.acs.org/doi/10.1021/acs.jmedchem.8b01523 
Granberg KL, J. Med Chem. 2019, 62, 3, 1385-1406. 

One thing that attracted me to this method is that the ratio of the methyl sulfonamide to base to the chlorophosphate is 1:2:1; in other words, there is not the approximate twofold of excess of the methyl sulfonamide over the phosphorylating agent that I found in most other protocols.  As to what is different, my speculation is that the steric bulk of this base prevents it from removing a proton from the product, which is more acidic than the starting material.
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Analytical Chemistry Forum / RSD Volumetric Solutions (European Pharmacopeia)
« Last post by becchino on Yesterday at 05:24:03 AM »

Dear.. as indicated in paragraph 4.2.2 of the European Pharmacopoeia, it is necessary that the replications relating to the correction factor respect a max rsd of 0.2 it is really difficult to obtain this repeatability. especially for low concentrations.. do you have any ideas?

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