# Tag Info

11

From a 2007 paper:: Here we show that instrumental advances in Raman optical activity, combined with quantum chemical computations, make it possible to determine the absolute configuration of (R)-[$\ce{^2H1}$, $\ce{^2H2}$, $\ce{^2H3}$]-neopentane. This saturated hydrocarbon represents the archetype of all molecules that are chiral as a result of a ...

6

[Comment by Poutnik] Important is also en.wikipedia.org/wiki/Grotthuss_mechanism for the proton interchange. Mobility of H3O+ and OH- gives a hint it must be fast. If you compare the diffusion coefficient of hydroxide ($\pu{5.270e9 m^2/s}$) to that of fluoride ($\pu{1.460e9 m^2/s}$), you might be surprised to see such a difference despite their comparable ...

5

Optical rotation (OR) emerges from a difference in the index of refraction of a compound towards left/right circularly polarized light. All chiral have some difference in these indices of refraction. Your question specifically relates to isotopically chiral molecules where the effect is more subtle. You are correct that (OR) is fundamentally an electronic ...

4

There are a couple reasons this could be happening. The most interesting possibility: isotope effects during ion fragmentation You are performing LC-MS/MS, i.e., your mass spectrometer is chemically reacting the estradiol and estradiol-$d_5$ with gas molecules in the collision cell of the instrument. This process, known as CID or collisionally induced ...

3

Let's look at just the carbon-14 atoms. Assune 18.5% of your body mass is carbon and you weigh 80 kg. One carbon atom in a trillion is carbon-14. Working out the resulting mass of carbon-14 atoms in grams, dividing by 12.01 g/mol and multiplying by Avogadro's Number leads to roughly $7.4×10^{14}$ atoms. Carbon-14 has a half-life of about 5730 years. ...

3

On 2019-11-29 Ben Krasnow uploaded a YouTube video DIY mass spectrometer measures potassium in dietary salt substitute showing an outstanding construction of a mass-spec apparatus in his home shop based on the articles by Dewdney [1] and Stong [2] with some variations and improvements, like altered electrical scheme and increased emission current. The main ...

2

Does the distillation of alcohol cause the fractioning of isotopes[...]? The short answer is it depends. Distillation of ethanol from water can be done nearly to completion. There are published methods for determining isotopic composition of sugars in fruit juices which involve fermentation of the juice to yield ethanol, followed by nearly quantitative ...

2

It is not possible to measure the decay profile vs time as this is too long so the average number of disintegrations /time interval can be counted instead. From a consideration of the distribution of radioactive events the mean number of events in time $t$ is $M=N_0(1-e^{-kt})$ where $k$ is the decay constant and $N_0$ the initial number of atoms. For small ...

2

Old question, but in the interim Cody's lab has released this video (among others) on tasting heavy water. His conclusion was that $\ce{^2H_2}\ce{^{16}O}$ tasted sweeter than $\ce{^1H_2}\ce{^{16}O}$ but $\ce{^1H_2}\ce{^{18}O}$ didn't. He wasn't able to tell the difference after eating. Of course, chemists absolutely freak out at the suggestion that one ...

1

The notation is strange, but the result is correct. For example, if you have 100 dioxygen molecules (so 200 oxygen atoms), 10% of the atoms are of the 16-O isotope and we distribute them randomly, we get the following: 81 both 18-O 18 mixed species 1 both 16-O To visualize this, take all the numbers from 00 to 99, and say that the digit zero represents the ...

1

Isotopes differ in mass. Otherwise the same molecules but with the different mass have the different mean speed. The different speed means the different molecular collision rate. The different collision rate means the different kinetic constants. There are some indirect effects of different isotop mass on the kinetics, but these are much smaller than the ...

1

According to Wikipedia, this type of isomerism is known as Isotopomerism Isotopomers or isotopic isomers are isomers with isotopic atoms, having the same number of each isotope of each element but differing in their positions. The result is that the molecules are either constitutional isomers or stereoisomers solely based on isotopic location. For example,...

1

I don't know of any such tables. For chemistry the values are so close as to make no difference except for very light elements such as hydrogen. All in all you should be able to get a good idea of the difference by using the difference in reduced mass, $m_\mathrm{r}$. m_\mathrm{r} = \dfrac{m_\mathrm{electron}m_\mathrm{nucleus}}{m_\mathrm{electron}+m_\...

1

The key word is "mixing". If you take a glass cylinder and fill it halfway with D2O (the heavier water, so put it on the bottom) and fill the cylinder ever so gently with H2O, the mixing will be determined by diffusion (NO mechanical mixing). But the experimental techniques required to analyze and determine the rates would be expensive and time-consuming. ...

1

As a general matter, it seems possible that neutron isotopes are actually not physically similar to their elements, since, for example, a given isotope might not be stable. It was very well known (pre-1940s) that the number of protons (Z) distinguish one element from the other. If we talk about the simplest element with Z=1, whether it contains 0, 1 or 2 ...

1

Not by a homebuilt mass spectrometer, you can't. At least not with a reasonable amount of effort. A mass spectrometer is a very complicated and sensitive charged-particle optics instrument. A useful mass spectrometer for materials that are not a gas or vapor at near room temperature is far more complicated and expensive than that. A mass spectrometer ...

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