# 6.1 Determination of energetics of fluxional molecules by nmr  (Page 3/4)

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$\frac{1}{t}=\frac{1}{{t}_{a}}+\frac{1}{{t}_{b}}$

For reference, the exact lineshape function (assuming two equivalent groups being exchanged) is given by the Bloch Equation, [link] , where g is the intensity at frequency v , and where K is a normalization constant

$g\left(v\right)=\frac{\text{Kt}\left({v}_{a}+{v}_{b}{\right)}^{2}}{\left[0\text{.}5\left({v}_{a}+{v}_{b}\right)-v{\right]}^{2}+{4\pi }^{2}{t}^{2}\left({v}_{a}-v{\right)}^{2}\left({v}_{b}-v{\right)}^{2}}$

## Low temperatures to coalescence temperature

At low temperature (slow exchange), the spectrum has two peaks and Δ v >>t. As a result, [link] reduces to [link] , where T 2a’ is the spin-spin relaxation time. The linewidth of the peak for species a is defined by [link] .

$g\left(v{\right)}_{a}=g\left(v{\right)}_{b}=\frac{{\text{KT}}_{2a}}{1+{T}_{2a}^{2}\left({v}_{a}-v{\right)}^{2}}$
$\left({\mathrm{\Delta v}}_{a}{\right)}_{1/2}=\frac{1}{\pi }\left(\frac{1}{{T}_{2a}}+\frac{1}{{t}_{a}}\right)$

Because the spin-spin relaxation time is difficult to determine, especially in inhomogeneous environments, rate constants at higher temperatures but before coalescence are preferable and more reliable.

The rate constant k can then be determined by comparing the linewidth of a peak with no exchange (low temp) with the linewidth of the peak with little exchange using [link] , where subscript e refers to the peak in the slightly higher temperature spectrum and subscript 0 refers to the peak in the no exchange spectrum.

$k=\frac{\pi }{\sqrt{2}}\left[\left({\mathrm{\Delta v}}_{e}{\right)}_{1/2}-\left({\mathrm{\Delta v}}_{0}{\right)}_{1/2}\right]$

Additionally, k can be determined from the difference in frequency (chemical shift) using [link] , where Δ v 0 is the chemical shift difference in Hz at the no exchange temperature and Δ v e is the chemical shift difference at the exchange temperature.

$k=\frac{\pi }{\sqrt{2}}\left({\mathrm{\Delta v}}_{0}^{2}-{\mathrm{\Delta v}}_{e}^{2}\right)$

The intensity ratio method, [link] , can be used to determine the rate constant for spectra whose peaks have begun to merge, where r is the ratio between the maximum intensity and the minimum intensity, of the merging peaks, I max /I min

$k=\frac{\pi }{\sqrt{2}}\left(r+\left({r}^{2}-r{\right)}^{1/2}{\right)}^{-1/2}$

As mentioned earlier, the coalescence temperature, T c is the temperature at which the two peaks corresponding to the interchanging groups merge into one broad peak and [link] may be used to calculate the rate at coalescence.

$k=\frac{{\mathrm{\pi \Delta v}}_{0}}{\sqrt{2}}$

## Higher temperatures

Beyond the coalescence temperature, interchange is so rapid (k>>t) that the spectrometer registers the two groups as equivalent and as one peak. At temperatures greater than that of coalescence, the lineshape equation reduces to [link] .

$g\left(v\right)=\frac{{\text{KT}}_{2}}{\left[1+{\mathrm{\pi T}}_{2}\left({v}_{a}+{v}_{b}-2v{\right)}^{2}\right]}$

As mentioned earlier, determination of T 2 is very time consuming and often unreliable due to inhomogeneity of the sample and of the magnetic field. The following approximation ( [link] ) applies to spectra whose signal has not completely fallen (in their coalescence).

$k=\frac{0\text{.}\text{5π}{\Delta v}^{2}}{\left({\mathrm{\Delta v}}_{e}{\right)}_{1/2}-\left({\mathrm{\Delta v}}_{0}{\right)}_{1/2}}$

Now that the rate constants have been extracted from the spectra, energetic parameters may now be calculated. For a rough measure of the activation parameters, only the spectra at no exchange and coalescence are needed. The coalescence temperature is determined from the NMR experiment, and the rate of exchange at coalescence is given by [link] . The activation parameters can then be determined from the Eyring equation ( [link] ), where k B is the Boltzmann constant, and where ΔH - TΔS = ΔG .

$\text{ln}\left(\frac{k}{T}\right)=\frac{{\mathrm{\Delta H}}^{‡}}{\text{RT}}-\frac{{\mathrm{\Delta S}}^{‡}}{R}+\text{ln}\left(\frac{{k}_{B}}{h}\right)$

For more accurate calculations of the energetics, the rates at different temperatures need to be obtained. A plot of ln(k/T) versus 1/T (where T is the temperature at which the spectrum was taken) will yield ΔH , ΔS , and ΔG . For a pictorial representation of these concepts, see [link] .

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
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Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
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many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
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