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Experiment 1 NMR (Nuclear Magnetic Resonance Spectroscopy

Objective

To introduce or re-acquaint you to the fundamentals of Nuclear Magnetic Resonance spectroscopy (NMR spectroscopy) and to show you how the information obtained from this technique can be used to determine molecular composition and structure. Mass (MS), infrared (IR), and nuclear magnetic resonance (NMR) spectrums ( 1 H size 12{ {} rSup { size 8{1} } H} {} and 13 C size 12{ {} rSup { size 8{"13"} } C} {} ) are useful tools for analyzing unknown organic compounds.

Grading

  • The correctness and thoroughness of your observations.
  • The ability to deduce the chemical structure from the NMR spectra.
  • Completion of Laboratory Revision Questions and Report Questions.

Background Information

Nuclear Magnetic Resonance (NMR) spectroscopy is an analytical technique based upon the nuclear properties of some types of atoms. Many atoms have isotopes which possess a nuclear magnetic moment, just as the electron does, having a spin of 1/2. Atomic nuclei may have no spin, spin of 1/2, or other spins which are increments of 1/2 (1, 2, etc.). For organic chemists, the most useful nuclei for observation are usually those with spin 1/2. Nuclei with other spins may be studied, but their signals are sometimes observed only under special circumstances and will not be discussed here. A number of nuclei have spin 1/2 and are very useful for study by NMR spectroscopy. Table 1 lists a number of these elements and their natural abundances. 1 H size 12{ {} rSup { size 8{1} } H} {} , 13 C size 12{ {} rSup { size 8{"13"} } C} {} , 31 P size 12{ {} rSup { size 8{"31"} } P} {} , 19 F size 12{ {} rSup { size 8{"19"} } F} {} , and 15 N size 12{ {} rSup { size 8{"15"} } N} {} are of particular interest to organic chemists.

Table 1. Common Nuclei with Spin 1/2

Nucleus Natural Abundance (%)
1 H size 12{ {} rSup { size 8{1} } H} {} 99.985
13 C size 12{ {} rSup { size 8{"13"} } C} {} 1.11
31 P size 12{ {} rSup { size 8{"31"} } P} {} 100.0
15 N size 12{ {} rSup { size 8{"15"} } N} {} 0.37
19 F size 12{ {} rSup { size 8{"19"} } F} {} 100.0
103 Rh size 12{ {} rSup { size 8{"103"} } ital "Rh"} {} 100.0
107 Ag size 12{ {} rSup { size 8{"107"} } ital "Ag"} {} 51.8
109 Ag size 12{ {} rSup { size 8{"109"} } ital "Ag"} {} 48.2
117 Sn size 12{ {} rSup { size 8{"117"} } ital "Sn"} {} 7.7
119 Sn size 12{ {} rSup { size 8{"119"} } ital "Sn"} {} 8.6
77 Se size 12{ {} rSup { size 8{"77"} } ital "Se"} {} 7.6
125 Te size 12{ {} rSup { size 8{"125"} } ital "Te"} {} 7.0
195 Pt size 12{ {} rSup { size 8{"195"} } ital "Pt"} {} 33.8
203 Tl size 12{ {} rSup { size 8{"203"} } ital "Tl"} {} 29.5
205 Tl size 12{ {} rSup { size 8{"205"} } ital "Tl"} {} 70.5
207 Pb size 12{ {} rSup { size 8{"207"} } ital "Pb"} {} 22.1
In the absence of an external magnetic field, nuclei with a spin of 1/2 have two possible spin states that are equal in energy. These are labeled +1/2 and -1/2.

If we place the nuclei in a strong external magnetic field, these energy levels are no longer equal.

If we then apply a magnetic field that corresponds in energy to the separation energy ( Δ size 12{Δ} {} E), the molecule will absorb that energy and cause the nucleus to go from the parallel spin state to the anti-parallel spin state. The energy that is applied to cause this change in spin state is in the radiofrequency range of the electromagnetic spectrum.

Most commonly a sample solution is prepared and placed in a glass tube that is very uniform and has thin walls. The sample is then placed inside a high field magnet. In older instruments, a variable Rf frequency was applied to the sample to sweep out a range of radiofrequencies, thereby generating a spectrum of the radiofrequency energy absorbed. In newer instruments, a short pulse of radiofrequency energy is used that excites nuclei over a range of frequencies, and the response of all of these nuclei is measured all at once. The spectrum is then obtained by a mathematical transformation of the total signal using the Fourier Transform technique. This is known as FT-NMR. NMR spectra may also be obtained on solid samples, but the technical difficulties are much greater and will not be covered here.

Questions & Answers

so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
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.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
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
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Chem 215 spring08. OpenStax CNX. Mar 21, 2008 Download for free at http://cnx.org/content/col10496/1.8
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