NMR Flashcards
WHAT CAN NMR be used to hel do
find the structures of very complex molecules
what is applies
a magnetic field is applied to a sample which is surrounded by a source of radio waves and a reciever
what does thi sgenerate
an energy change in the nuclei of the atom in the sample which is detected
what happens to the energy
electromagnetic energy is emitted which can be interpreted by a computer
what the difference between carbon 12 and 13
carbon 12 has no nucleas spin and carbon 13 does
what is the difference between the carbon 13 in a compound
they will not all resonante with the same frequency when a magnetic field is applied
why do they resonate diferently
the carbon atoms have different functional groups so feel the magnetic field differently as the nuclei is shielded by the electrons
what happens to the nuclei with more electrons round them
better shielded so smaller magnetic field felt by the nucleas and lower the resonance frequency
what does the nmr show
graph of energy absorbed against the resonant frequency
what is the chemical shift
the difference in resonating nucleas of the nucleas ti tms and that of the measured one
what is tms and what it chemical shift value
tetramethyl silane with a chemical shift value of zero
what happens when oxygen is connected to the carbon
the oxygen is electronegative so draws electrons twoards itself deshielding the carbon nucleas so it resonates more
why is tms used
it is inert, not toxic and easy to remove from the sample
why is proton nmr easier
the h1 nucleas being examine nearly all exist in this state compared to the carbon 13
what feels the magnetic field
the hydrogen which is attached to different functional groups that feel the magnetic field
