Page 2 :
Spectroscopy, Sample at, Equilibrium, , Radiation, , Observation, Excited State, , Spectrum, , Relaxation, , UV-Visible:Presence of chromophoric system / conjugation, in the molecules, IR Spectroscopy:Presence of Functional Groups in the molecules, 1H, , NMR Spectroscopy:, , These spectroscopic techniques are mutually complimentary and a, combination of these three-along with a Mass Spectroscopy form a, powerful device in the determination of structure of organic molecules., 4
Page 3 :
Information from 1H-NMR, spectra:, 1., , Number of signals: How many different types of hydrogens in the, molecule., , 2., , Position of signals (chemical shift): What types of hydrogens., , 3., , The, in ppm) gives a clue as to the type of, hydrogen generating the peak (alkane, alkene, benzene,, aldehyde, etc.), , 4., , Relative areas under signals (integration): How many hydrogens of, each type. (number of Hydrogens), , 5., , Splitting pattern: How many neighbouring hydrogens.
Page 4 :
NMR Spectroscopy, NMR uses energy in the radio frequency range., This energy is too low to cause changes in electron energy levels or, in the vibrations of molecules., NMR can cause changes in the spin of particles in the nucleus of, some atoms., Nuclear magnetic resonance (NMR) is a physical phenomenon in which, nuclei in a magnetic field absorb and re-emit electromagnetic radiation., This energy is at a specific resonance frequency which depends on the, strength of the magnetic field and the magnetic properties of the isotope of, the atoms; in practical applications, the frequency is similar to VHF and, UHF television broadcasts (60 1000 MHz)., NMR allows the observation of specific quantum mechanical, magnetic properties of the atomic nucleus., 4
Page 5 :
Nucleus, The atomic nucleus is the small, dense region consisting of, protons and neutrons at the center of an atom., Protons and Neutrons form the nucleus of the atom, electrons, orbit the nucleus in electron shells., , 5
Page 6 :
All nucleons, that is neutrons, and protons,, composing any atomic nucleus, have the intrinsic, quantum property of spin., The overall spin of the nucleus is determined by the, spin quantum number S / I., The spinning charged nucleus generates a magnetic, field., , 6
Page 7 :
NUCLEAR SPIN, The nuclei of some atoms have a property called SPIN, These nuclei behave as if they were spinning., , This is like the spin property of an, electron, which can have two spins: +1/2, and -1/2 ., Each spin-active nucleus has a number of spins defined by its spin quantum, number, I., , 7
Page 8 :
Magnetic Properties of Nuclei, l, , Nucleii, spin + charge, , Spinning charged, Spinning charged, particle is a magnet, , The spinning of positively charged particle produces:, (1) Spin angular momentum or Spin quantum number (I), (2) Magnetic moment ( ) along the axis of spin, (3) Electric quadrupole moment (Q), (as a result of non-spherical distribution of nuclear, charge), , 8
Page 9 :
Nuclear Magnetic Resonance Spectroscopy, Principle, Nuclear spins are oriented randomly in the absence (a) of an external magnetic, field but have a specific orientation in the presence (b) of an external field,, Some nuclear spins are aligned parallel to the external field, Lower energy orientation, More likely, Some nuclear spins are aligned antiparallel to the external field, Higher energy orientation, Less likely
Page 11 :
Is all nuclei are NMR active?, The angular momentum of spinning nucleus is described in terms of, spin quantum no.I, The spin quantum no. I is a characteristic constant of a nucleus, and, is dependent on the number of protons and neutrons., In general three rules apply to the nuclear spins., 1) Nuclei with odd mass number and odd or even no. of protons have, half integral spin, such as 1/2, 3/2, 5/2 etc., 2) Nuclei with even mass number and odd no. of protons have integral, spin such as 1, 2, 3, 3) Nuclei with even mass number and even no. of protons always, have zero spin (Due to pairing of oppositely directed spins in the, nucleus), , (Mass Number:-the total numbSeIRraJo/MfSpcr/NoMtoRns and neutrons in a nucleus.), , 1
Page 12 :
Requirements of nuclei to be NMR active, Three important characteristics:, o Nuclei should have Spin no. I > 0 and magnetic momemtum > 0, o Nuclei should have even charge distribution that is nucleus should be, spherical in shape so as Q = 0., o Nuclei should have high % of natural abundance, , 1H, 13C, 19 F, , and 31 P nuclei have I = 1/2 and, > 0 These nuclei are spherical in shape, (even charge distribution) and Q = 0, So observed by NMR technique., 1H, 19F and 31P have high % abundance, , 12C, , and 16O nuclei are also spherical in shape Q =, 0; but I = 0 and = 0, So non-magnetic and not observed by NMR
Page 13 :
In the presence of a strong magnetic field, the tiny, magnetic field due to spinning charged particles aligns to, be either with or against the magnetic field.
Page 14 :
Behavior of Magnetic Nuclei, For nuclei with spin I = ½, Two possible orientations, as per equation 2I + 1, ElectromagneticRadiation in, R F range with energy E = Ep, , Randomly oriented nuclear, spins of equal energy in the, absence of any magnetic field, , _1, 2, Ho, , _ 1, 2, , EP, + 1, 2, , +1, 2, , Precisely oriented nuclear spins, in the presence of Magnetic field, , In NMR, we are measuring the energy required for the flipping of the nucleus, 14
