Chemistry Notes for B.Sc. and M.Sc.

  Some Important IR Regions: ü  N ear-IR region:   4 ,000 cm –1  - 13 000 cm –1 . ü  Mid-IR region: 670-4000 cm -1 Ø  Functional group region: 1450 cm –1  - 4000 cm –1 . Ø  F ingerprint  region: 67 0 cm –1  - 1450  cm –1 . ü  F ar-IR region: 1 0 cm –1  - 67 0 cm –1     Near Infra-red (NIR) Spectroscopy: ü  The near-IR extends from approximately 13,000 cm –1  - 4000 cm –1 ü  The absorption bands in the near-infrared often are overtones and combination bands of these group frequencies (of O-H, C-H and N-H) ü  The instrumentation for NIR spectroscopy, both in transmission mode and in reflectance mode, is similar to that for UV/visible spectrometers and for mid-IR spectrometry.   Applications of NIR Spectroscopy ü  Near-infrared spectroscopy is  used in astronomy for studying the atmospheres of various  stars   by detecting the  vibrational and rotational signatu...

  Q 1: Explain the effect of conjugation, hydrogen bonding and steric factor on vibrational frequency? Q 2: Application of Far, Near and Mid-IR spectroscopy? Q 3: Application of NMR Spetcroscopy? Q 4: Applications of Mass Spectrometry or its advantages over other spectroscopic techniques? Q 5: Why Carbon NMR is less sensitive than proton NMR or disadvantages of Carbon NMR over proton NMR Q 6: Advantages of FT-NMR over CW-NMR or difference between FT-NMR and CW -NMR Q 7: Short Notes on Following: a.  McLafferty rearrangement b.  Magnetic Anisotropy (for alkenes, alkynes, aromatic compounds and aldehydes with diagrams) c.  Mechanism of spin-spin interaction or splitting of signals d.  Coupling constant and factors affecting it e.  Long range coupling f.  Simplification of complex spectra (High Field strength, Double irradiation or spin-spin decoupling, Use of Shift Reagents) g.  Nitrogen rule. h.  EI (Electron Impact Ionization) i.  CI (Ch...

  Q 1: Explain the effect of conjugation, hydrogen bonding and steric factor on vibrational frequency? Q 2: Application of Far, Near and Mid-IR spectroscopy? Q 3: Application of NMR Spetcroscopy? Q 4: Applications of Mass Spectrometry or its advantages over other spectroscopic techniques? Q 5: Why Carbon NMR is less sensitive than proton NMR or disadvantages of Carbon NMR over proton NMR Q 6: Advantages of FT-NMR over CW-NMR or difference between FT-NMR and CW -NMR Q 7: Short Notes on Following: a.  McLafferty rearrangement b.  Nitrogen rule. c.  EI (Electron Impact Ionization) d.  CI (Chemical Ionization) e.  FAB (Fast Atom Bombardment) f.  Metastable peak g.  Base Peak h.  DEPT i.  HSQC j.  HMBC k.  INADEQUATE l.  Instrumentation of Mass spectrometry m.  Proton decoupled Carbon NMR or Noise decoupled carbon NMR n.  Off-resonance proton decoupled Carbon NMR o.  Fourier Transform Carbon NMR OR Pulsed NMR...

  The effect which changes the intensity of one spin system (either same or different kind of nuclei like H or C) when the transition of another spin system (another nuclei like H) is perturbed from equilibrium population (via saturation or relaxation processes) by irradiating with a second tunable radiofrequency pulse applied at the precessional frequency of latter nuclei. The NOE effect will be homonuclear when both the nuclei are same (like H and H) and will be heteronuclear when both the nuclei will be different (like C and H). It may be positive as well as negative and its magnitude depends on the gyromagnetic ratios of the nuclei involved in dipolar coupling. It will be positive when the gyromagnetic values of both the nuclei are positive and is given by below equation:   NOE max  = ½ (γ irr /γ obs ) While the total intensity = 1 + NOE max The nuclei which are irradiated with the second radiofrequency is represented as S and its gyromagnetic ratio as γ irr . While t...

NMR-Spectroscopy Principle  NMR spectroscopy involves the absorption of electromagnetic radiation in the radiofrequency region and the principle of NMR spectroscopy revolves around the non- zero value of nuclear spin i.e. I   S. No. Number of Protons Number of Neutrons Nuclear Spin (I) examples 1 even even 0 6 C 12 , 8 O 16 2*             odd even Half integer (1/2, 3/2, 5/2) 1 H 1 , 9 F 19 , 15 P 31 3**             even odd Half integer (1/2, 3/2, 5/2) 6 C 13 4***              odd odd Full integer 7 N 14 *This is possible when both atomic number and mass...

Gross selection rule   tells whether a molecule will be active or inactive in a particular Spectroscopy.   Specific selection rule tells about the allowed changes in the magnitude of energy when it is active in a particular Spectroscopy.     Rotational or Microwave Spectroscopy Gross selection rule: permanent dipole moment  Specific selection rule: ∆J = +1 or -1 ( for rigid rotor) 2. Vibrational or IR Spectroscopy Gross selection rule: change in dipole moment during vibrations Specific selection rule: ∆v = +1 or -1 ( for harmonic oscillator) 3. Raman Spectroscopy Gross selection rule: change in polarizability  Specific selection rule:   ∆J = 0, +2 or -2   ∆v = +1 or -1  4. Electronic or UV-Visible Spectroscopy Gross selection rule: No stringent rule Specific selection rule: ∆s = 0  and ∆l = +1 or -1 5. Nuclear Magnetic  Resonance or Radio waves Spectroscopy Gross selection rule: nuclear spin should be no zero  Specific se...