Q.4.(c) Write an exhaustive note on DSA technique, its principle and pharmaceutical applications.
Q.4. (b) Explain Index of hydrogen deficiency and its significance
Ans.4.(b) Index of Hydrogen Deficiency
Q.4. (a) Discuss the theory of Mass spectroscopy
Ans.4.(a) Theory: Mass spectrometry is the most accurate method for determining the molecular mass of the compound and its elemental composition. In this technique, molecules are bombarded with a beam of energetic electrons. The molecules are ionized and broken up into many fragments, some of which are positive ions. Each kind of ion has a particular ratio of mass to charge, i.e. m/e ratio (value). For most ions, the charge is one and thus, m/e ratio is simply the molecular mass of the ion.
Q.3. (c) Discuss non first order spectra in PMR spectroscopy and its resolution by shift reagents, deuterium labeling and other methods.
Q.3. (c) What do you understand by terms “Broad band decoupling” and “off resonance decoupling” in 13C NMR? Discusses their role in structure elucidation of organic compounds
Q.3. (b) Explain spin labeling & Hyperfine splitting in ESR spectrometry and its application in study of macromolecules
Ans.3.(b) Spin labeling: Site-directed spin labeling (SDSL) is a technique for investigating the structure and local dynamics of proteins using electron spin resonance. The theory of SDSL is based on the specific reaction of spin labels with amino acids. A spin label's built-in protein structure can be detected by EPR spectroscopy. SDSL is also a useful tool in examinations of the protein folding process. A spin label (SL) is an organic molecule which possesses an unpaired electron, usually on a nitrogen atom, and the ability to bind to another molecule. Spin labels are normally used as tools for probing proteins or biological membrane-local dynamics using EPR spectroscopy. The site-directed spin labeling (SDSL) technique allows one to monitor a specific region within a protein. In protein structure examinations, amino acid-specific SLs can be used. The goal of spin labeling is somewhat similar to that of isotopic substitution in NMR spectroscopy. There one replaces an atom lacking a nuclear spin (and so is NMR-silent) with an isotope having a spin I≠0 (and so is NMR-active).
Q.3. (b) Explain the significance of magnitude of “J” constant in structure elucidations.
Ans.3. (b) Coupling constant: The distance between the centers of the two adjacent peaks in a multiplet is usually constant and is usually called the coupling constant. The value of the coupling constant is independent of the external field. It is measured in Hertz (Hz) or in cps (cycles per second). It is denoted by the letter J.
Q.3. (a) Illustrate the following with suitable examples
(ii)Correlation Spectroscopy and its significance
(i). Diamagnetic Anisotropy: Diamagnetic anisotropy is the shielding and deshielding depending on the orientation of the molecule with respect to the applied magnetic field.
Anisotropy is the property of a molecule in different orientations which show variations in physical properties along different axes of the molecule.
Q.3. (a) Discuss briefly the theory of ESR spectroscopy, spin-spin splitting and its qualitative applications
Ans.3. (a) Electron Spin Resonance It is a branch of absorption spectroscopy in which radiation having frequency in the microwave region is absorbed by paramagnetic substances to induce transitions between magnetic energy levels of electrons with unpaired spins. The magnetic energy splitting is done by applying a static magnetic field.
Q.2. (b) Show how you would distinguish between the following by spectroscopy
(i) Aldehyde and Ketone
(ii) Alcohol and Ether
(iii) Mono substituted benzene and Di-substituted benzene