Published on: Mar 4, 2016
Transcripts - Poonam more
Structural elucidation is the determination of the chemicalstructure of chemically uncharacterised substances such asnatural products. It is preceded by the extraction and isolationsteps. It makes use of various chromatography techniques(MPLC, HPLC) as well as spectrometric techniques (MS, 1D and2D NMR). MS spectrometers like ions traps can use thefragmentation techniques to further investiguate the structureof the molecule.It is a technique used notably in phytochemistry, for instance tocharacterise polyphenol oxidation products.
Spectroscopic methods are the main tool of modern chemistry forthe identification of molecular structures, to monitor reactions andto control the purity of compounds, most essential methods for theorganic chemistry are the Nuclear Magnetic Resonance (proton),Nuclear Magnetic Resonance( C13) ,Infrared Spectroscopy , Massspectroscopy , UV Visible spectroscopy
In proton NMR spectroscopy determine the number ofHydrogen atom present in the molecule by using n+1 rule.
Using IR spectroscopy determine the what type offunctional group present in the molecule.
Mass spectroscopy determine the molecular weight of themolecule.Molecular weights of compounds can be measuredspectrophotometrically by preparing the suitable derivativesof these compounds.For example, if we want to determinethe molecular weight of amine then it is converted in toamine picrate. Then known concentration of amine picrate isdissolved in a litre of solution and its optical density ismeasured at λmax 380 nm. After this the concentration of thesolution in gm moles per litre can be calculated by using thefollowing formula.
"c" can be calculated using above equation, the weight "w"of amine picrate is known. From "c" and "w", molecularweight of amine picrate can be calculated. And themolecular weight of picrate can be calculated using themolecular weight of amine picrate.
By using these above spectroscopy we find out the strcture ofmolecule . After knowning the strcture of molecule apply theUV spectrophotometry for measurement of avelengthmaximum.
We will find that the effect of substituent groups can bereliably quantified from empirical observation of known conjugated structures and applied to new system. This quantification is referred to as the Woodward- Fieser Rules which we will apply to three specific chromophores: 1.Conjugated dienes 2.Conjugated dienones 3.Aromatic systems
BY using Beer Lambert’s Law determine theconcentration of chromophoric grouppresent in molecule.
1. William Kemp: Organic Spectroscopy, third edition, published by Palgrave, New York,1991,56,57,171- 181.2. Pavia D.L.,Lampman G.M., Kriz G.S., Vyvyan J.R.,: Spectroscopy, India Edition, published by Cengage Learning,2007,125,126.3. Skoog D.A., Holler F.J., Nieman T.A.,: Principles of Instrumental Analysis, fifth edition, published by Thomson,2003,4984. www.google.co.in.