Organic Spectroscopy | Rochester Institute of Technology

University:
Rochester Institute of Technology
Course:
CHEM-151 | General Chemistry
Academic year:

2021
Views:

25

Pages:

39
Author:

OgreM

ORGANIC SPECTROSCOPY * 13 C-NMR SPECTROSCOPY- C13-NMR (Nuclear Magnetic Resonance) is a relatively new technique. There are Considerable differences between 4'-NMR And els-NMR spectra bolts in the mode of recording as well as appearance. The Nuclear magnetic resonance of es com be observed almest lly of si For example if it' observed at 400MHz, c Same magnetic field is observed. at 100MHz with The most significant mickel other than proten in an organic molecule is cls whose I = 1/2. :. It is a spin active nuchi. Like proton the e's nuclei also gives the NMR spectum called as CMR. The natural abundance of 2-13 isotope is only 1.11% The low abundance further reduces the Sensitivity of absorption. Although the low abundance had been a major obstacle for the advent of c'? NIMR. The multiplicity al each carbon SFORD" Spectrum gives the information about no. of hydrogens attached with Each carbon. Because the multiplicity of each carton is only due to Coupling with its own hydrogens. If a chemical shift difference between two Sets of carbons is too small. Their multiplicities. are overlaped in SFORD Spectrum. That makes a Spectrum become Compler and it is not possible to identify the Correct multiplizily. To avoid the above problem, there is another techmique known as Selective proton decoupling technique. In this method all the interactions between selected Carbon and all protons are. ~ation cor) toy decoupling. eliminated by double irradi Therefore the Selected Carbon Signal appear as A Singlet, remaining Carbon Signals appeared with the multiplet like. SFORD Gated decoupled Spectra:- mery To get Sufficient Coupling information we the special experimental technique. which is known as Gated decoupling technique. Successfully handbe spin-spin Couplings and inter- -sity distortions. It is based on the different time scales are chara- -cteristic (for the decoupling Experiment) experiment and the nuclear over hauser effect. In this experiment, the i broad bond decoupling applied only during the delay time (DT) net Power during acquition time. (AT) - Compared 13 to H', crme chemical shift range very wide because c's nucleus is change in chemical environment. very is Sensitive for The reason for H for 5 values of (~20 ppm), berause ~250 to 300 ppm), Rebut in e's the group which effects (Shielding / deshielding) the chemical shift is directly attached to the e's nucleous. The Given range is not rigid, Some of the Carbons groups may deviate from this range According to EN factor from top to bottom Sc.s" of carbon should be Ipurease. But NMR Shown decrease in See with mereare in no. of iodine atoms. It is due to heavy atom effects. (Steric crowding 7. effect (or) - Gauche effect :- In the long carbon chain having at 8-position. & c.s's decrease decrease in S E.N group. in large extent. c.st at 8-position 7-gauche effects in c3. Called as 4-effects In gauche Conformation of this molecule, substs- tuent and I-Carbon are in steric interaction (gauche interaction) decreases Scis" at 8-caroon