NMR SPECTROSCOPY

NMR SPECTROSCOPY

1. GURU NANAK KHALSA COLLEGE ORGANIC CHEMISTRY BY SMITA. S. JADHAV MSC:-1 SEM :-2

2. TOPIC:- NMR SPECTROSCOPY PROTON MAGNETIC RESONANCE SPCTROSCOPY

3. CONTENT:- Proton Magnetic Resonance Spectroscopy:- Spin-spin Coupling Coupling Constant(j) Factor Affecting (J) Geminal, Vicinal, And Long Range Coupling First Order Spectra

4. FACTORS AFFECTING (J) VALUE :- the value of coupling constant is increases with increase in bond angle. the increase in the electronegativity of an atom or group with withdraw sigma electron , increase the value of coupling constant. the value of (j) decreases with the substituent withdraw electron from pi bonded carbon

5. TYPES OF COUPLING:- GEMINAL COUPLING VICINAL COUPLING LONG RANGE COUPLING FIRST ORDER SPECTRA

6. GEMINAL COUPLING:- two bond coupling are common in NMR spectra, they are called geminal coupling . because the two nuclei are attached to same carbon atom it self. the two bonds coupling are smaller than one bond coupling. in case of geminal protons the value of (j) depends upon H-C--H bond angle called as bond dihydral angle.

7. VICINAL COUPLING :- three bond coupling are called vicinal coupling because the interacting atom are attached to the adjucent carbon atom ‘c’ . it is designated as J3 for the vicinal proton the coupling constant values with the dihydral angle. a plot of (j) values verses dihydral angle of vicinal proton is as shown when the two bonds are parallel or antiparallel the coupling constant of the greatest value of the other hand if the two C-H bond are perpendicular there is little or no spin interaction hence j3 values are minimum.

8. LONG RANGE COUPLING:- usually no coupling is observed if the distance between the two absorbing nuclei is more than three covalent bonds . but in unsaturated compounds or in fluoro compounds, appreciable coupling is observed with the help of high resolution spectrometers even if the concerned nuclei are three bonds apart it is called long range coupling. EXAMPLE:- CH3-CH=CH2

9. FIRST ORDER SPECTRA:--- spectra that can be interprited by the N+1 rule are called 1 s t order spectra if two sets of nuclei are seprated by a large chemical shift they generally shows speeds order spectra CHEMICAL AND MAGNETIC EQUIVALENT :- two or more atoms are symmetrically equivalent , they are set to be chemically equivalent a plane or axis of symmetry makes the hydrogen atom chemically equivalent.

10. REFERENCES:- WILLIAM KEMP ( THIRD EDITION) PAGE NO:- 135-148 ,152-164 . JAG MOHAN (SECOND EDITION) PAGE NO :-241-258. ORGANIC CHEMISTRY (SHEATH PUBLICATIONS), C.T.BHASTANA , U.B.RAICHORA , M.A.DAVE , J.N.KADALI, PAGE NO:-391-396. P.S.KALASI, 5 th EDITION SPECTROSCOPY OF ORGANIC COMPOUND , PAGE NO:- 183-240 , 269 . MECHANISM IN ORGANIC CHEMISTRY, PETER SYKES, 6 th EDITION , PAGE NO:-123-134.