NMR applications
- 1. Applications of NMR Spectroscopy A .Investigation of dynamic properties of molecules like conformational isomerism, molecular asymetry,hydrogen bonding etc.can be done. B. Determination of optical purity. C. Study of drug receptor interactions.
- 2. D. Qualitative Analysis- Elucidation of structure of organic compounds Information from 1H-nmr spectra: 1. Number of signals: How many different types of hydrogens in the molecule. 2. Position of signals (chemical shift): What types of hydrogens. 3. Relative areas under signals (integration): How many hydrogens of each type. 4. Splitting pattern: How many neighboring hydrogens.
- 3. 1. Number of signals: How many different types of hydrogens in the molecule. Magnetically equivalent hydrogens resonate at the same applied field. Magnetically equivalent hydrogens are also chemically equivalent. # of signals? CH4 CH3CH3
- 7. 2. Position of signals (chemical shift): what types of hydrogens. primary 0.9 ppm secondary 1.3 tertiary 1.5 aromatic 6-8.5 allyl 1.7 benzyl 2.2-3 chlorides 3-4 H-C-Cl bromides 2.5-4 H-C-Br iodides 2-4 H-C-I alcohols 3.4-4 H-C-O alcohols 1-5.5 H-O- (variable) Note: combinations may greatly influence chemical shifts. For example, the benzyl hydrogens in benzyl chloride are shifted to lower field by the chlorine and resonate at 4.5 ppm.
- 9. 3. Integration (relative areas under each signal): how many hydrogens of each type. a b c CH3CH2CH2Br a 3H a : b : c = 3 : 2 : 2 b 2H c 2H a b a CH3CHCH3 a 6H a : b = 6 : 1 Cl b 1H
- 10. C CH3H3C C H3C CH3 CH3 CH3 a a a b a a a 12 H a 12 H a 6 H a 6 H b 4 H integration
- 11. 4. Splitting pattern: how many neighboring hydrogens. In general, n-equivalent neighboring hydrogens will split a 1H signal into an ( n + 1 ) Pascal pattern. “neighboring” – no more than three bonds away n n + 1 Pascal pattern: 0 1 1 singlet 1 2 1 1 doublet 2 3 1 2 1 triplet 3 4 1 3 3 1 quartet 4 5 1 4 6 4 1 quintet
- 12. note: n must be equivalent neighboring hydrogens to give rise to a Pascal splitting pattern. If the neighbors are not equivalent, then you will see a complex pattern (aka complex multiplet). note: the alcohol hydrogen –OH usually does not split neighboring hydrogen signals nor is it split. Normally a singlet of integration 1 between 1 – 5.5 ppm (variable).
- 13. C CH3H3C C H3C CH3 CH3 CH3 a a a b a a a 12 H singlet a 12 H singlet a 6 H singlet a 6 H singlet b 4 H singlet splitting pattern?
- 14. Information from 1H-nmr spectra: 1. Number of signals: How many different types of hydrogens in the molecule. 2. Position of signals (chemical shift): What types of hydrogens. 3. Relative areas under signals (integration): How many hydrogens of each type. 4. Splitting pattern: How many neighboring hydrogens.
- 18. p-xylene H3C CH3 a a b a singlet 6H b singlet 4H
- 19. tert-butyl bromide C CH3H3C Br CH3 a singlet 9H
- 20. ethyl bromide a b CH3CH2-Br a triplet 3H b quartet 2H
- 21. 1-bromopropane a b c CH3CH2CH2-Br a triplet 3H b complex 2H c triplet 3H
- 22. isopropyl chloride a b a CH3CHCH3 Cl a doublet 6H b septet 1H
- 23. E. Quantitative Analysis- a. Assay of components- Single component or multicomponents Area under curve can be used for estimation. b. Hydrogen analysis- % of H in organic compound can be determined. c. Moisture analysis- Since H2O can give characteristic peak, % can be determined from peak ratio of water peak and component peak.